Solar cookers

What is it?A solar cooker is a device that uses heat energy from the sun to cook food. Solar cooking involves no recurring expenses on

fuel. Solar cookers if used properly can save three or four LPG cylinders per year. Since solar cooking is a slow process, it ensures better and more nutritious food. These are durable and simple to use. These work well only on clear sunny days. However, if an electrical heater is built in, these can be used on cloudy days too.

Types of solar cookers: Two types of solar cookers are available in the market, box type and dish type.

A box solar cooker: It is suitable for a family of four or five can cook most of the dishes except frying or for making chapattis. It is an ideal device for domestic cooking during most of the year except on cloudy days. Some models are available with electrical backup, so it can be used even in non-sunshine hours. These can be procured from manufacturers, suppliers, district and head offices of state agencies as well as from ‘Aditya’ solar shops.

A dish solar cooker: It uses a parabolic dish to concentrate incident solar radiation. This solar cooker commonly known as an ‘SK-14’ solar cooker is useful for homes and small establishments. This can meet the needs of about 15 people and can be used for eight to nine hours during the day. Upon full use at small establishments, these can save upto 10 LPG cylinders per year.

How do these work?A box type solar cooker consists of an outer box made of either fibre glass or aluminium sheet, a blackened aluminium tray, a double glass lid, a reflector, insulation and cooking pots. The blackened aluminium tray is fixed inside the box with insulating material in between to prevent heat loss from all sides. A double glass lid with toughened glass acts as the cover of the cooking tray. A reflecting mirror, fitted on the inside of the outer box cover, reflects the solar radiation and helps in increasing the solar energy input. The cooking pots are made of steel or aluminium and painted black on the outer side. The food to be cooked is placed in the cooking pots which are then placed in the aluminium tray and covered by the double glass lid. The cooker is kept facing the sun appropriately to cook the food.

A dish solar cooker uses a parabolic dish to concentrate the incident solar radiation. It has a aperture diameter of 1.4 m and a focal length of 0.28 m. The reflecting material used for fabrication of this cooker is anodised aluminium sheet which has a reflectivity of over 80 per cent. The cooker has to track the sun and has to be adjusted manually after every 15 -20 minutes. The cooker can deliver power of about 0.6 kW which can boil two or three litres of water in half an hour. The temperature achieved at the bottom of the vessel could reach 350 to 400 degrees celsius which is sufficient for roasting, frying, and boiling.

What are the benefits? A box type solar cooker can be used to prepare all kinds of dishes, except frying or making chapattis. A normal size of this cooker is sufficient for a family of four to five members. A dish solar cooker however can meet the needs of about 15 people and can be used for eight to nine hours during the day. It can save up to 10 LPG cylinders per year upon full use at small establishments. 

What is the life span and cost? The box type solar cooker has a life of 10 to 12 years. The cost varies from Rs 1,200 to Rs. 2,500 depending on its size and features. The payback period is 2 to 3 years depending upon the extent of use and place of use. The cost of a dish solar cooker may vary from Rs. 4,300 to Rs. 5,000 depending on the type of reflector and supporting structure. Its payback period ranges from 2 to 3 years depending on the extent of its place of use. The life of this cooker is estimated at about 20 years for the metallic structure. However, the reflecting sheets may have to be replaced once in five years due to degradation in their reflectivity.

Government subsidy? In case of box type solar cookers, the MNRE provide incentives to state nodal agency (SNA) which is Rs. 200 per cooker of ISI brand and Rs. 100 per cooker of non-ISI brand. In addition, Rs. 1.50 lakh is given to SNA for publicity or conducting workshops etc. The manufacturers also get 50 per cent fee reimbursement for obtaining BIS approval. Inorder to encourage the use of dish type solar cookers, an incentive of 50 per cent of the cost of the dish solar cooker is provided, which is limited to Rs. 2,500 per cooker. 

Where can we get them? The MNRE website has a list of manufacturers and suppliers of concentrating solar cookers (dish and scheffler cookers). 

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Community solar cooker

What is it? A community solar cooker is a parabolic reflector cooker like a dish solar cooker. It is commonly known as a Scheffler cooker and is larger than the dish solar cooker (SK-14 type).

How does it work? It can cook food using solar energy inside the kitchen itself. The cooker has a large reflector ranging from 7 to 12 sq m aperture area. This reflector is placed outside the kitchen so that it reflects solar rays into the kitchen through an opening in its north wall. A secondary reflector further concentrates the rays on to the bottom of the pot/frying plan

which is painted black to absorb maximum heat. The temperature attained is so high up to 400 degrees celsius that the food can be cooked quickly.

The cooker is provided with a mechanical clockwork arrangement that rotates the primary reflector outside to automatically track the sun. The cook has to set this reflector in focus only once a day in the morning. By shifting two arms provided in the reflector frame, it is possible to change the curvature of the parabolic reflector for seasonal adjustment thus keeping fully tracked on to the sun during all seasons.

i. Outside view (solar dishes), ii. Inside view of kitchen

What is the benefit? It is possible to cook food for about 40 to 50 persons with this cooker. One dish may take about 60 to 90 minutes to cook depending on the type of dish and solar insulation available. The cooker works nicely in areas where solar insulation is good during most part of the year and it is possible to cook two meals a day with this cooker. Due to the high temperature attained with this cooker, it is suitable for making almost all traditional dishes. When not in use for cooking, the cookers can be used to hear or boil water. These can be used in schools, institutional kitchens, canteens, religious ashrams, hotels, hospitals, police and armed forces’ kitchens etc.

What is the lifespan and cost? The cost of this cooker is about Rs. 50,000. The payback period is 4 to 5 years. 

Government subsidy? In case of Scheffler or community type cooker, the MNRE provides Rs. 25,000. 

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Solar photovoltaic (SPV) systems

Outdoor lights can be powered by small photovoltaic (PV) modules that convert sunlight directly into electricity. Solar outdoor lights also come as stand alone fixtures. An 11 W CFL, with a 74 W photovoltaic module and a 12 V/75 AH battery, costs Rs. 22, 000 to 24 000. When fully charged, the battery can power the light from dusk to dawn.

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SPV lantern

What is it? Solar lantern is a portable device for lighting. Due to its light weight, it can be carried around and is therefore ideal for both indoor and outdoor usage.

How does it work? A solar lantern consists of three main components -- PV module of 8 W to 10 W capacity, a sealed maintenance free battery of 12 V, 7 ampere hours (AH) capacity and a CFL of 5W or 7W rating. It does not require installation. The PV module is placed in the sun during the day and is connected through a cable to the lantern unit. The incident solar radiation is converted into electricity which in turn charges the battery. A green LED light indicates the charging of the battery.

What is the benefit? A solar lantern, which is commonly used for lighting purposes, can save about 50 liters of kerosene in a year by replacing a kerosene lantern.  It is meant to provide light for three to four years daily and can function like this for three days without sunlight. During night, the lantern is simply detached, the battery provides power to the lamp and is used wherever required.

What is the life span and cost? The average cost of a solar lantern is around Rs. 3,500.  Low cost models with smaller PV modules and battery capacity are also available.

Government subsidy? The MNRE provides a subsidy of Rs. 2,400 on purchase of solar lantern in northeast and special areas.  This is mostly in unelectrified villages and hamlets of special category states and UTs/islands.  There is however no subsidy in other areas.  Under the solar lantern programme, the Ministry will also provide Rs.100 per lantern as service charges to the SNAs/departments and the Akshaya Urja shops. The SNAs/departments will also get Rs. 100 per lantern towards inspection charges of solar lanterns sold by the Akshaya Urja shops. Subsidy will be provided only on eligible models of solar lanterns, procured from the pre-qualified manufacturers, after competitive bidding.   

In addition, one girl child from a BPL family studying in class IX to XII and residing in the un-electrified villages and hamlets of the special category states and UT islands is eligible to get one solar lantern free of cost during her entire period of school study. This has been done to encourage a girl child belonging to the BPL family to continue her studies. The distribution of solar lanterns is organised by the concerned SNAs through the district administration. 

Where can you get it? One can get the solar lanterns from Akshay Urja Shops established in various states and union territories.

Any concern? At present, CFL is being used as the light source in solar lanterns. The Ministry of Renewal Energy is supporting development of white LED based solar lanterns, for replacing CFL, which is expected to further reduce the cost of the solar lanterns. The draft performance specifications of white LED based solar lanterns have been prepared for product development and performance evaluation. 

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SPV home lighting system

What is it? A solar home lighting system provides solar electricity for indoor lighting. It can operate lights in one or more rooms of a house along with power to run small DC fan or a 12 V DC television with the system. It consists of a PV module of 18, 37 or 74 W capacity, a sealed, maintenance free or flooded lead acid battery of 12 V and 20, 40 or 75 AH capacity and CFLs of 9W or 11 W rating. There are several models with one, two or four CFLs.

