PV Gap

Gail Said:

How can electrons keep being generated by solar panels?

We Answered:

It's because the photovolcaics are closed-loop systems. A photon will come in and basically knock an electron across what is called a "junction" and create current, but it is "caught" (really simplified version) on the other side of the junction and kind of "bounced back" into place.

It's like Formula 1 racing or NASCAR. The car will be sitting in the Pit, just waiting to go, then will tear out, run a few laps until it requires more fuel, then stops in the Pit again, gets refueled, and just waits for the signal from the Pit Boss to get going again.

The limiting factor on solar cells isn't the cell itself, as in the electrical circuits and semiconductors, but rather the very slow degradation of the (usually plastic) that holds each small cell in place, so that it can create a useful photovoltaic cell. Since modern plastics can be treated with UV coatings to prevent degradation, and are practically immune to water, the only thing that can really hurt them is somebody whacks it with a hammer or drops it while installing it on the roof.

They're excellent. The south face of my roof is sufficient, along with a small vertical-axis wind turbine, to generate more power than I need, and it actually gets sold back to Sempra Energy/SDG&E.

Troy Said:

How many solar panels do I need to run my two bedroom townhouse without electricity from the grid?

We Answered:

The issue is more complicated than you might imagine. You can learn how many kilowatt hours you use from your electric bill. This will be an average, but if you want to be off the grid, you will need a system large enough to deliver the maximum amount you use. This will not be practical, unless you have batteries on the system.

My 6 kW system delivers about 20 kWh per day, in an area where the insolation value (suns energy) is about 5. You can find your area's insolation value on the Internet, under SOLAR INSOLATION.

My installation is situated for maximum utility, in that my ridge runs east and west, and the panels are on the south slope.

Using this information and your utility bill, you should be able to approximate the size system you need.

If your utility has net metering, you may be better off not having batteries, but spend the money on the largest system you can afford. This way you will maximize the amount of savings. Batteries cost money, have to be maintained, must be replaced every few years, and take away from the efficiency of the system.

There are many kinds of solar panels. Look them up on the Internet to learn their characteristics. Keep in mind that the system output will be only about 70 to 75 percent of the rated output. This is due to inefficiencies in system components.

Myrtle Said:

How many solar panels do I need to run a pump?

We Answered:

Are you sure you want those panels? It would probably be more cost-effective to get higher-wattage panels. From those specs, it sounds like you need about 800 watts of panels. That's 4 200-watt panels.

I would skip the inverter, and look for a pump that runs off DC. In fact, many AC motors will run off DC, although that's a trial-and-error sort of thing that no one will guarantee. Typically you would lower the voltage input to do so, so a 110-volt AC induction motor would run off maybe 70-80 volts DC, to avoid burning out the motor. But if you get a pump rated for DC, then you'll certainly have something that works right.

Chad Said:

How to make my microwave work only using solar panels?

We Answered:

There's a lot of important details, but the short answer is that you would need a system capable of supplying around 1000W, at 120VAC and capable of handling the current (which would be around 8A).

The specific requirements would depend on how you intend to use the microwave oven (i.e. how long its on for and how often you turn it on). Based on the usage you'd be able to come up with an idea of how many batteries you need (for storing the energy) versus how many solar panels you need (for charging the batteries).

In any case, it would be a fairly expensive way to heat food. Even if you made it cheap (i.e. so that the system could only be used occasionally), I'd guess it would cost at least $1000 for the inverter, batteries and other electronics plus another $1000 for a (relatively low power) solar panel.
If you wanted to make it more of an 'on demand' system, you'd be looking at a pretty high price tag.
You'd probably be better off with a solar cooker.

That being said, such a system would be able to power many other household things as well, it wouldn't be limited to just powering microwave ovens. However economically, solar power isn't (currently) reasonable (assuming you have access to the grid).

Byron Said:

how many solar panels would I need to power my home?

We Answered:

Solar panels produce DC electricity, not AC. So, they would have to charge a bank of batteries, then you'd need an inverter to convert DC to AC.

You need to find what your peak wattage is (consumption) and how long you want to run things for and work backwards from there.

Suffice to say, a roof-full of panels probably won't be enough.