PHYS 471PHYS 471Solar Energy Solar Energy

2004-12004-1

Concentrating CollectorsConcentrating Collectors

Instructor : Prof.Dr Ahmet EcevitInstructor : Prof.Dr Ahmet Ecevit

Prepared by:Prepared by:Serkan KapucuSerkan Kapucu

Table of ContentsTable of Contents1.Introduction1.Introduction2.Concentrating collectors2.Concentrating collectors3.Types of concentrating collectors 3.Types of concentrating collectors 4.Working principles of concentrating collectors4.Working principles of concentrating collectors5. Technology5. Technology Comparison Comparison6. Calculations6. Calculations7. Economic and Environmental Considerations7. Economic and Environmental Considerations8. Conclusions 8. Conclusions

1. Introduction1. Introduction For applications such as air conditioning, central power For applications such as air conditioning, central power generation, and numerous industrial heat requirements, flat generation, and numerous industrial heat requirements, flat plate collectors generally cannot provide carrier fluids at plate collectors generally cannot provide carrier fluids at temperatures sufficiently elevated to be effective. temperatures sufficiently elevated to be effective.

They may be used as first-stage heat input devices; the They may be used as first-stage heat input devices; the temperature of the carrier fluid is then boosted by other temperature of the carrier fluid is then boosted by other conventional heating means.conventional heating means.

Alternatively, more complex and expensive concentrating Alternatively, more complex and expensive concentrating collectors can be used. collectors can be used.

These are devices that optically reflect and focus incident These are devices that optically reflect and focus incident solar energy onto a small receiving area. solar energy onto a small receiving area.

2. Concentrating 2. Concentrating collectorscollectors

Concentrating, or focusing, collectors intercept direct Concentrating, or focusing, collectors intercept direct radiation over a large area radiation over a large area and focus it onto a small absorber area. and focus it onto a small absorber area. These collectors can provide high temperatures more These collectors can provide high temperatures more efficiently than flat-plate collectors.efficiently than flat-plate collectors. However, diffused sky radiation cannot be focused onto However, diffused sky radiation cannot be focused onto the absorber.the absorber. Most concentrating collectors require mechanical Most concentrating collectors require mechanical equipment that constantly orients the collectors toward the equipment that constantly orients the collectors toward the sun and keeps the absorber at the point of focus.sun and keeps the absorber at the point of focus.

3. Types of concentrating 3. Types of concentrating collectorscollectors

Parabolic trough systemParabolic trough systemParabolic dish Parabolic dish Power towerPower towerStationary concentrating collectors Stationary concentrating collectors 

There are four basic types of concentrating collectors:

3.1. Parabolic trough 3.1. Parabolic trough systemsystem  

Parabolic troughs are devices that are shaped like the Parabolic troughs are devices that are shaped like the letter “u”letter “u”.. The troughs concentrate sunlight onto a The troughs concentrate sunlight onto a receiver tube that is positioned along the focal line of the receiver tube that is positioned along the focal line of the trough. Sometimes a transparent glass tube envelops the trough. Sometimes a transparent glass tube envelops the receiver tube to reduce heat loss [3].receiver tube to reduce heat loss [3].

Figure 3.1.2 Parabolic trough system [3]. Figure 3.1.1 Crossection of parabolic trough [4].

The parabolic trough sytem is The parabolic trough sytem is shown in the figure 3.1.2 below.shown in the figure 3.1.2 below.

TTheir shapes are like letter heir shapes are like letter “u”“u” as shown figure 3.1.1 below.as shown figure 3.1.1 below.

Parabolic troughs often use single-axis or dual-axis Parabolic troughs often use single-axis or dual-axis trackingtracking..

Figure 3.1.3 One Axis Tracking Parabolic Trough with Axis Oriented E-W [8].

Figure 3.1.4 Two Axis Tracking Concentrator [8].Axis Tracking Concentrator [8].

The below figure 3.1.3 shows one axis The below figure 3.1.3 shows one axis tracking parabolic trough with axis tracking parabolic trough with axis oriented E-W.oriented E-W.

The below figure 3.1.4 shows two The below figure 3.1.4 shows two axis tracking concentrator.axis tracking concentrator.

