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15 comments on Solar House competition

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joule on October 13, 2005 - 4:26pm Permalink | Subthread | Comments top
During the late 1970s and early 1980s I was very much interested in solar energy and did some amateur dabbling in various aspects of it. One of the things that I made a few crude attempts at doing was to analyze domestic solar heating in terms of the amount of energy invested in creating the system and how many long it took of absorbing solar energy to pay back that energy.

 I no longer have those calculations, but I do recall being rather surprised at how many years it took to recoupe the energy invested ( I vaguely recall a number like 6 or 7 years). The big problem in doing such an analysis is deciding where to draw the envelope, and that question leads to all sorts of arguments as to what should and should not be included.  

Does anyone have a handle on this question or who could lead me to a website that addresses it?   I would think (hope) that the energy payback period has improved  over the last 25 years.  But I suppose that my main point is that the attractiveness of a domestic solar heating system should be viewed not just in financial terms but in terms of energy payback (the two not being the same). After all, isn't that the whole point of the thing in the first place?

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Bubba on October 13, 2005 - 5:08pm Permalink | Subthread | Parent | Comments top
Check out this guy. He really seems to know what he is talking about.

http://ergosphere.blogspot.com/2005/09/faq.html

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pariah on October 13, 2005 - 5:19pm Permalink | Subthread | Parent | Comments top
checkout RETScreen international .  Among other things, there is an introduction to the concept of using perforated metal sheeting as a solar collector .  
I was unaware of the concept .  For those of us who are  not engineers , I think that some homes could be retrofitted with minimal cost and minimal skill .  It is my WAG that such a system would repay its cost over one winter .  
An aside: I have the impression that few people are aware of , or willing to discuss, scaling .  How many people are really willing to live on 5% of the energy which they consume now .  How many people really buy the hydrogen hoax ?        
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csprings on October 13, 2005 - 6:35pm Permalink | Subthread | Parent | Comments top
Since solar efficiency has increased and cost per watt has somewhat decreased, the payback period is reduced.  The EROEI goes from very low (1.x) to moderate (13) depending on what assumptions you wish to make and what religion you believe in.

One could argue that
  a) even if EROEI is relatively low, it is still a better use of current cheap energy than pouring it down a auto gas tank.
  b) homeowners decide based on purchase price payback, not EROEI.

the people I talked to at the solar home tour a couple of weeks ago are thinking more about what the payback period is on utility savings and home value rather than strict EROEI.  This requires some guessing at future energy prices.  While in the past, it looked like the payback period was as long as 25 years, the payback period has improved to the point that solar is on the edge of looking like a reasonable investment, regardless of what you believe about the grid.  I toured 900-1500 square foot homes that were very comfy, and the people had the same amenities as I, running on 900-1.2 kWatt solar systems.  The 900 kWatt system was installed for 7,800 total, including replacing main breaker panel and some old wiring that was below code. With $3000 federal tax credit, perhaps $2000 energy buy-back credits (Colorado), and estimated $4000 increased home value, it seemed like he was ahead of the game before even adding in the negative balance he has consistently run on his utility bill, and the fact that electric rates may begin marching up rather steeply.  A common thread with the people who install solar is that they become aware of where every watt is going, and by using those watts efficiently, they find they can live comfortably on fewer than most people think possible.

I am trying to work it into my remodeling plans, if I can figure out the wickets to not lose any valuable tax credits.  (Complete 1924 bungalow remodel, which my wife would appreciate having insulated before winter!)

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ChrisPhoenix on October 13, 2005 - 9:32pm Permalink | Subthread | Parent | Comments top
c) If oil is underpriced today, then even an EROEI of 1 is good; buying a $10,000 solar installation with an EROEI of 1 is like buying and storing $10,000 worth of gasoline, except you don't need the tank.

Or something like that.

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csprings on October 13, 2005 - 11:12pm Permalink | Subthread | Parent | Comments top
typos: 900 Watts, $2000 Federal tax credit.  The tax credit and corresponding / conflicting state rebates get confusing.  
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