How does it work? The PV module is usually mounted on the roof of the house so that it is exposed to direct solar radiation throughout the day. The module converts incident radiation into electricity which in turn charges the battery which is placed inside the house. The battery provides power to the CFLs and to the television and fan as required. A change controller prevents overcharging and deep discharge of the battery.

What is the benefit? The system is designed to provide service for 3 to 4 hours daily and can function for three cloudy days. In addition to lighting, it is also possible to run a fan or a television with the system.

What is the lifespan and cost? The cost of an SHS depends on the load to be supported, the capacity of the PV modules used to meet the load requirement and the capacity of the battery to meet the required autonomy. The indicative costs of the five different SHS models are model I (one 9W CFL) Rs. 6000; model II (two 9W CFLs) Rs. 10,000; model III (one 9W CFL and one fan) Rs.  11,000; model IV (two 9W CFLs and a fan/television) Rs. 18,500; and model V (four 9W CFLs) Rs. 17,500. The indicative costs do not include the cost of the fan/ television as there could be variations due to local taxes, additional transportation costs etc.

However, the lifespan of the components varies. A typical SPV panel has a reported lifespan of 20 to 25 years, a CFL around battery 2 to 5 years.

Government incentives? The MNRE provides subsidy of Rs. 4,500 to 8,600 for northeast and special areas and Rs. 2,500 to 4,800 for general areas depending on the model.  The eligible category of beneficiaries includes all individuals and non-profit institutions or organizations. (Except for beneficiaries from remote un-electrified census villages) No individual would be given more than one system.  

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Rooftop SPV systems

What is rooftop solar photovoltaic (SPV) system?Rooftop SPV systems can reduce dependency on diesel gensets during load shedding and to utilize the existing roof space of building.

How does it work? A roof top SPV system could be with or without grid interaction.  In grid interaction system, the DC power generated from SPV panels is converted to AC power using power conditioning unit and is fed to the grid either of 11 KV three phase line or of 220 V single phase line depending on the system installed at institution/commercial establishment or residential complex. They generate power during the daytime which is utilized fully by powering the captive loads and feeding excess power to the grid as long as grid is available. In cases, where solar power is not sufficient due to cloud cover etc. the captive loads are served by drawing power from the grid. The grid interactive rooftop SPV systems thus work on net metering basis wherein the beneficiary pays to the utility on net meter reading basis only. Ideally, grid interactive systems do not require battery back up as the grid acts as the backup for feeding excess solar power and viceversa. However, to

enhance the performance reliability of the overall systems, a minimum battery back of one hour of load capacity is strongly recommended. In grid interactive systems, it has , however to be ensured that in case the grid fails, the solar power has to be fully utilized or stopped immediately feeding to the grid (if any in excess) so as to safeguard any grid person/technician from getting shock (electrocuted) while working on the grid for maintenance etc.

Non-grid interactive systems ideally require a full load capacity battery power back up system. However, with the introduction of advanced load management and power conditioning systems, and safety mechanisms, it is possible to segregate the day-time loads to be served directly by solar power without necessarily going through the battery back-up. As in the previous case of grid-interactive systems, minimum one hour of battery back-up is, however, strongly recommended for these systems also to enhance the performance reliability of the systems. The non-grid interactive system with minimum battery back are viable only at places where normal power is not available during daytime. In case the SPV power is to be used after sunshine hours, it would require full load capacity battery back up which will increase the cost of system which may not be economically viable even with support from Government.

Government scheme and subsidy? In February 2009, the MNRE has announced a revised scheme on ‘Demonstration and Promotion of Solar Photovoltaic Devices/Systems in Urban Areas and Industry’ which has major focus on rooftop SPV systems. This scheme pertains to diesel abatement in institutions, government buildings, commercial establishments example malls, hotels, hospitals, nursing homes, industry excluding manufacturers of SPV cells/modules and housing complexes facing huge power shortage during daytime. The scheme has a target of 4.25 MW during rest of the Eleventh Plan.

The MNRE provides central financial assistance (CFA) for rooftop SPV systems at the rate of Rs. 75 per watt of SPV panels to a maximum of 30 per cent of the cost of the systems to profit making bodies availing depreciation benefits and at the rate of Rs. 100 per watt to a maximum of 40 per cent of the cost of systems to non-profit making bodies (with or without grid interaction) limited to 100 kW capacity mainly for daytime use. Minimum capacity of installation is 25 kW. Smaller systems (not less than 10 kW) may be considered as special case. No targets are set for these systems to state or urban local bodies. Proposals will be considered on first come first served basis through SNAs. Sanction of CFA will be based on the existing diesel consumption level of the establishment.

Benefits of the scheme? The pay pack period is 5 to 6 years. The life is 25 to 30 years. No air and noise pollution. No moving parts and zero maintenance except cleaning of SPV panel once in a while. The beneficiary has to decide supplier on cost and quality competitive basis. List of suppliers is available on the MNRE’s website. A 100 kW capacity rooftop system could save around 50,000 litres of diesel per year.

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Solar generator

What is it? It is a small capacity, stand alone SPV power system based on a PV array connected to a battery bank of appropriate size and an inverter of 12, 24 or 48 V.

What is the benefit? It is designed to supply power to limited loads such as lights, fans, credit card operating machines and personal computers for a period of two to three hours.

What is the life span and cost? The MNRE promotes four models of solar generators with capacities of 150, 350, 450 and 600 W. These are meant to replace the conventional small capacity petrol based generators that are used during routine load shedding periods in urban areas by shops, clinics and other small establishments. The cost varies from Rs. 3,500 to Rs. 1.45 lakh

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Solar thermal system for water heating in Santorini, Greece.

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Solar thermal energy (STE) is a technology for harnessing solar energy for thermal energy (heat). Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are flat plates generally used to heat swimming pools. Medium-temperature collectors are also usually flat plates but are used for heating water or air for residential and commercial use. High-temperature collectors concentrate sunlight using mirrors or lenses and are generally used for electric power production. STE is different from and much more efficient than[1][2][3] photovoltaics, which converts solar energy

directly into electricity. While existing generation facilities provide only 600 megawatts of solar thermal power worldwide in October 2009, [note 1] plants for an additional 400 megawatts are under construction and development is underway for concentrated solar power projects totalling 14,000 megawatts.[4]

Contents

 [hide]  1 Low-temperature collectors

o 1.1 Heating, cooling, and ventilation o 1.2 Process heat

2 Medium-temperature collectors o 2.1 Solar drying o 2.2 Cooking o 2.3 Distillation

3 High-temperature collectors o 3.1 System designs

3.1.1 Parabolic trough designs 3.1.2 Power tower designs 3.1.3 Dish designs 3.1.4 Fresnel reflectors 3.1.5 Linear Fresnel reflector technologies 3.1.6 Fresnel lenses 3.1.7 MicroCSP

4 Heat Collection and Exchange 5 Heat storage

o 5.1 Steam accumulator o 5.2 Molten salt storage o 5.3 Graphite heat storage o 5.4 Phase-change materials for storage

6 Use of water 7 Conversion rates from solar energy to electrical energy 8 Levelised cost 9 Standards 10 See also 11 Notes 12 References

13 External links

[edit] Low-temperature collectors

Of the 21,000,000 square feet (2,000,000 m2) of solar thermal collectors produced in the United States in 2007, 16,000,000 square feet (1,500,000 m2) were of the low-temperature variety.[5] Low-temperature collectors are generally installed to heat

swimming pools, although they can also be used for space heating. Collectors can use air or water as the medium to transfer the heat to their destination.

[edit] Heating, cooling, and ventilation

Main articles: HVAC, Solar air heat, Passive solar building design, Thermal mass, Trombe wall, Solar chimney, and Solar air conditioning

MIT's Solar House #1 built in 1939 used seasonal thermal storage for year round heating.

In the United States, heating, ventilation, and air conditioning (HVAC) systems account for over 25 percent (4.75 EJ) of the energy used in commercial buildings and nearly half (10.1 EJ) of the energy used in residential buildings.[6][7] Solar heating, cooling, and ventilation technologies can be used to offset a portion of this energy.

Thermal mass materials store solar energy during the day and release this energy during cooler periods. Common thermal mass materials include stone, concrete, and water. The proportion and placement of thermal mass should consider several factors such as climate, daylighting, and shading conditions. When properly incorporated, thermal mass can passively maintain comfortable temperatures while reducing energy consumption. A solar chimney (or thermal chimney) is a passive solar ventilation system composed of a hollow thermal mass connecting the interior and exterior of a building. As the chimney warms, the air inside is heated causing an updraft that pulls air through the building. These systems have been in use since Roman times and remain common in the Middle East.

