On 11/07/2011 5:33 PM, Alan Erskine wrote:
On 11/07/2011 10:41 AM, Sylvia Else wrote:
The Australian Government has, for reasons that have much to do with
politics, and little to do with the environment, decided to throw $Au 10
billion into the bottomless pit that is renewable energy.

Lest it all get turned into yet more solar panels and windfarms, I
invite all comers to submit their plans for orbital power satellites. At
least then we might get some technological advance for our money, even
though I doubt we'd actually see any orbital power.

Sylvia.

How can a SSPS be more efficient than PV on roofs? Also, it will help
the environment - I'm studying sustainability at the moment for a future
career.

Well, it does have the advantage of not being subject to the vagaries of
the weather, and (if not in LEO) is in sunlight for most of the time -
it has no significant night time. The economics of surface PV are
complicated by the need to include the cost of backup generation
capacity (the cost is usually ignored by proponents).


PV isn't the only way of generating electricity. Queensland (an
Australian state) is going to get several 250mW solar thermal power
plants - small by coal standards, but it helps. ST (Solar Thermal) could
also be installed on factory and warehouse roofs for power production
(look up SEGS - Solar Electricity Generating System) for about half the
cost per kW of PV (solar cells); ST is just not as pretty as PV,
especially if the PV is BIPV (Building-Integrated Photo Voltaic).

Solar thermal has some advantage in terms of being able to deliver power
overnight, but still has the limitation that weather can render it
powerless.


Also, there is TDP (my favourite subject; that I first learned about on
one of the sci.space groups in 2003) that can economically turn
agriculture and forestry waste into liquid fuels for transport; gas for
heating/electricity production and carbon-rich solids (commonly known as
'bio-char') for soil improvement. A TDP plant can pay for itself in less
than three years - with just the sale of oil at $60/bbl - petrol
(gasoline to Americans) would cost about $0.80 per litre compared to the
current price of $1.30ish.

Now, what's the payback period for an SSPS and how many do we need?

The payback period depends, among other things, on the price that the
power can be sold for. I rather doubt that the price will ever be high
enough to allow payback. I've only made the suggestion on the basis that
if the money is going to be wasted anyway, it might as well be wasted in
a way that might have some spin-off benefit.


How do we economically get the power down to the users on Earth?

What are the environmental risks of getting the power down to the users
on Earth?

Someone a couple of months ago suggested using laser-powered LV's for
payload to LEO - fine, until you try to find the electricity to power
those HUGE lasers! Those three questions above have never been answered
adequately; please try.


I think the idea was completely debunked anyway, on the grounds that the
proposed numbers were totally wrong.

Sylvia.