CCS and hydrogen turbines ‘essential’ for creating net zero energy system
Gas turbines fuelled by hydrogen or fitted with carbon capture and storage (CCS) will be “essential” for creating a net zero energy system, according to analysis from Aurora Energy Research.
In a new report, the consultancy forecast that the electrification of heating and transport will push peak power demand to 80GW by 2050, requiring large amounts of flexible and firm low-carbon generation to keep the lights on during extended periods of low renewable output.
Aurora modelled a hypothetical situation in which a week of high demand over winter of 2050 coincides with a typical lull in renewable generation, of which there is assumed to be 100GW of capacity as a baseline.
It said the remaining shortfall, which would amount to 3,900GWh over the week, could be filled by 45GW of gas turbines either fitted with CCS or fuelled by hydrogen, with the capital expenditure amounting to £38 billion.
The consultancy said this gap could also be filled using nuclear power, pumped hydro storage and lithium-ion batteries but noted their limitations in this context: “Nuclear provides firm capacity but is not able to vary its output quickly to complement renewables. Pumped storage can be operated highly flexibly but its deployment is limited by cost and availability of suitable sites.
“Whilst lithium-ion batteries are highly effective in providing short duration storage and managing grid frequency, their limited storage duration means they are not well-suited to respond to an extended wind lull.”
Aurora said closing the shortfall with only renewables and battery storage would be “challenging and prohibitively expensive.” Overbuilding renewables would require 250GW of wind at a cost of £240 billion, whilst relying solely on battery storage would require 976GW of 4-hour lithium-ion batteries at a cost £546 billion. Using a more optimal combination of nuclear (5GW), wind (60GW) and four-hour batteries (175GW) would still cost £174 billion.
Marlon Dey, GB research lead at Aurora Energy Research, said the figures presented only cover the capital costs of the generation and storage capacity and do not include operational costs or the costs of upgrading, and connecting the capacity to, the power grid.
“It is clear that wind and solar will provide a growing and cheap source of power to meet our needs as we electrify heating and transport,” he stated. “But questions remain in terms of how we ensure security of supply in a decarbonised power system.
“This is due to the variability of renewables, especially when we experience extended periods of low wind output. We already have seen examples of this happening earlier this year, in January, when wind load factors stayed below 10 per cent for an entire week.”
He continued: “During periods like this, storage technologies such as lithium-ion batteries or pumped hydro which have maximum durations of less than half a day, can only contribute so much. Looking out to 2050, gas-fired assets still look to remain the only feasible option we will have to keep the lights on.
“Carbon capture and hydrogen technologies therefore present a technically viable pathway for gas assets to deliver energy security, whilst being able to drastically cut their emissions in line with net zero goals.”
If going by costs alone, Dey said the hydrogen turbines suggested by Aurora would be fuelled with blue hydrogen produced by reforming methane and capturing the carbon dioxide emissions.
Aurora estimated the current cost of green hydrogen produced by electrolysing water at £140/MWh compared to £54/MWh for blue hydrogen and £21/MWh for natural gas (including carbon costs). The consultancy said it expects this gap to narrow by 2050 but not close entirely, with green and blue hydrogen remaining more expensive by £25/MWh and £12/MWh respectively.
“What we’ve tried to do here is explore a hydrogen that is closer to commercial viability, which would be blue hydrogen,” said Dey. “We’re not saying it’s the only solution but we used that as a case study.”
Aurora forecast that blue hydrogen generation could offer carbon emissions that are 75 to 93 per cent lower per megawatt hour when compared to unabated natural gas generation.
It did not give its view of overall greenhouse gas emissions, which a US controversial study recently argued should discount blue hydrogen from being considered as a clean fuel. The study has faced criticism over a number of its assumptions, including methane leakage rates from the production and transportation of the natural gas used as feedstock and the timeframe over which they are considered.
Dey said the requirement for firm low-carbon generation highlighted in its report could possibly be met by other emerging technologies such as hydrogen fuel cells or liquid air energy storage but said these remain prohibitively expensive in the case of the former and at an early stage of development in the case of the latter. He said existing turbines could potentially be converted to run on hydrogen, minimising the capital costs and speeding up the transition.
He additionally noted the ability of gas turbines to provide multiple critical grid services, mostly notably, as form of synchronous generation, inertia: “Inertia can’t come from batteries, for example. You need a synchronous plant with spinning mass to get inertia.”
Aurora’s report also drew attention to the growing costs of avoiding each additional tonne of carbon emissions as the energy system gets closer to net zero, predicting that the last 1 per cent of emissions would cost in excess of £1,500 per tonne.
“There are diminishing returns to removing carbon from the power sector because the low-hanging fruit is converting gas assets to a form of low-carbon generation such as hydrogen or CCS that are running baseload or at high load factors,” said Dey. “If you spread that cost over a large number of running hours, which translates the large amount of carbon removed, then the cost per tonne is relatively low.”
“If you then want to remove the last few tonnes, its coming plants that are essentially running very few hours in the year,” he added.
Dey said it may therefore make more economic sense to leave a small amount of backup gas generation running unabated and spend the money that is saved offsetting the emissions in other sectors or even other countries.