Image for Digesting grass or burning forests is not the answer

Paul Spackman (who writes for Farmers Weekly) writing in his business blog on October 10, 2011 says that the UK could be using grass as a bio fuel in the future.

“There was an interesting take on the “food versus fuel” debate at last week’s ‘Power of 3’ event at Stoneleigh, Warwickshire.”, he writes.

“Addressing the issue of the increasing feedstock required to supply more anaerobic digestion plants, Masstock’s Roger Hellawell suggested land had already become available due to the decline in cattle numbers.

“Defra census figures showed cattle numbers had fallen by 300,000 head over the past five years, which at a stocking rate of two per hectare, equated to around 150,000ha of land. At a grass yield of 40t/ha freshweight, that gave a potential 6mt of grass, enough to supply about 90 250kW AD plants, he said.

“The figures may have to be taken with a pinch of salt, but they at least illustrate the potential that already exists to meet the growing demands from renewables.”

Now this is a curious development.

The use of biodigesters to produce energy from “waste” such as pig, poultry or cow manure would appear to have some validity, assuming that using such manures as directly applied fertilizer was ignored.

However to burn fossil fuel to produce fertilizers to fertilise the grass, to power tractors to harvest the grass, to power trucks to cart the grass to the digesters not to mention the energy embodied in constructing the digesters seems to me to be somewhat of a folly.

And this is not in invitation for the forestry aplologists to come in & say we should be burning our waste wood.  There is no waste in a correctly managed forest.

As Private Forests Tasmania member John Lord says:

“The management of our native forests, (in the drier forests such as our own, by careful selective harvesting,) occurs without the use of chemicals, either as fertilizers or sprays. The bark and leaves are left on the forest floor, allowing the elements needed for tree growth to remain as a slow release fertilizer, with only the barked logs being removed. “

The mix of future energy sources is surely going to be a major problem, but I can’t see digesting grass or burning forests as being the answer.