Solar space heating with solar air heat collectors is more popular in the USA and Canada than heating with solar liquid collectors since most buildings already have a ventilation system for heating and cooling. The two main types of solar air panels are glazed and unglazed.

Glazed Solar Collectors are designed primarily for space heating and they recirculate building air through a solar air panel where the air is heated and then directed back into the building. These solar space heating systems require at least two penetrations into the building and only perform when the air in the solar collector is warmer than the building room temperature. Most glazed collectors are used in the residential sector.

Unglazed, "transpired" air collector

Unglazed Solar Collectors are primarily used to pre-heat make-up ventilation air in commercial, industrial and institutional buildings with a high ventilation load. They turn building walls or sections of walls into low cost, high performance, unglazed solar collectors. Also called, "transpired solar panels", they employ a painted perforated metal solar heat absorber that also serves as the exterior wall surface of the building. Heat conducts from the absorber surface to the thermal boundary layer of air 1 mm thick on the outside of the absorber and to air that passes behind the absorber. The boundary layer of air is drawn into a nearby perforation before the heat can escape by convection to the outside air. The heated air is then drawn from behind the absorber plate into the building's ventilation system.

A Trombe wall is a passive solar heating and ventilation system consisting of an air channel sandwiched between a window and a sun-facing thermal mass. During the ventilation cycle, sunlight stores heat in the thermal mass and warms the air channel causing circulation through vents at the top and bottom of the wall. During the heating cycle the Trombe wall radiates stored heat.[8]

Solar roof ponds are unique solar heating and cooling systems developed by Harold Hay in the 1960s. A basic system consists of a roof-mounted water bladder with a movable insulating cover. This system can control heat exchange between interior and exterior environments by covering and uncovering the bladder between night and day. When heating is a concern the bladder is uncovered during the day allowing sunlight to warm the water bladder and store heat for evening use. When cooling is a concern the covered bladder draws heat from the building's interior during the day and is uncovered at night to radiate heat to the cooler atmosphere. The Skytherm house in Atascadero, California uses a prototype roof pond for heating and cooling.[9]

Active solar cooling can be achieved via absorption refrigeration cycles, desiccant cycles, and solar mechanical processes. In 1878, Auguste Mouchout pioneered solar cooling by making ice using a solar steam engine attached to a refrigeration device.[10] Thermal mass, smart windows and shading methods can also be used to provide cooling. The leaves of deciduous trees provide natural shade during the summer while the bare limbs allow light

and warmth into a building during the winter. The water content of trees will also help moderate local temperatures.

[edit] Process heat

Main articles: Solar pond, Salt evaporation pond, and Solar furnace

Solar Evaporation Ponds in the Atacama Desert.

Solar process heating systems are designed to provide large quantities of hot water or space heating for nonresidential buildings.[11]

Evaporation ponds are shallow ponds that concentrate dissolved solids through evaporation. The use of evaporation ponds to obtain salt from sea water is one of the oldest applications of solar energy. Modern uses include concentrating brine solutions used in leach mining and removing dissolved solids from waste streams. Altogether, evaporation ponds represent one of the largest commercial applications of solar energy in use today.[12]

Unglazed transpired collectors (UTC) are perforated sun-facing walls used for preheating ventilation air. UTCs can raise the incoming air temperature up to 22 °C and deliver outlet temperatures of 45-60 °C. The short payback period of transpired collectors (3 to 12 years) make them a more cost-effective alternative to glazed collection systems. As of 2009, over 1500 systems with a combined collector area of 300,000 m² had been installed worldwide. Representatives include an 860 m² collector in Costa Rica used for drying coffee beans and a 1300 m² collector in Coimbatore, India used for drying marigolds.[13]

[14]

A food processing facility in Modesto, California uses parabolic troughs to produce steam used in the manufacturing process. The 5,000 m² collector area is expected to provide 4.3 GJ per year.[15]

[edit] Medium-temperature collectors

Main article: solar water heating

These collectors could be used to produce approximately 50% and more of the hot water needed for residential and commercial use in the United States.[16] In the United States, a

typical system costs $4000–$6000 retail ($1400 to $2200 wholesale for the materials) and 30% of the system qualifies for a federal tax credit + additional state credit exists in about half of the states. Labor for a simple open loop system in southern climates can take 3–5 hours for the installation and 4–6 hours in Northern areas. Northern system require more collector area and more complex plumbing to protect the collector from freezing. With this incentive, the payback time for a typical household is four to nine years, depending on the state. Similar subsidies exist in parts of Europe. A crew of one solar plumber and two assistants with minimal training can install a system per day. Thermosiphon installation have negligible maintenance costs (costs rise if antifreeze and mains power are used for circulation) and in the US reduces a households' operating costs by $6 per person per month. Solar water heating can reduce CO2 emissions of a family of four by 1 ton/year (if replacing natural gas) or 3 ton/year (if replacing electricity).[17] Medium-temperature installations can use any of several designs: common designs are pressurized glycol, drain back, batch systems and newer low pressure freeze tolerant systems using polymer pipes containing water with photovoltaic pumping. European and International standards are being reviewed to accommodate innovations in design and operation of medium temperature collectors. Operational innovations include "permanently wetted collector" operation. This innovation reduces or even eliminates the occurrence of no-flow high temperature stresses called stagnation which would otherwise reduce the life expectancy of collectors.

[edit] Solar drying

Solar thermal energy can be useful for drying wood for construction and wood fuels such as wood chips for combustion. Solar is also used for food products such as fruits, grains, and fish. Crop drying by solar means is environmentally friendly as well as cost effective while improving the quality. The less money it takes to make a product, the less it can be sold for, pleasing both the buyers and the sellers. Technologies in solar drying include ultra low cost pumped transpired plate air collectors based on black fabrics. Solar thermal energy is helpful in the process of drying products such as wood chips and other forms of biomass by raising the heat while allowing air to pass through and get rid of the moisture.[18]

[edit] Cooking

Main article: Solar cooker

The Solar Bowl above the Solar Kitchen in Auroville, India concentrates sunlight on a movable receiver to produce steam for cooking.

Solar cookers use sunlight for cooking, drying and pasteurization. Solar cooking offsets fuel costs, reduces demand for fuel or firewood, and improves air quality by reducing or removing a source of smoke.

The simplest type of solar cooker is the box cooker first built by Horace de Saussure in 1767. A basic box cooker consists of an insulated container with a transparent lid. These cookers can be used effectively with partially overcast skies and will typically reach temperatures of 50–100 °C.[19][20]

Concentrating solar cookers use reflectors to concentrate light on a cooking container. The most common reflector geometries are flat plate, disc and parabolic trough type. These designs cook faster and at higher temperatures (up to 350 °C) but require direct light to function properly.

The Solar Kitchen in Auroville, India uses a unique concentrating technology known as the solar bowl. Contrary to conventional tracking reflector/fixed receiver systems, the solar bowl uses a fixed spherical reflector with a receiver which tracks the focus of light as the Sun moves across the sky. The solar bowl's receiver reaches temperature of 150 °C that is used to produce steam that helps cook 2,000 daily meals.[21]

Many other solar kitchens in India use another unique concentrating technology known as the Scheffler reflector. This technology was first developed by Wolfgang Scheffler in 1986. A Scheffler reflector is a parabolic dish that uses single axis tracking to follow the Sun's daily course. These reflectors have a flexible reflective surface that is able to change its curvature to adjust to seasonal variations in the incident angle of sunlight. Scheffler reflectors have the advantage of having a fixed focal point which improves the ease of cooking and are able to reach temperatures of 450-650 °C.[22] Built in 1999, the world's largest Scheffler reflector system in Abu Road, Rajasthan India is capable of cooking up to 35,000 meals a day.[23] By early 2008, over 2000 large cookers of the Scheffler design had been built worldwide.

[edit] Distillation

Solar stills can be used to make drinking water in areas where clean water is not common. Solar distillation is necessary in these situations to provide people with purified water. Solar energy heats up the water in the still. The water then evaporates and condenses on the bottom of the covering glass.[18]

[edit] High-temperature collectors

The solar furnace at Odeillo in the French Pyrenees-Orientales can reach temperatures up to 3,800 degrees Celsius.

Concentrated solar power plant using parabolic trough design.

Where temperatures below about 95 °C are sufficient, as for space heating, flat-plate collectors of the nonconcentrating type are generally used. Because of the relatively high heat losses through the glazing, flat plate collectors will not reach temperatures much above 200 °C even when the heat transfer fluid is stagnant. Such temperatures are too low for efficient conversion to electricity.

