Submitted by darthatheos t3_10ve1np in space
certain_people t1_j7hdwzq wrote
Reply to comment by [deleted] in Rolls-Royce Nuclear Engine Could Power Quick Trips to the Moon and Mars by darthatheos
Not left off so much as can't be shown. What's the energy density of wind?
[deleted] t1_j7hg3vn wrote
They measured it in joules/kg. Solar is infinite. Wind I'm not so sure.
certain_people t1_j7hgogl wrote
It's just not the right way to compare nuclear with solar and wind. And you can't put wind or sunlight in a fuel tank.
[deleted] t1_j7hh9tb wrote
Seems reasonable to me? Light is zero kg, so infinite energy per kg. I can't put uranium in my fuel tank either. Just not practical for the everyday person.
moral_luck t1_j7hxh0p wrote
Nuclear reactors use light as the energy for power.
Coal generators use light as the energy for power.
Natural gas generators use light as the energy for power.
Geothermal generators use light as the energy for power.
Light is the way energy is transferred from one atom or molecule to another atom or molecule.
Heat is light.
For example:
Coal is burned, the chemical reaction creates lots of photons. Those photons get absorbed by water molecules. The water molecules become excited. Excited water molecules move faster. Faster moving water molecules have more kinetic energy. Steam is the result. High velocity steam spins a turbine. The turbine spins a magnetic field inside an coil. This produces electricity.
Energy density is really a measure of the number and energy of the photons generated by a certain fuel. Light is not the fuel (hint: fusion).
[deleted] t1_j7i6i75 wrote
Fusion is what happens on the sun
Not what we do on earth
moral_luck t1_j7i7s57 wrote
Yes, exactly. Solar energy is fusion.
moral_luck t1_j7ia3xp wrote
Depends on the car.
moral_luck t1_j7hwh78 wrote
Solar power is neither infinite in energy density, total amount of energy or duration of energy.
Not sure what you mean by "Solar is infinite."
[deleted] t1_j7hwnqn wrote
How many megajoules per kg is it?
moral_luck t1_j7i2c65 wrote
Einstein's most famous equation (E=mc^(2)) limits energy density of any fuel to 9 x 10^(10) MJ/kg
And that would be an antimatter reactor. Physics means no fuel can have infinite density.
[deleted] t1_j7i5cy1 wrote
Light. Zero mass. Lots of energy.
moral_luck t1_j7i7wee wrote
Where did the light come from?
SowingSalt t1_j7jjchk wrote
Therefore in the ratio mJ/kg, light is undefined and cannot be on the chart; which was the original point.
moral_luck t1_j7hz7ym wrote
Solar energy is hydrogen fusion, deuterium–tritium fusion is about 338,000,000 MJ/kg.
But we don't have the technology to create miniature suns in our rockets.
BTW, U-235 fission has an energy density of about 144,000,000 MJ/kg.
Another source puts the energy density of the sun's core around 6.43 x 10^(8) MJ/kg, or 643,000,000 MJ/kg.
The second source is titled The Source of Solar Energy.
[deleted] t1_j7i5md1 wrote
That's fusion reactors not solar energy on the surface of the earth
moral_luck t1_j7i7uhl wrote
Where does the solar energy on the surface of the earth come from?
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