Not very big news – three FSADs equal one FGW. (It’s about fracking, by the way).


Also while we’re on the subject of Shale gas and today’s hoo-ha, it’s probably worth disinterring and updating the piece I produced on shale gas and biogas some time ago (here).

What I said in that piece was that it might be worth comparing and contrasting what you might get out of a farm size anaerobic digester by way of useable biogas (with just a little bit of cleaning up you can inject biogas into the grid, use it to produce electricity or as a fuel for vehicles) and what you might get out of the lifetime of a drilled and fracked gas well (same provisions, same use).

The two methods of producing gas can be summarised thus:

Biogas                                                                                                   Fracked gas

Costs about  £2 million to build a farm plant Costs £6-10 million to drill a well
Needs lots of cow poo etc. Needs 6 million gallons of water to frack
Lasts as long as cows keep on producing Lasts about seven years
Emits about 11g CO2 per kwh of electricity produced Emits about 400g per kwh of  electricity produced
Doesn’t look that great at the end of your road Doesn’t look that great at the end of your road
Can be used to store hay if you don’t produce Needs to be capped and made safe when exhausted
Good for energy security Good for energy security


Well I was a bit wrong in my estimates on the relationship between farm sized AD plants (FSAD) and fracked gas wells (FGW).  My original projection was that the output over 20 years of four FSADs would equal the output of one FGW.  Not a bad comparison – about the same overall price range and much cleaner gas. However, looking at some of the detailed literature on the results of fracked well lives over a period from the US (e.g.  Arthur Berman 2009) I was a bit out. Berman suggests that the average life of horizontal wells is far less than initially suggested by promoters – in fact about 7.5 years, during which time an average well in Barnett shale will produce  about 0.81 billion cubic feet, which translates as about 22.6 million cubic metres of gas.

A farm AD plant, on the other hand will produce about 6.2 million cubic metres of gas over a 20 year period.  True, you can drill another well after 7.5 year if we want to make strictly fair comparisons, but that does double your cost.

So, here’s the metric:   three farm sized AD plants at the bottom of three lanes give you slightly under the likely production of one fracked well at the end of one lane.  I’m not sure the residents of the respective lanes would really take to either, but at least with the AD plants they would be able to rest in the knowledge that they would be contributing to low carbon energy, rather than participating in forcing a lot more high carbon energy out of the ground.  Oh, and some of the farmers and their families down the lane might keep the income from the digesters  instead of having to be sweetened up to allow someone else to walk off with it.

Of course, though, there won’t be any development and production allowances to assist with the development of farm AD, because, well, it’s just not strategic or exciting is it?  So I guess the cows will go on doing what they do and the frackers what they do. Shame really.