The efficiency of heat engines increases with the temperature of the heat source. To achieve this in solar thermal energy plants, solar radiation is concentrated by mirrors or lenses to obtain higher temperatures – a technique called Concentrated Solar Power (CSP). The practical effect of high efficiencies is to reduce the plant's collector size and total land use per unit power generated, reducing the environmental impacts of a power plant as well as its expense.

As the temperature increases, different forms of conversion become practical. Up to 600 °C, steam turbines, standard technology, have an efficiency up to 41%. Above 600 °C, gas turbines can be more efficient. Higher temperatures are problematic because different materials and techniques are needed. One proposal for very high temperatures is to use liquid fluoride salts operating between 700 °C to 800 °C, using multi-stage turbine systems to achieve 50% or more thermal efficiencies.[24] The higher operating temperatures permit the plant to use higher-temperature dry heat exchangers for its thermal exhaust, reducing the plant's water use – critical in the deserts where large solar

plants are practical. High temperatures also make heat storage more efficient, because more watt-hours are stored per unit of fluid.

Since the CSP plant generates heat first of all, it can store the heat before conversion to electricity. With current technology, storage of heat is much cheaper and more efficient than storage of electricity. In this way, the CSP plant can produce electricity day and night. If the CSP site has predictable solar radiation, then the CSP plant becomes a reliable power plant. Reliability can further be improved by installing a back-up system that uses fossil energy. The back-up system can reuse most of the CSP plant, which decreases the cost of the back-up system.

With reliability, unused desert, no pollution, and no fuel costs, the obstacles for large deployment for CSP are cost, aesthetics, land use and similar factors for the necessary connecting high tension lines. Although only a small percentage of the desert is necessary to meet global electricity demand, still a large area must be covered with mirrors or lenses to obtain a significant amount of energy. An important way to decrease cost is the use of a simple design.

[edit] System designs

During the day the sun has different positions. For low concentration systems (and low temperatures) tracking can be avoided (or limited to a few positions per year) if nonimaging optics are used.[25] For higher concentrations, however, if the mirrors or lenses do not move, then the focus of the mirrors or lenses changes (but also in these cases nonimaging optics provides the widest acceptance angles for a given concentration). Therefore it seems unavoidable that there needs to be a tracking system that follows the position of the sun (for solar photovoltaic a solar tracker is only optional). The tracking system increases the cost and complexity. With this in mind, different designs can be distinguished in how they concentrate the light and track the position of the sun.

[edit] Parabolic trough designs

Main article: Parabolic trough

Sketch of a parabolic trough design. A change of position of the sun parallel to the receiver does not require adjustment of the mirrors.

Parabolic trough power plants use a curved, mirrored trough which reflects the direct solar radiation onto a glass tube containing a fluid (also called a receiver, absorber or collector) running the length of the trough, positioned at the focal point of the reflectors. The trough is parabolic along one axis and linear in the orthogonal axis. For change of the daily position of the sun perpendicular to the receiver, the trough tilts east to west so that the direct radiation remains focused on the receiver. However, seasonal changes in the in angle of sunlight parallel to the trough does not require adjustment of the mirrors, since the light is simply concentrated elsewhere on the receiver. Thus the trough design does not require tracking on a second axis.

The receiver may be enclosed in a glass vacuum chamber. The vacuum significantly reduces convective heat loss.

A fluid (also called heat transfer fluid) passes through the receiver and becomes very hot. Common fluids are synthetic oil, molten salt and pressurized steam. The fluid containing the heat is transported to a heat engine where about a third of the heat is converted to electricity.

Andasol 1 in Gaudix, Spain uses the Parabolic Trough design which consists of long parallel rows of modular solar collectors. Tracking the sun from East to West by rotation on one axis, the high precision reflector panels concentrate the solar radiation coming directly from the sun onto an absorber pipe located along the focal line of the collector. A heat transfer medium, a synthetic oil like in car engines, is circulated through the absorber pipes at temperatures up to 400 °C and generates live steam to drive the steam turbine generator of a conventional power block.

Full-scale parabolic trough systems consist of many such troughs laid out in parallel over a large area of land. Since 1985 a solar thermal system using this principle has been in full operation in California in the United States. It is called the SEGS system.[26] Other CSP designs lack this kind of long experience and therefore it can currently be said that the parabolic trough design is the most thoroughly proven CSP technology.

The Solar Energy Generating System (SEGS) is a collection of nine plants with a total capacity of 350MW. It is currently the largest operational solar system (both thermal and non-thermal). A newer plant is Nevada Solar One plant with a capacity of 64MW. Under construction are Andasol 1 and Andasol 2 in Spain with each site having a capacity of 50MW. Note however, that those plants have heat storage which requires a larger field of solar collectors relative to the size of the steam turbine-generator to store heat and send heat to the steam turbine at the same time. Heat storage enables better utilization of the steam turbine. With day and some nighttime operation of the steam-turbine Andasol 1 at 50MW peak capacity produces more energy than Nevada Solar One at 64 MW peak capacity, due to the former plant's thermal energy storage system and larger solar field.

553MW new capacity is proposed in Mojave Solar Park, California.[27] Furthermore, 59MW hybrid plant with heat storage is proposed near Barstow, California.[28] Near Kuraymat in Egypt, some 40MW steam is used as input for a gas powered plant.[29][30] Finally, 25MW steam input for a gas power plant in Hassi R'mel, Algeria.[31]

[edit] Power tower designs

Main article: Solar power tower

Solar Two. Flat mirrors focus the light on the top of the tower. The white surfaces below the receiver are used for calibrating the mirror positions.

Power towers (also known as 'central tower' power plants or 'heliostat' power plants) capture and focus the sun's thermal energy with thousands of tracking mirrors (called heliostats) in roughly a two square mile field. A tower resides in the center of the heliostat field. The heliostats focus concentrated sunlight on a receiver which sits on top of the tower. Within the receiver the concentrated sunlight heats molten salt to over 1,000 °F (538 °C). The heated molten salt then flows into a thermal storage tank where it is stored, maintaining 98% thermal efficiency, and eventually pumped to a steam generator. The steam drives a standard turbine to generate electricity. This process, also known as the "Rankine cycle" is similar to a standard coal-fired power plant, except it is fueled by clean and free solar energy.

The advantage of this design above the parabolic trough design is the higher temperature. Thermal energy at higher temperatures can be converted to electricity more efficiently and can be more cheaply stored for later use. Furthermore, there is less need to flatten the ground area. In principle a power tower can be built on a hillside. Mirrors can be flat and plumbing is concentrated in the tower. The disadvantage is that each mirror must have its own dual-axis control, while in the parabolic trough design one axis can be shared for a large array of mirrors.

In June 2008, eSolar, a Pasadena, CA-based company founded by Idealab CEO Bill Gross with funding from Google, announced a power purchase agreement (PPA) with the utility Southern California Edison to produce 245 megawatts of power. Also, in February 2009, eSolar announced it had licensed its technology to two development partners, the Princeton, N.J.-based NRG Energy, Inc., and the India-based ACME Group. In the deal with NRG, the companies announced plans to jointly build 500 megawatts of concentrating solar thermal plants throughout the United States. The target goal for the ACME Group was nearly double; ACME plans to start construction on its first eSolar power plant this year, and will build a total of 1 gigawatt over the next 10 years.

eSolar's proprietary sun-tracking software coordinates the movement of 24,000 1 meter-square mirrors per 1 tower using optical sensors to adjust and calibrate the mirrors in real time. This allows for a high density of reflective material which enables the development of modular concentrating solar thermal (CSP) power plants in 46 megawatt (MW) units on approximately π square mile parcels of land, resulting in a land-to-power ratio of 4 acres (16,000 m2) per 1 megawatt.

BrightSource Energy entered into a series of power purchase agreements with Pacific Gas and Electric Company in March 2008 for up to 900MW of electricity, the largest solar power commitment ever made by a utility.[32] BrightSource is currently developing a number of solar power plants in Southern California, with construction of the first plant planned to start in 2009.

In June 2008, BrightSource Energy dedicated its 4-6 MW [33] Solar Energy Development Center (SEDC) in Israel's Negev Desert. The site, located in the Rotem Industrial Park, features more than 1,600 heliostats that track the sun and reflect light onto a 60 meter-high tower. The concentrated energy is then used to heat a boiler atop the tower to 550 degrees Celsius, generating superheated steam.[34]

A working tower power plant is PS10 in Spain with a capacity of 11MW.

