Global system value of tidal stream energy for cost-effective decarbonisation

The world is racing toward a future where electricity comes almost entirely from the sun and the wind. This shift is essential to stop climate change, but it brings a tricky problem: the sun does not always shine, and the wind does not always blow. When the weather is calm, power grids can run short, forcing engineers to build massive amounts of battery storage to hold energy for later. These batteries are expensive and require huge amounts of rare materials to build. Scientists have long known that the tides offer a different kind of power. Unlike wind and solar, the rise and fall of the ocean is driven by the gravitational pull of the moon and sun, making it perfectly predictable and completely independent of the weather. The big question has always been whether this reliable power is worth the high price tag of building underwater turbines, or if it is just a niche curiosity.

A new study by researchers at the University of Oxford and the University of Plymouth has finally answered that question by looking at the entire electricity system, rather than just the cost of a single power plant. They used a sophisticated computer model to simulate how electricity grids would work in twenty different locations around the world, ranging from the windy coasts of Scotland to the sunny islands of Indonesia. In these simulations, they tested how adding tidal stream energy—power generated by underwater turbines that spin with the current—changed the total cost and design of a net-zero electricity system. The results show that tidal power is far more valuable than previously thought, not because it is cheap to build, but because it acts as a perfect partner to wind and solar, allowing the whole system to run with far less expensive battery storage and fewer total resources.

The researchers found that the value of tidal energy depends heavily on what other power sources are already available in a region. In places where the wind is the main source of renewable energy, adding tidal power creates a powerful combination. Because the wind can be unpredictable for days at a time, grids usually need to build huge amounts of extra wind turbines and batteries to ensure there is always enough power. However, the tides follow a strict, predictable schedule, rising and falling twice a day with short breaks in between. When this predictable rhythm is added to a windy system, it fills the gaps that the wind leaves behind. The study shows that in these wind-heavy regions, adding tidal energy can cut the total cost of the electricity system by more than 20 percent. It does this by drastically reducing the need for battery storage, which is often the most expensive part of a green grid. In fact, the amount of battery capacity needed dropped by between 20 and 55 percent in these simulations.

In regions where solar power is the dominant renewable source, the story is slightly different but still positive. Solar panels produce power during the day and stop at night, a pattern that is very regular. Adding tidal power here still helps, but the savings are more modest, generally reducing system costs by less than 15 percent. This is because solar and batteries are already quite good at handling the daily cycle of day and night. However, even in these sunny regions, tidal energy still played a crucial role. It reduced the need for battery storage by about 15 percent and helped smooth out the supply of electricity, proving that it has a place in almost any mix of renewable energy. The study suggests that the unique timing of the tides provides a different kind of stability that wind and solar cannot offer on their own.

One of the most surprising findings was how much tidal energy could reduce the physical footprint of the energy transition. Building a net-zero world requires vast amounts of land for solar farms and wind parks, as well as huge quantities of critical materials like lithium for batteries. The simulations showed that by including tidal power, the total area needed for development could be cut by more than 30 percent in many wind-dominated locations. Similarly, the demand for lithium, which is needed to make batteries, dropped significantly. In some cases, the need for battery capacity fell by as much as 80 percent. This means that tidal energy could help solve the problem of where to build all these new power plants and where to get the materials to build them, easing the pressure on the environment and global supply chains.

The researchers also looked at how the value of tidal energy changes as the world moves closer to zero carbon emissions. In wind-dominated systems, the value of tidal power actually grows as carbon limits get stricter. As the grid becomes cleaner and relies less on fossil fuels, the need for that predictable, weather-independent power becomes more critical. In contrast, in solar-dominated systems, the value remains steady but does not grow as dramatically. The study identified that the ratio of wind to solar resources in a region is a good predictor of how much tidal energy will help. If a location has a lot of wind and less solar, tidal power will likely be a major cost-saver. If the location is very sunny, tidal power will still help, but it will be a smaller piece of the puzzle.

This work challenges the old way of thinking about new energy technologies. For a long time, experts judged technologies like tidal power solely on their own cost per unit of electricity. Because underwater turbines are currently expensive to build and maintain, they were often seen as too costly to compete with cheap solar panels. This new research argues that this view is too narrow. It suggests that the true value of a technology lies in how it fits into the whole system. Even though tidal turbines cost more to build than solar panels, they save the system money by reducing the need for other expensive components like batteries and extra wind turbines. The study concludes that tidal stream energy is not just a local curiosity for a few specific coastlines, but a globally significant tool for building a cheaper, more efficient, and more resilient net-zero future.

The researchers were careful to test their findings against different scenarios, including changes in future technology costs and different patterns of electricity demand. Even when they assumed that the cost of batteries or wind turbines might go up or down significantly, the benefit of adding tidal power remained consistent. The simulations showed that tidal energy makes the entire system more robust, meaning it is less likely to be thrown off balance by unexpected changes in the cost of other technologies. This resilience is a key part of its value. The study also noted that while the best tidal resources are found in a few specific locations, such as the Pentland Firth in Scotland and the Cook Strait in New Zealand, the benefits are not limited to these giant sites. Smaller sites around the world, including those in Japan and Indonesia, also showed significant system-wide benefits.

Ultimately, the paper paints a picture of a future energy system where the ocean plays a central role. By harnessing the predictable rhythm of the tides, we can build electricity grids that are not only cleaner but also cheaper and less demanding on the planet's resources. The research provides a clear roadmap for where and when tidal energy should be deployed, suggesting that it is a vital missing piece in the puzzle of global decarbonization. It is a reminder that solving the climate crisis will require a diverse mix of technologies, each playing to its unique strengths, rather than relying on a single solution. The tides, with their ancient and unchanging rhythm, offer a steady hand to guide the transition to a sustainable world.