Alex Buckman, networks and energy storage practice manager at the Energy Systems Catapult, describes its new Storage and Flexibility Model, a number-crunching tool that can calculate the future storage and renewable generation capacity needed to meet variable demand in a net-zero world.
Reaching net zero means building an energy system radically different to what we have today, with storage and flexibility expected to play a much larger role.
As demand for electricity rises, and intermittent renewables become more prevalent, storage technologies such as batteries and hot water tanks will help ensure that networks can cope, whilst allowing homes and businesses to save money by avoiding times of peak demand.
Until now, we have relied on carbon-based energy storage, such as gas and oil. These are generally kept in either large storage sites before being used in refineries, or independent storage sites before being sent to smaller storage tanks at petrol stations.
Energy consumption in the UK is still incredibly reliant on fossil fuels (see chart, below), with gas and petroleum the incumbent giants. Coal has seen a dramatic reduction in recent years, and whilst this is welcome, it risks distracting us from the vital flexibility that natural gas and petroleum still provide to the energy system.
Take three examples across different timescales:
Season by season: The average daily gas demand on distribution networks in winter is approximately five times higher than in summer, balanced through a mix of imported gas and increasing gas extraction to above average demand.
Hour by hour: When the so-called "Beast from the East" struck in 2018, electricity demand increased by 11 GW within three hours. In fact, 80% of the increase in total electricity demand was met by gas and coal - an energy volume of 28.8 GWh, equivalent to the output of 2.5 Dinorwig power stations. Any electrification of heat supply would increase this energy volume substantially.
Second by second: The electricity network requires real-time balancing to make sure that the frequency on the network remains within operational limits - this becomes more difficult with more renewables in the energy system. The "balancing mechanism" is one of the ways we can procure flexibility to help balance the electricity system. In the year leading up to September 2019, however, it's worth noting that approximately 80% of the energy volume procured by the balancing mechanism was fossil fuel-based.
Clearly, a net zero energy system will have profound impacts on the role of storage and flexibility, way beyond the well-known challenges of integrating high amounts of renewables. The flexible roles of natural gas and petroleum will need to be replaced, even if optimistic rates of carbon capture and storage can be achieved (which is far from guaranteed).
Replacing their flexibility within our current system would be extremely difficult; replacing them in a net zero energy system will be nothing short of heroic.
Low carbon supply technologies are typically less flexible, whilst electrified demands do not benefit from the luxury of gas "linepack" - the volume of gas contained within the system - to reduce real-time balancing requirements. When you then add the volumes of seasonal energy storage supplied by fossil fuels, it becomes increasingly complex to find the most appropriate system design and storage mix.
A net-zero energy system will need to be able to balance supply and demand across energy vectors, network levels and timeframes, but the exact role storage and flexibility will take is dependent on the system that emerges.
A model future
The Energy Systems Catapult has therefore launched the Storage and Flexibility Model (SFM), which provides a comprehensive representation of the role of storage and flexibility, exploring multiple energy vectors, network levels, geographic regions and timeframes; from sub-hourly system services to decadal planning.
It is designed to help the sector answer some crucial questions, taking a whole system perspective, including:
- Taking a whole energy system approach, what is the future role of energy storage and flexibility
- What is the scale of the different future service requirements (e.g. in MW or, MWh) for storage and flexibility?
- What is the value of various forms of storage and flexibility to the system?
- How do the key drivers of uncertainty (both short and long-term) affect the potential role of storage and flexible alternatives?
Even when investigating the previous target of 80% emissions reduction by 2050, we discovered some important trends. For example, substantial increases in thermal and electricity storage volumes are likely to be required to cover increasing reserve requirements.
We also see an increased role for building-level thermal storage to help the electricity sector cope with large fluctuations in electrified heat demand. Add in a degree of short-term uncertainty, and hybrid technologies - such as hybrid heat pumps and combined heat and power - become more important sources of flexibility.
Although we haven't yet explored the impact of net zero, we have explored what happens when gas usage is restricted - with the removed flexibility replaced with a variety of other technologies including hot water tanks, managed charging and excess generation technology. This gives us an insight into how we can start to address flexibility challenges of a net-zero system, but we need to, and will do, more.
One of the greatest challenges of a decarbonising energy system is maintaining energy security and reliability as generation and demand characteristics change. It is more important than ever to prepare for the future and its implications for how we transform the system - and we hope the SFM will help identify and assess the types of innovation required to meet this challenge.
To explore find out more about the Catapult's Storage and Flexibility Model, visit es.catapult.org.uk/sfm