The 15MW Solar Tres plant with heat storage is under construction in Spain. In South Africa, a 100MW solar power plant is planned with 4000 to 5000 heliostat mirrors, each having an area of 140 m².[35] A 10MW power plant in Cloncurry, Australia (with purified graphite as heat storage located on the tower directly by the receiver).[36]

Morocco is building five solar thermal power plants around Ouasarzate. The sites will produce about 2000 MW by 2012. Over ten thousand hectors of land will be needed to sustain all of the sites.[37]

Out of commission are the 10MW Solar One (later redeveloped and made into Solar Two) and the 2MW Themis plants.

A cost/performance comparison between power tower and parabolic trough concentrators was made by the NREL which estimated that by 2020 electricity could be produced from power towers for 5.47 ₡/kWh and for 6.21 ₡/kWh from parabolic troughs. The capacity

factor for power towers was estimated to be 72.9% and 56.2% for parabolic troughs.[38] There is some hope that the development of cheap, durable, mass producible heliostat power plant components could bring this cost down.[39]

[edit] Dish designs

A parabolic solar dish concentrating the sun's rays on the heating element of a Stirling engine. The entire unit acts as a solar tracker.

A dish stirling system uses a large, reflective, parabolic dish (similar in shape to satellite television dish). It focuses all the sunlight that strikes the dish up onto a single point above the dish, where a receiver captures the heat and transforms it into a useful form. Typically the dish is coupled with a Stirling engine in a Dish-Stirling System, but also sometimes a steam engine is used.[40] These create rotational kinetic energy that can be converted to electricity using an electric generator.[41]

The advantage of a dish system is that it can achieve much higher temperatures due to the higher concentration of light (as in tower designs). Higher temperatures lead to better conversion to electricity and the dish system is very efficient on this point. However, there are also some disadvantages. Heat to electricity conversion requires moving parts and that results in maintenance. In general, a centralized approach for this conversion is better than the decentralized concept in the dish design. Second, the (heavy) engine is part of the moving structure, which requires a rigid frame and strong tracking system. Furthermore, parabolic mirrors are used instead of flat mirrors and tracking must be dual-axis.

In 2005 Southern California Edison announced an agreement to purchase solar powered Stirling engines from Stirling Energy Systems over a twenty year period and in quantities (20,000 units) sufficient to generate 500 megawatts of electricity.[42] Stirling Energy Systems announced another agreement with San Diego Gas & Electric to provide between 300 and 900 megawatts of electricity.[43] In January 2010, Stirling Energy Systems and Tessera Solar commissioned the first demonstration 1.5-megawatt power plant ("Maricopa Solar") using Stirling technology in Peoria, Arizona.[44] At the beginning of 2011 Stirling Energy's development arm, Tessera Solar, sold off its two large projects, the 709 MW Imperial project and the 850 MW Calico project to AES

Solar and K.Road, respectively,[45][46] and in the fall of 2011 Stirling Energy Systems applied for Chapter 7 bankruptcy due to competition from low cost photovoltaics.[47]

In July 2011, Iran inaugurated Iran's biggest solar power plant in Mashhad which produces 72,000 kilowatt-hour electricity per year.[48]

[edit] Fresnel reflectors

Wind load is avoided by the low position of the mirrors. Light construction of tracking system due to separation from the receiver.

A linear Fresnel reflector power plant uses a series of long, narrow, shallow-curvature (or even flat) mirrors to focus light onto one or more linear receivers positioned above the mirrors. On top of the receiver a small parabolic mirror can be attached for further focusing the light. These systems aim to offer lower overall costs by sharing a receiver between several mirrors (as compared with trough and dish concepts), while still using the simple line-focus geometry with one axis for tracking. This is similar to the trough design (and different from central towers and dishes with dual-axis). The receiver is stationary and so fluid couplings are not required (as in troughs and dishes). The mirrors also do not need to support the receiver, so they are structurally simpler. When suitable aiming strategies are used (mirrors aimed at different receivers at different times of day), this can allow a denser packing of mirrors on available land area.

Recent prototypes of these types of systems have been built in Australia (CLFR [49] ) and by Solarmundo in Belgium.

The Solarmundo research and development project, with its pilot plant at Liège, was closed down after successful proof of concept of the Linear Fresnel technology. Subsequently, Solar Power Group GmbH (SPG), based in Munich, Germany, was founded by some Solarmundo team members. A Fresnel-based prototype with direct steam generation was built by SPG in conjunction with the German Aerospace Center (DLR[50]).

Based on the Australian prototype, a 177MW plant had been proposed near San Luis Obispo in California and would be built by Ausra.[51] But Ausra sold its planned California solar farm to First Solar. First Solar (a manufacturer of thin-film photovoltaic solar cells) will not build the Carrizo project, and the deal has resulted in the cancellation

of Ausra’s contract to provide 177 megawatts to P.G.& E.[52] Small capacity plants are an enormous economical challenge with conventional parabolic trough and drive design – few companies build such small projects. There are plans for SHP Europe, former Ausra subsidiary, to build a 6.5 MW combined cycle plant in Portugal. The German company SK Energy GmbH (company)|SK Energy[53]]) has plans to build several small 1-3 MW plants in Southern Europe (esp. in Spain) using Fresnel mirror and steam drive technology (Press Release [54] ).

In May 2008, the German Solar Power Group GmbH and the Spanish Laer S.L. agreed the joint execution of a solar thermal power plant in central Spain. This will be the first commercial solar thermal power plant in Spain based on the Fresnel collector technology of the Solar Power Group. The planned size of the power plant will be 10 MW a solar thermal collector field with a fossil co-firing unit as backup system. The start of constructions is planned for 2009. The project is located in Gotarrendura, a small renewable energy pioneering village, about 100 km northwest of Madrid, Spain.

A Multi-Tower Solar Array (MTSA) concept, that uses a point-focus Fresnel reflector idea, has also been developed,[55] but has not yet been prototyped.

Since March 2009, the Fresnel solar power plant PE 1 of the German company Novatec Biosol is in commercial operation in southern Spain . The solar thermal power plant is based on linear Fresnel collector technology and has an electrical capacity of 1.4 MW. Beside a conventional power block, PE 1 comprises a solar boiler with mirror surface of around 18,000m². The steam is generated by concentrating direct solar irradiation onto a linear receiver which is 7.40m above the ground. An absorber tube is positioned in the focal line of the mirror field in which water is evaporated directly into saturated steam at 270 °C and at a pressure of 55 bar by the concentrated solar energy.

[edit] Linear Fresnel reflector technologies

Main article: Compact Linear Fresnel Reflector

Fresnel solar power plant PE 1 in southern Spain

Rival single axis tracking technologies include the relatively new linear Fresnel reflector (LFR) and compact-LFR (CLFR) technologies. The LFR differs from that of the parabolic trough in that the absorber is fixed in space above the mirror field. Also, the

reflector is composed of many low row segments, which focus collectively on an elevated long tower receiver running parallel to the reflector rotational axis.[56]

This system offers a lower cost solution as the absorber row is shared among several rows of mirrors. However, one fundamental difficulty with the LFR technology is the avoidance of shading of incoming solar radiation and blocking of reflected solar radiation by adjacent reflectors. Blocking and shading can be reduced by using absorber towers elevated higher or by increasing the absorber size, which allows increased spacing between reflectors remote from the absorber. Both these solutions increase costs, as larger ground usage is required.

The CLFR offers an alternate solution to the LFR problem. The classic LFR has only one linear absorber on a single linear tower. This prohibits any option of the direction of orientation of a given reflector. Since this technology would be introduced in a large field, one can assume that there will be many linear absorbers in the system. Therefore, if the linear absorbers are close enough, individual reflectors will have the option of directing reflected solar radiation to at least two absorbers. This additional factor gives potential for more densely packed arrays, since patterns of alternative reflector inclination can be set up such that closely packed reflectors can be positioned without shading and blocking.[57]

CLFR power plants offer reduced costs in all elements of the solar array.[57] These reduced costs encourage the advancement of this technology. Features that enhance the cost effectiveness of this system compared to that of the parabolic trough technology include minimized structural costs, minimized parasitic pumping losses, and low maintenance. Minimized structural costs are attributed to the use of flat or elastically curved glass reflectors instead of costly sagged glass reflectors are mounted close to the ground. Also, the heat transfer loop is separated from the reflector field, avoiding the cost of flexible high pressure lines required in trough systems. Minimized parasitic pumping losses are due to the use of water for the heat transfer fluid with passive direct boiling. The use of glass-evacuated tubes ensures low radiative losses and is inexpensive. Studies of existing CLFR plants have been shown to deliver tracked beam to electricity efficiency of 19% on an annual basis as a preheater.[56]

[edit] Fresnel lenses

Prototypes of Fresnel lens concentrators have been produced for the collection of thermal energy by International Automated Systems. No full-scale thermal systems using Fresnel lenses are known to be in operation, although products incorporating Fresnel lenses in conjunction with photovoltaic cells are already available.[58]

The advantage of this design is that lenses are cheaper than mirrors. Furthermore, if a material is chosen that has some flexibility, then a less rigid frame is required to withstand wind load. A new concept of a lightweight, 'non-disruptive' solar concentrator technology using asymmetric Fresnel lenses that occupies minimal ground surface area

and allows for large amounts of concentrated solar energy per concentrator is seen in the 'Desert Blooms' [59] project, though a prototype has yet to be made.

