[jacques_chester]

The thing is that in the time when solar orbital was first discussed, solar panels sucked and oil was super-expensive. I think the O'Neill designs were based on concentrating mirrors and turbines. He claimed it could pay for itself within a standard utility company's financial planning horizon of 30 years.

And then oil prices went back to normal.

The real conceptual competitor at the time -- in fact, it's still the real competitor -- is plain old fission.

[justincormack]

Oil prices went back to "normal" for a bit but have since gone back up. This chart http://inflationdata.com/Inflation/Inflation_Rate/Historical... is out of date, but we are roughly back at the 1980 peak in real terms again (Brent was $113 last time I looked, US prices are probably slightl lower).

[jacques_chester]

Absolutely, but in the meantime solar panels have improved enormously also. The third part of the equation is launch costs, which haven't really fallen at all.

[justincormack]

Launch prices basically are energy costs, plus a markup, so they are never going to make this work unless you could make the whole thing extremely light...

[jacques_chester]

O'Neill's plan was to bootstrap manufacturing in situ, starting with robotic mining of moon dust or rock. The ore would be sent to L5 by linear launchers and then smelted into simple metals to make reflective surfaces.

[angersock]

But nuclear is evil and not cleantech.

[kamaal]

Solar energy is actually nuclear energy.

[schiffern]

All energy is actually nuclear energy.

(Of course Earth-based nuclear power doesn't have the entire mantle of the sun as radiation shielding. So there's that…)

[dredmorbius]

No, some is gravitational: tidal, arguably hydroelectric, though that's a combination of solar (feeding the water cycle) and gravitational (capturing gravitational potential of lifted water).

Geothermal is in part latent residual heat of formation, which is arguably either kinetic or gravitational energy again. Some is _also_ the result of radioactive decay, though I don't have the precise breakdown.

I suppose there might be some ways of tapping planetary or stellar magnetic fields, which aren't directly caused by nuclear power.

Similarly energy systems based on collapsed stars (white dwarves, neutron stars, black holes) would not be directly driven by nuclear processes.

But yes, your point generally stands: most available energy on Earth is largely ultimately derived from nuclear reactions.

[schiffern]

True, tidal isn't nuclear. Basically everything else is.

>Some is _also_ the result of radioactive decay, though I don't have the precise breakdown.

Neither do I, but here's my logic: if there were no nuclear power in the center of Earth, Lord Kelvin tells us it would solidify in only ~40 million years[1]. The Earth being 100 times older, the amount of residual heat left today must be insignificant.

Stellar magnetic fields come from the convective mantle, which is nuclear powered. Not sure about planetary magnetic fields, but the above analysis suggests nuclear as well. Collapsed stars will be heated by gravitational potential, but we don't see a lot of those 'round these parts.

[1] https://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kel...

[dredmorbius]

My point wasn't that the vast, vast majority of energy available to humans on Earth isn't ultimately nuclear in origin. Just that there are energy potentials in the Universe which aren't nuclear in origin. If you trace back the formation of the Solar System itself, as a generation 3-4 system, even the gravitational potential represented in it originates from nuclear reactions.

The Big Bang (background microwave radiation) and Dark Energy would also come to mind as non-nuclear energy systems.

Not of much practical use to us on Earth, however.