Overview of state-of-the-art emerging technologies

for

Solar Photovoltaics and

Concentrating Solar Power (CSP)

Contents1.Introduction

1.1 The Sun _ Resource1.2 Spectrum of Solar Radiation1.3 Harvesting sunlight

2. State-of-the-art Emerging Photovoltaic Technologies2.1 Wafer based c-Si state-of-the-art technologies (p-type wafer: BSF & PERC, High efficiency >20%, n-type wafer: IBC & HIT)2.2 Concentrated PV : III-V group alloy semiconductors e.g. GaAs 2.3 Polycrystalline thin-Films (CdTe & CIGS) & a-Si/µc-Si tandem cells2.4 Dye Sensitized solar cells (DSSC) and OPV etc.

3. State-of-the-art Emerging CSP3.1 Parabolic trough Collectors3.2 Linear Fresnel lens collectors3.3 Solar Towers (Heliostat field collectors) 3.4 Parabolic Dish Reflectors /Sterling Engine

4. Case studies List/ References

5. Conclusions & outlook

1.1 Sun-The Resource

Most of the third world countries fall in the solar belt of the Globe

 If installed in areas marked by the six discs in the map, solar cells with a conversion efficiency of only 8 % would produce, on average, 18 TW electrical power.  The colors show a three-year average of solar irradiance, including nights and cloud coverage.

Fig. 1. Global solar radiation map

1. Introduction

1.2 Spectrum of Solar Radiation

The spectrum nearly resembles to that of a black body at 6000 KThe spectrum ranges from a fraction of nm to hundreds of meter wavelengthThe region between 200 to 380 nm wavelength is called Ultra Violet radiation and contains 6% of energyThe region between 380 and 780 nm wavelength is called visible radiation and contains 48% of energyThe region between 780 and 3000 nm wavelength is called Infrared radiation and contains 46% of energy

Fig. 2. Solar radiation spectrum

1.3 Harvesting sunlight

The energy of sunlight reaching the surface of the earth is more than 5,000 times the total primary Energy supply (TPES).  It is available directly as sunlight, as wind due to temperature differences, or as hydropower from rainfall of evaporated water. 

Several routes exist to directly convert sunlight into useful energy:Plants (via photosynthesis) => Biomass  (low efficiency, needs water and soil)Solar thermal => Heat, Electricity  (efficient, complex structures, long gestation period, Centralized power gen)Photovoltaics => Electricity  (efficient, quick installations, distributed power gen )

2. State-of-the-art Emerging PV Technologies

Properties required for candidate PV materials and device structures

The most essential ones concern optical and electrical conditions:

i)Strong light absorption over a large spectral range. This property implies that a tunable band gap is desirable. The peak of absorption should be at 1.4–1.5 eV, for optimal efficiency.

ii) Good carrier collection properties for both - minority and majority carriers, a low carrier recombination loss (in the bulk, at grain boundaries and at the front and back surfaces).

iii) Low cost, so that the thin film structures are preferable.

iv) Stability as functions of both time and illumination conditions (stable active materials, stable metal contacts, resistance to corrosion);

v) High abundance of the raw materials (for large-scale production);

vi) Environment friendly technology;

Fig.3. Market share trend of different PV Technologies (Ref: Fraunhofer ISE, 2013)

2012: C-Si: 86%, Thin-films: 11%, other: 3%

Market share YOY trend of different PV Technologies

Fig.4. Best Efficiency solar cells showing “Emerging PV “

2.1 High Efficiency wafer based c-Si state-of-the-art PV technologies

Remarkable success of the PV industry is largely attributed to the following three critical relative advantages of c-Si technology:

1)Highest conversion efficiency for any commercial-scale single junction PV module2)An established product ‘bankability’ for qualified suppliers (a warranty for 80% of original performance after 25 years of service )3)A consistent ability to offer price-competitive modules ( Due to an ability to reduce costs throughout the c-Si supply chain)

Fig. 5. The primary steps of the wafer-based c-Si module supply chain.

