Whether it comes from nuclear plants or fossil fuel-fired power stations with carbon capture and storage (CCS), the UK will need 30-40 GW of new “firm” low-carbon baseload generation by 2050 to meet the net-zero emissions target, Greg Clark reportedly said, just before being replaced by Andrea Leadsom as UK government Department for Business, Energy and Industrial Strategy (BEIS) Secretary of State. That view underlined the consultation on the proposed pre-build “regulated asset base (RAB)” consumer surcharge subsidy for new nuclear. RAB has not been without its critics. But is the capacity-need rationale right?
First off, it has to be said that “baseload” plants, “firm” capacity and “dispatchable power” are not the same thing. As BNEF’s Michael Liebreich told Carbon Brief: “Any case for ‘firm’ power is essentially valueless without knowing the detail of the assumptions. Firm power which cannot be switched off when you don’t need it will be as much of a problem as variable power which cannot be switched on when you do. What is called for is flexibility, in huge quantities and of all types.” Nuclear plants of the current type can’t provide that, and gas turbines with CCS may find it hard to load-follow economically, with inefficient part-time use of costly CCS kit. What we need to do is to plan the whole new system coherently, not just add on odd bits.
At present, peak wintertime UK power demand is around 60 GW and the summer night-time minimum demand is about 20 GW. Most of the latter is met from nuclear-, gas- and coal-fired plants run continuously and meeting the so-called baseload, although with coal on the way out, PV solar, which has over 13 GW in place, is edging into the market. Wind, with more than 21 GW in place, is more available in winter and, if not, is backed up by flexible gas plants, with these inputs, along with extra from gas and biomass plants, and the “baseload” plant inputs, meeting winter demand.
Renewables like wind and solar are variable. So, as we expand from the current 33% renewable contribution, we will need to use flexible plants more often — the inflexible nuclear plants can’t help — and also add other balancing measures. But it doesn’t have to be fossil gas-fired back-up plants. Biogas and green syngas-fired plants would avoid the need for costly CCS, and storable hydrogen syngas could be made from the occasional surplus renewable power outputs, via Power to Gas (P2G) electrolysis, maybe soon at reasonable overall costs — as renewable costs fall, the economics of P2G/hydrogen do seem to be improving.
It is possible that, at some point soon, we could meet near 100% of power demand from renewables most of the time. National Grid offshoot ESO says “there soon will be times in the year when the market could meet the total demand for electricity through renewable generation only and these periods will increase as more and more renewables are connected and more load actively participates in the market”.
Then there would, at times of low demand, be a substantial surplus, available, if it was P2G converted and stored, to meet the occasional demand peaks and longer lulls in renewable availability without much need for other storage. Although compressed air/liquid air storage are also options for longer-term bulk storage, with perhaps better round-trip efficiencies than P2G. Pumped hydro and batteries can help with shorter-term balancing, for hours or at most days. Some easily-varied biogas-fired Combined Heat and Power plant outputs, linked to heat stores/district heating networks, could also help with that, with the heat stores being topped up using solar heat and heat made with surplus wind/PV power. And demand-side management (DSM) could delay the peaks for a while. We may also be able to import green power to meet local lulls — balanced by exports at other times, when we have a surplus.
Will all that suffice? The current plan is to switch most heating and transport over to electricity — heat pumps and electric vehicles (EVs). That has some issues: the power grid may not be up to it, as power demand would be pushed up at peak times, unless evening EV-charging was delayed. But let’s say maximum demand rose to 70 GW (despite the fact that power use has actually been falling). With, say, 100 GW of renewables on the grid, that demand could be met most of the time, with DSM helping to cut peaks and P2G-fed plants topping up when there are long lulls in wind/PV.
That does mean green gas plants must be there for occasional extra back-up but arguably it would not require 70 GW. If DSM can delay peaks and the UK briefly imported some power, less back-up should be needed, and that’s forgetting that wind and PV are unlikely to both get to zero at the same time. In addition to the (stored) biomass, there would also be inputs from hydro and, possibly, geothermal (all “firm” sources) and tidal plants (variable but predictable), plus wave energy (variable, but less so than wind). With load factors improving all the time — over 60% is claimed for some new offshore wind turbines — my guess, in line with the modelling I did some while back for Pugwash, is that it would be rare to need more than 30-40 GW of partly P2G-fed green power capacity available for backup by 2050, depending on how the rest of the system was developed and run, and the level of demand reduction that can be made.
Given that we don’t yet know what the optimal mix/scale of renewables/P2G would be, it is hard to assess the overall cost of this system. It is usually said that balancing costs will rise significantly as the variable renewable proportion increases. But, against that, some smart grid-balancing measures will reduce system costs by matching energy supply and demand more efficiently. As the National Infrastructure Commission (PDF) noted, an integrated flexible supply and demand management system, with smart grids, storage and also grid interconnector imports/exports, could save the UK £8 billion p.a. by 2030. A study by Imperial College London/OVO Energy claimed that just adding residential flexibility in domestic energy use (including for electric vehicle charging) could reduce whole system costs by up to £6.9 billion p.a, or 21% of total electricity system costs. It was suggested that these savings could more than offset the cost of upgrading the power system. That does seem credible for some of the options. For example, introducing variable time-of-use energy tariff charges requires no capital outlay but could lead to reduced energy use and user costs and reduced system costs. In all, it has been suggested that improved system flexibility could save the UK up to £40 billion by 2050.
What’s more, as I noted in an earlier post, we also do not have to stick with just 100 GW of renewables. Some say you can expand renewables much further, in which case demand could be met even more of the time (reducing the need for back-up), and there would also be more surpluses, which could be used not just to deal with times when current output can’t meet demand, but for other purposes as well, including transport, heating and export.
In a scenario with renewables much expanded, demand would not change (indeed, hopefully in such a future, it might be reduced). But, while there would not be a need for more back-up power, there would be a need for more P2G conversion if the surpluses are to be used as hydrogen more widely, so that would push up the cost — although that has to be set against the value of the wider use of P2G energy. Alternatively, some of the surplus could just be exported as power, earning valuable income.
The UK government’s advisory Committee on Climate Change (CCC) says you can only go so far with the proportion of energy supplied by renewables before balancing costs start to rise, so we will need nuclear or CCS to provide some firm power. But it assumes that nuclear will get 28% cheaper by 2050 and that CCS will be viable at scale. In reality, renewables are here now and are getting ever cheaper and, as I have suggested above, the system economics could improve as renewables expand — depending in part on the viability of P2G.
Overall, the technology is changing fast and as the CCC admits,”there is good reason to believe that the range of options could be wider and/or cheaper than we have assumed”. With the UK likely to miss its next climate targets and the UN Climate Change COP26 roadshow due to descend on the UK next year, BEIS arguably has to up its game and look to a wider set of options, beyond nuclear and more fossil gas.
Prof David Elliot
This article first appeared in Physics World