# Why is my solar panel more efficient as the temperature increases, rather than less efficient?

I have recently performed an experiment in which I placed a solar panel inside a closed box, together with a heater and a lamp (60W). I increased the temperature using a heater from 20ºC to 50ºC. The lamp remained switched on the whole time.

I´ve read on the internet that the optimum temperature at which solar panels work is 25ºC. After that, the efficiency starts to decrease. Nonetheless, my data shows the opposite. The higher the temperature, the more efficiency it has. I don´t understand how this is possible. The current is supposed to increase, and the voltage to decrease, but in my data both of them increase linearly. I don´t know if it´s because I have a small solar panel, which has different purposes, or if there´s a systematic error. I used a milliammeter and a millivoltmeter. If anyone could help, or explain why this happens I would really appreciate it. Thank you!

• What kind of a lamp were you using? Heat-bulb, LED, or fluorescent? If it was the later, these lamps have the tendency to slowly increase their light output after they have been switched on. The increase happens over a period of at least a quarter of an hour, likely more. You usually don't notice this slow increase of the light level, but the difference between the freshly switched on light (after a long cool-down period) and a light that's been on for many hours on end is quite significant. – cmaster - reinstate monica Jul 17 '19 at 16:10
• p=u*i, but what is your "efficiency"? Also, can you describe how you measured voltage and current? at the same time? where was the meter? what kind? etc. – bukwyrm Jul 17 '19 at 18:44

Your voltages are increasing with temperature. This is in contraction to what one expects!

Was optical input power kept constant? Solar cells do get more efficient as sunlight is concentrate on to them. The voltage increase as you are seeing here. That’s one possible explanation. If the input power was kept constant, then this effect cannot be due to light concentration. So the next most likely explanation is you are improving the diode characteristic of the cell, by increasing the average carrier density and saturating trap states? Likely if you solar cell is a-Si (i.e. the reddish looking type often used in calculators).