[1] Ref: A Wafer-Based Monocrystalline Silicon Photovoltaics Road Map: Utilizing Known Technical Improvement Opportunities for Further Reductions in Manufacturing Costs, Alan Goodrich*, Peter Hacke*, Qi Wang, Bhushan Sopori, Robert Margolis, Ted James, David Hsu, and Michael Woodhouse* , SOLMAT 114(2013) 110-135.

Fig. 6. Process flow for fabricating a standard Al-BSF c-Si solar cell. Ref: [1]

Fig.7. Model process flow for fabrication (LDSE+PERC+Bifacial+LBSF+Cu/Ni LIP) of solar cells Technology (Eff : 20-22%) Ref: [1]

C-Si solar cell /module efficiency improvement and Cost reduction strategies

Strategy Present Value (2013 )

Predicted Value (2024)

Remarks

Minimum as-cut c-Si wafer thickness (um)

200 125 Cost reduction due to Si material saving

Use of silver per cell (156x156 mm2) gm/cell

0.14 0.03 Saving due to less Ag usage

Contacting high sheet resistance emitter (Ohm/sq)

60-80 120 Current improvement

Finger width reduction (um)

65 30 Reduced front shadow

Stabilized cell efficiency improvement (%)

17.5 (p-type mono)

22 (n-type IBC)

19(p-type mono )

26 (n-type IBC)

New cell technology

Source: ITRPV 2014

Fig 8. Expected market share of different c-Si solar cell technologies

Competitive wafer/cell/ module technologies ->Improved market penetration -> sustainable energy supply

Fig 9. BOS cost for PV system >100 kW in Asia

Fig 10. Calculated LCOE values for different insolation conditions. (Financial terms: 80% debt, 5% Interest rate, 20 year loan tenor, 2%/a inflation rate, 25 yrs usable system life)

Summary Table - Key Data and Figures for PV Technologies

Ref: Yinghao Chu & Peter Meisen, Review and Comparison of Different Solar Energy Technologies, Global Energy Network Institute (GENI), August 2011

2.2 Concentrating Photovoltaics

In this technology, lenses (e.g., Fresnel lenses) or mirrors are used to focus sunlight onto a much smaller photovoltaic cell. Systems typically use a tracking device to follow the sun.

Fraunhofer Institute for Solar Energy Systems, and the Helmholtz Center, Berlin have achieved a new world record efficiency of 44.7% at a concentration of 297 suns using a new solar cell structure with four solar subcells based on III-V compound semiconductors.

AdvantagesSunlight concentration dramatically decreases the size of the solar cell, allowing more effective use of costly semiconductor material.

Smaller cell size allows more expensive, higher efficiency solar cell materials, including stacks with variable bandgap semiconductor layers that absorbs almost full solar spectrum.

DisadvantagesAdvanced multi-layer PV materials & process equipment are more expensive than those used in conventional PV systems. For the best efficiency of solar cell operating under high sunlight concentration, it is inevitable to cool the device efficiently. The equipment needed to concentrate and track the sun must be particularly accurate and stable, and is therefore expensive.

To overcome the cost barrier, concentrating systems will need to develop light-weight, low-cost reflector surfaces, inexpensive and strong but accurate tracking mechanisms, and a cost-effective technique for cooling the PV panels.

Fig 11. Schematic illustration of the PV effect and Band structure of the Tunnel Junction

2.3 Thin-Films PV Technologies (CdTe, CIGS & a-Si/uc-Si)

Fig 13. Roll PV, flexible solar laminate By United Solar Ovonic

Fig 12. Amorphous-Si thin-film modules on glass substrates

The materials commonly adopted for thin-film are: Cadmium Telluride (CdTe), Copper Indium Gallium Selenide (CIGS), amorphous or micromorphous Silicon (a-Si or µc-Si) deposited on glass substrate, SS, plastics.

Thin-Film PVThin-film PV systems use advanced manufacturing techniques to apply very thin layers of semi-conductor materials, substantially reducing the amount of semiconductor material required.

