The Energy Transition
The energy transition to a zero-carbon economy is, quite correctly, seeing widespread roll-out of tens of GW of renewable generation. We’re already at over 30GW and, because of load factors, to supply our 56GW peak demand the UK will need over 200GW nameplate renewable energy storage capacity for intermittent renewables before the last fossil fuelled power station can be retired.
We expect that demand to grow substantially in both power and energy as heating, transportation and industry are decarbonised – each of those three sectors consumes roughly as much energy as the entire electricity sector, so we can reasonably assume that electricity demand will increase between two-fold and four-fold. It may even be more, as conversion of energy into different forms for different uses always carries inefficiencies; and all this assumes that our total demand for energy is not going to increase.
Most of renewable generation technologies—solar, wind, wave and tidal—are intermittent. However predictable they are, they generate not when we need the energy, but when nature dictates. So how do we move all that electricity from when we don’t want it, to when we do?
Renewable Energy Storage Capacity: The UK Needs It
The simple solution to this problem is large-scale, long duration storage. To balance the grid during evening peaks, we need what the government itself identified in its 2014 Technology Innovation Needs Analysis, or TINA report: 27.4GW of new storage with an average duration of 5 hours.
To cover baseload demand as well, and the weather patterns we can expect, we need storage to be at least equal to:
- Power: peak demand plus supply margin, minus zero carbon dispatchable generation
- Energy: all energy that may be used over a 2-week period, minus zero carbon dispatchable generation
There are only two technologies available today that can deliver this: pumped hydro and Compressed Air Energy Storage (CAES).
There are few potential locations for pumped hydro, and every one of them is remote from both supply and demand. Moreover, the cost is prohibitive, besides the fact that each scheme requires flooding two valleys.
CAES, on the other hand, is less than one-third of the cost of pumped hydro. Storelectric’s versions are more efficient than batteries, and the potential locations are both widespread and conveniently close to both supply and demand. There is more than enough geological storage capacity in the UK for enough renewable energy to power the whole country for a fortnight’s weather patterns, probably with exports too.
Storelectric’s CAES
Storelectric has two types of CAES that will help the UK achieve the renewable energy storage capacity it requires. One is the world’s most efficient version, entirely emissions-free and profitable in today’s market. The other can be linked to suitably located existing power stations, giving new life to stranded assets by almost halving their emissions, cutting costs and increasing revenue streams. Both can be built using today’s technologies, and therefore have very low technical risk. And both have been supported by the analyses of engineering multinationals. All we need is the funds to build the first of each.
Other Proposals to Balance the Grid
Currently, the solutions targeted by BEIS, National Grid and Ofgem are inadequate for the job of keeping the lights on cost-effectively. Currently, the UK and Europe are not considering long-duration energy storage seriously enough and are focussing instead on three solutions, which will be costly and on their own will not balance the grid. These proposals are: demand side response, battery storage, and interconnectors.
Demand Side Response
Demand Side Response (DSR) mechanisms function by offering financial incentivises to businesses or individuals who reduce their non-essential energy use when renewable generation is low, and shift this demand to when generation is higher. This balances energy supply and demand to prevent power outages, increases overall grid capacity, and ultimately keeps bills lower.
However, National Grid evaluated the economy’s potential for DSR in 2015 as ~5% of total demand, which is about 3GW at most. Since DSR cannot be called upon more than once in a period, the maximum volume available needs to be divided by the number of occasions on which it may be called during the period. For example, refrigerators can be turned off for no more than 15 minutes during an evening peak, else food will spoil. Three “calls” during that peak means that the total MW volume of refrigerators needs to be divided by three to determine how much is available for any specific call. If this were applied to National Grid’s total evaluation, this gives us only 1GW flexibility per call.
The maximum duration of DSR is 15-30 minutes. After sunset on a windless winter evening, DSR will be exhausted by around 6pm and there will be no way to power another peak and overnight demand. DSR is a cheap option to cope with short duration spikes in generation and demand but cannot give the UK total energy security.
Batteries
Currently National Grid, BEIS and Ofgem say that we don’t need lots of storage, just lots of flexibility, so they are planning on installing lots of batteries. These are typically up to 40MW size, with 20-60 minutes duration.
However, their efficiencies are much lower than advertised: while their internal gross efficiency may indeed be their quoted as between 85-95%, their true net grid-to-grid efficiency has been measured at 42-69% on day one.
The differences are largely due to two factors. The smaller factor is AC-DC-AC power conversion and signal conditioning, and the larger factor is heating and cooling. By the time the cells are swapped out at 80% of capacity, they emit three times as much heat as on day one, thereby enormously reducing that efficiency. Their proper role is therefore for short duration peaks and troughs in demand and generation, not for grid balancing.
Interconnectors
Interconnectors operate at the Gigawatt scale, and the country is planning for 19GW within a decade or so. In fact, all scenarios in National Grid’s Future Energy Scenarios have UK-based dispatchable supply dropping below demand in 2020 or 2021, meaning that we will be relying on imported electricity not only for our supply margin but also for actual demand.
But this meets with challenges: natural cycles, and Brexit.
Natural Cycles
Natural cycles cycles mean that renewable energy stops producing regularly. So when the sun goes down on a windless winter evening, we will have negligible renewable generation and will have to rely on imports. But the same thing will have happened in our neighbouring countries, so they won’t have any spare to export, killing all benefits from interconnectors during that time.
Weather patterns extend these daily cycles to cover multiple days at a time, often over large swathes of the continent simultaneously. The biggest and worst (from an energy point of view) of these cycles is known in Germany as the kalte dunkel Flaute, the cold dark doldrums. This is a high pressure system that sits over most of the continent for up to a fortnight at a time. Its maximum occurs every couple of years, but shorter durations and narrower geographies are much more frequent, with interconnectors effectively useless for the entire duration.
So the proper use of interconnectors is for supplementary capacity above the sum of total demand and supply margin, in order to keep our normal energy prices competitive.
Brexit
Another challenge is Brexit. The only two things that prevent our neighbours saying “I don’t care how much you want to pay, our consumers are more important than yours” are the Single Market and the European Court of Justice. Having exited these, we can’t insist on our neighbours exporting to us when we need the energy, however much we offer to pay for it. This makes interconnectors a very unreliable, and likely expensive option.
Global Needs
The above is an argument based on the United Kingdom’s energy system. However it applies, with variants, to energy systems world-wide. Indeed, in the first and smallest phase (balancing grids to supply variable demand with low-carbon generation), Storelectric estimates that the capital investment required globally is $1trn, with annual revenues at roughly ¼ of this figure. The second (baseload) and third (supporting the decarbonisation of heating, transportation and industry) phases are much bigger.
And while CAES currently targets salt basins, these are plentiful world-wide, and in future Storelectric plans to develop CAES in other geologies.
