SPS versus other energy sources

>
> My summary is as follows.
>
> Only one source of terrestrial renewable energy has enough
capacity to
> supply the world's energy needs, and that is terrestrial solar.
The
> other renewable sources simply do not have enough capacity.
>
> There are many pros and cons, I can actually imagine a mix of
> terrestrial and space solar power, they can service different
types of
> markets. Here are some interesting numbers which William Mook
posted
> to Usenet in July 2000:
>
> > At the latitudes of North America the Sun during high noon at
summer
> > radiates about 600 watts per square meter incident radiation
normal to
> > a surface oriented to the sun. In space there is about 1,370
watts per
> > square meter. So, more than half is lost. The space value varies
plus
> > or minus 15 watts per square meter primarily in the UV region
due to
> > changes on the surface of the Sun.
> >
> > Of course in winter months and at sunrise and sunset more energy
is
> > absorbed by the atmosphere, reducing the amount of power
available per
> > unit area by half again as much. (only 250 watts/square meter
getting
> > through!)
> >
> > And at night and on overcast days, things are worse yet.
> >
> > In most parts of the US there are between 1500 and 2000 hours of
> > sunlight a year. There are 8766 hours in a year. So, about 5/6
to 4/5
> > of the time the sun is unsuable. Then add the atmospheric losses
and
> > you find that 19/24 to 9/10 of the sunlight available per unit
area is
> > actually available on the Earth's surface.
> >
> > Tracking the sun in space is much easier than tracking the sun
on the
> > ground. So, on the ground you don't do that. This limits your
> > conversion efficiency so your collector area increases for a
given
> > pwoer output by an order of 3 or 4. Also, ground based
collectors must
> > withstand gravity and weather. This triples costs again! So,
overall
> > a square meter in space can be equivalent to 288 square meters
on the
> > ground worst case, or 30 square meters best case.
> >
> > Then, you've got the added inefficiencies and costs of energy
storage.
> > To take energy and make fuel is not 100% efficient. And to take
fuel
> > and make energy is not 100% efficient. Furthermore, the
equipment to
> > do this conversion and storage is not free. Finally, the
conversion
> > equipment must be sized for peak solar output, so is not as
economic as
> > it might otherwise be. Assuming 30% efficiencies for each step
and a
> > doubling again of the capital costs to make fuels of solar
power, we
> > have another 28.89 fold increase (1/.3 x 1/.3 x 2) meaning solar
based
> > power requires 832 times the cost on Earth for collector, and
energy
> > management than an equivalent power in space.
>
> We also need to consider the environmental impact of popular power
> storage systems on which terrestrial solar power systems completely
> depend, it is actually a very high price. Most commercial
batteries,
> e.g. NiCd and Lead-Acid, contain highly toxic materials. This
> represents a massive toxic waste problem, on the same scale of
dealing
> with nuclear waste.
>
> However, the numbers above are not complete. They ignore two more
> things: 1) the transmission losses of SPS and 2) launch costs for
SPS
>
> Here is a nice summary of the SPS losses presented by Tom Musgave
to
> this SSI list in June 2001:
>
> DC to RF 0.85
> Antenna 0.98
> Atmosphere 0.98
> Energy Collection 0.88
> RF to DC 0.89
> DC to RF 0.85
> Antenna 0.98
> Atmosphere 0.98
> Energy Collection 0.88
> RF to DC 0.89
> Grid .97
>
> =.97*.85*.98*.98*.88*.89*.85*.98*.98*.88*.89*.97
> =.385 = 38.5%
>
> Bottom line then is as follows:
>
> Take the ratio of 832 to 1, multiply by 38.5 %, we get:
>
> Space solar power has a performance per square meter advantage of
290 to
> one over terrestrial solar power, if we ignore launch costs.

Is this correct? In going back to the original Tom Musgrave post on
this list, I see that the discussion thread was beamed power from
earth station, to space rectenna, back to earth station, and that's
what the efficiency ratios above refer to.

By my calculation, the numbers for a SPS to rectenna scenario should
be as follows:

DC to RF 0.85 Conversion at the SPS
Antenna 0.98 Power sent from SPS
Atmosphere 0.98 Atmospheric attneuation
Energy Collection 0.88 Earth Rectenna Efficiency
RF to DC 0.89 Conversion at the Rectenna
Grid .97 Convert DC to AC with Inverter

Thus, .85*.98*.98*.88*.89*.97 = 62.02%

Then take the ratio 832:1 mentioned above, multiply it by 62%, we
get:

Space solar power has a performance per square meter advantage of
516:1 over terrestrial solar power, if we ignore launch costs.