Something that shocks people is when you tell them the power density of our Sun from nuclear fusion is less than the power density of a human from metabolism.
Most of the fusion that takes place in the Sun happens in the core - almost all of it happens in a region that is 25% of the radius. The power density for the core is about 275 watts per cubic meter .. a 70 kg person has a 100 watt metabolism on average which works out to about 1400 watts per cubic meter. A really good athlete can spike that by an order of magnitude for a short period.
The energy density of the Sun is more on par with the metabolism of a reptile. Of course the Sun is big enough to run for about 10 billion years and the Earth collects enough light to easily supply our demands as we are small - even with the machines we have created so far..
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