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UK ‘Green light’ least cost 2050 energy scenario

Prof. Mark Barrett at University College London has produced an update of his Green Light UK 2050 scenario, with a few additions from the 2023 version. The conclusions remain the same: renewables can supply just about all power needed. But some of the new details are interesting: aviation can’t be decarbonised easily, so we have to compensate with atmospheric carbon removal- Direct Air Carbon Capture and Storage (DACCS).

In 2050, his scenario has offshore wind generating 931 TWh, which is 83% of total generation. Solar generates 118 TWh and onshore wind 40 TWh. Nuclear generates 25 TWh or 2% of total and there is 57 GW of flexible generation plant which outputs 3 TWh, operating at a capacity factor of under 1%. He says that ‘an alternative assumption that flexible generation uses stored hydrogen is also modelled but optimisation shows this to increase costs’. 

He notes that ‘in the least cost 2050 systems 20-30% of potential generation is spilled, and this is, at first sight, a surprising optimisation result. Essentially this is because it’s cheaper to build ‘excess’ renewables than more absorption capacity with storage or demand - e.g., grid storage, DH heat pumps or electrolysers - which would be operating at increasingly low capacity factors and therefore higher unit capital costs’. But he admits that ‘this spillage is in a system with no interconnector trade which other analysis …has shown can reduce storage needs or spillage’. 

He says that ‘Aviation is a hard problem. Aviation demand management, shifting to modes such as electric rail, more efficient aircraft & operational changes all have limited potential in the context of rapid demand growth. For the foreseeable future, long range aircraft need kerosene which has carbon in it, & engine emissions of water and nitrogen oxides from any fuel at high altitude cause global warming’. He concludes that ‘beyond limited waste biomass, it is hypothesised it is cheaper to use DACCS driven to balance fossil kerosene emissions from aviation, rather than using synthesising kerosene from DAC carbon and renewable hydrogen in Fischer Tropsch plant,’ which he says would increase total cost. He admits that ‘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 required negative emission costs, aviation incurs about 20% of the total net zero energy system cost’. 

However, using DACCS feels a bit odd. He says that ‘if hydrogen electrolysers and DACCS run on electricity that is surplus to all other demands, their capacity factors range 60- 70%. In practice, this would mean that their electricity costs would be relatively low’. Well maybe, but with the CO2 concentration in the atmosphere only being 0.04%, DACCS is bound to be an energy intensive operation. Barrett though claims that it is ‘a relatively simple process for which energy consumption & costs can be approximately estimated’, although  he admits it is ‘not implemented at commercial scale and its environmental impacts are uncertain’. He says ‘other negative emissions options such as afforestation are not modelled here because of uncertainty and impacts but may play a role. Bioenergy carbon capture and storage (BECCS) has the problem of biomass supply. Negative emission options are the least proven technical elements of system design’.  

In fact, in this study, Biomass is 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’. Heat is supplied mainly by heat pumps using green power but also district heating (DH) via CHP plants, possibly using biomass wastes, with big heat stores.

Interestingly, as noted above, nuclear only offers a small contribution: he notes that, since it is not cost competitive and slow to build, ‘nuclear generation does not appear in the least cost mix, beyond Hinkley C which is presumed committed and operational in 2050’. Historically, he says ‘nuclear capacity has suffered large unplanned outages which require back-up supply’.  He notes that ‘the UK nuclear fleet capacity factor has averaged 70% and ranged between 50% (2008) and 80% since 1996. There seems to be a slight ageing effect: capacity factors were 6% higher during 1996-2000 than 2017-2021. In 2008, the nuclear fleet had a capacity of 10 GW output and its output fell by about 17 TWh below the average. The maximum annual loss of nuclear generation compared to the average has been 32% over this period’. So, it’s not really any good as baseload. 

Instead, in addition to flexible demand and supply systems, ‘electricity supply 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’, with large scale battery units being favoured as being more efficient than domestic units. Interestingly, he notes that ‘the electricity storage option of combined electrolytic hydrogen, hydrogen storage and hydrogen generation was tested in the optimisation but was found uneconomic because of its high capital cost and low throughput efficiency.’ However, while not being seen as cost efficient for home heating, green hydrogen is used for to power some industrial plants, and for example for ammonia production in Haber plants, with ammonia being used as a fuel for ships. 

The study does not look at energy trading via interconnectors (which might avoid some of the spillage issues) but even without that, it concludes that its UK scenario optimization ‘results in high, dispatchable (using stored energy) power capacities operating at low capacity factors to meet rare shortfalls. Grid storage has an optimized output capacity of about 10 GWe operating at around a 2% capacity factor. The fuelled dispatchable generation has an optimized capacity of about 50 GW and operates at a capacity factor of around 1%. These dispatchable sources constitute about 3% of total system costs.’ 

So it seems viable in power security terms. But what about total overall cost? With the least cost generation mix being mainly offshore wind, but with some onshore, and a substantial solar capacity, he rather boldly claims that ‘Net zero 2050 designs cost about the same as the current system assuming fossil prices close to those current, using the same costing model. Apart from fossil kerosene, these net zero designs are not subject to unpredictable international fuel prices and events affecting imports, and therefore offer security both economically and technically’.

Will it happen?  Well the UN had just produced a new report calling on all countries to ‘seize the moment of opportunity’, given that their ‘plummeting costs mean that solar and wind have become the fastest growing sources of electricity in history’, and there is ‘the economic imperative and opportunity’ for ‘accelerating the transition away from fossil fuels to clean energy, with a particular focus on the roles of renewables, electrification, and energy efficiency’. And, as Mark Barrett claims, the UK is very well placed to join the leaders in this, without excessive costs. 

 

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