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Heat only
Biogas can be combusted to produce heat alone. When burned, one cubic metre of biogas produces around 2.5 kWh of thermal power. Some of this heat energy can be used on site to maintain the temperature of the digester and nearby buildings. However, even small plants will have an excess of heat. The heat can be transferred via hot water to remote users by a district heating system, a concept widely used in some European countries e.g. Denmark.
Increasing use of district heating requires investment in new infrastructure, and installations can benefit from the Renewable Heat Incentive support. The RHI includes support for biogas combustion, as well as biomethane injection into the national grid.
Electricity only
Electricity generation is a relatively straightforward use for biogas and it can be the most profitable. The biogas requires minimal investment in cleaning and upgrading and electricity earns ROCs, LECs and FiTs. Electricity is easier to transport than gas or heat and supply is easily measured.
Electricity storage, however, is not simple and connecting to the electricity network is costly. Renewables East have produced an easy to read guide to grid connection including alternatives in connections that may improve the viability of a project. The same organisation provide a guide to power purchase agreements, the contract between a generator and an electricity supplier that sets down the conditions and pricing that will govern the supplier’s purchase of electricity from the generator. Also see this report by the NNFCC and Andersons Centre for more information on how to sell your electricity.
Combined Heat and Power ( CHP)
Combined heat and power (CHP) is the simultaneous production of useable heat and electricity. As the process of AD requires some heat it is suited to CHP. Whilst coal and gas-fired power stations have an efficiency of around 34% and 55% respectively, CHP plants can achieve overall efficiencies in excess of 70% at the point of use.
There are schemes to encourage CHP including Enhanced Capital Allowance and Climate Change Levy Exemption Certificates (LECs). Both require certification that the CHP is 'Good Quality' from the CHP Quality Assurance Programme. Renewables East provide a simple guide to Quality Assured CHP and ECA for biomass projects. Also see this report by the NNFCC and Andersons Centre for more information on how to sell your electricity.
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