Combined Heat and Power Generation Services
Anaerobic digestion can provide a valuable source of on-site renewable energy. The biogas produced by anaerobic digestion can be used to generate electricity or fed to on-site boilers. In addition, treated biogas can be fed directly into the gas grid.
At present, on most anaerobic digestion plants, renewable electricity is generated from Combined Heat and Power (CHP) engines, along with surplus heat.
Electricity generated can either be used on site (to replace bought-in power), or sold to the national power grid at a premium over purchased electricity costs. By generating renewable energy, on-site anaerobic digestion will reduce treatment costs and replace fossil fuel derived energy and reduce the carbon footprint of the site.
The renewable electricity Feed in Tariff (FIT) was extended with two additional FIT bands in 2011, to provide higher rates for gas combustion in a CHP generator from smaller scale anaerobic digestion.
These index linked payments are now set at 15.16 per kW for plants producing less than 250kW and 14.02 for 250 to 500 kW, and 9.24p per kW for plants that generate over 500kW. In addition there is a payment of at least 4.5p per kW, when electricity is exported to the grid. There will be regression for the value of FIT payments (possibly by 2.5% each year) for plants registered after April 2014.
Also, to encourage the use of renewable heat, the Renewable Heat Incentive (RHI) was introduced in November 2011. It too is index linked and now provides a payment of 7.3p per kW of heat value, for biogas that is up-graded to bio-methane for injection into the gas grid.
The RHI is also available for direct use of biogas - up to 200kW, for the surplus thermal energy from biogas that is fed to a CHP unit or if it is used in a biogas boiler. DECC will bring a second phase of the RHI in April 2014 for heat from direct (on-site) use of biogas over 200kW thermal.
On-site liquid anaerobic digestion has a significant advantage over aerobic effluent treatment, as well as reducing energy and treatment costs, it will generate significant revenue from these incentives.
- FIT - Feed in Tariff - for smaller AD projects - payable monthly, index linked - 20 year duration
- RHI - Renewable Heat Incentive – 7.3p < 200kW thermal
- LEC - Levy exemption certificates - require Ofgem registration - negotiated with generators
- Site Power – reflects the cost saved when the renewable power is used. The actual figure will depend upon the cost of power pertaining on the site.
Clearfleau is working with Ener-G a leading provider of CHP generators. The CHP unit is tailored to expected biogas flow. To offer greater flexibility, it is possible to lease or hire the CHP unit.
The energy generated on a specific site will depend on the biogas potential of the feedstocks. This can be assessed on our model and verified with a laboratory trial or by using the mobile anaerobic digestion trials unit (Small Scale Production Plant - SSPP).
Clearfleau’s anaerobic digestion plants are tailored to the specific waste stream and can be installed on a confined site. Based on the biogas potential, the appropriate CHP unit is selected to meet output and finance requirements.