[ExI] More Thoughts on Space based solar power (alternatives)

hkhenson hkhenson at rogers.com
Thu Nov 27 05:34:07 UTC 2008

At 06:24 PM 11/26/2008, Emlyn wrote:
>2008/11/27 BillK <pharos at gmail.com>
> >
> > It's not an either / or situation.  We could have both!
> >
> > It only takes a few businessmen and factories will soon be churning
> > out cheap thin-film solar cells and the population will be happily
> > coating their roofs, walls and windows, car roofs, hats, every
> > portable device, etc. This will be happening before the mega projects
> > have got off the ground.
>How's the patent landscape in thin film solar? That is, can a few
>businessmen actually do this, or are there legal obstructions?

Being an engineer, an electrical engineer at that, I tend to wonder 
about how they connect from something very thin to serious wire thickness.

Let's say you coat a roof with them.  Say 8 meters by 16 meters (26 x 
52 feet--not an exceptionally large suburban roof).  128 sq 
meters.  Figure the power at 1000W/m^2 and the efficiency at 10%.

So at a peak (mid day plus or minus an hour) you get 12.8 kW.  Cells 
have to be put in series and parallel since the voltage per cell is 
hard to use--less than half a volt.

Given the current set of laws, the output voltage needs to be under 
48 volts or you have to go to more trouble with insulation and 
keeping little kid fingers from getting across the hot wires.  12,800 
watts/48 volts is 267 amps.  This requires *huge* wires, 4/0 at 90 
deg C rise, almost half an inch in diameter to the inverter.  I have 
no idea about how you hook this size wire to thin film solar 
cells.  The laws will need to be changed and people will have to deal 
with roof rats shorting out their solar power collectors at 
times.  Even going to 128 volts would mean feeding as much as 100 
amps back through the meter.

Most houses built since the 70s have meter connections this 
large.  However the pole transformers are another matter, seldom more 
than 2-3 kW/house, so many transformers would have to be changed to 
larger ones (with higher off peak loses).  The same is true of 
substation transformers.  On a bright cool day with little air 
conditioning load they would be feeding huge amounts of power into 
the grid.  This level would almost certainly burn out substations if 
everyone in a neighborhood were to coat their roof with thin film 
solar cells of this efficiency.

If this were average instead of peak for a few hours mid day, cheap 
thin film solar cells would be the answer.  But that's not the 
case.  There would be huge swings in available power.  It would take 
some interesting source controls on individual inverters for the 
power companies to deal with the generation swings or there would 
have to be huge upgrades in transmission lines.

It's *not* simple.


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