On 11/07/2011 6:00 PM, Sylvia Else wrote:
On 11/07/2011 5:33 PM, Alan Erskine wrote:
On 11/07/2011 10:41 AM, Sylvia Else wrote:


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).

It _is_ subject to the vagaries of the weather - microwaves are absorbed
by clouds. Sure, pick a site for the rectenna where there are no clouds
- the same areas where there are no people. Then you have to take into
account the huge line losses (look up "voltage drop") on the power lines.




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.

No. When there's no Sun available, the alternative energy source comes
into play - usually natural gas at the moment, but wood gas or another
biomass-derived fuel is used to heat the working fluid - that's why it
works when there's no Sun. That's the main reason for it being less
expensive than PV.



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.


The money isn't going to be wasted; half is going to compensate for
increased power bills from the big power companies that are the main
source of carbon pollution. The other half is to be invested in
renewable energy. This will also encourage the big polluters to improve
things for their existing systems and eventually replace them with RE
(Renewable Energy) systems.

I remind you that we are not the first country to go this route -
Germany announced in May that they are eliminating nuclear power
altogether by 2020 - nine years away. The way they are doing that is to
increase the efficiency of their coal-fired power plants (technology
that can be used here in Australia) and also for more RE.