What is biogas energy?
This section is about the use of biogas in industry for the purpose of energy creation (heat and electricity) and/or non-transport fuel that can be released back into the grid for general public use.
Biogas is produced via a process called Anaerobic Digestion (AD), which results in the production of numerous gases that can then be burnt to produce energy. Anaerobic digestion is the breakdown of various plant and animal material (known as biomass) by bacteria in an oxygen-free environment. For example, the waste plant material is sealed in an airtight container, then bacteria is added, which is encouraged to multiply and grow, releasing methane and other gases as the by-product of the process. In addition, there are other by-products produced in the process which are rich in nutrients and can be used as fertiliser. The inputs in the process can be any number of biomass materials including any of the following: food waste, energy crops, crop residues, slurry and manure. In practice the process can take on waste from households, supermarkets and industry, therefore reducing the waste that goes to landfill.
The two major gases that make up biogas are methane (CH4), which accounts for about 60%-70% of the total and also carbon dioxide (CO2) which accounts for 30%-40%. Small traces of other gases can be found. Overall the way biogas is composed depends on the inputs or feedstock that goes into the AD process. In industry, biogas can be enhanced to filter out pure methane and removing other gases, which then becomes biomethane.
Biogas energy and industrial uses
Heat-only biogas energy
Biogas can simply be burned through the combustion process to produce heat only. When burned, one cubic metre of biogas produces around 2.0/2.5 kWh of thermal energy. A proportion of the heat generated in the plant can be used first hand to power the digester and the nearby buildings. The remaining heat is discharged, and unless it is then heating and transferring hot water through a local pipe network into the home, it is wasted. This concept of heating water and transferring to homes as part of central heating is popular in some Scandinavian countries.
In the UK, to increase the concept of district heating, requires investment in new infrastructure. The generators that make this upfront investment can hopefully by the end of 2012, make good use of the Renewable Heat Incentive support.
Electricity-only biogas energy
Electricity can be generated from the combustion of biogas, which is a relatively simple process, but this requires an upgrade of the plant. Electricity is easier to transport and measure than heat and gas supply, but requires the infrastructure to feed into the grid, which is not simple and may be expensive. Generating green electricity can benefit the generators (households and communities) by making the use of Feed-in Tariffs (FiTs) or for bigger players can maximise the Renewable Obligation Certificates (ROCs) for industrial scale production.
Combined heat and power (CHP) biogas energy
CHP or cogeneration is a process that simultaneously produces useable heat and electricity. The process of heat generation makes biogas plants more efficient than other conventional power plants, as the process to create the various gases requires heat, therefore less is wasted. In addition to then generating the heat, the plants also generate electricity, which is transported and sold like the excess heat. If generators can support the cogeneration process, then they are able to make good use of the RHI, FiTs and ROCs available to them.
Biomethane liquid biogas energy
Biogas needs to be purified by extracting out the carbon dioxide and trace gases, therefore making a purer form of methane which then becomes biomethane. In the UK, the process of purification has to take place for it to be acceptable in the gas grid, where the gases are dried and upgraded to a higher methane content (upwards of 95%) so it then resembles the qualities of natural gas. This approach is already followed in the US, and other Western European countries. Refer to the National Grid for more information and supporting documentation that look at maximising the opportunities for biomethane into national supply. The DECC have announced that when the RHI scheme is finalised, it will not only include support payments for biogas combustion (see above), but biomethane injection too as a consumption fuel for homes and businesses.
Biomethane transport fuel biogas energy
Biogas energy, like the process for domestic heating fuel, can be cleaned further from other gases (carbon dioxide and trace gases), then upgraded to a pure form of biomethane and used as transport fuel. Biogas is eligible for support under the Renewable Transport Fuel Obligation.
The combustion of biomethane from vehicles are more environmentally friendly than that of burning of transport fuels such as modern petrol and diesel, thereby helping reduce greenhouse emissions. Examples of renewable transport fuels in vehicles that are formed out of biogas are compressed natural gas (CNG) or liquefied natural gas (LNG). In the UK, the number of vehicles that are CNG or LNG is a relatively low percentage compared to Germany and Sweden. As the number of of vehicles using CNG and LNG is lower in the UK, the infrastructure to support these vehicles, such as refuelling stations, is also therefore less developed than some of those countries mentioned.
Biogas energy policy development
Biogas energy hasn’t really taken off as a fuel alternative as of yet in the UK. This is partly due to the lack of infrastructure to support its development and secondly, more importantly, there is a lot uncertainty from the government around the RHI. Generators do not yet know what is actually going to form part of this scheme and the level of support that will be given to both fuel and combustion. Biogas energy generation is more expensive than conventional fossil fuels that enjoy benefits of scale and lower fuel price. The government needs to support these generators if they want the investment to happen and the price to come down in the long term.
Smaller scale producers currently benefit from the FiTs and larger scale producers from the ROCs (only for electricity generation – on the assumption the AD facility has been completed post 15th July 2009). If you are an accredited generator of renewable energy, you could be entitled to benefit from the Renewables Obligation, if you are not already doing so. To find out more information and how to benefit from renewable obligation, please visit OFGEM.
- Rich leftover products that can be harnessed as fertiliser.
- Biogas creation is made from plant and animal waste that would otherwise end up in landfill sites.
- Biogas power plants can make use FiT and ROCs for electricity generation and RHI for heating.
- Biomethane (from biogas) is a fuel that powers CNG or LNG vehicles, emits less greenhouse gases.
- Purifying biogas by removing CO2 and trace gases, turns the gas into biomethane which can be used as alternative for domestic consumption.
- With a piping infrastructure, biogas power plants can provide heating to local communities and districts that is greener and more sustainable.
- Biogas power plants are more efficient in using the heat they generate than conventional coal, oil and gas plants.
- Electricity distribution start-up costs can be high as requires the producer to connect to the grid and agree a tariff with their distribution partners.
- Local infrastructure needs to be upgraded, which may be costly, so that heat generated can be effectively passed to homes as a central heating solution.
- In the UK the volume of CHG and LNG vehicles is relatively low compared to countries like Germany and Sweden.
- If the plant was built pre-July 2009, the producer will not be able to benefit from FiT and RHI.
- Poor choice of feedstock will mean poor yields of biogas.
- Ensure regular supply of feedstock, otherwise this may lead to large variations in production.