Andrew Wade, senior reporter
Whenever we write about renewables at The Engineer, there are inevitably voices decrying their intermittency. The sun does not always shine and the wind does not always blow, we are reminded.
Renewables have many benefits, but their intermittency does indeed carry a cost. That cost is something the UK Energy Research Centre (UKERC) has been examining, and a new report published this week looks at where those costs are and how they can be minimised.
The study is an update of a 2006 review on intermittency when renewable generation was expensive, but the costs of adding the flexibility to accommodate it was low. However, variable renewables made up just 3 per cent of the energy mix at the time, and the authors did not anticipate levels above 20 per cent, a figure which many countries are today exceeding.

“You’ve got (renewable) energy available to you which is potentially, a few years from now, the cheapest option that’s available to you,” said report co-author Dr Robert Gross, a senior lecturer in energy policy at Imperial College and a UKERC director. “The system costs then become the fundamental constraining factor, and it’s therefore extremely important that you make the system as flexible as possible.”
“We’ve certainly reached a point where it’s as important to be thinking about flexibility, as it is to be thinking about building new renewables capacity.”
According to Gross and lead-author Dr Phil Heptonstall, with the proper flexibility built into the grid, the costs of intermittency will be modest. Due to the complex nature of the grid and multiple overlapping costs, it is difficult to put an exact figure on it. Back in 2006, integration costs for wind and solar were estimated at around £5-£8 per megawatt hour (MWh). Inflation, combined with our increased reliance on renewables, means that cost has grown, but only marginally.
“If you wanted a very approximate ballpark for the UK you could say it was below £10, or of the order of £10 per MWh,” said Gross. “But, we being academics would be quite nervous about oversimplifying that because, as I’ve said, there are two categories of cost that don’t just add up. They don’t just add on to one another, they kind of overlap.”
That cost per MWh will jump dramatically if we continue to add more wind and solar into the energy mix, yet don’t embed more flexibility into the overall system to counteract intermittency. For example, if variable renewables were to account for 50 per cent of generation and the grid did not to evolve, additional costs could be as high as £45/MWh. How then, are we to ensure that a situation like that does not arise?
“If we are going to continue to make progress towards a decarbonised power system, then we have to actively plan to make a low-cost and optimised low-carbon power system,” Gross explained. “It won’t just happen by itself, and if you just provide subsidies for renewables, and don’t think about the configuration of the rest of the system, you could end up in a very sub-optimal and very expensive place.”
According to UKERC, there are a number of actions that can be taken to incentivise change, including allowing the wholesale price of energy to become more volatile, reflecting the current inflexibility in the system.
“On occasion (the energy price) will shoot up to £3,000 per MWh, and those price signals need to feed through, because they will offer a market-friendly incentive to companies to invest in flexible generation,” said Gross.

UKERC suggests allowing price signals to hit the market without a price cap and also bringing in a smarter, more specific capacity mechanism. Thirdly, the system operator can have a direct impact by tendering for more flexible generation capacity, something that has already happened in the UK.
“National Grid has created this new enhanced frequency response service, which asks for very, very quick changes in output,” Gross said. “And essentially the only technology that can deliver that is storage. So in a way, National Grid have deliberately set out to tender for storage, but they haven’t explicitly said that they’re tendering for storage.”
But storage alone is not the answer. It’s neither practical nor cost effective to meet those flexibility demands exclusively with storage systems, and it must work in combination with demand side response, more flexible generation and interconnection.
“What the UK suffers from is the fact that we are a relatively small island with a large population, so we’re meeting quite large demand swings,” explained Gross. “If we had more interconnection built into western Europe, that would help with this.”
“There were plans to build an interconnector put on ice because of Brexit, and that’s now going ahead. It’s sensible to build transmission capacity. It’s almost always sensible to build transmission capacity…copper wires are cheaper than power stations.”
With nuclear new-builds like Hinkley C hitting a strike price in excess of £90/MWh, the last thing the energy system needs is additional costs of £45/MWh due to inflexibility. UKERC is urging the government to act on all fronts to avoid such a mess.
A very sensible and interesting article.
There is much more to National electrical energy supply than the simple cost of each energy source/kwh.
Of course the authors do not mention the elephant in the room that is the real cause of UK electricity becoming riskier than it has ever been and more expensive in real terms. That is the Climate Change Act which has led to the justification of power generation at double the cost of generation without this. The implications of our rapidly increasing electricity prices ( and coming low reliability) on industry are horrendous.
