David, you are such a tease! Bill, everything David says is correct, as there is lots of complexity in how ER will be awarded for small digesters. But, (without going into the details, and given you get lots of systems together under similar conditions, and that you are using the gas productively on-site for thermal energy and using a design that doesn't leak excessively) we are able to commercialize credits that are based ONLY ON ENERGY OFFSET at a rate of about 4.1-4.7 kg CO2/m3 of biogas. <br>
<br>It is difficult to get methane capture and destruction credits as baseline conditions vary a lot across small farms, but (assuming that animal waste is stored in a deep pit under anaerobic conditions for more than a month) that would roughly be worth about 100-140 kg of CO2/pig/yr. That same pig will produce about 36 m3 of biogas over the course of the year worth about 0.81 GJ of energy which will offset about 150 kg CO2/yr. This means that each pigs waste that is managed by a digester (given credit for fuel displacement AND methane capture) could in theory produce around 250-300 kg CO2/yr in Emissions Reductions. <br>
<br>Again, we are only able to account for energy offsets at this time, so a back of the envelope estimate for us is generally about 150 kg CO2/yr. Cows can be considered about six pigs. Again, this is very rough, but it is nice to have order of magnitude estimates sometimes! As David says, each project would have to be considered separately, and obviously all digesters and wastes are not the same. <br>
<br>Cheers and Happy New Year to the Group!<br><br>A<br><br><br><br><br><br><div class="gmail_quote">On Sun, Jan 2, 2011 at 5:06 PM, David <span dir="ltr"><<a href="mailto:david@h4c.org">david@h4c.org</a>></span> wrote:<br>
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<br>
Bill,<br>
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On 1/1/2011 11:53 PM, Bill Rucks wrote:
<blockquote type="cite">
<pre>Some one must have a idea on that very simple equation 1000 - 10 m3 of biogas is equal to 1 tonne of co2 equivalents ?????? We will never build a large multiple of these system unless we have a idea on that ratio - an surly building lots of small systems will benefit lots more people - than big companies - the big companies have got us into this predetermine that we find our selves in !!!
</pre>
</blockquote>
<br></div>
Do forgive me if it was not clear, but if you consider my previous
answer carefully, you will see that CO2 equiv is not a fixed
metric-- there is no such fixed ratio between volume of biogas
produced and CO2 equiv saved, <i>it does not and cannot exist</i>,
to be quite clear about it-- but rather is situational. In order to
earn carbon credits, one must demonstrate, in a rather specific way
and for a specific situation, that a given digester or group of
digesters is likely to be saving a certain tonnage of CO2 equiv.
Explore the UNFCCC website, and if you can wade through the somewhat
unsatisfactory search process provided, you can uncover a wealth of
documents about small biogas digester projects that have gone
through the process and produced their answers.<br>
<br>
My exploration of those documents and a wealth of other information
leads me to believe that it should be possible in many situations to
experience an annual CO2 equiv savings of a bit better than a tonne
and a half per cu m digester, but so many factors intervene that one
must also assert that the ballpark is rather large. For example, if
the digesters built for a given project have a tendency to leak,
then by rights the very powerful effect of methane as a GHG should
be factored in to the calculations, and might even erase a major
portion of the claimed savings.<br>
<br>
You've simply got to widen the scope of your question in order to
come to any reasonable answer. What is the situation now, how many
tonnes of CO2 equiv are presently being produced, and, under the
circumstances that apply-- weather, number of animals per family,
size of digester, etc., etc.-- how much of that can be offset by
using the expected biogas?<div class="im"><br>
<br>
<br>
<br>
d.<br>
<div>-- <br>
<div><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>
<i>Vahid Biogas</i>, an alternative energy consultancy <code><a href="http://www.vahidbiogas.com" target="_blank">www.vahidbiogas.com</a><br>
<br>
</code></div>
<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 <i>Delight of Hearts</i>,
p. 77) <br>
<br>
<a href="http://bahai.us/" target="_blank">http://bahai.us/</a></div>
</div>
</div>
</div>
</div></div>
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<br></blockquote></div><br><br clear="all"><br>-- <br>Alexander Eaton<br>Sistema Biobolsa<br>IRRI-Mexico<br>RedBioLAC<br><br>Mex cel: (55) 11522786<br>US cel: 970 275 4505<br><br><a href="mailto:alex@irrimexico.org" target="_blank">alex@irrimexico.org</a><br>
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