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Concentrated photovoltaic solar technology is used in commercial projects. Power plants have a great advantage, especially for large-scale utility-grade power plants. Concentrating photovoltaic technology is the “destructive technology†of the solar energy industry. In large-scale power plant projects in areas with dry and sunny climates, it may replace conventional thin film and crystalline silicon photovoltaic technologies. Concentrating photovoltaic power generation does not require water during operation, and it can make better use of land, generating more electricity per acre than any other technology. Especially in areas with abundant sunshine, limited land, and lack of water resources, the development of concentrated photovoltaics is the best choice.
Concentrating photovoltaic systems incorporating inexpensive optical components can greatly reduce the use of crystalline silicon. The optical design of a successful high concentrator photovoltaic system must be balanced on the optical system, including cost, efficiency, manufacturing, tracking error sensitivity, heat load, and durability.
For example, the Amonix Concentrating Photovoltaic System uses a high-efficiency, low-cost acrylic Fresnel lens to collect sunlight. The Fresnel lens is thinner, larger, and flatter than traditional lenses. It was originally designed to focus light from a lighthouse. A Fresnel lens with dedicated secondary optics can concentrate 500 times the normal intensity of light onto a III-V multijunction solar cell. Group III-V multijunction solar cells are fabricated from layered, semiconducting materials with different bandgap. The sunlight enters the top layer. The top layer has the largest band gap. The sun continues to pass through the solar cell until the band gap is smaller than the photon energy. Photons will be absorbed. By matching the bandgap and photon energy in this way, multijunction solar cells are more efficient than single junction solar cells. Because of this, the heat loss of photon energy during absorption is reduced. The conversion efficiency of currently commercially available III-V multi-junction solar cells can reach about 40%.
Although the III-V multi-junction cell technology has a long tradition, there is still much room for improvement in their use in concentrating photovoltaics. In the past year, the optimized optical design has increased the rated power of the system by more than 10%. In order to continue to seek new breakthroughs, engineers are exploring trade-offs, alternative optical designs, materials, and thermal management.
To achieve a good optical design, the following are the key factors to consider:
Tracking sensitivity
A high-capacity photovoltaic design with good fault tolerance can produce better efficiency and power generation capability. However, in order to increase the light gathering effect, it must involve the trade-off between efficiency.
Thermal management
Increased concentration of light can save costs and, to some extent, improve battery efficiency. However, higher spotlight intensity also increases the solar cell's thermal load, which in turn reduces cell efficiency. Therefore, the optimum spotlight intensity must achieve a good balance between efficiency and temperature.
Fresnel lens
III-V multi-junction solar cells can achieve a high fill factor for uniform power flux distribution. Unfortunately, the Fresnel lens produces uneven flux distribution. The design of a suitable Fresnel lens improves the flux distribution to reduce the loss caused by the series resistance of the solar cells and achieve a relatively high fill factor at higher concentrating power.
If you do not pay attention to cleaning, the performance of solar cells will decline over time. For high concentration photovoltaics, the height of the lens from the ground has an important impact on reducing the surface contamination of the battery. A study conducted in Las Vegas found that the pollution rate in 3 months reached 2%. This coincides with the observed drop in power generation capacity.
Influence of optical components
Optical design has a major impact on the operational performance of concentrator photovoltaic systems. Multi-junction solar cells using suitable optical designs can greatly increase the power generation capacity while reducing the consumption of semiconductor materials. But to achieve the best results, concentrator photovoltaic systems need to maintain a balance between cost, material, and operating factors.
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