PV Gap

Monica Said:

in solar cells, why does the no-load voltage increase at a decreasing rate with respect to light intensity?

We Answered:

To answer your question as worded, as the light intensity increases, the voltage produced first increases but then begins to level off and will not increase continuously with light intensity because the solar cell becomes "saturated". The cell has only a finite number of sites from which electrons can be knocked free by photons of light. After all the sites have their electrons knocked free, no more voltage can be produced.

Here's a little something extra. Depending on what they are constructed of, solar cells can be more sensitive to some wavelengths than to others. If the light is in the far infrared, the photons may not have enough energy to knock electrons free in the solar cell. Depending on what the solar cell is constructed of, it can be made more sensitive to IR or UV light by adjusting how tightly the electrons are held to their atoms.

Gerald Said:

The effects of temperature on solar cell voltage out put.?

We Answered:

You're logic isn't right.

First off, V=IR (voltage = current * resistance).

Depending on the type of material, higher temperature could have different affects on the electrical resistance of that material type - there is no "all general rule" for this - ESPECIALLY when you're talking about different types of semi conductors.

Now, when it comes to solar cells, the following is true under open circuit conditions (NO CURRENT!):
Higher temperatures = LOWER voltages
Lower temperatures = HIGHER voltages

You can verify this by looking at ANY solar panel's data sheet. They will have a temperature coefficient related to voltage, and you will see that voltage goes UP for low temperatures.

If there is a load attached (closed loop, NOT open circuit), this should generally still remain true. However, things may become more complex than just a simple temperature coefficient.

Hope this helps!

Juan Said:

Connecting Different Voltage Solar Cells in Parallel?

We Answered:

That would not be a good choice. Best bet would be to make groups of them.
By this, group them by output voltage.
Whichever group has the highest count of solar cells with the same voltage rating is the one you want to work with.
Save the other groups, another project is always waiting.
Solar cells that have the same output voltages can be paralleled.
Paralleling miss matched voltages will cause all kinds of reverse currents.
I think that is an answer. If not you can be assured someone will correct me.
Hope that answered your question

Wingman

Evelyn Said:

Why does the voltage drop from solar cells in series when I add a load? 22+ VDC drops to around 6vDC?

We Answered:

It's dropping to 6V because the battery is 6V. Solar cells act as current sources in use and limit their voltage at the maximum current that the cell can supply.

The purpose of the controller is to limit the voltage when the battery is charged (otherwise it will attempt to go to the open circuit voltage).

In other words, you can connect any battery to the solar panel and it will still charge (so long as the o/c voltage is greater than the battery charge voltage). However, the controller should be selected for the battery you want to use.

By the way. Solar panels consist of multiple cells. Each produces about 0.5V. What you have described above is several panels connected in series (not cells).

Ethel Said:

in the context of solar cells, is the no-load voltage the same as open-circuit voltage?

We Answered:

No load voltage is the same as open-circuit voltage (otherwise, you have some type of load).