Securing the UK’s net carbon future: how bioenergy with carbon capture and storage can guarantee supply

Renewables’ weather-dependency can make securing consistent power difficult. Simone Bruckner, managing director of power resistor manufacturer for renewables Cressall, explores how biomass can ensure a reliable electricity supply on a renewable grid.

The Committee on Climate Change’s (CCC) Sixth Carbon Budget report explains that, in order to achieve net-zero emissions, the UK must eliminate all fossil fuel-generated power by 2035 and increase variable renewable energy production by 80% by 2050.

In addition to executing this shift, the electrification of other areas of industry, such as the automotive sector, will see a rise in electricity demand from the current 300TWh-610TWh by 2050.

Transforming the grid

Meeting this increased demand solely from renewable sources cannot be guaranteed, since renewables such as wind power are heavily weather dependent.

The amount of electricity generated by renewables varies since it is determined by a natural, uncontrolled source, such as wind speed. Therefore, an additional energy source will be required for periods when renewables cannot meet demand.

In line with the target to fully decarbonise electricity generation by 2035, this alternative, dispatchable source must be low-carbon or carbon neutral. The CCC estimates that, as part of the renewable grid, this source will be responsible for generating 50TWh of electricity. But which source meets all these criteria?

Enter bioenergy with carbon capture and storage (BECCS): a two-step, carbon neutral energy generation method.

Burning biomass

The first step of BECCS involves burning biomass to generate energy. The International Renewable Energy Agency further classifies biomass sources as traditional, which includes wood and animal waste, or modern, which refers to waste from anaerobic digestion of residues and wood pellet heating systems.

This organic waste produces electricity in the same way as fossil fuels – combustion of biomass produces heat, which in turn produces steam to turn a turbine to power a generator and produce electricity.

The crucial difference between biomass combustion and fossil fuel combustion is the carbon emissions. Biomass absorbs CO2 as it grows and re-releases the same amount when burned, making biomass combustion carbon neutral.

Collecting carbon

Bioenergy production can be made more sustainable by combining biomass combustion with carbon capture and storage (CCS) technology. The CO2 produced when burning biomass can be captured directly from the air in many ways, however the simplest CCS technology is oxyfuel combustion.

When fossil fuels are burned, anything from 3%-15% of the waste gas produced could be CO2. However, separating out the harmful CO2 can be challenging.

In oxyfuel combustion, biomass is burned in pure oxygen, which results in waste gas that is almost exclusively CO2 and water vapour. In this way, the CO2 can easily be compressed to form a liquid, which can be transported to an underground storage space.

Combining carbon neutral biomass combustion with CCS technology results in a carbon negative electricity generation that is available when required to fill any gap between energy production from variable renewables and demand.

Guaranteeing supply

BECCS is vital to ensure a reliable, renewable energy supply in a decarbonised UK, acting as an on-demand energy source in periods of low renewable energy production. However, for biomass plants to turn fuel into a reliable form of power, these facilities must make use of suitable power protection equipment to prevent electrical faults that may impact delivery.

To ensure a reliable supply, the plants must be protected against the impact of power problems like fault currents and transient overvoltages. Medium voltage neutral earthing resistors (NERs) can mitigate the impact of these faults. In the event of a fault, NERs limit the current that can flow through the neutral point of a transformer or generator and dissipate the excess energy as heat, preventing damage to network equipment.

Metallic NERs are more effective than liquid resistors, cooling down in just a third of the time to provide protection against consecutive faults. They are easy to install, with no site calibration required and they have a service life of 25 years or more.

According to the Energy Technologies Institute, BECCS could deliver up to 55 million tonnes of net negative emissions per year, which would account for around half of the UK’s emissions target by 2050.

In the future, this could help to mitigate the negative impact of sectors such as heavy duty transport that prove more challenging to decarbonise and therefore will continue to produce more than their projected carbon emissions.

Integrating BECCS into a competent electricity grid, protected by NERs, would give difficult-to-decarbonise industries some leeway in rapid emission reduction, securing the UK’s net-zero target and providing power to our increasingly electrified nation.