Green light: Net zero emission energy system designs for the UK

Mark Barrett

Summary

This report describes least cost designs for net zero carbon emission energy systems for the UK that might be developed over three decades. A central aim is to show that the systems designed will work in engineering terms hour by hour across the year. Not all possible technologies and system configurations can be assessed.

The most difficult problems of system design are aviation fuelling and high altitude warming, negative emissions and heating and cooling. Considerable space is given to a comparative analysis of nuclear and renewable generation as two leading options for zero carbon primary supply. Most primary energy in the scenarios is renewable electricity. Nuclear power is not cost competitive even assuming it is baseload, and is slow to build. Biomass is assumed to be restricted to waste biomass because of competition with food, the environmental impacts of biocrops, and the insecurity of UK production and import availability given climate change and population growth.

Most major energy demands are met with electricity, including most equipment and heating and cooling in the stationary sectors, and road and rail transport. Oil for ships is replaced with ammonia made from electricity, air and water. Heating with heat pumps in consumer systems or district heating is lower cost than hydrogen.

Reversible heat pumps can heat and cool and provide resilience to climate change, but like all consumer heat pumps will cause some disruption. These systems will require large scale energy network development and there is uncertainty as to the technicalities and costs of this. Some industrial processes require temperatures and chemicals that cannot be met with electricity, and renewable hydrogen or hydrocarbons are needed there.

Zero carbon electricity can be produced by renewables and nuclear power. The least cost generation mix found in this study is mainly offshore wind but with some onshore, and a substantial solar capacity. Nuclear generation does not appear in the least cost mix, beyond Hinkley C which is presumed committed and operational in 2050. Historically, nuclear capacity has suffered large unplanned outages which require back-up supply. System dynamic surpluses and deficits are managed with the storage of electricity in vehicle batteries and grid stores, heat in district heat stores, and chemical energy in hydrogen, biomass and fossil fuel stores. Hydrogen electrolysis and direct air capture and carbon sequestration (DACCS) use electricity surplus to other demands. It is found that spilling 20% or more of renewable generation is lower cost than investing in extra storage or usage process capacity such as of electrolysers or DACCS, but a major modelling limitation here is that interconnector trade with other countries, which can reduce both spillage and storage, is not included.

Aviation is a hard problem. Aviation demand management, shifting to modes such as electric rail, and more efficient aircraft have limited potential. For the foreseeable future, long range aircraft need kerosene which has carbon in it, and engine emissions of water and nitrogen oxides from any fuel at high altitude cause global warming. Beyond limited waste biomass, it is hypothesised that it is cheaper to use electrically driven direct air capture (DAC) to capture and sequester atmospheric CO₂ (DACCS) to balance fossil kerosene emissions from aviation, rather than using DAC carbon with renewable hydrogen to synthesise renewable kerosene in Fischer Tropsch plant. A preliminary analysis of synthesising renewable kerosene this way indicates this would increase total system cost but more research on this complex issue is needed. Plainly the assumed continued use of fossil kerosene has the political implications attached to allowing one major sector to continue emitting CO₂ at scale. Accounting for the costs of the required negative emission, aviation incurs about 20% of the total net zero system cost.

DACCS is an option for negative emissions to balance aviation and other greenhouse gas emissions such as from cement production. DACCS is a relatively simple process for which energy consumption and costs can be approximately estimated, but it is not implemented at commercial scale and its environmental impacts are uncertain. Other negative emissions options such as afforestation or bioenergy carbon capture and storage (BECCS) are not modelled here because of uncertainty and impacts but may play a role. Negative emission options are the least proven elements of system design.

At the 2023 fossil prices, net zero 2050 designs cost about the same as the current system, using the same costing model. Apart from fossil kerosene, zero designs are not subject to unpredictable international fuel prices and events affecting imports, and therefore provide security both economically and technically.

Banner photo credit: Alireza Attari on Unsplash