[edit] MicroCSP

"MicroCSP"[60][61] references solar thermal technologies in which concentrating solar power (CSP) collectors are based on the designs used in traditional Concentrating Solar Power systems found in the Mojave Desert[62] but are smaller in collector size, lighter and operate at lower thermal temperatures usually below 315 °C (600 °F). These systems are designed for modular field or rooftop installation where they are easy to protect from high winds, snow and humid deployments.[63] Solar manufacturer Sopogy completed construction on a 1MW CSP plant at the Natural Energy Laboratory of Hawaii.[64]

MicroCSP is used for community-sized power plants (1MW to 50MW), for industrial, agricultural and manufacturing 'process heat' applications, and when large amounts of hot water are needed, such as resort swimming pools, water parks, large laundry facilities, sterilization, distillation and other such uses.

[edit] Heat Collection and Exchange

More energy is contained in higher frequency light based upon the formula of E = hν, where h is Planck's constant. Metal collectors down convert higher frequency light by producing a series of Compton shifts into an abundance of lower frequency light. Glass or ceramic coatings with high transmission in the visible and UV and effective absorption in the IR (heat blocking) trap metal absorbed low frequency light from radiation loss. Convection insulation prevents mechanical losses transferred through gas. Once collected as heat, thermos containment efficiency improves significantly with increased size. Unlike Photovoltaic technologies that often degrade under concentrated light, Solar Thermal depends upon light concentration that requires a clear sky to reach suitable temperatures.

Heat in a solar thermal system is guided by five basic principles: heat gain; heat transfer; heat storage; heat transport; and heat insulation.[65] Here, heat is the measure of the amount of thermal energy an object contains and is determined by the temperature, mass and specific heat of the object. Solar thermal power plants use heat exchangers that are designed for constant working conditions, to provide heat exchange.

Heat gain is the heat accumulated from the sun in the system. Solar thermal heat is trapped using the greenhouse effect; the greenhouse effect in this case is the ability of a reflective surface to transmit short wave radiation and reflect long wave radiation. Heat and infrared radiation (IR) are produced when short wave radiation light hits the absorber plate, which is then trapped inside the collector. Fluid, usually water, in the absorber tubes collect the trapped heat and transfer it to a heat storage vault.

Heat is transferred either by conduction or convection. When water is heated, kinetic energy is transferred by conduction to water molecules throughout the medium. These

molecules spread their thermal energy by conduction and occupy more space than the cold slow moving molecules above them. The distribution of energy from the rising hot water to the sinking cold water contributes to the convection process. Heat is transferred from the absorber plates of the collector in the fluid by conduction. The collector fluid is circulated through the carrier pipes to the heat transfer vault. Inside the vault, heat is transferred throughout the medium through convection.

Heat storage enables solar thermal plants to produce electricity during hours without sunlight. Heat is transferred to a thermal storage medium in an insulated reservoir during hours with sunlight, and is withdrawn for power generation during hours lacking sunlight. Thermal storage mediums will be discussed in a heat storage section. Rate of heat transfer is related to the conductive and convection medium as well as the temperature differences. Bodies with large temperature differences transfer heat faster than bodies with lower temperature differences.

Heat transport refers to the activity in which heat from a solar collector is transported to the heat storage vault. Heat insulation is vital in both heat transport tubing as well as the storage vault. It prevents heat loss, which in turn relates to energy loss, or decrease in the efficiency of the system.

[edit] Heat storage

Heat storage allows a solar thermal plant to produce electricity at night and on overcast days. This allows the use of solar power for baseload generation as well as peak power generation, with the potential of displacing both coal and natural gas fired power plants. Additionally, the utilization of the generator is higher which reduces cost.

Heat is transferred to a thermal storage medium in an insulated reservoir during the day, and withdrawn for power generation at night. Thermal storage media include pressurized steam, concrete, a variety of phase change materials, and molten salts such as sodium and potassium nitrate.[66][67]

[edit] Steam accumulator

The PS10 solar power tower stores heat in tanks as pressurized steam at 50 bar and 285 °C. The steam condenses and flashes back to steam, when pressure is lowered. Storage is for one hour. It is suggested that longer storage is possible, but that has not been proven yet in an existing power plant.[68]

[edit] Molten salt storage

A variety of fluids have been tested to transport the sun's heat, including water, air, oil, and sodium, but molten salt was selected[who?] as best.[69] Molten salt is used in solar power tower systems because it is liquid at atmosphere pressure, it provides an efficient, low-cost medium in which to store thermal energy, its operating temperatures are compatible with today's high-pressure and high-temperature steam turbines, and it is non-flammable

and nontoxic. In addition, molten salt is used in the chemical and metals industries as a heat-transport fluid, so experience with molten-salt systems exists in non-solar settings.

The molten salt is a mixture of 60 percent sodium nitrate and 40 percent potassium nitrate, commonly called saltpeter. New studies show that calcium nitrate could be included in the salts mixture to reduce costs and with technical benefits. The salt melts at 220 °C (430 °F) and is kept liquid at 290 °C (550 °F) in an insulated storage tank. The uniqueness of this solar system is in de-coupling the collection of solar energy from producing power, electricity can be generated in periods of inclement weather or even at night using the stored thermal energy in the hot salt tank. Normally tanks are well insulated and can store thermal energy for up to a week. As an example of their size, tanks that provide enough thermal storage to power a 100-megawatt turbine for four hours would be about 9 m (30 ft) tall and 24 m (80 ft) in diameter.

The Andasol power plant in Spain is the first commercial solar thermal power plant to utilize molten salt for heat storage and nighttime generation. It came online March 2009.[70] On July 4, 2011, a company in Spain celebrated an historic moment for the solar industry: Torresol’s 19.9 MW concentrating solar power plant became the first ever to generate uninterrupted electricity for 24 hours straight. It achieved this using a molten salt heat storage design.[71]

[edit] Graphite heat storage

This article's factual accuracy may be compromised due to out-of-date information. Please help improve the article by updating it. There may be additional information on the talk page. (June 2011)

DirectThe proposed power plant in Cloncurry Australia will store heat in purified graphite. The plant has a power tower design. The graphite is located on top of the tower. Heat from the heliostats goes directly to the storage. Heat for energy production is drawn from the graphite. This simplifies the design.[72]

IndirectMolten salt coolants are used to transfer heat from the reflectors to heat storage vaults. The heat from the salts are transferred to a secondary heat transfer fluid via a heat exchanger and then to the storage media, or alternatively, the salts can be used to directly heat graphite. Graphite is used as it has relatively low costs and compatibility with liquid fluoride salts. The high mass and volumetric heat capacity of graphite provide an efficient storage medium.[73]

[edit] Phase-change materials for storage

Phase Change Material (PCMs) offer an alternate solution in energy storage. Using a similar heat transfer infrastructure, PCMs have the potential of providing a more efficient means of storage. PCMs can be either organic or inorganic materials. Advantages of

organic PCMs include no corrosives, low or no undercooling, and chemical and thermal stability. Disadvantages include low phase-change enthalpy, low thermal conductivity, and flammability. Inorganics are advantageous with greater phase-change enthalpy, but exhibit disadvantages with undercooling, corrosion, phase separation, and lack of thermal stability. The greater phase-change enthalpy in inorganic PCMs make hydrate salts a strong candidate in the solar energy storage field.[74]

[edit] Use of water

A design which requires water for condensation or cooling may conflict with location of solar thermal plants in desert areas with good solar radiation but limited water resources. The conflict is illustrated by plans of Solar Millennium, a German company, to build a plant in the Amargosa Valley of Nevada which would require 20% of the water available in the area. Some other projected plants by the same and other companies in the Mojave Desert of California may also be affected by difficulty in obtaining adequate and appropriate water rights. California water law currently prohibits use of potable water for cooling.[75]

Other designs require less water. The proposed Ivanpah Solar Power Facility in south-eastern California will conserve scarce desert water by using air-cooling to convert the steam back into water. Compared to conventional wet-cooling, this results in a 90 percent reduction in water usage at the cost of some loss of efficiency. The water is then returned to the boiler in a closed process which is environmentally friendly.[76]

[edit] Conversion rates from solar energy to electrical energy

Of all of these technologies the solar dish/stirling engine has the highest energy efficiency. A single solar dish-Stirling engine installed at Sandia National Laboratories National Solar Thermal Test Facility produces as much as 25 kW of electricity, with a conversion efficiency of 31.25%.[77]

Solar parabolic trough plants have been built with efficiencies of about 20%.[citation needed] Fresnel reflectors have an efficiency that is slightly lower (but this is compensated by the denser packing).