AdvantagesThe system uses less semiconductor material and employs high-speed, mass-manufacturing techniques that can dramatically lower costs. The mechanical flexibility of most thin-film materials allows them to be molded to a variety of surfaces, creating the potential to embed PV power in a wide variety of devices and appliances.

DisadvantagesThin-film materials typically are less efficient than conventional PV systems, offsetting the technology’s manufacturing cost savings and making its cost per kWh roughly equivalent to conventional systems.

Lower efficiency means that, for a given energy output, a larger system will be needed. Efficiency of thin-film systems tends to decrease much more rapidly over time than conventional PV materials.

Fig 14. Spectral response of solar cell with different active materials

Fig 15. Mechanism of Dye sensitized Solar Cell

Fig 16. Semi Transparent Dye sensitized Solar Cell modules & their applications

2.4 Dye Sensitized & organic solar cells

Advantages of DSSCs

Use of low-cost materials, simple to manufacture and technically attractive.

DSSCs work even in low-light conditions, allowing them to work under cloudy skies and non-direct sunlight. The cutoff is so low that this technology is being considered for indoor use, collecting energy for small devices from the lights in the house. DSSCs operate at lower internal temperatures and hence less reduction in efficiency at high ambient temperature.

Drawbacks

Current efficiency still relatively low compare with traditional semiconductor solar cells.

Dyes degradation in ultraviolet radiation limits the lifetime and stability of the cells. Generally, DSSC technology uses liquid electrolyte that has temperature stability problems.

Organic PV Cell

Fig 17.Operation of organic Solar Cell

Fig 18. PV process, Device Fabrication & highest effi in organic Solar Cell

Fig 19. Principles of Si microspheres solar cells Source: Clean venture 21

Fig 20. Nano ink based solar cells by M/s Nanosolar

Fig 21. DSC application (top) & Expected Roadmap for OPV Source: Solarmer

3. State-of-the-art Emerging Concentrating Solar Power (CSP)

There are four types of concentration solar power collectors, as given below:

3.1 Parabolic trough Collectors3.2 Linear Fresnel lens collectors3.3 Solar Towers (Heliostat field collectors) 3.4 Parabolic Dish Reflectors /Sterling Engine

Features of CSP technologies:

CSP technology systems use reflective surfaces to gather and concentrate direct normal solar radiation to create heat

The requirement for unscattered (direct normal irradiance) radiation limits CSP plants to certain locations, primarily desert regions with limited cloud cover

Three (viz., parabolic trough, linear Fresnel, power tower)

of the four CSP technologies use the collected heat to power conventional Rankine steam cycles, similar to those used for coal and nuclear plants

Dish-engine systems use the concentrated sunlight to power a small heat engine at the dish’s focal point

Advantages of CSP systems

resemble traditional power plants generation based on steam and is large scale use standard equipment for power generation

can be built in small sizes and added to as neededcan achieve high steam operating temperatures, allowing more efficient power generationcapable of combined heat and power generation

steam for absorption chillers, industrial process heat, desalination

Non-carbon emitting power generation

incorporates storage storage not major part of generation cost size of steam power plant that lacks storage

does not have to be increased when storage added

added storage cost effective if energy sold at peak hours

allows generation to match utility load profile can be hybridized with intermittent renewables

Dish/Stirling Engines

A parabolic dish is used to concentrate sunlight onto a receiver that converts sunlight into high-temperature energy that is used to drive an engine mounted at the focal point of the dish.

AdvantagesHigh solar concentration combined with high-efficiency, high-temperature engines currently offers the most efficient (although not the lowest cost) form of solar conversion to electricity.

Dish engines usually do not need any water for cooling.

DisadvantagesEnergy storage is difficult because very hot fluids must be transported from the receiver—which moves as the dish tracks the sun—to a stationary storage facility located on the ground.

Engines and receivers for these high temperatures are more expensive and have not demonstrated the durability needed for commercial use.

Fig 22. Dish Engine system

Linear Fresnel Lens technology Linear Fresnel technology uses a set of long narrow mirrors, or occasionally lenses, to concentrate sunlight onto a receiver tube. Similar to a parabolic trough system, this technology uses long rows of collector/receivers with extensive piping to transport the heated fluid to and from the engines.

