PV Gap

Joanne Said:

Why cant we harvest the heat of the centre of the earth as energy?

We Answered:

Geothermal is the right term; in some places, we do use geothermal energy--the problem with it is that this form of energy is very geography-dependent. In places where the heat from the center of the earth vents out on the earth's surface, such as geysers. A heat vent ideal for energy conversion is stable and predictable, and releases a lot of energy--this just doesn't happen in most places. Where geothermal energy is available and efficient (such as The Geysers, in California), we use it; even so, it makes up for less than 1% of our global energy consumption. An analogy to wind power and tidal power is appropriate; both of these energy sources are excellent where available, and environmentally friendly. But they aren't available everywhere. Check out Wikipedia (Geothermal Energy) for two paragraphs on advantages and disadvantages.

As for your question about sending a satellite to the sun to harvest solar energy: if we sent a satellite closer to the sun, it would be able to collect solar energy more efficiently, but problems would arise in two areas. First, even though the satellite solar cell might be more efficient, it won't necessarily provide more energy than a larger, less efficient solar cell here on earth. Sending a solar cell large enough to solve our energy problems towards the sun would cost a lot of money and use a lot of energy in itself.

The second problem is transporting the energy back to earth. If the satellite was very far away from earth, it would have a difficult time transmitting the energy back to earth efficiently. Solar power systems in orbit around the earth have been proposed as practical solutions, however, a lot of the sun's energy is absorbed by the atmosphere by the time it reaches the earth. These systems suggest using microwave radiation to transport the energy from orbiting satellites to power centers on earth. However, such a network of solar cells would be costly to maintain and, as it turns out, not that much better than using solar cells on the ground. The best achievements in solar cell technology (at least in the near future) will be improvements in technology rather than location.

One more thing about geothermal power. A geothermal power plant is essentially a heat engine. In thermodynamics, there is something called the Carnot cycle, which is used to predict the maximum theoretical efficiency of a heat engine (it is about 40%). Therefore, because geothermal energy comes from heat, a geothermal power plant can be at best 40% efficient.

Ricardo Said:

How do Solar Towers work?

We Answered:

a Solar tower is a large tower which receives all of the reflected sunlight from many mirrors on the ground beneath it, water flows through the tower in many pipes. As the water is heated, it generates steam which flows through turbines to generate electricity.