PV Gap

Micheal Said:

Why do solar panels stop working?

We Answered:

Panel degradation can occur in many ways, but they generally take a long time (40yr old panels are still working...).


One problem is diffusion. Since the cells are at a finite temperature and receive energy from the light, atoms in the structure can migrate around the cell. If you mix up materials from either side of the junction, you can reduce or remove the internal field and so charge separation no longer occurs, meaning no more current output.

This is generally a very, very slow process.




My current research is on the back contacts of cadmium-telluride solar cells. CdTe forms a junction with metals, and this junction has a built in electric field that tries to stop the current going out of the cell. This is bad! It reduces the power you get out.

To overcome this, copper is sometimes added. This really cuts down on the restrictions on current, but copper is very diffusive. Within weeks at room temperature it can jiggle its way along grain boundaries (the solar cells aren't one big crystal, but a load of small grains. Our lab makes ones about 0.006mm across). Whilst copper at the back contact is good because it cancels out the effect of the field there, once it gets to the cell junction it has a worse effect. It can act as a 'recombination centre' or 'shunting pathway' - it either absorbs the free charges or takes them somewhere useless and cuts the power output.

Copper is a very obvious and quick acting cause of solar panels reducing in output. I believe a similar effect is true for other cells, just with different materials. The quality of the junction degrades slowly as heat and light give energy to atoms in the lattice and make them jiggle around a bit. Once you have things out of place, performance degrades.

Donald Said:

Why won't my solar panels drive a motor?

We Answered:

The solar cells you have are not providing enough current to operate the motor.
There are special low power motors which can operate directly from a solar cell but it sounds like you do not have one of these. Instead you have a common 1.5V DC hobby motor which requires substantially more current to operate.

You can use the original circuit to charge the batteries and use the charged batteries to run the motor. The batteries would be able to supply enough current to operate the motor, but for a limited time. 8 hours of charging might give you less than 15 minutes of motor operation.

An LED will draw about 20ma. In a solar light such a small current draw from an LED or two can provide hours of light. A Small DC motor might easily require 300ma to run and over 500ma to start.
Running a motor from the same battery at over 15 times the current draw will result in less than 1/15 of the run time compared to the low current LED.

So if an LED operates for 300 minutes the motor would run for less than 20....

The small solar cell size cannot provide enough current to operate the motor directly. Only by slowly charging a battery first would you be able to use the collected and stored Solar energy to operate your motor.

Olga Said:

How can I hook my bus up with solar panels?

We Answered:

The laptops and other things wouldn't be a problem, the ovens however use alot of power. I would use gas for the ovens and install a solar panel to charge a battery and then hook it up to an outlet to charge your laptops etc.