What is “Solar”?

Solar adj. “Of, concerned with or determined by the sun” (Oxford English Dictionary).

In green circles and alternative energy circles, energy derived from the sun is a very hot topic (appropriately enough – after all the sun is a source of heat).  You can often hear discussions of:

• solar electricity generation
• passive solar heating
• passive solar cooling
• solar water heating
• solar house design

Benefits of Solar Energy

Solar energy in all its forms is very attractive to people concerned about sustainability and looking after the planet for a number of reasons.  Solar energy is readily world wide, consumes no fuel, is likely to be available for many, many years to come, produces no emissions and does not contribute to global warming (all right; if you’re pedantic, you could say that all global warming is solar, seeing as the planet is heated by the sun – but that’s not what’s meant by solar energy).

Availability of Solar Energy

Just how much solar energy is available from the sun? The sun, of course, is a massive nuclear reactor that gives off heat, light and other forms of electromagnetic radiation (including UV rays, magnetism and X-rays).  This forms the so-called solar wind that spreads throughout the solar system and affects the planets and stray comets spinning around the sun.  The amount of solar energy that reaches the earth’s atmosphere is 174 Petawatts (that’s 174 x 1015 watts.  By way of comparison, the total average power consumption of the whole world in 2004 was 15 terawatts or 15 x 1012 watts).  Most of this is reflected back by clouds and the like (the planet would be uninhabitable if this albedo effect didn’t happen), but some satellites can make use of this solar energy depending on where in the atmosphere they are orbiting.

The amount of solar radiation that actually gets to the earth’s surface is still more than enough to meet all the world’s energy needs.  Much of the sun’s energy is used by natural processes, but much is not, and this is just dissipated into heat and goes back into space again.   The potential for using solar energy is there, all right!

What Solar Energy Powers

Arguably, nearly all forms of renewable energy are derived from the sun and are solar energy at second remove:

• Wind (for wind energy) is generated by differences in atmospheric pressure and temperature caused by the sun.
• Rain (which collects in lakes, rivers and dams for hydro energy) is produced by the weather cycle, which needs the sun to get it going and cause evaporation.
• Plants (for biofuel, firewood or for the food that fuels you) use the sun’s rays for photosynthesis, which turns solar energy, water and carbon dioxide into sugars and some proteins (and vitamins and fibre).

What Doesn’t Use Solar Energy?

About the only forms of renewable energy that are not solar in origin are tidal electricity generation (which uses the tides, which are created by the moon’s gravity – although the sun’s energy does have some effect on the tides) and geothermal energy (which uses the heat of the planet’s core).