From a renewable energy point-of-view, “biomass” refers to organic material which is either used directly or processed to provide a source of energy for heating, electricity generation or transport. Although use of biomass contributes to greenhouse gas emissions, it is regarded as “renewable” or “carbon-neutral” since the CO2 released during use is theoretically reincorporated into the live, growing material destined to provide energy in immediate future years. The timescale of carbon cycling is therefore miniscule in comparison with using fossil fuels and much less likely to disrupt the global carbon balance.
Examples of biomass energy systems include growth of woody or stemmy plants for burning e.g. fast-growing trees and grasses, producing “biodiesel” from oilseed crops, extracting starch or sugar from crops to ferment into ethanol e.g. cereals or sugar cane and anaerobic digestion of a wide range of organic materials to produce methane. The latter is more commonly referred to as “biogas”.
Traditionally, the most common form of biomass energy use in Orkney has been harvesting of peat. This is now quite rare and, as well as having a relatively slow rate of carbon recycling, it raises concerns about habitat loss. Work pioneered by the Agronomy Institute at Orkney College UHI investigated the viability of using Short Rotation Coppice (SRC) as an energy source in the county and more widely across the North of Scotland. Trials identified some willow clones which yielded biomass in sufficient quantities to merit consideration along with suitable methods of establishment, but project funding has not extended far enough to develop viable mechanisms for harvesting the crop efficiently.
More recently, the Agronomy Institute, in collaboration with Forestry Commission Scotland, is assessing the potential of Short Rotation Forestry (SRF) at a couple of sites in Orkney. One of the key differences between SRF and SRC is that the trees are allowed to grow for 15-20 years before harvesting compared with 2-4 years for SRC. Initial measurements have begun to identify which species grow and survive best in the prevailing conditions.
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Whereas the products of the above trials have not progressed to the stage of being used to provide heat, a number of domestic and business properties in Orkney are using wood pellets as a heating fuel. This material is obtained as a forestry by-product on mainland UK and metered automatically into specialised pellet boilers. From discussion with local pellet suppliers, it is estimated that up to 50 premises (mostly domestic) have installed pellet boilers consuming an average of 6 – 6.5 tonnes of pellets per annum. There is anecdotal evidence that some users have reverted to oil heating as after-sales support has been disappointing in some instances where boilers problems have occurred.
One other biomass system which has been considered in Orkney is the conversion of organic material such as slurry and other farm waste into methane by anaerobic digestion. Although the county potentially has considerable quantities of feedstock in addition to slurry e.g. wastes from distilling, brewing, fish processing and cheese production, there are currently no proposals to investigate or develop this technology further.
Installations using many of the technologies mentioned here are eligible for Renewable Heat Incentive, a UK Government payment based on characteristics of the property and the associated estimate of heat requirement. Eligibility for these payments depends on certification of the equipment to be installed and there is a suggestion that certified boilers carry a cost premium which, for some people considering these systems, might negate the value of the RHI payments.
More information on RHI and current tariffs can be found here:
- Tariffs: https://www.ofgem.gov.uk/environmental-programmes/domestic-rhi/contacts-guidance-and-resources/tariffs-and-payments-domestic-rhi/current-future-tariffs
- Product eligibility: https://www.ofgem.gov.uk/publications-and-updates/domestic-renewable-heat-incentive-product-eligibility-list-pel