Periods of sustained excess or shortfall in a future net-zero world will tend to persist far longer than the four-hour spells where conventional batteries excel, however. Attention has turned to hydrogen and other synthesised fuels as a cost-effective way of storing energy for hundreds (and even thousands) of hours. Only fuels can provide cost-sensible solutions for such long times.
But what about the middle ground, between roughly four and 200 hours, over which the costs of batteries per unit of stored energy make them relatively unsuitable, and the poor turnaround performance and high power-costs of using hydrogen (or synthesised fuels) are also unattractive?
Like a middle child that is overlooked in favour of older and younger siblings, medium duration energy storage (MDES) technologies are often underappreciated and ignored. In future, however, more than 90% of all the energy that comes out of storage (or other grid-balancing provisions) will emerge in this medium duration range. Attendees at the MDES 2024 event that I organised at IMechE headquarters on 12 January heard that MDES technologies could take on the main responsibilities of balancing electricity grids in the near future.
Major opportunity
In September last year, a Royal Society report on large scale electricity storage showed that it is possible and affordable for the UK to operate an energy system in which wind and sunshine provide most of the primary generation, and in which making hydrogen and re-generating electricity forms the basis for nearly all storage.
Modelling work supporting that report also showed that overall system costs can be reduced by upwards of 5% if a suitable blend of MDES technologies is incorporated. In that case, more than 65% of all energy emerging from storage is discharged from the MDES systems, and more than half of the spend on storage facilities would be dedicated to these.
The third event in a series started in March 2020, MDES 2024 and its predecessors were made possible by funding support from the Research England Policy Support Fund. Westminster was the optimal location, because the main problem to be solved for affordable net-zero systems is how to ensure that the MDES technologies develop to the point where they can deliver major cost savings and other benefits based around stimulated economic activity to the UK. Batteries and hydrogen are quite rightly enjoying government commitments to support these technologies with hundreds of millions of pounds.
MDES technologies are getting some support – but it is not nearly proportionate. This is especially ironic in the UK, which fathered mechanical engineering, and which has an especially strong opportunity to profit from MDES technologies because of its wealth of wind resources. There is an amazing opportunity to develop solutions for ourselves first, before exporting widely.
Billion-dollar ambitions
The programme for MDES2024 featured four start-up companies supported under the Longer Duration Energy Storage (Lodes) competition, funded by the Department for Energy Security and Net Zero: RheEnergise, which is developing high-density hydro energy storage; Cheesecake Energy, which is combining thermal energy storage and compressed air; SynchroStor, which has a patented new approach for pumped thermal energy storage; and Flasc, which converts electricity from wind power into hydraulic power for offshore storage.
The event also featured three research projects funded by the Engineering and Physical Sciences Research Council (EPSRC), and technology talks on compressed air energy storage, pumped-thermal (and other thermal) energy storage, pumped-hydro energy storage, and one non-mechanical MDES technology – the iron-air battery by Form Energy. MDES markets are going to be very big, said the company’s European policy lead Cillian Totterdell, and they should be approached with ambitions that are “billion-dollar big”.
The penultimate session was dedicated to system modelling, with useful insights into how substantial the effects of MDES are likely to be. The modellers agreed on the value that can be added by MDES to the UK. There were some differences about how much MDES will be present in a cost-optimised system, but the optimal quantities are highly sensitive to assumptions about performance and cost values.
The final session was a busy panel session led by event co-chair Tom Bent, in which four energy industry experts presented their views and interacted with attendees. Some of the main emerging themes were:
1. The discussion on MDES is extremely timely and topical, given the recently opened consultation into the UK policy framework for long duration storage, which includes MDES.
2. Revenue support instruments are needed to reward technology for doing ‘the right thing, at the right time, in the right location’. Without these, there will be insufficient investor, lender and developer confidence, and storage assets will not materialise. This is particularly true of MDES technologies which have longer lives and high capital expenditure.
3. Long-term policy certainty is especially important for those researching and developing new technology.
4. The UK made early advances in battery installation due to a conducive investment environment and accessible market structure, but is losing its early lead as other markets offer higher, less-risky returns for the scarce resource of capital.
5. Low-cost debt is a vital component in making storage viable and affordable. Support instruments are one route that allows new infrastructure to secure cheaper debt.
6. Most MDES technologies provide multiple services to the grid and so add greater value, but we are not close to having a market structure that can reward them suitably.
7. MDES technologies can make a vitally important contribution to national system resilience and asset diversity.
8. No model can perfectly accommodate and predict all unknown future parameters and developments, particularly innovation. We should not delay support for new assets over a relatively minor degree of disagreement and uncertainty. Achieving ‘learning-by-doing’ in MDES is vital.
9. Many stakeholders would like to see time-series data and cost/performance assumptions underpinning all policy decisions. Commercial analysts and academic experts that invest in developing the models are not necessarily keen to share those models, but the data can be open.
10. The pipeline of engineers required to execute and install storage assets remains a serious concern, as in other areas of energy transition.
All presentations and videos are available on the event website.
The government consultation on long duration electricity storage runs until 5 March.
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