PV Gap

Grace Said:

How do you find out the efficiency of a solar cell with voltage and current measurements?

We Answered:

If you want an accurate measurement, you need a variable power resistor.

2 v and 0.2 amps is about 10 ohms, and the power is 4 watts. So if you can get a 20 ohm variable power resistor, you can measure the voltage and current at different load resistors, and calculate the power for each setting. Find the point where the power is at a maximum, and that is the maximum power output.

You need to make these measurements with full sun on the panel and all the measurements should be made with the same sun conditions.

You can get a rough idea by 2v x 0.2 amps = 4 watts, but that may not be very accurate.

Once you have the max power, you can compare it to the theoretical maximum solar power to calculate the efficiency. The maximum solar power you can get as a power per square foot for your location and time of year.

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Jane Said:

Solar PV Cell how made at home?

We Answered:

You may want to think about building your own solar panels…

Let me start off by saying we (Agua-Luna) are a non-profit organization that live, promote & teach 100% “off grid” living & complete self sufficiency”. To give you an idea of this, we typically don’t leave the Ranch but once or twice a year.

The following steps were taking directly out of a DIY guide I offer to those who would like to run their homes on solar power, reducing their monthly utility bills or even selling power back the electrical companies. The entire guide is available at http://www.agua-luna.com/diy_guides.html… It’s pretty simple but if you have any problems feel free to email us directly at info@agua-luna.com we can walk you threw the process.

Materials you will need…

A sheet of copper flashing from the hardware store. This normally costs about $5.00 per square foot. We will need about half a square foot.
Two alligator clip leads.
A sensitive micro-ammeter that can read currents between 10 & 50 microamperes. Radio Shack sells small LCD multimeters that will do, but I used a small surplus meter with a needle.
An electric stove. My kitchen stove is gas, so I bought a small one-burner electric hotplate for about $25. The little 700 watt burners probably won't work -- mine is 1100 watts, so the burner gets red hot.
A large clear plastic bottle off of which you can cut the top. I used a 2 liter spring water bottle. A large mouth glass jar will also work.
Table salt. We will want a couple tablespoons of salt.
Tap water.
Sand paper or a wire brush on an electric drill.
Sheet metal shears for cutting the copper sheet.

The first step is to cut a piece of the copper sheeting that is about the size of the burner on the stove. Wash your hands so they don't have any grease or oil on them. Then wash the copper sheet with soap or cleanser to get any oil or grease off of it. Use the sandpaper or wire brush to thoroughly clean the copper sheeting, so that any sulphide or other light corrosion is removed.
Next, place the cleaned & dried copper sheet on the burner & turn the burner to its highest setting.
As the copper starts to heat up, you will see beautiful oxidation patterns begin to form. Oranges, purples, & reds will cover the copper.
As the copper gets hotter, the colors are replaced with a black coating of cupric oxide. This is not the oxide we want, but it will flake off later, showing the reds, oranges, pinks, & purples of the cuprous oxide layer underneath.
The last bits of color disappear as the burner starts to glow red.
When the burner is glowing red-hot, the sheet of copper will be coated with a black cupric oxide coat. Let it cook for a half an hour, so the black coating will be thick. This is important, since a thick coating will flake off nicely, while a thin coat will stay stuck to the copper.
After the half hour of cooking, turn off the burner. Leave the hot copper on the burner to cool slowly. If you cool it too quickly, the black oxide will stay stuck to the copper.
As the copper cools, it shrinks. The black cupric oxide also shrinks. But they shrink at different rates, which makes the black cupric oxide flake off.
The little black flakes pop off the copper with enough force to make them fly a few inches. This means a little more cleaning effort around the stove, but it is fun to watch.
When the copper has cooled to room temperature (this takes about 20 minutes), most of the black oxide will be gone. A light scrubbing with your hands under running water will remove most of the small bits. Resist the temptation to remove all of the black spots by hard scrubbing or by flexing the soft copper. This might damage the delicate red cuprous oxide layer we need to make to solar cell work.
Cut another sheet of copper about the same size as the first one. Bend both pieces gently, so they will fit into the plastic bottle or jar without touching one another. The cuprous oxide coating that was facing up on the burner is usually the best side to face outwards in the jar, because it has the smoothest, cleanest surface.
Attach the two alligator clip leads, one to the new copper plate, & one to the cuprous oxide coated plate. Connect the lead from the clean copper plate to the positive terminal of the meter. Connect the lead from the cuprous oxide plate to the negative terminal of the meter.
Now mix a couple tablespoons of salt into some hot tap water. Stir the saltwater until all the salt is dissolved. Then carefully pour the saltwater into the jar, being careful not to get the clip leads wet. The saltwater should not completely cover the plates -- you should leave about an inch of plate above the water, so you can move the solar cell around without getting the clip leads wet.
now place in the sun with the magnified on top.
The solar cell is a battery, even in the dark, & will usually show a few microamps of current.
That’s it it’s that simple. If you’d a more detailed process & some pics (could

Bernard Said:

what is the maximum possible theoretical efficiency of solar PV cell?

We Answered:

Photovoltaic mechanism transforms 40.8 percent of the light that goes through it into energy. This is the highest confirmed efficiency of any photovoltaic device to date.

Priscilla Said:

Is there a difference between the terms "solar cell" and "PV cell" ?

We Answered:

The two terms are often used interchangeably, but in some rare cases, a solar cell refers to a photo resistive cell, that has a lower electrical resistance when light shines on it. These solar (resistive) cells are used (with additional circuitry) to turn street lights on at sundown, for example. A PV (PhotoVoltaic) cell, specifically generates electrical power when illuminated.

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Regards,

John Popelish

Ramona Said:

How many Suns can be focused on a Solar Cell? What is limitation. What causes this limitation?

We Answered:

The problem is heat. All the light that is NOT turned into electricity converts to heat.
With a photo cell with 20% efficiency, 80% of the incoming radiation will just become heat. ~
Solar cells can only stand so much heat, and then they fry.
Full sunlight gives up about 1 horsepower (735W European to 745 W American) per sq meter.