The gross conversion efficiencies (taking into account that the solar dishes or troughs occupy only a fraction of the total area of the power plant) are determined by net generating capacity over the solar energy that falls on the total area of the solar plant. The 500-megawatt (MW) SCE/SES plant would extract about 2.75% of the radiation (1 kW/m²; see Solar power for a discussion) that falls on its 4,500 acres (18.2 km²).[78] For the 50 MW AndaSol Power Plant[79] that is being built in Spain (total area of 1,300×1,500 m = 1.95 km²) gross conversion efficiency comes out at 2.6%

Furthermore, efficiency does not directly relate to cost: on calculating total cost, both efficiency and the cost of construction and maintenance should be taken into account.

[edit] Levelised cost

Since a solar power plant does not use any fuel, the cost consists primarily of capital cost with minor operational and maintenance cost. If the lifetime of the plant and the interest rate is known, the cost per kWh can be calculated. This is called the levelised energy cost.

The first step in the calculation is to determining the investment for the production of 1 kWh in a year. Example, the fact sheet of the Andasol 1 project shows a total investment of 310 million euros for a production of 179 GWh a year. Since 179 GWh is 179 million kWh, the investment per kWh a year production is 310 / 179 = 1.73 euro. Another example is Cloncurry solar power station in Australia. It is planned to produce 30 million kWh a year for an investment of 31 million Australian dollars. So, if this is achieved in reality, the cost would be 1.03 Australian dollar for the production of 1 kWh in a year. This would be significantly cheaper than Andasol 1, which can be partially explained by the higher radiation in Cloncurry over Spain. The investment per kWh cost for one year should not be confused with the cost per kWh over the complete lifetime of such a plant.

In most cases the capacity is specified for a power plant (for instance Andasol 1 has a capacity of 50MW). This number is not suitable for comparison, because the capacity factor can differ. If a solar power plant has heat storage, it can also produce output after sunset, but that will not change the capacity factor; it simply displaces the output. The average capacity factor for a solar power plant, which is a function of tracking, shading and location, is about 20%, meaning that a 50MW capacity power plant will typically provide a yearly output of 50 MW × 24 hrs × 365 days × 20% = 87,600 MWh/year, or 87.6 GWh/yr.

Although the investment for one kWh year production is suitable for comparing the price of different solar power plants, it does not give the price per kWh yet. The way of financing has a great influence on the final price. If the technology is proven, an interest rate of 7%[80] should be possible. However, for a new technology investors want a much higher rate to compensate for the higher risk. This has a significant negative effect on the price per kWh. Independent of the way of financing, there is always a linear relation between the investment per kWh production in a year and the price for 1 kWh (before adding operational and maintenance cost). In other words, if by enhancements of the technology the investments drop by 20%, the price per kWh also drops by 20%.

If a way of financing is assumed whereby the money is borrowed and repaid every year, in such way that the debt and interest decreases, the following formula can be used to calculate the division factor: (1 - (1 + interest / 100) ^ -lifetime) / (interest / 100). For a lifetime of 25 years and an interest rate of 7%, the division factor is 11.65. For example, the investment of Andasol 1 was 1.73 euro per kWh, divided by 11.65 results in a price of 0.15 euro per kWh. If one cent operation and maintenance cost is added, then the

levelized cost is 0.16 euro per kWh. Other ways of financing, different way of debt repayment, different lifetime expectation, different interest rate, can lead to a significantly different number.

If the cost per kWh may follow the inflation, the inflation rate can be added to the interest rate. If an investor puts his money in a savings account for 7%, then he is not compensated for inflation. However, if the cost per kWh is raised with inflation, then he is compensated and can add 2% (a normal inflation rate) to his return. The Andasol 1 plant has a guaranteed feed-in tariff of 0.21 euro for 25 years. If this number is fixed, after 25 years with 2% inflation, 0.21 euro will have a value comparable with 0.13 euro now.

Finally, there is some gap between the first investment and the first production of electricity. This increases the investment by the interest realised over the period in which the plant is not active. The modular solar dish (but also solar photovoltaic and wind power) have the advantage that electricity production starts after first construction.

Given the facts that solar thermal power is reliable, can deliver peak load and does not cause pollution, a price of US$0.10 per kWh[81] starts to become competitive, although a price of US$0.06 has been claimed[82] With some operational cost a simple target is 1 dollar (or lower) investment for 1 kWh production in a year.

[edit] Standards

EN 12975 (efficiency test)

[edit] See also

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Energy portal

Renewable energy portal

Sustainable development portal

Solar thermal collector Central solar heating plant Concentrating solar power (CSP) Energy tower EnerWorks Heliostat List of solar thermal power stations Ocean thermal energy conversion Solar cooling Solar heating Solar power plants in the Mojave Desert

Solar tracker Solar updraft tower SolarPACES Photovoltaic thermal hybrid solar collector

[edit] Notes

1. ̂ according to Dr David Mills of Ausra

[edit] References

1. ̂ "Solar Thermal vs. Photovoltaic (PV) – Which Should You Choose?". http://greenrednecks.com/2009/05/09/solar-thermal-vs-photovolatic-pv-%E2%80%93-which-should-you-choose/.

2. ̂ "Solar Thermal vs. Photovoltaic". http://www.solar-thermal.com/solar_vs_pv.html.

3. ̂ "Solar Thermal and PV Efficiency Breakthrough – Stanford Solar Energy Researchers Make Big Claims". http://www.solarthermalmagazine.com/2010/08/03/solar-thermal-and-pv-efficiency-breakthrough-stanford-solar-energy-researchers-make-big-claims/.

4. ̂ Manning, Paddy (10 October 2009). "With green power comes great responsibility". Sydney Morning Herald. http://www.smh.com.au/business/with-green-power-comes-great-responsibility-20091009-gqvt.html. Retrieved 2009-10-12.

5. ̂ EIA Renewable Energy- Shipments of Solar Thermal Collectors by Market Sector, End Use, and Type

6. ̂ "Energy Consumption Characteristics of Commercial Building HVAC Systems" (PDF). United States Department of Energy. pp. 1–6, 2–1. Archived from the original on 2008-04-10. http://web.archive.org/web/20080410212543/http://www.eere.energy.gov/buildings/info/documents/pdfs/hvacvolume1finalreport.pdf. Retrieved 2008-04-09.

7. ̂ Apte, J. et al.. "Future Advanced Windows for Zero-Energy Homes" (PDF). ASHRAE. http://windows.lbl.gov/adv_Sys/ASHRAE%20Final%20Dynamic%20Windows.pdf. Retrieved 2008-04-09.

8. ̂ "Indirect Gain (Trombe Walls)". United States Department of Energy. http://www.eere.energy.gov/consumer/your_home/designing_remodeling/index.cfm/mytopic=10300. Retrieved 2007-09-29.

9. ̂ Douglass, Elizabeth (2007-11-10). "His passion for solar still burns". Los Angeles Times. Archived from the original on 2007-12-15. http://web.archive.org/web/20071215081145/http://www.latimes.com/business/la-fi-haroldhay10nov10,1,5782216.story?coll=la-headlines-business. Retrieved 2007-11-14.

10. ̂ Butti and Perlin (1981), p.7211. ̂ http://www.nrel.gov/learning/re_solar_process.html

12. ̂ Bartlett (1998), p.393-39413. ̂ Leon (2006), p.6214. ̂ "Solar Buildings (Transpired Air Collectors   – Ventilation Preheating)"

(PDF). National Renewable Energy Laboratory. http://www.nrel.gov/docs/fy06osti/29913.pdf. Retrieved 2007-09-29.

15. ̂ "Frito-Lay solar system puts the sun in SunChips, takes advantage of renewable energy". The Modesto Bee. http://www.modbee.com/1618/story/259206.html. Retrieved 2008-04-25.

16. ̂ Denholm, P. (March 2007) (PDF). The Technical Potential of Solar Water Heating to Reduce Fossil Fuel Use and Greenhouse Gas Emissions in the United States. National Renewable Energy Laboratory. http://www.nrel.gov/docs/fy07osti/41157.pdf. Retrieved 2007-12-28.

17. ̂ Kincaid, J. (May 2006). Durham Campaign for Solar Jobs. Archived from the original on 2007-07-15. http://web.archive.org/web/20070715053709/http://www.cleanenergydurham.org/why/solarjobreport.doc. Retrieved 2007-12-28.

