Optimising tidal-to-hydrogen systems: EMEC’s modelling insights for tidal energy alternative offtakes
EMEC has delivered a detailed modelling study exploring how to optimise the integration of tidal energy and battery storage with alternative offtake routes (e.g. hydrogen production) to overcome barriers to commercial scale tidal energy deployments.
The study has been published as part of the FORWARD2030 project, supported by the European Union’s Horizon 2020 research and innovation programme. FORWARD2030 aims to deliver a series of high-impact cost reductions to achieve large-scale tidal energy array deployment by 2030.
Challenge and opportunity
Many of the UK’s most promising tidal stream sites are in remote coastal areas with limited and frequently disrupted grid connections. These grid limitations pose a barrier to meeting national and international deployment targets.
The introduction of alternative offtake routes is a promising opportunity where local businesses can take advantage of the local generation of green electricity at advantageous pricing as part of a behind-the-meter power purchase agreement . This not only reduces reliance on expensive retail electricity or diesel generators but also opens the door to attracting new industries to these regions.
The predictability of tidal stream energy makes it a strong candidate for alternative offtake applications. While tidal generation varies throughout the day, its cyclical nature means this variability can be accurately forecast.
When coupled with battery storage to smooth generation, continuous power can be fed to the grid or to an offtake.
However there has been limited practical analysis of how such integrated systems would operate in real-world conditions.
Modelling with real-world data
EMEC developed a comprehensive model to explore how tidal energy could be optimally used to power local offtake, using its vanadium flow batteries and hydrogen electrolyser as a case study.
The model uses EMEC’s resource data collected at its tidal energy test site in Orkney, alongside site acceptance data from its adjacent onshore R&D facilities where integration of tidal energy converters, battery storage and hydrogen are gearing up to be trialled.
This real-world data was used to undertake a detailed analysis to understand what tidal generation will look like for a typical annual cycle, how batteries may be used to ensure consistency of supply and how operation of a partially islanded system can maximise a limited grid connection.
The findings from the model were then qualitatively assessed to understand how they may be extended to larger tidal farms and how these may be integrated with wind farms. This was then extended to investigate the potential for grid balancing services and other potential offtake industries such as synthetic fuel production.
Key findings
The modelling revealed that tidal energy technologies, when combined with appropriately-sized energy storage systems, can deliver stable, near-continuous behind-the-meter power to industrial offtakes.
An example of model energy outputs for one day with symmetric 300 kW vanadium flow battery charge and discharge rate. The blue line shows near-continuous hydrogen production.
Achieving this stability depends on several critical factors:
- The offtake must have a high ‘turndown rate’, allowing it to remain operational during neap tides when generation will be lower.
- The tidal resource must be accurately modelled to inform system design and scheduling.
- The battery must be correctly sized to match both the tidal resource and the offtake’s operational profile.
- The predictability of tidal cycles should be leveraged to schedule plant downtime, thereby maximising the system’s capacity factor.
From the modelling, the team identified several key takeaways:
- Optimal hydrogen production can be maintained when the above critical factors are met (with the exception of the weakest neap tides).
- Lower operations and maintenance costs can be achieved by reducing the quantity of start-up cycles and aligning maintenance with these predictable weak neap tides.
- Ideal windows for planned maintenance for servicing the electrolyser, batteries and tidal energy converters occur approximately every six months during periods of lowest tidal generation.
- Tailored scheduling to meet the need of specific offtake industries can be achieved when accounting for predictable seasonal variation in tidal generation (e.g. planning maintenance during neap tides or timing energy-intensive processes with spring tides).
- Aligning plant operations with tidal cycles can maintain high electrolyser efficiency and capacity factor, avoid curtailment by exporting excess energy during spring tides, schedule maintenance during neap tides when generation is lowest and respond flexibly to load fluctuations and grid balancing needs.
- Early detailed modelling, based on local tidal resource data and equipment specifications, is essential to determine the optimal configuration and economic operating profile for each individual system and offtake industry.
- Some offtake opportunities may be better suited to respond to excess power from the system than others. For example, direct air capture systems are passive absorbent for collection of CO2. They only require electricity to release the CO2, which can be performed flexibly in response to available energy surplus.
Modelled electrolyser power for one year showing vanadium flow battery optimum scheme. The spikes show the regularity of when there is not enough energy to produce hydrogen and thus ideal windows for planned maintenance.
Industrial offtake: a pathway to commercialisation
Behind-the-meter systems offer a compelling route to commercialising tidal energy and EMEC is due to be the first site in the UK to go live under this arrangement under the CfD scheme .
By supplying power directly to local industries, these systems can:
- enable higher generation than constrained grid connections allow;
- reduce curtailment and improve energy utilisation;
- support new markets such as hydrogen or synthetic fuel production; and
- provide ancillary services to the grid, including balancing and flexibility.
Next steps
The next step for EMEC is to put the model into practice, with the team gearing up for a live demonstration integrating tidal energy, battery storage and hydrogen production at its R&D test site in Eday, Orkney.
Ongoing collaboration with industry partners will be key as EMEC explores new offtake markets and opportunities for alternative offtake demonstrations, supporting grid balancing and the commercialisation of tidal energy at scale.
Report download:
‘Recommendations for the Optimisation of Tidal to Hydrogen Systems’ was prepared by Richard Sey, EMEC Senior Metocean Engineer and Catrin Garrett, EMEC Hydrogen R&D Engineer.
Read the full report to dive deeper into the modelling, results and recommendations for optimising tidal-to-hydrogen systems.
Learn more about EMEC’s modelling capabilities:
- Call us: 01856 852060
- Email: commercial@emec.org.uk
- Visit: EMEC metocean services
Further reading:
Alternative Offtake Routes for Tidal Stream Energy – Public Summary Report
