The issue here is that your looking for a commercially available system. Smaller systems are not commercially manufactured due to business models proving the larger capital returns from the larger systems. Their are many individuals that are "the garage inventors" that have successfully put together these smaller systems. Generally these systems have been created using re-purposed material which has put the capital investment cost down to near to nothing. My suggestion would be to get a small team of these ingenious individuals together and create your own solution. Once proven, simply market your solution as it appears to be an available niche market. <br>
<br><div class="gmail_quote">On Tue, Jan 10, 2012 at 11:46 AM, David <span dir="ltr"><<a href="mailto:david@h4c.org">david@h4c.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"><div class="im">
<br>
<br>
On 1/9/2012 8:34 PM, Gould, Charles wrote:
<blockquote type="cite">
<div>Mr. Harris,</div>
<div><br>
</div>
<div>I like your suggestion of smaller digesters. The problem is I
have not been able to find a digester design robust enough yet
cheap enough for a 100 cow dairy. Do you know where such a
design exists? I have just about given up the notion that such a
thing exists.</div>
</blockquote>
<br></div>
This highlights a difficulty which may be partially fundamental (and
to that degree absolute) but which seems largely conceptual, which
is that because situations differ so much, and the need sufficiently
moderate that there are few if any standard "replicable" designs for
digesters, of the sort that would be used for, say, a large block of
tract houses, where 1,000 houses might share four or five basic
floor plans. And no doubt specifics in this area vary
country-to-country...<br>
<br>
AgSTAR, of the US EPA, which could be said to be the primary
government-based promoter of biogas in the US, is aimed strictly at
manure-using digesters for farms with 500+ animals. For example,
although it could hardly be said to be a digester at a modest scale
(cost: $US10M+), the AgSTAR site deliberately (according to my
conversation with a staffer) does not mention the Stahlbush Island
Farms digester in Corvallis, OR, because it is fed plant matter
exclusively-- therefore it is not a manure-based digester.<br>
<br>
It becomes a kind of self-fulfilling prophecy, because the system
(in its academic support, among its industrial implementers and so
on), becomes adapted to larger digesters, and therefore has that
much more difficulty accommodating a different scale of thinking.
But as well, it seems that the variability of energy prices in the
US, where feed-in tariffs appear to be a political impossibility,
has prevented the establishment of an industry that might work its
way down to "smaller" digesters, after the larger digesters on the
megafarms have been built, similar to what seems to be happening in
Germany.<br>
<br>
I think there may well be a number of lower-cost building and
process control technologies, perhaps along with energy crop
co-digestion strategies, which could be put together in the proper
circumstances to reduce the cost of digesters of a size below the
AgSTAR limit in the US; but it would require a funder with vision to
realize such an outcome.<span class="HOEnZb"><font color="#888888"><br>
<br>
d.<br>
<div>-- <br>
<div style="font:Georgia"><span style="font-size:110%">David
William House<br>
</span>
<div style="padding-left:3em;font-size:80%">"The Complete
Biogas Handbook" <code><a href="http://www.completebiogas.com" target="_blank">www.completebiogas.com</a></code><br>
<em>Vahid Biogas</em>, an alternative energy consultancy <code><a href="http://www.vahidbiogas.com" target="_blank">www.vahidbiogas.com</a><br>
<br>
</code></div>
<code>
<div style="padding-left:2em">"Make no search for water.
But find thirst,<br>
And water from the very ground will burst."
<div style="padding-left:2em;font-size:80%">(Rumi, a
Persian mystic poet, quoted in <em>Delight of Hearts</em>,
p. 77) <br>
<br>
<a href="http://bahai.us/" target="_blank">http://bahai.us/</a></div>
</div>
</code></div>
</div>
</font></span></div>
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