CPV – Concentrator Photovoltaics

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Small Solar Cells, High Concentration

Explore the spectrum of solar power.

How Does High Concentration CPV Work?

Concentrator photovoltaics (CPV) uses optics to focus the sun’s power on small high-efficiency, multi-junction solar cells. Multi-junction solar cells were originally designed, and are still used today, for space applications.  In the early 2000’s scientists started using multi-junction solar cells for terrestrial concentrator solar applications. Using high-efficiency, small solar cells paired to less expensive optics made from glass or acrylic allows for a reduction in the amount of expensive semiconductor material while retaining superior performance. The resulting solar modules are highly efficient and allow the generation of electricity at a lower cost than traditional silicon solar panels.

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Fresnel Lens

Remember discovering the sun’s power as a child using a magnifying glass to light a match or burn a leaf? A Fresnel lens is a flat, high-precision magnifying lens that uses a number of concentric rings to focus the suns incoming rays onto a single point. A Fresnel lens can be made from many materials but the most popular for concentrator photovoltaic applications are acrylic or silicone on glass (SOG). Suncore’s optical engineers have experimented with both materials and have settled on using a SOG Fresnel lens to ensure long term reliability for our modules. Suncore went the extra mile by developing the required optics manufacturing processes and now produces the SOG lenses in house.

Solar Cell

Multi-junction solar cells use multiple solar cells each stacked on top of one another. Each of these solar cells in the stack are tuned to a specific wavelength of light to maximize the conversion efficiency of incoming light into electricity. The conversion of a wider solar spectrum into electricity is key to gaining higher solar cell efficiencies. Conventional single layer silicon solar cells will never be as efficient as a multi-junction semiconductor. Currently, most multi-junction concentrator solar cells consist of 3 cells but scientists are currently working on 4 and 5 junction solar cells to reach even higher efficiencies. It is forecasted that we will be able to use 50% efficient multi-junction solar cells in CPV systems by 2020!

Shown below, on the left and right diagrams, is the ability of a triple junction solar cell to absorb large portions of the sun’s light spectrum creating greater efficiency. The middle diagram shows the portion of the incoming solar radiation used by a conventional PV (SI) cell, while the right diagram shows the portion of the incoming solar radiation used by our triple junction (CTJ) cells: with greater amounts of the sun’s light spectrum available for electrical generation, the CTJ cells result in higher efficiencies.

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Direct Normal Irradiance

Why isn’t CPV used all over the world with its amazing efficiencies and low cost modules? The answer lies in the fact that CPV relies on the direct beam component of sunlight known as Direct Normal Irradiance (DNI). Direct sunlight is the light that reaches the ground when there are no clouds to scatter the light. Just like with the magnifying glass when you were a kid, it’s not possible to catch the leaf on fire if it’s cloudy. Similarly it’s not possible for CPV to concentrate the light if we don’t have clear skies.  CPV is a great fit in regions with little annual cloud cover where DNI exceeds 2000 kWh/m2/year (5.5 kWh/m2/day). In order to capture the direct sunlight and concentrate it into a single point over the cells, CPV modules must be pointed towards the sun. To achieve this, CPV modules are placed on precision dual axis tracking systems ensuring that the Fresnel lenses are always pointed within 1 degree of the sun’s current position.

CPV Advantages

The ability to convert more of the sun’s power into electricity is at the heart of CPV’s competitive advantage. While even the best PV cells have maximized their efficiency at 25%, multi-junction solar cells currently reach efficiencies over 39%. Cells with efficiencies over 40%-45% are just around the corner. High efficiency is one of the main methods for reducing the cost of solar power. Not only does it reduce the cost of solar equipment but it also reduces the amount of land/roof space needed. Less modules, less space, more savings!

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Yes, you can make power by placing a solar panel on the ground, but peak power can only be achieved by pointing that module at the sun as it crosses the sky! Much like a sunflower, CPV systems follow the sun’s path to maximize the amount of energy captured.  CPV achieves this by the use of tracking systems, which provide more consistent power output throughout the day.  This means more energy generation during the peak hours of the day when electricity consumption is at its highest. CPV uses dual axis tracking systems to precisely follow the sun within 1 degree of its current position, ensuring maximum sunlight to electricity conversion..

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