Hi All

You're probably right to an extent, but there's only so much of either that can be produced before hitting some wall. Tar sands will run dry, as will underground coal gasification etc. And only so much land can be turned over to energy crops. Think it through - plants are ~ 1% efficient at most and only 10% of 30% of Earth's land surface is arable. Thus energy crops give us 3/10,000 of the net solar energy received by Earth - 375% present energy usage. Yet we still need to eat and people are still building houses on arable land in how many Western nations???

Both have no hope for substantially improving their energy-of-production costs - eg. harvesting and milling oil-seed takes an essentially fixed energy. Likewise rendering abattoir wastes, heating oil sands, gasifying coal etc etc. And they're either net carbon polluters, or rob humans/ livestock of viable agricultural resources.

Space-based PVs/solar-dynamics do have plenty of potential areas of real improvement, but improvements that won't happen unless someone makes a start.

Don't get me wrong - I'm all for filling the gaps that oil and gas will leave when they're gone with near-term products, but there's not a lot of future growth in either low-grade kerogens, subsea clathrates or biomass. 9 billion people by 2050 are going to want collectively about ~ 60 terawatt.years per year. There might be a few trillion tons of good kerogen locked up in shales, but when it takes a barrel of oil to make two barrels out of it things are looking grim for the future and the rest of humanity who will want the power usage available to the minority.

When the oil-sands are no longer oily it will then be too late to make PowerSats - we have to do it NOW while power is still cheap!

Pete Glaser was right and is still right - real growth in energy supplies can only come from space. Else we have a no-growth future looming and a totalitarian State will be the end result - or the Energy Wars will mean no future at all.

Adam