18. ^ a b "Solar Thermal Energy". http://practicalaction.org/icts/docs/technical_information_service/solar_thermal_energy.pdf. Retrieved Oct. 8, 2009.

19. ̂ Butti and Perlin (1981), p.54-5920. ̂ "Design of Solar Cookers". Arizona Solar Center.

http://www.azsolarcenter.com/technology/solcook-4.html. Retrieved 2007-09-30.21. ̂ "The Solar Bowl". Auroville Universal Township.

http://www.auroville.org/research/ren_energy/solar_bowl.htm. Retrieved 2008-04-25.

22. ̂ "Scheffler-Reflector". Solare Bruecke. http://www.solare-bruecke.org/English/scheffler_e-Dateien/scheffler_e.htm. Retrieved 2008-04-25.

23. ̂ "Solar Steam Cooking System". Gadhia Solar. Archived from the original on 2007-11-11. http://web.archive.org/web/20071111132802/http://gadhia-solar.com/products/steam.htm. Retrieved 2008-04-25.

24. ̂ ORNL's liquid fluoride proposal.25. ̂ Roland Winston et al.,, Nonimaging Optics, Academic Press, 2004

[ISBN 978-0127597515]26. ̂ SEGS system27. ̂ Israeli company to build largest solar park in world in US Ynetnews, 26

July 2007.28. ̂ Solar thermal electric hybrid power plant for barstow29. ̂ Iberdrola to build 150MW Egyptian thermal solar plant30. ̂ Solar Millennium Tochter Flagsol erhält Auftrag für erstes

Parabolrinnen-Kraftwerk Ägyptens31. ̂ Abener Signs Contract for Solar Thermal Electric - Combined Cycle

Hybrid Plant, Solarbuzz.com

32. ̂ "BrightSource Energy signs whopper solar contract with PG&E". CNET News. 2008-03-31. http://news.cnet.com/8301-11128_3-9907089-54.html. Retrieved 2008-06-11.

33. ̂ "SOLAR ENERGY DEVELOPMENT CENTER (SEDC)   – NEGEV, ISRAEL". BrightSource Energy. http://www.brightsourceenergy.com/projects/sedc.

34. ̂ "BrightSource / Luz II Dedicate Negev Solar Energy Development Center". Cleantech Investing in Israel. 2008-06-12. http://cleantech-israel.blogspot.com/2008/06/brightsource-luz-ii-dedicate-negev.html. Retrieved 2008-06-12.

35. ̂ 100 MW Solar Thermal Electric Project in South Africa36. ̂ Cloncurry to run on solar alone37. ̂ "Ain Beni Mathar, Morocco Solar Thermal Power Station Project".

http://www.afdb.org/en/projects-and-operations/project-portfolio/project/p-ma-fac-012/. Retrieved 2011-05-18.

38. ̂ Assessment of Parabolic Trough and Power Tower Solar Technology Cost and Performance Forecasts

39. ̂ Google's Goal: Renewable Energy Cheaper than Coal November 27, 2007

40. ̂ ANU 'Big Dish', http://solar-thermal.anu.edu.au/41. ̂ Stirling Energy Systems Inc. - Solar Overview42. ̂ World's largest solar installation to use Stirling engine technology43. ̂ Stirling Energy Systems Signs New Contract for 300 MW44. ̂ O'Grady, Patrick (23 January 2010). "SES, Tessera debut new solar

plant in Peoria". Phoenix Business Journal. http://phoenix.bizjournals.com/phoenix/stories/2010/01/18/daily87.html. Retrieved June 17, 2010.

45. ̂ http://www.pv-tech.org/news/aes_solar_buys_tessera_solars_imperial_valley_project_with_intent_to_turn_c

46. ̂ http://gigaom.com/cleantech/tessera-solar-sells-troubled-850mw-project-to-k-road/

47. ̂ Runyon, Jennifer (2011 [last update]). "Solar Shakeout Continues: Stirling Energy Systems Files for Chapter 7 Bankruptcy". renewableenergyworld.com. http://www.renewableenergyworld.com/rea/news/article/2011/09/solar-shakeout-continues-stirling-energy-systems-files-for-chapter-7-bankruptcy. Retrieved November 14, 2011.

48. ̂ Iran's biggest solar power plant inaugurated in Mashhad49. ̂ CLFR50. ̂ DLR - Institut für Technische Thermodynamik - Home51. ̂ PG&E links with Ausra for 177 megawatts of solar thermal power52. ̂ Ausra Sells Planned Plant to First Solar53. ̂ SK Energy GmbH54. ̂ SK Energy GmbH: neuer deutscher Hersteller steigt in den Markt für

kleine bis mittelgroße solarthermische Kraftwerke ein

55. ̂ Mills, D (January 2004). "Advances in solar thermal electricity technology". Solar Energy (Elsevier) 76 (1): 19. doi:10.1016/S0038-092X(03)00102-6.

56. ^ a b Mills, D. "Advances in Solar Thermal Electricity Technology." Solar Energy 76 (2004): 19-31. 28 May 2008.

57. ^ a b Mills, D, and Morrison L. Graham. "Compact Linear Fresnel Reflector Solar Thermal Powerplants." Solar Energy 68 (2000): 263-283. 28 May 2008.

58. ̂ SunCube59. ̂ Desert Blooms Land Art Generator Initiative Competition60. ̂ http://www.seia.org/galleries/pdf/2008_Year_in_Review_Slides.pdf61. ̂ Hawaiian Firm Shrinks Solar Thermal Power62. ̂ SEGS63. ̂ MicroCSP in Idaho64. ̂ http://www.hawaii247.org/2009/12/11/sopogy-introduces-new-solar-

technology-at-nelha/65. ̂ Canivan, John. "Five Solar Thermal Principles." JC Solarhomes. 26

May 2008 <http://www.jc-solarhomes.com/five.htm>.66. ̂ Sandia National Lab Solar Thermal Test Facility67. ̂ National Renewable Energy Laboratory68. ̂ Ausra, article in Scientific American69. ̂ "High temperature storage - Solar thermal application".

http://www.ese.iitb.ac.in/activities/solarpower/storage.pdf. Retrieved 11 October 2011.

70. ̂ http://www.solarmillennium.de/front_content.php?idart=155&lang=271. ̂ http://thinkprogress.org/romm/2011/07/05/260438/solar-can-be-

baseload-spanish-csp-plant-with-storage-produces-electricity-for-24-hours-straight/

72. ̂ Lloyd Energy Storage, see news, Cloncurry Solar Thermal Storage Project

73. ̂ Forsberg, Charles W., Per F. Peterson, and Haihua Zhao. "High Temperature Liquied Fluoride Salt Closed Brayton Cycle Solar Power Towers." Journal of Solar Energy Engineering 129 (2007): 141

74. ̂ Zalba, Belen, Jose M. Marin, Luisa F. Cabeza, and Harald Mehling. "Review on Thermal Energy Storage with Phase Change: Materials, Heat Transfer Analysis and Applications." Applied Thermal Engineering 23 (2003): 251-283.

75. ̂ "Alternative Energy Projects Stumble on a Need for Water" article by Todd Woody in The New York Times September 29, 2009

76. ̂ BrightSource & Bechtel Partner on 440-MW Ivanpah CSP Project Renewable Energy World, September 10, 2009.

77. ̂ "Sandia, Stirling Energy Systems set new world record for solar-to-grid conversion efficiency" (Press release). Sandia National Laboratories. 2008-02-12. http://www.sandia.gov/news/resources/releases/2008/solargrid.html.

78. ̂ Major New Solar Energy Project Announced By Southern California Edison and Stirling Energy Systems, Inc., press release

79. ̂ 2x50 MW AndaSol Power Plant Projects in Spain80. ̂ Solar Thermal Industry Needs Loan Guarantees81. ̂ "Under 10 cents is sort of the magic line"82. ̂ Development of Two Solar-thermal Electric Hybridized Power Plant

Debuts in Southern California

[edit] External links

Wikimedia Commons has media related to: Solar thermal energy

"It's solar power's time to shine". MSN Money. http://articles.moneycentral.msn.com/Investing/SuperModels/ItsSolarPowersTimeToShine.aspx?page=1. Retrieved 2008-06-05.

Onsite Renewable Technologies at United States Environmental Protection Agency website

Renewable solar energy websites at the Open Directory Project Assessment of the World Bank/GEF Strategy for the Market Development of

Concentrating Solar Thermal Power Solar thermal energy calculator Concentrating Solar Power An overview of the technology by Gerry Wolff,

coordinator of TREC-UK NREL Concentrating Solar Power Program Site Comprehensive review of parabolic trough technology and markets Nevada Gets First U.S. Solar Thermal Plant

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