Notes on Solar Power from an Engineer

My dad is an engineer for the electric company, and these are his thoughts on the use of solar power.

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I've had a few discussions lately about alternative energy. It seems that you can't go a day without hearing some environmentalist shooting off his mouth about needing to go "green" and getting off fossil fuels. Renewable energy is a noble idea but it is a long way off yet.

If you have not heard what the real cost of converting your house over to solar cell energy you might want to take a look at these facts.

The typical solar cell today has at best a 15% efficiency rating. The most efficient solar cells achieve a 40.7% rating. The cost of these experimental units are only affordable by the military and government. Go figure?! So if you really want to live in the 1800s and assume a life of crushing inconvenience read on and take a look at the real truth.

The typical solar panel contains 4 cells, and each of them can produce 0.45 volts and 100 milliamps, or 45 milliwatts. Each cell measures 2 inches by 0.5 inches. In other words, with these solar cells you can generate 45 milliwatts in one square inch (6.45 square cm). For the sake of discussion, let's assume that a panel can generate 70 milliwatts per square inch.

To calculate how many square inches of solar panel you need for a house, you need to know:

- How much power the house consumes on average.

- Where the house is located (so you can calculate mean solar
days, average rainfall, etc.). This question is impossible to
answer unless you have a specific location in mind. We'll
assume that on an average day the solar panels generate their
maximum power for 5 hours living in suntan acres.

The first question is actually pretty interesting, so let's work on it. A "typical home" in America can use either electricity or gas to provide heat for the house, hot water, the clothes dryer and the stove/oven. If you were to power a house with solar electricity, you will have to give up the use of these items and convert to gas appliances because solar electricity is so expensive, see below (note: you’re already behind the goal because the last time I checked, gas is a fossil fuel and is not a renewable resource).

This means that what you would be powering with solar electricity are things like the refrigerator, the lights, the computer, the TV, stereo equipment, motors in things like furnace fans and the washer, etc. Let's say that all of those things average out to 600 watts on average. This is probably a very conservative estimate because the power company usually estimates the average load for a typical home to be around 5 to 8 kw, but I digress. Over the course of 24 hours, you need 600 watts * 24 hours = 14,400 watt-hours per day.

From these calculations and assumptions above, we know that a solar panel can generate 70 milliwatts per square inch * 5 hours = 350 milliwatt hours per day. Therefore you need about 41,000 square inches of solar panel for the house. That's a solar panel that measures about 285 square feet (about 16' by 16'). That would cost around $16,000 right now. Then, because the sun only shines part of the time, you would need to purchase a battery bank, an inverter and regulator, a storage facility (away from the house because batteries produce hydrogen sulfide gas with is highly flammable) etc., and that can double or triple the cost of the installation.

If you want to have a small room air conditioner in your bedroom, double everything.

Because solar electricity is so expensive, you would normally go to great lengths to reduce your electricity consumption. Instead of a desktop computer and a monitor you would use a laptop computer. You would use fluorescent lights instead of incandescent. You would use a small B&W TV instead of a large color set. You would get a small, extremely efficient refrigerator. By doing these things you might be able to reduce your average power consumption to 100 watts. This would cut the size of your solar panel and its cost by a factor of 6, and this might bring it into the realm of possibility.

The thing to remember, however, is that 100 watts per hour purchased from the power grid would only cost about 24 cents a day right now, or $91 a year. That's why you don't see many solar houses unless they are in very remote locations. When it only costs about $100 a year to purchase power from the grid, it is hard to justify spending thousands of dollars on a solar system.

So before you let the next tree hugging wacko ruin your day with his guilt trip remember some of what we talked about here and go home and get you a tall glass of iced tea, kick back in your Lazyboy and watch a good football game on your 50" plasma and thank God what He has blessed you with and be prudent with all that He has given you.