3.2. Parabolic dish 3.2. Parabolic dish systems systems 

A parabolic dish collector is similar in appearance to A parabolic dish collector is similar in appearance to a large satellite dish, but has mirror-like reflectors a large satellite dish, but has mirror-like reflectors and an absorber at the focal point. It uses a dual and an absorber at the focal point. It uses a dual axis sun tracker [3]. axis sun tracker [3].

Figure 3.2.2 Parabolic dish collector with a mirror-like reflectors and an absorber at the focal point [Courtesy of SunLabs - Department of Energy] [3].

Figure 3.2.1 Crossection of parabolic dish [4].

The below figure 3.2.1 shows The below figure 3.2.1 shows crossection of parabolic dish.crossection of parabolic dish.

The Parabolic dish collector is The Parabolic dish collector is shown in the below figure 3.2.2.shown in the below figure 3.2.2.

3.3. Power tower system 3.3. Power tower system A heliostat uses a field of dual axis sun trackers that A heliostat uses a field of dual axis sun trackers that direct solar energy to a large absorber located on a direct solar energy to a large absorber located on a tower. To date the only application for the heliostat tower. To date the only application for the heliostat collector is power generation in a system called the collector is power generation in a system called the power towerpower tower [3]. [3].

Figure 3.3.2 Heliostats [4].Figure 3.3.2 Heliostats [4].Figure 3.3.1 Power tower system [4].

Heliostats are shown in Heliostats are shown in the figure 3.3.2 below.the figure 3.3.2 below.

The Power tower system is The Power tower system is shown in the figure 3.3.1 below.shown in the figure 3.3.1 below.

3.4. Stationary concentrating 3.4. Stationary concentrating solar collectorssolar collectors

Stationary concentrating collectors use compound Stationary concentrating collectors use compound parabolic reflectors and flat reflectors for directing solar parabolic reflectors and flat reflectors for directing solar energy to an accompanying absorber or aperture through energy to an accompanying absorber or aperture through a wide acceptance angle. a wide acceptance angle.

The wide acceptance angle for these reflectors The wide acceptance angle for these reflectors eliminates the need for a sun tracker. eliminates the need for a sun tracker.

4. Working principles of 4. Working principles of concentrating collectorsconcentrating collectors

Unlike solar (photovoltaic) cells, which use light to Unlike solar (photovoltaic) cells, which use light to produce electricity, concentrating solar power systems produce electricity, concentrating solar power systems generate electricity with heat.generate electricity with heat.

Concentrating solar collectors use mirrors and lenses to Concentrating solar collectors use mirrors and lenses to concentrate and focus sunlight onto a thermal receiver, concentrate and focus sunlight onto a thermal receiver, similar to a boiler tube.similar to a boiler tube.

The receiver absorbs and converts sunlight into heat. The receiver absorbs and converts sunlight into heat.

The heat is then transported to a steam generator or The heat is then transported to a steam generator or engine where it is converted into electricity.engine where it is converted into electricity.

A concentrating solar power system that produces 350 A concentrating solar power system that produces 350 MW of electricity.MW of electricity.

7. Economic and Environmental 7. Economic and Environmental ConsiderationsConsiderations

The most important factor driving the solar energy The most important factor driving the solar energy system design process is whether the energy it system design process is whether the energy it produces is economical.produces is economical.

Although there are factors other than economics that Although there are factors other than economics that enter into a decision of when to use solar energy; i.e. no enter into a decision of when to use solar energy; i.e. no pollution, no greenhouse gas generation, security of the pollution, no greenhouse gas generation, security of the energy resource etc., energy resource etc.,

This or some similar economic parameter, gives the This or some similar economic parameter, gives the expected cost of the energy produced by the solar expected cost of the energy produced by the solar energy systemenergy system..

8. Conclusions8. ConclusionsConcentrating solar power technology for electricity Concentrating solar power technology for electricity generation is ready for the market.generation is ready for the market. Various types of single and dual-purpose plants have Various types of single and dual-purpose plants have been analysed and tested in the field.been analysed and tested in the field.Parabolic and Fresnel troughs, central receivers and Parabolic and Fresnel troughs, central receivers and parabolic dishes will be installed for solar/fossil hybrid parabolic dishes will be installed for solar/fossil hybrid and solar-only power plant operation.and solar-only power plant operation. In parallel, decentralised process heat for industrial In parallel, decentralised process heat for industrial applications will be provided by low-cost concentrated applications will be provided by low-cost concentrated collectors.collectors.