Essential Research on the Journey to Zero Offshore Wind Curtailment
Assessing the sizing of Hydrogen storage on the HyCoRe project.
Project Information
Company Name: Ofgem Strategic Innovation Fund
Energy Type: Hydrogen
Project Type: Research
Background
Curtailment of renewable generation is literally a waste of energy and results in increased energy cost to the consumer due to payments to the curtailed generator.
Curtailment refers to the practice of intentionally reducing the output of energy generation, particularly for wind and solar farms, when their production exceeds grid demand. This can occur during periods of high renewable energy generation and low demand, or when the grid is congested and unable to transmit the energy to areas where it is needed. Curtailment is a wasted opportunity, preventing the utilization of clean energy. In addition, there is a cost to curtailment, since the operator is paid to shut-down generation. This cost is ultimately passed to the consumer, leading to increased energy prices.
Producing hydrogen from offshore wind energy would provide the following key advantages:
- reduced need for curtailment by utilising excess wind power
- potentially allows more renewable energy to be integrated into the grid by utilizing the gas grid for transport and bypassing electrical grid constraints
After converting excess renewable energy into hydrogen through electrolysis, it can be stored and later used as a fuel for various applications such as heat, transportation or industrial processes, or it could be converted back into electricity. It is worth noting that there is inherent storage in gas pipelines (know as “line packing”) and that salt caverns have been used for decades to store hydrogen[1]. In addition, where the electrical grid is locally constrained, the energy can be integrated into the natural gas network and converted to electricity at different locations, potentially circumventing congested areas of the electrical network.
The project
The £500k Hydrogen Cost Reduction (HyCoRe) project was funded through the Ofgem Strategic Innovation Fund (SIF). Kinewell Energy worked alongside Northern Gas Networks, Arup, Offshore Renewable Energy Catapult, Newcastle University, Unasys. The project was developed to respond to the challenges faced by the energy networks as the energy system decarbonises. There is a presumption of huge growth for the electricity network whilst gas network usage may see declines. HyCoRe challenges this conventional wisdom. The project aims to provide benefits to all users of the UK energy system using a multi-vector approach to enable greater utilisation of the gas network and reduced pressure on the electricity network.
In the Alpha phase of the project in the Routes to Market work package, Kinewell Energy assessed the sizing of hydrogen storage to mitigate curtailment, Arup assessed the regulatory barriers and the Offshore Renewable Energy Catapult assessed supply chain maturity.
The Hydrogen storage study was considered a 1.5 GW windfarm located in the North East of England. This region was selected based on the offshore and onshore suitability for hydrogen from offshore wind by work from another project work package. The windfarm model considered 15 MW turbines and used 40 years of hourly wind speed data. The hydrogen demand data was based on natural gas distribution demands from local distribution zones (LDZ): Northern (NO), North East (NE), South West (SW), East Midlands (EM) and Scotland (SC) distribution zones (LDZ) to give a good range of generation to demand ratios. Hydrogen demands were based on 20% and 5% hydrogen (by volume) blended with natural gas. In December 2023 the UK government announced it’s support of blending Hydrogen up to 20%. The EU Hydrogen and Gas Market Decarbonisation package has suggested a 5% blend by volume.
What we did
The Kinewell team developed models of generation and demand profiles along with a model of storage and windfarm maintenance, in order to calculate curtailment. These models represented the deterministic and random (stochastic) aspects of offshore wind power demand. They were used to create 1,000 representative time-varying profiles of demand and generation which were coupled with a model of hydrogen storage. Considerations included:
- Rated capacity of the wind turbines
- Wind speed profiles during the year from historic data
- Hydrogen demand , based on natural gas demand and assuming a gas blend
- Daily demand as well as seasonal fluctuations
- Planned wind turbine maintenance
7 scenarios were considered:
| LDZ | Blend | ||
| North East | 20% / 80% | ||
| Northern | 20% / 80% | ||
| South West | 20% / 80% | ||
| Northern + North East | 5% / 95% | ||
| East Midlands | 5% / 95% | ||
| Scotland | 5% / 95% | ||
| Scotland | 5% / 95% | ||
Results
The results were produced as a series of graphs showing the reduction in wind farm curtailment with increasing storage sizes.
This gave storage sizes for each scenario for zero curtailment (meaning that all the energy created was utilised) in 95% of the cases, as shown in the table below. The generation to demand ratio is the annual generation energy divided by the annual demand energy. In general, we would expect more curtailment at higher ratios. However, the relative shapes of the profiles is a significant factor.
| LDZ | Blend | Annual Generation to Demand Ratio |
Storage* (GWh) |
||||
| North East | 20% / 80% | 0.22 | 19 | ||||
| Northern | 20% / 80% | 0.26 | 30 | ||||
| South West | 20% / 80% | 0.27 | 110 | ||||
| Northern + North East | 5% / 95% | 0.53 | 245 | ||||
| East Midlands | 5% / 95% | 0.63 | 525 | ||||
| Scotland | 5% / 95% | 0.74 | 580 | ||||
| Scotland** | 5% / 95% | 0.54 | 229 | ||||
*to give zero curtailment in 95% of cases
**including maintenance
For lower levels of curtailment the storage requirement reduces significantly. This can be seen in the graph below, which shows the impact of storage size and the reduction in curtailment for each scenario.
Modelling planned maintenance had a significant impact on the amount of storage required as shown in the brown and pick curves. This means that maintenance should be considered where possible. During any wind turbine downtime (including planned maintenance) there is less curtailment since the total generation output is lower.
The work was agnostic to storage technology, but for comparison the combined line pack capacity within all local distribution networks is roughly 243 GWh, or 24 million cubic metres, of natural gas[1]. Across the UK’s 11 distribution networks this gives an average of 0.3 GWh and 1.3 GWh of hydrogen storage in a given distribution network for 5% and 20% blends respectively.
As another comparator, salt caverns have capacities of 10s of GWh, e.g. at Teesside the capacity of 3 caverns is 25GWh.
Conclusion
Curtailment of renewable energy is a lost opportunity and mitigating curtailment reduces the levelised cost of energy. Production of hydrogen from offshore wind allows for a range of storage options, including linepack (within the pipeline) and salt caverns.
Calculating the total storage required for a given reduction in curtailment is not a trivial task, since the curtailment is due to the time-varying profiles of generation and demand. For this reason, generation to demand ratios are not an accurate indication of storage size required
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[1] G. Wilson and P. Rowley. “Flexibility in Great Britain’s gas networks: analysis of linepack and linepack flexibility using hourly data.” Report, UK Energy Research Centre (2019)
[2] J.D.O. Williams et al., “Does the United Kingdom have sufficient geological storage capacity to support a hydrogen economy? Estimating the salt cavern storage potential of bedded halite formations.” Journal of Energy Storage 53 (2022)