Anaerobic Digestion and distributed energy
 
Anaerobic Digestion (AD) can contribute electricity and heat. Alternatively it can generate enough electricity for internal use and export biogas, which can be cleaned up and injected into the grid or to provide motive fuel when compressed. It is fed with farm energy crops or food and industrial waste.
 
Dealing with electricity first, see http://en.wikipedia.org/wiki/Distributed_generation
 
Not much is made of the fact that in the UK electricity generation has fallen 10.5% since 2005 (398.4 TWh in 2005 down to 356.6 TWh in 2013). This means that the market for electricity is declining and cannot support investment in new generation plants.  The adoption of LED lighting and other energy saving measures should continue to reduce demand, easing the needed generation margin. There will have to be some replacement of ageing plants, so will this best be served by building centralised plants or lots of smaller, distributed plants? 
 
If we distribute as much electrical generation as possible it subtracts from the load on the local network. In effect it makes use of the same wires. For example, the electricity from solar PV on an office block will subtract from its electrical input, such that the net load on the local distribution cables will be reduced.
 
So distributed energy is the antidote to having more big nuclear or gas-fired power stations. It will make the  march of huge power lines through the countryside unnecessary. For example, the twin EPRs proposed for Hinkley Point C will require National Grid to spend a billion to get the power up the Bristol Channel, while the twin EPRs as Sizewell C will mean routing pylons up the Stour valley. Distributed electricity, together with the adoption of energy saving appliances offers a more economic solution than building centralised nuclear power plants that take at least 10 years and cost a fortune.
 
The main source of local generation will be solar PV and wind generators, plus biomass combustion together with waste incineration and anaerobic digestion. By the end of the century there may be tidal, wave and sea current energy, but the oil, gas, the best of the coal and uranium will be uneconomically extracted and inadequate. By then we will have learned to live with less energy or failed to survive.
 
There are now over a 100 anaerobic digestion plants in the UK, generating electricity and making use of the waste heat from the generators. Gas production from AD is already being added to the gas grid, providing the same distributed energy as electricity. If a suitable local injection point is unavailable the methane from an AD plant it can be compressed into cylinders and transported to one that is available.

Dual fuel farm tractors are now available running on biogas/diesel mixtures, so a farm AD can provide a measure of self-sufficiency for agriculture.

The generators' business model is inappropriate for the current energy scenario where householders are applying solar PV to roofs and installing low energy appliances while increasing insulation. Investment in huge centralised power stations needs a rising volume of supply to match the overheads of interest payments and increasing fuel costs.

Distributed energy can make use of the existing electrical wires and gas distribution pipes. State subsidies should encourage energy saving and the building of renewables as there is no benefit in constructing huge generating stations unable to supply a declining market.

John Busby 20 December 2014