AdvantagesPlaced closer to the ground than troughs, Fresnel systems produce less shading, can be spaced closer together, and are less likely to be disrupted or damaged by winds. A stationary receiver tube eliminates issues with rotating joints or flexible tubing typically associated with troughs. Thermal storage allows dispatchability, maximizing the value of this system’s energy. Disadvantages

With a still relatively unproven design, there are a variety of technical issues that developers must resolve before broad commercialization is possible. As with trough systems, long piping runs reduce system efficiency and increase cooling water demand.

Fig 23.Linear Fresnel Lens Technology

Fig 24. A typical Parabolic trough CSP system

Fig 25. Solar Towers (Heliostat field collectors)

Comparison of different CSP technologies

4. Case study

4.1 The Photovoltaic Market Transformation Initiative (PVMTI)#

•Launched by the International Finance Corporation (IFC) as an innovative investment facility designed to provide finance in private sector projects to encourage the market development for PV.

•A total of 25 million USD of GEF funds invested by IFC for PV projects in India, Kenya and Morocco with break up of 15, 5 and 5 million USD, respectively.

Aims and objectivesThe specific focus was to stimulate PV business activities in India, Kenya and Morocco. This was achieved through:

• Providing finance for sustainable and replicable commercial PV business models,according to individual business plans through a competitive bidding process.

• Financing business plans with commercial loans at below-market terms or withpartial guarantees or equity instruments

• Provision of technical assistance through the External Management Team (EMT) to PV businesses on planning, financing operations and technology.

# Prepared by R. Gunning, IT Power, UK

Timeline: 10 years, from 1st July 1998.

PVMTI programme addressed the market barriers (Economic,skill,policy) by:

a)establishing marketing and customer service infrastructures;

b) securing the involvement of financial institutions in delivering appropriate customer credit schemes;

c) ensuring quality of systems design and installation, by increasing technical resources and competence through training.

Project Implementation in India: Through IT Power, UK & Indian Renewable Energy Development Agency (IREDA),

•29 proposals received from different industry segments including new credit schemes, new uses of PV technology, creative financing mechanisms and entry to new geographical markets. •Shri Shakti Alternative Energy Ltd. (SSAEL) -2.2 million USD. SSAEL increased significantly the consumer adoption of high quality PV products. •SREI International Finance Ltd- 2.35 million USD developed a retail and service network and provided consumer finance for the sale of photovoltaic (PV) solar home systems and portable PV power packs in West Bengal, India.•Shell Renewables India (SRI)- 4 million USD -open a network of Shell Solar Centres in Southern India

Ref: 16 Case Studies on the Deployment of Photovoltaic Technologies in Developing Countries, Sep 2003, Task 9 Deployment of Photovoltaic Technologies: Co-operation with Developing Countries, IEA PVPS International Energy Agency ,Implementing Agreement on Photovoltaic Power Systems , http://www.iea-pvps.org

Lessons Learned and Success Factors

The success of PVMTI to date can be judged by the following criteria.Sponsors – a number of strong new entrants have joined the market thus increasing competition in the countries.Profitability – several projects are likely to be commercially viable after only one round of concessional financing.Financing – third parties (e.g. banks) committed funds to PV deals in the three countries.

Key themes that underpin the success of the programme :

• Country unique business environment – each country is unique and one solution is not applicable to all.• Flexible investment – flexible PVMTI investment terms facilitate optimal structuring ofprojects.• Good management – a strong and experienced management team is vital component of the business plan.

Conclusions and Outlook• An overview of state-of-the-art and emerging SPV

& CPV technologies has been presented.• Based on predictions given by ITRPV 2014, wafer

based c-Si SPV technologies are expected to attain efficiencies to 20-26% leading to grid parity

• DSC & OPV technologies by 2017 will cost 0.4 EU/Wp@ 10% efficiency and life cycle of 10-20 years.

• Case study on PV Market Transformation Initiative (PVMTI) has been presented- showing possibility of stand-alone PV market developments

Thanks