How much energy is generated?

Question

Okay, the details I need are simply this: how much energy is generated by a fusion reaction? Also, how much is generated by a fission reaction? It would also be helpful if I knew how much energy is obtained by solar panels, and what the optimum size would be for absorbing energy.

Answer 1

It takes considerable energy to force nuclei to fuse, even those of the lightest element, hydrogen. But the fusion of lighter nuclei, creating a heavier nucleus and a free neutron, will generally release more energy than it took to force them together — an exothermic process that can produce self-sustaining reactions.

The energy released in most nuclear reactions is much larger than that in chemical reactions, because the binding energy that holds a nucleus together is far greater than the energy that holds electrons to a nucleus. For example, the ionization energy gained by adding an electron to a hydrogen nucleus is 13.6 electron volts — less than one-millionth of the 17 MeV released in the D-T (deuterium-tritium) reaction

Answer 2

The amount of energy generated by fusion or fission depends on the size of the reaction. For example when we get fusion running in modern labs, we don't get out as much as we put in. Contrast that with the sun. A solar panel a little over 2 ft square will give you about 100 watts in very bright sunlight and they will cost you about $5000 dollars for every 1000 watts.

Answer 3

There are several different fusion reactions, but in D-T fusion you get 17.6 MeV (2.82*10^-12 Joule) per fusion (http://en.wikipedia.org/wiki/Nuclear_fusion)

For the fission of one atom of uranium 235 generates 200 MeV (3.2 × 10-11 J) (http://en.wikipedia.org/wiki/Uranium-235).

So a single fission generates more energy than a single fusion. However, the hydrogen isotope mixture is far less dense than uranium so you get more fusion reactions than fission reactions per kg.

1kg of fission fuel would give you 1.7*10^14 Joules
1kg of fission fuel would give you 8.2*10^13 Joules
1kg coal yields about 24*10^6 Joules... over 10 million times less!

Solar panels are very inefficient in producing electricity, converting only about 12% on the sunlight they recieve into electricity. A single solar cell will generate about 2 Watts so you will need a large number of such cells to give a large output.

Answer 4

The energy generated is given by the formula

E = mc²

where m is the change in mass that occured in the fusion or fission reaction, and c is the speed of light.

For example, if you lost 1 gram in the nuclear reaction, you will have released 25 Gigawatt-hours of energy (Giga means 10 to the 9th power)