By Dr Danny Coles, Research Fellow at the University of Plymouth
During Autumn 2021, rising global demand for natural gas increased its wholesale day-ahead price in the UK by approximately 100% over just one month. At the time, the UK was already heavily dependent on imported natural gas due to dwindling domestic natural gas reserves. The problem was compounded by lower than average domestic wind and nuclear power supply.
A 3 week lull reduced wind energy production by 60% relative to the expected level for the time of year. Ongoing nuclear power plant shutdowns limited their combined output to 5.5 GW, 32% lower than the total 9.5 GW installed capacity. The after effects of these simultaneous events included over 30 energy suppliers ceasing trading, a 54% rise in the retail price cap of energy, and Treasury spending an estimated £2.2 billion to keep a larger energy supplier operational.
It is becoming apparent that energy produced in the UK is the safest route to delivering secure affordable, sustainable supply. The UK has targets to increase offshore wind capacity from its current level of approximately 10 GW to 50 GW by 2050. Whilst wind will rightly be the primary source of renewable power in the UK, how will another extended period of low wind resource be managed in order to keep the lights on our as reliance on its supply increases?
The UK’s energy security strategy highlights that opportunities offered by tidal energy are now being aggressively explored. It is estimated that energy harnessed from the tides using tidal stream turbines and tidal lagoons has the potential to provide 26% of the UK’s current electricity demand. Not only that, but unlike most other renewable power technologies, the tides provide a predictable, reliable and cyclic energy resource. But what do these characteristics actually mean, in terms of the benefits the tidal resource can provide to energy systems as a whole?
The reliability of tidal power means its able to supply approximately the same amount of energy every month, regardless of weather conditions. Whilst the energy produced by wind and solar will dip below expected seasonal levels again in the future, there is certainty that tidal energy supply will remain consistent. This helps to improve the resilience of energy systems to extreme weather, by reducing reliance on expensive imported energy to make up for unpredictable domestic supply deficits when they occur.
The timing and magnitude of tidal power generation is dictated by the motions of the Sun, Earth and Moon, which are well understood. With this knowledge of exactly when and how much power tidal turbines and lagoons can generate any time in the future, it becomes far easier to design energy systems capable of balancing supply with demand. For example, with predictable supply, energy storage plants can be designed to take the excess tidal power generated during spring tides, when the tidal resource is highest, and shift it to neap tide periods when tidal power generation is lower. This prevents having to oversize systems to help overcome inconsistent supply, which would incur additional cost.
Research shows that the cyclic nature of tidal power generation means it can be integrated with short duration energy storage, such as lithium-ion batteries. Tidal stream turbines generate power when the tide comes in and out. This creates four periods of power generation per day, with each power period separated by slack tide. This cyclic power behaviour helps limit the duration that energy must be stored to balance supply with demand. This is beneficial, because in general it is easier and cheaper to store energy for short periods than long periods.
Whilst wind provides a cheap source of power at face value (i.e. based on levelised cost of energy), dig a little deeper and findings from the recent energy crisis highlight that its unpredictability brings with it significant challenges to energy system resilience. The predictable, reliable, cyclic nature of tidal power generation has the potential to compliment wind power production.
It goes without saying that for tidal power to contribute significantly to future energy systems, projects must first demonstrate they can remain operational over long periods without significant downtime for maintenance. The sector must also demonstrate cost reduction. This will require similar levels of subsidy support to that received by wind and solar PV to date, that drives cost reduction mechanisms such as technology innovation and economies of volume.
Future subsidy support allocation for new technologies must reflect the whole-system benefits they can provide, which is something they do not currently do. In the case of tidal turbines and lagoons, this can only be achieved by understanding the system benefits of predictable, reliable, cyclic power supply.