UK | NEW BUILD Left:


Dinorwig pumped storage power station in Snowdonia National Park, currently the UK’s largest has a storage capacity of 9GWh Photo credit: Matthew Troke/ Shutterstock.com


of 4GW) and store too little energy to address the storage needs of 2050, when levels of storage of 100GW and 50TWh will be required. There is a wide choice of energy storage technologies –


(see box). Profiles of demand and supply over many years show


several different storage needs: ● Short-term – daily with a relatively small volume, ~100GWh, and 30-50 cycles per year;


● Medium term – weekly, requiring a few TWh, and several cycles per year;


● Long term – monthly, seasonal or multi-year, requiring many tens of TWh, and one or fewer cycles per year.


Energy storage for a renewable energy system will be large — many tens of thousands GWh equal to more than 20 days of demand — and a thousand times the size of planned UK electricity storage including the batteries in electric vehicles. Also it will be much bigger than the largest energy stores in the world (see table). Options for minimising the size and cost of energy


storage include: getting the right mix of solar and wind; providing extra renewable capacity; choosing the right mix of storage technologies; trading-off higher efficiency versus costs; and providing a share of baseload supply.


Economics of highly renewable systems Energy supply technologies are often judged by their stand-alone energy costs (on a levelised cost of energy or LCOE basis). This simple cost parameter does not value the dependability of sources of electricity. This was not important when intermittent technologies were a minor part of the energy system and flexible back-up supply was available; in the future that will not be the case. A fairer and more transparent way to compare


technologies is to include the cost of compensating for unreliability, levelling up the cost comparison to include the costs of matching reliable supply. That would be a ‘levelised cost of shaped energy’ (LCOSE) calculated from: renewable energy costs + cost of overcapacity + storage energy costs + baseload share. It would not include any additional grid costs.


Initial calculations of LCOSE for the UK in 2050 (Roulstone


& Cosgrove. (2021). Working Paper – UK Multi-year Energy Storage Systems Cost Investigation. April 2021. U of Cambridge. http://dx.doi.org/10.13140/RG.2.2.12555.41760 ) show that storage costs will increase the forecasted future renewable energy costs from £34/MWh to at least £60-70/ MWh. Costs could be much higher, more than £100/MWh, if the costs of storage do not fall as predicted and the ways of sharing the store power requirements are not developed.


2050 energy system design options Coal will be excluded from electricity by 2025 and gas will be gone by 2040. Almost any of the scenarios for 2050 depend on wind and solar. They require very large amounts – many tens of TWh — of long-term energy storage for weekly, monthly, seasonal and year-to-year backup. Providing 30% overcapacity of renewables, high power interconnectors and 25GWe of baseload would together cut the storage needs to 7.5% of annual demand — 27 days. Alternatively, the large costs of balancing and backing up


an intermittent, highly renewable system by energy storage could be reduced, but not eliminated, by two possible energy strategies for the 2050, both of which would have cost impacts: Reduce the size of the electricity system, by using


large numbers of heat pumps for space heating and large amounts of natural gas to produce ‘blue’ hydrogen — ie from steam methane reforming with carbon capture and storage. Increase the flexibility of the energy system and limit


the size of wind and solar to 50% share, by providing up to 16% of the UK’s electricity (double what is proposed by the Committee on Climate Change) from biomass with carbon capture and storage and producing 33% from flexible nuclear. This would require modern light water reactors (including small modular reactors), providing an economic incentive for them to operate in a flexible manner. ■


Largest energy stores (GWh) World


Li-ion battery CAES LAES


Pumped hydro Hydrogen


Vistra California 1.2 McIntosh Alabama 2.8 Highview 0.25 Bath County 28


Moss Bluff Texas 146 UK Wiltshire 0.26


Dinorwig 9 Teesside 27


Energy storage technologies ● Electro-chemical: Li-ion and flow batteries etc.


High round trip efficiency of 90-95%, but with high energy storage costs – ~1,000 times


chemical storage; ● Physical: pumped hydro, compressed air, liquid air, thermal energy, gravitation etc. Medium round-trip efficiencies of 45-80%, with lower energy storage costs – ~10 times


chemical storage; ● Chemical: hydrogen, ammonia, methane, synthetic-gas etc. Low round-trip efficiencies of 25-42%, with very low energy storage costs. ■


www.neimagazine.com | January 2022 | 23


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