The future will be low carbon generation based poverty for most UK citizens unless action is taken soon.
Storage should have been costed as part of the “unreliables” advance. It is amusing that Germany has recently learned this and is restricting “new unreliables” to below 1 GW per year, which is still a problem for their grid.
The chickens home come have roost to ….. comes to mind.
Actually, the cost of electricity per household is estimated to be only £100-150 higher by 2030 as a result of policies to decarbonise the supply. In most cases these costs will also be offset by energy efficiency costs. A small price to pay compared to the potential costs of significant warming.
not a single sausage mentioned about electric cars in expected millions properly incentivised to charge on low demand and act as storage in times of peak demand, both helping efficienctly use renewables and smooth the dips…… you only have comments based on yesteryears generation & grid…. could do better Mr.Engineer
I wrote a feature that covered that last month Alistair. The “expected millions” is just that at the moment: expected. I suspect this is one of the reasons why the report and its authors don’t dwell on it. How much flexibility electric vehicles and home storage will provide is a huge unknown right now.
The availability of “storage” using electric cars will always be an unpredicable quantity since not all will be connected at any one time AND does using the car battery as a “on line” storage device reduce the working life of the battery?
Good article on what is becoming a more and more complex set of interconnected issues. There is so much emphasis (from government) on getting value for their (our) money, that short term cost issues are getting in the way, for example the gas powered station in Peterhead not getting contracts because of the “costs” of it being remote.
Is there any merit in at least having a ‘register’ of generating capacity in private (semi-public ) hands. Stand-by, camping, farming, back-ups for public services -disaster relief, and so on. Yes, I know that these primarily need fossil fuels (though water power did ‘drive’ much of the earliest Industrial ‘R-evolution! (R=rapid!) but as the vehicle for peak-load ‘topping’ do these have a place? Indeed is there a place for shared facilities between say large multi-occupancy buildings, sides of a street, etc Not really my field, but I recognise that throughout history mankind has managed to ‘get-by’ during times of difficulty using Ing-enuity (the basis of the word that defines our Continental brothers in technology!) and facilities already present, yet under-utilized.
A disaster invariably brings out unknown (or at least under valued) skills and abilities?
I am thinking about
Interconnects are only part of the solution. Australia, as the old inefficient and dirty coal powered generators are being decommissioned, replacing them with renewables is already cheaper than new “clean’ coal, but as always, engineering and economical decision making has been politicised. The recent black out of the entire state of South Australia due to transmission towers collapsing in a freak storm and the failure of the private supplier to fire up expensive gas generation cause the interconnect to Victoria to overload and shut down, but that was blamed on the SA’s high penetration of renewables for political reasons. It’s not an engineering problem!
The future lies in despatchable renewable energy. PV is still the cheapest renewable, cheaper than new coal powered stations, and definitely cheaper than new “clean” coal. So either we solve the battery cost problem, or use CSP (Concentrated Solar, producing superheated steam) with thermal storage. Another option is floating PV on hydro dams. But without government support, none of these are getting funded.
Yes a better grid is needed, but despatchable renewable power is where we should be going next.
“…but despatchable renewable power is where we should be going next.”
Somewhere in the depths of my memory is a recollection that in the 30s the USSR purchased train-mounted mini-power stations (from Metro-Vic) to move generation to where it was needed rather than power: because their ‘grid’ was not then in full operation? Does anyone have any knowledge of this? I have no idea what was the energy source? wood, coal, oil, biomass, natural gas?
How can wind and solar power it would be “despatchable”. Fundamentally, it is not.
If wind and solar power are, as they claim, cheaper than conventional generation why do they only exist in countries that pay massive subsidies? I would be quite confident that there is no country that has no subsidies that has spawned a thriving and expanding wind and solar business .
Wind and solar power are simply another way of ripping off taxpayers and poor consumers so that rich developers can make even more money.
How right I feel Brian Leyland is. There is only one renewable source that is reliable and would involve some good UK engineering input and that In my opinion is tidal. The tidal ranges are some of the best in Europe and are predicable for some 1000 years so why are we not pursuing this more vigorously than at present with ever more blots on the landscape and the annoying drone. Also no mention of synchronicity and the export and import of VArs which is essential to a stable grid