Solar Power

There are two kinds of solar power systems for domestic consumers.

The first generates a supply of warm or (on sunny days) hot water.

The second gives you electrical energy, which is used to charge lead-acid batteries. An inverter puts the voltage up to 250. You need a lot of batteries, and you won't get enough energy to power kettles or electric ovens.

The main cost of the water-heating system is the installation and plumbing, though the absorbers (black metal panels or evacuated tube collectors) are not cheap.

The electrical system uses PHOTOVOLTAIC CELLS. These are devices which convert from 5 to 10 percent of the sunlight falling on them into electrical energy. They are constructed of silicon - either crystalline (very expensive), polycrystalline (a bit less) or non-crystalline (amorphous silicon; the cheapest). The efficiency is reflected in the price.

Few photovoltaic cells will generate as much energy in their lifetime as it took to make them in the first place. Amorphous cells possibly scrape under the wire.

Solar panels are becoming a familiar sight to road users; they often power speed cameras and other road traffic devices. The box under the pole holding the solar panel contains car batteries.

Something which isn't so obvious ......

You could class fossil fuels as "solar energy". All those prehistoric plants, trees and micro-organisms needed sunlight to grow. Today's plants are solar energy converters, too. When you burn firewood you're releasing some of that energy.

For the record, the most efficient plants at converting sunlight to fuel (known in the trade as "biomass") do it with an efficiency of about 1%.


How much energy is in sunlight?

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