Xref: utzoo sci.energy:3665 sci.electronics:16583
Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!rochester!dietz
From: dietz@cs.rochester.edu (Paul Dietz)
Newsgroups: sci.energy,sci.electronics
Subject: Re: solar cells
Message-ID: <1991Jan1.185841.16857@cs.rochester.edu>
Date: 1 Jan 91 18:58:41 GMT
References: <939@venice.SEDD.TRW.COM> <1990Dec29.063939.20478@zoo.toronto.edu> <1990Dec31.173248.24523@bronze.ucs.indiana.edu> <-BS^0H*@rpi.edu>
Reply-To: dietz@cs.rochester.edu (Paul Dietz)
Organization: University of Rochester Computer Science Dept
Lines: 29

In article <-BS^0H*@rpi.edu> wrf@mab.ecse.rpi.edu (Wm Randolph Franklin) writes:
>In article <1990Dec31.173248.24523@bronze.ucs.indiana.edu> amirza@silver.ucs.indiana.edu (anmar mirza) writes:

>>What is really good about passive solar heating and geothermal systems
>>is that they *will* pay for themselves in savings compared to the old
>>system. The turn around time can be as little as 10 years.

>What interest rate does this assume?  Does it  take advantage of any tax
>breaks (if there are any left)?  Thanks.
>
>The reason I  ask is that  many "efficient" devices make  no sense in my
>home when interest  is included.  E.g.,  I take years to burn  out  a $1
>100W power 1700 lumen  1000 hour bulb.  Some haven't  burnt out since we
>bought the house 8 years  ago.   A  $10 fluorescent bulb  would  have to
>contain a nuclear  power source and  provide the   light free   to be as
>cheap if money costs 12%.

You have to be really careful here.  I suspect the *effective*
interest rate you would pay is much, much less than 12%.  Why?  Two
reasons:  taxes and inflation.  Unless you are careful, these effects
might actually give you a negative effective interest rate.

In contrast, the savings from personal capital investments like
increased efficiency are tax-free (unless they increase your assessed
property value), and are also inflation resistant, since energy prices
will likely tend to rise with inflation, at least roughly.

	Paul F. Dietz
	dietz@cs.rochester.edu