All the talk about nanosolar and other so-called 'cheaper' cells, may be
closer to wishful-thinking than to reality. Presently, and contrary to
what is often mentioned in the science press, the *installed* cost of
solar cells for homeowners is going up, not down in 2007.
I absolutely dispute the conclusions of the paper mentioned on Horace's
site about continuation of price-drops. From my recent experience
getting actual quotes - I think we reached the bottom in 2005-6 or
before, and now the prices are now going up!
I challenge anyone to find a source of available solar cells which make
economics sense for a home. Everytime a supposedly cheaper process comes
along - by the time it gets to the prototype level, costs have escalated
out of control. Nano-solar semiconductor cells will be no different.
The cost may be "claimed" by some writer to be under a dollar a watt at
some nebulous factory in China, but the installed 'turnkey' price, from
a licensed and bonded contractor is closer to $10 and NOT coming down -
probably NEVER for the homeowner in the USA, unless you do it yourself.
Larger installations may be cheaper.
The big solar conversion sites - the smart money for grid power - are
going to Stirling engines, and abandoning hope for actual direct
conversion cells. They have accountants and stockholders.
Solar cells have simplicity and 'status' appeal to homeowners, and as a
'green' symbol (which can never pay-off) and they do proclaim to the
world: "I care" - damn-the-cost ...
The largest Solar Installation in progress, which will produce up to 900
Megawatts is under construction now in California. "Stirling Energy
Systems" (SES) under contract with San Diego Gas & Electric will produce
approximately 30 times more solar power than is now being generated in
the whole San Diego region by rooftop cells. It will become the world's
largest solar installation, and several other desert sites are planned,
thanks to Sandia's work. The installed cost there was mentioned to
actually be less than what was quoted by Horace ($2 watt) but that is
not clear.
The problem for advanced nanosolar cells is this: it is NOT about
maximizing efficiency - it is about minimizing installed cost. Follow
the buck. The two variable are often contradictory.
There are possible alternative ways to approach this problem (on paper,
in addition to regressing a century, to the Stirling engine):
1) Use mirror or Fresnel light concentrators: EVERY process should use
concentrators, as Michael Foster reminds us. Without mirrors, even the
Stirling converter is a bust.
2) Abandon semiconductor cells altogether, in favor of the rectenna.
Mirrors are at least 3 orders of magnitude cheaper, per unit of surface
area, than are even the cheapest semiconductors.
The RECTENNA: The idea of collecting solar photon radiation with
antenna-rectifier (rectenna) structures was proposed three decades ago,
but has not yet been achieved commercially. The rectenna is basically a
fancy type of diode, and as critics opine, it may only a new type of
'cell' - since it does require micro-lithography, BUT it does not depend
on a band gap, or expensive semiconductors.
The idea has been promoted as having potential to achieve efficiency
approaching 100% but thermodynamic considerations imply a limit of 85%
for a non-frequency-selective rectenna, assuming maximal concentration.
This 6 year old paper reviews the history and technical context of "ITN
Energy Systems" solar rectenna, and discusses the major issues:
http://www.nrel.gov/docs/fy03osti/33263.pdf
Had we funded some of this tech fully back in 2002, using Daddy
Warbuck's death-machine-dollars, the rectenna would probably already be
in production. Instead of this, the US taxpayer is getting armor-plated
Humvees and more body bags.
Jones
