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 the use of biomass contributes to greenhouse gas emissions, it is regarded as “renewable” or “carbon-neutral” since the CO2 released had recently been captured by the, growing material. Its use, therefore, does not add to the overall global carbon balance. Care must be taken however that crops grown for biomass do not replace diverse habitats or disrupt other carbon sinks such as peat.
Examples of biomass energy systems include:
- Woody or stemmy plants for burning
- Starch or sugar from crops to ferment into ethanol
- Anaerobic digestion to produce biogas
Biomass in Orkney
One of the major funding schemes came in 2011 from the UK government. The Renewable Heat Incentive provided financial support to non-domestic participants, and later in 2014 to domestic participants, who met the eligibility criteria until March 2022. Technologies supported by the scheme included biomass boilers and biomass pellet stoves.
Peat has been used as fuel for centuries in Orkney. With no records kept, there only exists anecdotal evidence of the usage of peat which suggests domestic use has decreased to a low level. In the most recent Orkney energy audit, emissions in 2018 were estimated at 49 tonnes, all associated with the whisky-making process. For more details see the 2019 Orkney Energy Audit.
Today, Orkney is more conscious of the protection of biodiversity and the carbon capture potential of peat than as use for fuel.
This forestry by-product is typically imported to the county and is fed automatically into specialised pellet boilers. In 2016, 7.2 GWh of heat energy from wood pellets was estimated for domestic use, a reduction from previous years with the highest usage recorded at 9.2 in 2010. The total annual carbon emissions were estimated at 2,268 tonnes. For more details see the 2019 Orkney Energy Audit. A trial of short rotation coppiced willow has been tried, but abandoned, due to low energy yield rates.
Another biomass system which has been tried 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 feedstocks, the low energy content of slurry in particular means that there is currently not enough high-energy fuel that could contribute significantly to anaerobic digestion. At present farm, waste is still being treated on farms and household waste, including organic matter, goes to Shetland to be incinerated in the district heating scheme in Lerwick.