Subject: Re: PV Module Cost & System Sizing

From: [email-masked] (Mike Page)
Date: 7 Nov 1996 18:09:42 GMT

In article <[email-masked]>, Charles McCane <[email-masked]> writes:
|> After researching Solar Power for home use, I think I'm in shock over
|> the price, but maybe I miscalculated somewhere. Would someone please let
|> me know if I'm off on these numbers. I'm building a new house and I
|> estimate electical usage to be about 1700kW/hrs per month. With that
|> number in mind, I have calculated that PV modules alone would cost well
|> over $50,000 to develop that much power. Maybe I'm off on the estimated
|> power consumption value. This will be a typical 2400 sq. ft. house with
|> gas for heating, hot water, & laundry. 
|> 

As other people have noted, one important factor is to reduce the amount of 
energy needed in the first place.  I also think Nick Pine's regular 
observations about the overcomplication of solar heating systems in 
general are right on the button.  It is certainly best to use solar input 
as a source of heat, rather than a source of electricity, since the former 
conversion is far more efficient, and more easily accomplished.  Nevertheless, 
electricity generation from the sun remains desirable - the question is how 
might it best be accomplished?  You have drawn attention to the fact that 
PV systems are extremely expensive, this being partly to do with their 
embodied energy (i.e. the energy involved in their manufacture).  It might 
be better to go for a more low-tech solution, with similar efficiency (?) but 
potentially much lower cost.

I am thinking in particular of parabolic solar troughs, which concentrate 
incident solar energy via a reflective trough of parabolic cross section.  
This concentrated energy is used to heat water in a pipe located along the
linear focus of the parbola.  The water is turned to steam, which is used to 
drive a steam engine (or Tesla turbine - any comments??), to drive a 
generator.  Such systems have been suggested - for an example see the 
web site (http://www.chatlink.com/~soltherm) - though I can't tell whether they
are in production yet.

I'd be interested in any feedback as to the feasibility of such a design, what
drawbacks one might expect, and the likely generation capability.  Clearly, 
such a design would require direct sunlight, rather than diffuse lighting, and 
would require this sunlight to be incident for a certain time before generation
would begin.  These disadvantages might be outweighed by the cost, embodied 
energy and simplicity considerations.  I have no doubt Nick P. will be 
able to tell us how to build a parabolic reflective trough, a water supply 
system and perhaps even a small turbine - I await the plans with genuine 
interest.

Mike Page,

Cambridge, U.K.