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Is the solar energy coming from the sun infinite and will continue to be radiated to our earth forever? (discarding any outer factors) what's the sun's fuel?

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When you mention solar power, it makes me think you are thinking about photo-voltaic power or power extracted from solar panels. The power put out by the sun is about $3.95*10^{26}W$ per second. But solar panels can only capture a fraction of that energy. Even so, in 2008 humans used about $4*10^{13}W$ per second which is many orders of magnitude less than the sun puts out.

The suns life cycle will last billions of years fusing hydrogen, then helium and slowly working its way down to a white dwarf star.

time frames

As the temperature and radius changes of the sun, it's power output will fluctuate. But it will always put out more power than humans could use until the Earth is heated greatly during the red giant phase.

evolution

Considering homo sapiens have only been around 200,000 years and the Sun won't expand for another ~7,000,000,000 years that is approximately infinite in terms of human life spans which are about 80 years. What will exactly happen during this red giant phase is still under debate, but it is a long long time from now.

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The sun in powered by nuclear fusion of hydrogen to helium.

There is plenty of hydrogen remaining to keep the sun going for billions of years.

So, solar energy is not infinite, but it will last for billions of years.

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  • $\begingroup$ I would just add the fact that Earth will be probably be swallowed by the sun before the sun "runs out of energy". $\endgroup$ – cinico May 17 '14 at 12:26
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Two nuclear fusion processes known as the "proton–proton chain reaction" and the "carbon–nitrogen–oxygen cycle" give rise to energy generation in the sun. For the sun of our solar system, it is believed that the former is predominant. Obviously the fuels are protons and protons along with C,N,O respectively in the two processes. (I do not understand what you mean by "discarding any outer factors")

"Is the solar energy coming from the sun infinite?" Obviously not. If it were so, that would be a disaster for us. The number of protons and the ${}^{12}_{6}C$ nucleus are finite inside the sun and energy released by the corresponding processes (in each cycle) are also finite . Thus a finite amount of energy is generated inside the sun and is radiated.

"will (solar energy) continue to be radiated to our earth forever?" No. The earth will receive solar radiation as long as the fuel inside the sun is not exhausted and the sun continues to generate energy by the pp chain reaction. It is believed that this predominant mode of energy generation will last for 5.4 billion years more. What happens after that is different from what is taking place now. For more information you may consult relevant pages of wikipedia.

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