In the UK the National Grid has to run roughly 10% the grid load on Combined Cycle Gas Turbines (CCGT). This is the case even when there is excess wind and solar capacity available. This is required to respond to fluctuations in both generation and demand – to maintain grid frequency.
Short term grid storage with a capacity of hours is required to remove this need for background gas usage – and allow the grid to function entirely on renewables even for a short period.
In the longer term there will be days when there is excess renewable generation. This can first be managed using demand side management. This uses pricing mechanisms to encourage people to charge cars and run other high demand applications when there is excess generation.
At some stage though there will also need to be storage technologies which retain enough energy for days where there is little or no renewable generation. This long term need will see a switch to new battery technologies such as Vanadium Flow – and the use of Hydrogen to store power.
Battery Storage Technologies
- Lithium-ion (Li-ion) Batteries: These are the most popular battery storage technology for grid-scale applications. They offer high energy density, long cycle life, and fast charging capabilities. However, concerns about raw material availability and safety (risk of fires) have prompted research into alternatives. They also don’t scale well to high capacity applications.
- Vanadium Redox Flow Batteries: This technology separates the energy storage – in an electrolyte – and electrodes which generate power. This allows for very large capacity electrolyte tanks to be combined with relatively small and inexpensive electrodes and allowing long run times. The most common type is the Vanadium Redox Flow Battery – but other technologies are being developed. These batteries can offer long discharge durations and have a long cycle life – bit most important large electrolyte tanks support large storage capacity.
- Lead-Acid Batteries: Traditionally used for backup power, they are less efficient and have a shorter lifespan than Li-ion batteries. They are not a viable option for modern grid scale storage.
- Nickel-Metal Hydride (NiMH) Batteries: These are now obsolete for grid scale storage – superseded by Lithium Ion.
- Solid-State Batteries: These are an evolution of Li-ion batteries, where the liquid electrolyte is replaced with a solid. This can potentially offer higher energy densities and improved safety, although the technology is still in the development phase for grid-scale applications.
- Sodium-Sulfur (NaS) Batteries: These operate at high temperatures and offer high energy densities. They have been deployed in some grid-scale projects, especially in Japan.
Hydrogen as a Storage Mechanism
Hydrogen Storage: Hydrogen can act as an energy carrier and storage medium. Excess renewable energy can be used to electrolyze water, producing hydrogen. This hydrogen can be stored under pressure or in chemical compounds and then used later to produce electricity via fuel cells or traditional turbines.
Advantages:
- Scalability: Hydrogen can be stored in large quantities, making it suitable for long-duration storage and seasonal variations.
- Versatility: Beyond electricity generation, hydrogen can be used in transportation, heating, and as a feedstock for various industries.
Challenges:
- Efficiency: The round-trip efficiency of hydrogen (from electrolysis to electricity generation) is currently lower than batteries.
- Infrastructure: Widespread use of hydrogen requires substantial changes to energy infrastructure, including specialized storage tanks and pipelines.
UK’s Largest Grid Storage Facilities
| Facility Name | Capacity (GWh) | Power Output (GW) | Run Time |
|---|---|---|---|
| Dinorwig Power Station (Electric Mountain) | 9.1 | 1.7 | 5h |
| Ffestiniog Power Station | 0.5 | 0.36 | 1.5h |
| Cruachan Power Station | 7.1 | 0.44 | 16h |
In conclusion, while battery technologies provide immediate solutions for short-term grid balancing and ancillary services, hydrogen offers potential as a long-term and versatile energy storage solution. The UK, with its commitment to a renewable future, will need to leverage both these options to build a resilient and green energy system.