# Homework Help: Different colored light on solar panels?

1. Feb 17, 2004

### algilaera

would there be any difference if different wavelengths of light is shined on a solar panel? like red, blue and green light. would blue produce the must power becuse the frequency is the heighest? also would ultrviolet light work on solar panels? would it produce more energy?

2. Feb 17, 2004

### HallsofIvy

It depends upon the solar panel. Different materials are sensitive to different frequencies.

3. Feb 18, 2004

### Nice coder

Solar cells only use multiples of there absorbtion frequency, all other energy is dumped as heat.

Some types of solar cells absorb blue light so,
if you gave it red light, it takes a lot of potons to move the electron, so it generates verry little energy/light used
if you gave it UV light, it would take the energy it needed, then 'burn' off the rest as heat.
if you gave it blue light, it would thank you, and give you a lot of energy.

4. Feb 18, 2004

### Njorl

Single material solar cells have a cut-off frequency. Below the cut-off, no electricity is generated. The light passes through the active layer, and is lost. Light at the cut-off generates one electroon for each photon. Light above the cut-off generates one electron for each photon, but also creates unwanted heat.

There are composite solar cells that use 2 materials. The top layer lets low frequency light through, and converts high energy photons to electricity. The bottom layer converts the low frequency light, and is shielded from the more energetic photons that would cause heating.

Recent discovery of the band-gap of InN allows for the creation of a graded material. It would have a continuously varying band-gap that would allow for the design of a theoretically optimized solar cell, extracting the maximum conceivable electricity from sunlight.

Njorl

5. Feb 18, 2004

### algilaera

so you guys are saying different colored lights wount matter? and it wount matter if its a dim light or a bright light becasue if the lights strong enough to be above the "cut-off" point, it would produce the same amount of voltage?

6. Feb 19, 2004

### Njorl

Not quite.

The voltage produced is dependent on the structure of the cell.

The current produced depends on the number of photons absorbed.

The color of the light does matter. It needs to be of at least the cut-off frequency, or it won't power the cell. It is an all-or-nothing effect.

The brightness does matter. It is essentially a measure of the number of photons hitting the cell. This is a continuous effect - more brightness means more current. It is possible to saturate a cell though, in which case adding more photons will have diminishing returns.

Njorl