Concentrator photovoltaics, or CPV, are solar energy machines that use lenses or mirrors to focus sunlight onto very small solar cells. Instead of covering a large panel with semiconductor material, a CPV module uses optics to make intense spots of light on tiny high-efficiency cells. This matters because the best solar cells are expensive, so concentrating light can reduce the amount of cell material needed.
CPV works best in very sunny locations with clear skies and strong direct sunlight.
A typical CPV module has a front lens array, a small cell array, heat spreaders, and a tracking system that points the module at the Sun. Fresnel lenses are often used because they are thin, lightweight lenses with stepped grooves that bend incoming parallel rays toward a focus. The concentrated sunlight increases the electrical power from each cell, but it also creates heat that must be removed to keep efficiency high.
Because CPV needs accurate alignment with the Sun, two-axis tracking is usually required for maximum output.
Key Facts
- Concentration ratio: C = lens collection area / solar cell area.
- Electrical power output: P = IV, where I is current and V is voltage.
- Solar energy input to a lens: P_in = G A, where G is solar irradiance and A is lens area.
- Module efficiency: η = P_out / P_in.
- Higher concentration increases cell current, but overheating can reduce voltage and efficiency.
- CPV mainly uses direct normal irradiance, so clouds and haze strongly reduce performance.
Vocabulary
- Concentrator photovoltaic
- A solar power device that uses lenses or mirrors to focus sunlight onto small photovoltaic cells.
- Fresnel lens
- A thin lens made of concentric grooves that bends light like a much thicker curved lens.
- Concentration ratio
- The factor by which optics increase sunlight intensity on a solar cell compared with normal sunlight.
- Direct normal irradiance
- The solar power per square meter arriving in a straight line from the Sun onto a surface perpendicular to the rays.
- Heat sink
- A component that carries heat away from a device so its temperature stays within a safe range.
Common Mistakes to Avoid
- Assuming CPV works well with all sunlight is wrong because CPV mainly uses direct sunlight and cannot concentrate diffuse light from cloudy skies effectively.
- Ignoring the tracking system is wrong because even a small pointing error can move the focused spot away from the tiny solar cell.
- Thinking higher concentration always means higher efficiency is wrong because intense light also raises temperature, and hot solar cells usually produce less voltage.
- Using total panel area as the solar cell area is wrong because CPV has a large optical collection area but much smaller active cell area.
Practice Questions
- 1 A CPV lens has an area of 0.040 m2 and focuses sunlight onto a cell with an area of 0.00020 m2. What is the concentration ratio?
- 2 Direct normal irradiance is 900 W/m2 on a CPV module with total lens area 1.5 m2. If the electrical output is 420 W, what is the module efficiency?
- 3 Explain why a CPV module usually needs two-axis tracking, while a standard flat solar panel can still produce useful power without precise tracking.