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Concentrated Photovoltaics (CPVs)

Concentrated photovoltaic systems use optics and lenses to focus sunlight on small areas of photovoltaic panels. One of the limitations of photovoltaics is the concentration of sunlight that reaches the semiconductor material. Many panels have maximum efficiency ratings that are not attained in practical installations due to sub-maximal levels of solar irradiation. Concentrated systems attempt to address this problem by focusing sunlight from large collection areas on to smaller areas of semiconductors. This helps to ensure that the photovoltaic panels are always operating at or near maximum efficiency. Getting the most efficiency out of the PV cells means that fewer cells are needed for a system; this translates into reduced price per watt for the system.

Efficiency

Efficiency in PV systems is a matter of the sunlight that reaches the panels and the status of the junctions between the layers of the semiconductors. Concentrated systems address the level of sunlight reaching cells through lens and optic mirrors.

The status of the junctions in a concentrated PV system is most directly affected by temperature. High temperatures increase resistance to the flow of electrons and decrease overall efficiency in a system. Concentrated systems operate at higher temperatures than standard PV panels, which means they require some type of cooling mechanism in order to maintain efficiency. Concentrated PV systems are divided based on the level to which they concentrate sunlight as follows. This also determines the level of cooling required.

Low Concentration CPV (LCPV)

These systems concentrate sunlight 2 to 10 fold (2 to 10 suns). These use conventional PVcells and do not require active cooling. They rely on stationary heatsinks and passive cooling design.

The laws of optics mean that low concentration systems will have high acceptance angles. This means there is no need to actively track the sun during its transit. These are stationary systems and as such require few active components.

Medium Concentration CPV (MCPV)

These systems concentrate 10 to 100 suns. The higher concentrating ability of these systems means that they must actively track the sun. Single and dual-axis systems both exist. Dual-axis systems provide increased efficiencies, but at the cost of more moving parts and higher maintenance. MCPV systems may or may not require active cooling.

Large Concentration CPV (LCPV)

These systems concentrate sunlight more than 100 fold, sometimes up to 500 suns. These systems use multijunction PV cells and have system efficiencies as high as 24%. They require dual axis tracking with high precision to maintain perpendicular alignment to within +/- 0.1 degrees. They also require high efficiency heat sinks and active cooling.

These systems can produce temperatures as high as 1700 oC, which not only requires active cooling, but also allows for hybrid PV and thermal solar systems to be created. Such hybrid systems can increase overall efficiency.

There is currently work underway to produce CPV systems that can concentrate sunlight up to 1000 fold. These systems will be paired with high efficiency multijunction cells that require highly concentrated sunlight into order to function at optimum efficiency.

Grid Parity

The ability to concentrate sunlight means that CPV systems are able to produce more electricity per area of semiconductor than standard systems. This translates into reduce need for semiconductor materials and since semiconductors constitute the major component of cost in PV systems, CPV is less expensive than its standard PV counterparts.

While most PV systems cost around $1.50 to $3 USD per kilowatt-hour, CPV systems cost around $1.00 USD per kilowatt-hour. This reduction in cost has led to projections that CPV systems will reach grid parity by 2020 and certainly much faster than standard PV systems.
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