This feature continues to explore the pros and cons of decarbonising the UK’s electricity system by building capacity in the renewables sector. This is Part 2 of a two-part feature by John Barwise. Part 1 can be read here.
Bioenergy is energy derived from biomass or biofuel. Biomass power is defined as “carbon neutral electricity generated from plant-based fuels and organic waste” such as wood and other types of plant matter, and animal waste. It is the UK's second-largest source of renewable electricity, responsible for around 8%–12% of UK electricity supply.
Biomass is a renewable source of fuel. There are 78 operational biomass plants amounted to 4158 megawatts as of September 2020. The Drax Biomass Power Station (units 1–4) is the largest with an installed capacity of 2.6GW, but still burns coal at two of its units. Drax uses compressed wood pellets from low grade wood sourced from managed forests in the US, Canada, Europe and Brazil at four of its units — the other two still burn coal.
The problem with large scale plants is they need vast quantities of wood as a primary fuel. Drax, for instance, burns more wood than the UK produces every year, according to campaign group, Biowatchfuel, which brings into question whether biofuels are sustainable. Taking account of the full life cycle carbon footprint of harvesting, transporting and processing wood pellets, there are also questions over whether biofuels actually add to UK emissions, rather than reducing them.
Bioenergy also includes non-food crops, such as oilseed rape, maize and miscanthus, many of which are grown in the UK. Over 96,000 hectares of agricultural land in the UK are used to grow bioenergy crops, representing over 1.6% of the arable land in the UK, which might otherwise be used for food production.
Around 20% of land used for bioenergy is for biodiesel and bioethanol, producing 280 million litres/kilogramme of biofuel for the UK road transport market. Most of the remainder plant biomass is for heat and power production, representing just over 6.7 million tonnes of oil equivalent in the UK.
Energy from Waste (EfW)
Energy-from-waste (EfW) incinerators in the UK have doubled in less than 10 years to 55 operational sites, with a combined capacity of 15.4 million metric tons a year. It is estimated that the total power exported by EfW material in the UK in 2020 was 7,762GWh, representing around 2.5% of total net UK generation.
EfW is clearly a better option than landfilling waste, but there is concern that these plants emit pollutants damaging to health and also release greenhouse gases — burning plastics is a particular concern. Studies in Europe have shown higher emissions from EfW incinerators than electricity generated via conventional means such as fossil gas. Opinion is also divided on whether burning waste disincentivises industries from supporting the circular economy, or whether it is the best option for non-reusable waste that would otherwise end up in landfill.
Other renewables starting to make a mark
Heat pumps and deep thermal — as a share of renewables, these heat systems contributed 4.5% in 2020. The Heat Pump Association (HPA) says demand is growing with 67,000 heat pumps ordered by manufacturers for this year — nearly double the number of heat pumps currently on shelves. The Chancellor’s recent announcement of a £450 million package to install heat pumps around the country is likely to increase sales even further. Heat pumps can deliver up to three times more heat energy to a building than the electrical energy it consumes. They work well in buildings that are well insulated, which is why they are popular in Scandinavia. The problem for the UK is that most buildings are poorly insulated and because heat pumps operate at a lower temperature than gas boilers, they don’t deliver as much heat.
Marine, wave and tidal technologies — these can generate renewable energy from rivers and seas, but the industries needed to make this viable are still at an early stage. Marine technologies are expected to make a significant contribution to renewable power generation after 2020. The Government estimates that up to 27GWs could be deployed by 2050, as new innovative designs come on stream.
Biogas — anaerobic digestion and sewage gas. There are currently 650 operational AD facilities in the UK, contributing 295MW of capacity. Through the Renewable Heat Incentive (RHI), this increased by 9% in 2020. Together with sewage gas and landfill gas, biogas is generally used for heating, although is now also injected into the gas grid.
Hydrogen fuel cells — hydrogen is one of the most abundant elements on earth but is usually bonded to other elements and requires energy to isolate it. Even using a super-efficient electrolyser, it requires 39 kWh of electricity to produce 1 kg of hydrogen. Most hydrogen processing is achieved using fossil fuels (so called blue hydrogen) although renewables (green hydrogen) is also on the increase. The Government has been criticised for supporting the use of natural gas to produce hydrogen, which releases more carbon dioxide in the process. Once separated, hydrogen fuel cells can generate electricity of up to 65% efficiency but is overall much less efficient than electric battery cells.
In summary, the good news is that electricity generation in the UK was the greenest on record in 2020, according to the National Grid Electricity Systems Operator (ESO). The potential expansion of renewables and low carbon options will likely see this continue as the UK sets its sights on net zero by 2050.