PV Gap

Rachel Said:

How much energy is made for a year from solar energy?

We Answered:

Plants have stored the sun's for millions of years.The plants are the largest solar collector there is. The plants recycle the CO2 into O2 and the plants keep the C. Later the oil in the plants breaks down into petroleum.

Larry Said:

How is energy made from things such as wind turbines and solar panels?

We Answered:

There are two different mechanisms at work in these two devices. The wind turbine is simply a mechanical alternator. It generates electricity using a magnetic field, conductive wire and relative motion between the two. It is simply the same as the generator used in hydroelectric power but of a different physical size with wind providing the motion instead of water from a dam. In the solar cell, there are NO moving parts. A solar cell is much like a battery in that a potential difference is formed between the battery contacts because of a reaction. In the chemical battery, it is dissimilar metals. In the solar cell it is the location of electrons being moved when sunlight falls on them. Regardless of the power source, the electrons which were forced to move are run through converters and transformers to make the voltage and frequency compatible with the rest of the power grid.

Dustin Said:

how is solar energy made?

We Answered:

Basically a you get a semiconductor material (like silicon) which releases electrons when a photon hits it. Then you create a circuit for the electrons to travel around. Electrons in motion form an electrical current, which is how we get electricity.

See the links below for further explanation.

Alma Said:

How is energy in a solar or nuclear powerplant made?

We Answered:

nuclear fission

Nuclear power can come from the fission of uranium, plutonium or thorium or the fusion of hydrogen into helium. Today it is almost all uranium. The basic energy fact is that the fission of an atom of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal.

Natural uranium is almost entirely a mixture of two isotopes, U-235 and U-238. U-235 can fission in a reactor, and U-238 can't to a significant extent. Natural uranium is 99.3 percent U-238 and 0.7 percent U-235.

Most nuclear power plants today use enriched uranium in which the concentration of U-235 is increased from 0.7 percent U-235 to (nowadays) about 4 to 5 percent U-235. This is done in an expensive separation plant of which there are several kinds. The U-238 "tails" are left over for eventual use in "breeder reactors". The Canadian CANDU reactors don't require enriched fuel, but since they use expensive heavy water instead of ordinary water, their energy cost is about the same.

In 1993 there were 109 licensed power reactors in the U.S. and about 400 in the world. They generate about 20 percent of the U.S. electricity. (There are also a large number of naval power reactors.) The expansion of nuclear power depends substantially on politics, and this politics has come out differently in different countries. Very likely, after some time, the countries whose policies turn out badly will copy the countries whose policies turn out well.

For how long will nuclear power be available? Present reactors that use only the U-235 in natural uranium are very likely good for some hundreds of years. Bernard Cohen has shown that with breeder reactors, we can have plenty of energy for some billions of year.

Cohen's argument is based on using uranium from sea water. Other people have pointed out that there is more energy in the uranium impurity in coal than could come from burning the coal. There is also plenty of uranium in granite. None of these sources is likely to be used in the next thousand years, because there is plenty of much more cheaply extracted uranium in conventional uranium ores.

A power reactor contains a core with a large number of fuel rods. Each rod is full of pellets of uranium oxide. An atom of U-235 fissions when it absorbs a neutron. The fission produces two fission fragments and other particles that fly off at high velocity. When they stop the kinetic energy is converted to heat - 10 million times as much heat as is produced by burning an atom of the carbon in coal. See the supplement for some interesting nuclear details.

Besides the fission fragments several neutrons are produced. Most of these neutrons are absorbed by something other than U-235, but in the steady-state operation of the reactor exactly one is absorbed by another U-235 atom causing another fission. The steam withdrawn and run through the turbines controls the power level of the reactor. Control rods that absorb neutrons can also be moved in and out to control the nuclear reaction. The power level that can be used is limited to avoid letting the fuel rods get too hot.

The heat from the fuel rods is absorbed by water which is used to generate steam to drive the turbines that generate the electricity.

A large plant generates about a million kilowatts of electricity - some more, some less.

After about two years, enough of the U-235 has been converted to fission products and the fission products have built up enough so that the fuel rods must be removed and replaced by new ones.

What to do with the spent fuel rods is what causes most of the fuss concerning nuclear power.

Vivian Said:

How is solar energy made?

We Answered:

Solar energy is made in the sun from the fusion of hydrogen into helium.

But, I imagine you're wondering how it is collected here on Earth. There are three basic methods:

Photovoltaics - These are what you think of as "solar panels". These consist of a material (usually silicon) that have loose electrons. When light hits these panels it transfers enough electricity to the electrons to break them free and get them moving. Moving electrons is what we call 'electricity'.

Solar thermal - In this method you run water pipes through a box with black walls and a glass covering. Sun goes through the glass, hits the black walls and gets absorbed. This heats up the box which heats up the air which heats up the water in the pipes. The hot water can then be used to heat your home or to run a hot shower.

Solar steam generation - This method is usually used for solar power plants. Here, they use big mirrors to concentrate sunlight into bright beams (like you do with a magnifying glass). These beams are then directed at water to boil it. The steam from the boiling water is then used to turn a turbine which generates electricity.

Warren Said:

how would you explain how energy is made from alternative forms to a fourth grader ?

We Answered:

For alternative energy that comes from something that moves like geothermal, hydro, wind, tidal, you say that the stuff flows through a turbine, which has blades like an airplane propeller, and that turns a generator, like the one on your bike that runs the light. There are several kinds of solar, and some heat water to drive a turbine. You don't have to explain how solar cells work - you can point to a solar calculator, and say that this patch produces electricity, and it can be done with really big patches.

Fourth graders know how to do math, like multiply and divide. That's pretty sophisticated.