Renewables

[stevebowers]

But given fusion, even David Makay is optimistic.
Here is his chapter on Deuterium Fusion
http://www.withouthotair.com/c24/page_173.shtml

Deuterium fusion

If we imagine that scientists and engineers crack the problem of getting
the DD reaction going, we have some very good news. There’s 33 g of
deuterium in every ton of water, and the energy that would be released
from fusing just one gram of deuterium is a mind-boggling 100 000 kWh.
Bearing in mind that the mass of the oceans is 230 million tons per person,
we can deduce that there’s enough deuterium to supply every person in
a ten-fold increased world population with a power of 30 000 kWh per
day (that’s more than 100 times the average American consumption) for 1
million years

That is without considering the vast resources in the Solar System's Gas Giants, and the atmosphere of the Sun (Paul Birch noted that Sun Mining would be the most profitable source of fuel, thanks in part to the Sun's abundant energy). The fusion in the Sun gives off a billion times more energy than this planet can ever intercept, so a space-based civilisation should have ample power - but of course that is the entire premise of OA, and to get there we have to get through the energy bottleneck of the next century.

Note that every new colony in an extrasolar system faces a similar bottleneck - there is ample energy in almost every solar system, but to access it you have to expend a lot of energy to build the infrastructure.