Why should the best land be used for biogas?

Tuesday, June 5, 2012

Farmers see energy cropping for biogas as the right way ahead in Europe. But should biomass really be grown on the best land? Let's forget about corn and the like, and take another look at grass, say some researchers

by NORMAN DUNN

Solid political support is in place, the technology has been optimized – and the money is right. Biogas production from energy cropping now has European farmers in their tens of thousands investing in climate-friendly electricity output.

While wind power and even the solar route to non-fossil energy continue to experience peaks and troughs in public acceptance, electricity from biogas is generally welcomed everywhere. Little wonder, when guaranteed payments in the U.K., for example, currently reach the equivalent of 15.6 Canadian cents per kWh for biogas-sourced power (and up to 17 cents where combined electricity and heat is supplied). In every case, stresses the country's Office of Gas and Electricity Markets (OFGEM), payments for renewable power under present schemes are designed to leave a good profit, even if almost all initial investment capital is borrowed.

There are clouds on the horizon, though, which we've mentioned before. Energy crops are proving so efficient that the rental of land for forage feed production is becoming very expensive. The Italian example is just one of many nowadays in Europe. There, farmland in the largest dairy area is fetching rents up to 70 per cent more per acre than even three years ago, because farmers who've changed from milking to biogas production are snapping up the corn-growing land. Right across Europe, energy cropping continues to increase the cost of conventional farming.  

There's no doubt that some controls are coming soon – maybe a limit to pure energy cropping per on-farm biogas unit.

Another problem is the dominance of wholecrop corn for biogas. Corn hasn't the best methane output. This prize is easily won by fodder beet. This is extremely energy- and mechanization- intensive but can produce an average of around 2,500 cubic metres methane per acre according to the German Association for Technology and Structures in Agriculture (KTBL). The next best is wholecrop corn with an average 2,200 cubic metres and, of course, much simpler and more efficient to grow, harvest and ensile.

Wholecrop wheat/barley/rye and canola is being grown too, although these are regarded as the poorest producers of arable crop biogas substrates in Europe (around 1,500 cubic metres of methane per acre).

A promising crop in the arable energy stakes is sugar beet. New high-dry matter varieties bred especially for the energy market include two lines from international breeders KWS. Sugar beet certainly needs lots of energy and machinery input. But with the dedicated biogas varieties farmers are lifting over 26 tonnes of roots per acre and producing in the best cases, 2,300 cubic metres of methane – and getting a valuable opener for wheat in the rotation as well.

Plain old grass is by no means at the bottom of the biogas production league when ensiled and loaded into fermenters. On top of this, it grows well much further north than corn. The latest KTBL figures put methane production per acre at around an average 1,550 cubic metres. It's also much more energy efficient in production and therefore creates considerably less climate-changing gases. But there's nothing wrong with production rates in most situations from much more energy efficient semi-permanent swards.

Now, the innovative "PROGRASS" research program for grass crop development has come up with a possible solution that could make grass an even more attractive energy crop. The University of Kassel in Germany is involved and scientists there are suggesting: Why not increase the energy output from grass silage by separating juice and solids? The juice has proven to ferment rapidly and the residual solids make very efficient heating fuel.

A prototype processor has already been built. This first sprays grass silage on a moving belt for 30 minutes with 30 C warm water before feeding it into a press auger. The resultant juice is inoculated with fermenting bacteria. Pressing reduces dry matter content of the solid residue from 30 to 50 per cent and further drying is fuelled by previous residue before pelleting. The liquid approach, according to the Kassel researchers, increases methane output per acre by around 25 per cent compared with conventional grass silage substrate.

The PROGRASS idea is still in prototype mode. But, through increasing the activeness of grass silage as biogas substrate, it offers at least one solution to the growing unease in Europe about huge areas of good food and feed land being commandeered for energy production. BF

Norman Dunn writes about European agriculture from Germany.