“Energy storage stabilizes prices, manages renewable energy variability, and encourages investment."
A massive balloon looms over the Italian island of Sardinia. It is full of carbon dioxide, one of the main greenhouse gasses causing dangerous changes to our climate. Energy Dome uses the balloon, which it calls “the dome”, as the key component of its “super-battery”. The Milan-based startup believes the very gas responsible for global warming could play a pivotal role in combatting it.
“Renewables are currently taking the lead in terms of power production, but they come with a catch —the sun doesn’t always shine, and the wind is not always there,” says Paolo Cavallini, Energy Dome’s chief of staff. “At the same time, we need renewable electricity day and night. Hence, we need long-duration energy storage.”
Energy Dome’s balloon battery exploits the fact that, unlike air, carbon dioxide can be liquified under high pressure without the need for energy-intensive cooling. It uses excess energy from the local grid during the day, normally supplied by solar power, to compress and liquify the gas, storing it in steel tanks. The heat generated as a by-product during the process is stored in special Thermal Energy Storage units.
When there’s a need for electricity, the process is reversed. The liquid carbon dioxide is heated through the storage units, turning it back into a gas. The gas passes through a turbine, generating electricity, before going back into “the dome”.
“The whole process is a closed loop, giving back to the grid 75% of the energy initially used during charging, making it highly efficient,” says Cavallini. “It can last 30 years without any kind of degradation, contrary to other electrochemical technologies that quickly degrade."
The technique can store energy for up to 10 hours at about half the cost of lithium-ion batteries.
Energy Dome’s demo plant, the first of its kind, has been in operation for two years. It's building a full-scale plant in Ottana, Sardinia, that will be capable of generating 200 megawatt hours of electricity in a single discharge. That's equivalent to 2 439 Tesla Model 3 "Long Range" batteries.
Transition at a turning point
The transition is already well underway. According to energy think tank Ember, more than 30% of the world’s energy now comes from renewables and we have reached a turning point where power from fossil fuels should start to decline. Solar and wind power are growing much faster in the European Union than in the rest or the world. In 2023 new solar and wind capacity in Europe accounted for 17% of global total and the European Union generated 44% of its energy from renewables, the think tank says.
But to meet increasing demand for electricity and reconcile the mismatch between demand patterns and the weather, Europe has to invest massively not only in new generation capacity but in two other critical areas: energy storage and the power grid. Bruegel estimates that investment in electricity generation and storage alone may need to double to about 1% of annual European Union gross domestic product, while the European Commission puts the price tag on grid investments alone at €584 billion.
In this article, we look at a number of innovative energy storage technologies being developed in Europe—and the challenges of upgrading power grids to serve a decarbonised electricity system.
- Read about the history of renewable energy
The power of physics
While chemical batteries are a promising solution for many situations, they have some shortcomings for large scale application. Integrating batteries into the power grid can be expensive and they only provide power for a few hours. This limitation becomes particularly problematic on days without sunshine, when the shortfall in electricity generated can last several hours. Another disadvantage of batteries is that they require raw materials such as lithium that are not abundant in Europe and whose mining and extraction process can be environmentally damaging.
To deal with the challenge of intermittency, electricity systems need longer lasting solutions that can provide backup power for several hours or even days.
Energy in motion
Mechanical storage systems are arguably the simplest, drawing on the kinetic forces of rotation or gravitation to store energy. These systems often use mechanisms like flywheels or suspended weights to harness the stored potential energy in an elevated mass.
Gravitricity, a start-up based in Scotland, is developing a 4 to 8 megawatt mechanical energy storage project in a disused mine shaft. Its technology operates like an elevator, using excess electricity from renewables to elevate a solid, densely packed material. The denser the material, the greater the energy storage capacity. When energy release is required, the weight gradually descends under the influence of gravity. As it lowers, reinforced cables attached to the weight drive a series of motors, generating electricity.
The ability of Gravitricity's batteries to discharge energy for up to eight hours makes them ideal for storing solar power. They can absorb surplus solar energy during daylight hours and release it during the night, effectively balancing energy supply and demand.
Upon full implementation, Gravitricity anticipates each battery will be able to discharge between 1 megawatt and 20 megawatts at peak power, providing energy for up to eight hours. A 20MW power system could sustain 63 000 homes for each hour of discharge.
Following the successful operation of a 250 kilowatt demonstration project in Edinburgh, the European Investment Bank provided project development assistance through the Innovation Fund.
Pumping the energy
Pumped-hydro energy storage is one of the oldest and most widely used large scale energy storage technologies. It works like this:
- Water is stored in two reservoirs at different elevations.
- When there is surplus energy, water is pumped from the lower reservoir to the higher one.
- When the stored energy is needed to meet peak demand, the water is released back down to the lower reservoir, powering turbines as it descends and generating electricity.
The process is simple and effective. It’s cost-effective and energy efficient, all without generating greenhouse gas emissions during operation.
In northern Portugal, Iberdrola has built three large new hydroelectric dams, including a pumped-storage plant, on the Tâmega and Torno rivers. The facility has a total capacity of 1 158 megawatts and is the largest hydroelectric power plant to be developed in Europe in the last 25 years.
With an annual production capacity of 1 766 gigawatt hours, the Tamega complex can provide enough energy for nearby towns and cities, including Braga and Guimaraes, which have over 440 000 households. It can also store 40 million kilowatt hours, which is equivalent to the daily electricity consumed of 11 million people
By diversifying Portugal’s electricity generation and reducing oil imports, this project is expected to reduce carbon emissions by 1.2 million tonnes a year and cut over 160 000 tonnes of oil imports. It will also contribute to economic activity and employment in the region, with the construction phase of the project estimated to generate 3 500 direct jobs and 10 000 indirect jobs.
Iberdrola also plans to develop two wind farms with a combined capacity of 300 megawatts, which will transform the Tamega complex into a hybrid power plant. The European Investment Bank provided a €650 million loan to Iberdrola, signed in 2018, to finance the project.
A balancing act
Storage capacity isn’t the only investment electricity grids need to prepare for the integration of renewables. There are a number of other challenges for grids.
- The intermittent and weather-dependent supply of electricity from sunshine and wind makes it difficult for grid operators to predict and manage electricity supply and demand. At times, the amount of electricity being generated may exceed demand. Without adequate storage capacity, this can force wind farms, for example, to turn off turbines to reduce their output.
- Because wind farms and solar parks are often located far from consumers in cities or industrial sites, new transmission and distribution lines may be needed.
- Reliance on renewables can make it more difficult for grids to maintain a stable electrical frequency. This poses a risk to their stability, as it makes the system less able to withstand sudden disturbances, like the loss of a large generator, or a sudden drop in wind.
