The perfect storage mix: Pumps, batteries and green hydrogen

The energy transition cannot wait. In the current context, the European Commission issued the REPower EU communication focussing on reducing and mitigating dependence on fossil fuels for energy and accelerating the development of renewable energies, mainly wind and photovoltaic energy.

The main challenge is how to integrate the variability of renewable energy production into the pattern of electricity consumption. Renewable generation features marked cycles that are not always easy to forecast and not easily managed. In addition to the daily cycle of photovoltaics, wind power is characterised by high production levels for several consecutive days with strong wind, followed by other periods of very low production, while both have a marked seasonal cycle.

The success of this process of integrating a large volume of renewable energies will depend on the existence of storage and flexible systems capable of balancing the supply and demand of electricity.

There are a number of storage technologies, with different advantages and disadvantages. For the system to work properly it is essential to have a balanced mix of both storage technologies and energy generation. Future technical development will not only lower costs and increase performance, but will also add greater diversity to this mix. The new proposal of the National Integrated Energy and Climate Plan (PNIEC) sets a target of an additional 12 GW of storage by 2030, to which we should add the thermal storage of 2.5 GW in new solar thermal plants, making a total of 22 GW. 

Batteries to manage daily storage

Batteries, especially lithium-ion batteries, have benefitted from a reduction in costs and this is expected to continue for a number of years, although with the risk of concentration in certain countries and subject to volatility. We just need to be reminded that in 2022 the cost of Lithium Carbonate reached $68,000/t compared to $12,100t in 2019.

Together with improvements in recycling processes, many batteries can be produced with greatly reduced environmental footprints. In the medium and long term, new chemical technologies are being developed, including sodium batteries, which promise even lower impacts and costs.

Batteries are the ideal technology for the management of daily cycles. Photovoltaic energy generated at midday can be stored for use in the evening. The battery can be installed in the home, but you can also have batteries in electric cars and batteries installed in the power stations where the renewable energy is produced. This last possibility has the added interest that it enables the connection network to be optimised. Because batteries store energy during periods of high generation, the grid can be designed for a lower output power than the plant's peak generation power. This means that it is a technology that competes with the grid. The regulation of the networks needs to start taking this into account in order to maximise and optimise the use of the grid.

Batteries also have an extremely fast response, mere milliseconds. This makes them the ideal technology for providing a variety of system services, from secondary reserve to voltage control. Once again, these new possibilities need to be taken into account in the corresponding technical and market regulations. 

Pumping: Efficiency and flexibility with a huge potential in Spain

Pumping is an established technology, with a high level of technical efficiency and flexibility. Contrary to what is broadly felt, there is high potential for new pumped storage in Spain. Moreover, much of this potential does not have a major environmental impact because it may entail upgrading existing plants or new pumped storage installations associated with current hydroelectric plants. Endesa alone has a portfolio of new pumped storage projects with a potential of almost 4,000 MW.

Although the performance is lower than lithium-ion batteries, pumped storage has the advantage of having greater storage capacity, which makes it ideal for managing not only daily renewable production cycles but also longer periods, such as those of wind energy, weekly or even biweekly in some cases. 

Renewable hydrogen: The solution for seasonal storage

However, neither batteries nor pumped storage are ideal technologies to satisfy the requirements for seasonal storage. This need comes from the fact that photovoltaic generation is much higher in summer than in winter; and that wind generation tends to be higher in spring, but has a very high variability from one week to the next, while the highest demand occurs in autumn and winter. A balanced mix of photovoltaic and wind energy can minimise the need for storage to meet demand because it has a very different annual cycle. But it cannot be eliminated completely.

Hydrogen is presented as a possible solution. Electrolytic hydrogen can be produced in periods of high photovoltaic or wind production and used to replace fossil fuels in sectors where decarbonisation is difficult, such as transport (aviation, maritime or heavy road), or in industrial processes requiring very high temperatures. The use of hydrogen fuel cells or turbines powered by clean hydrogen for electricity production could be the answer in the long term and perhaps in small isolated systems, but there are much more efficient sustainable alternatives available today. Hydrogen will be stored, analogous to natural gas today, in surface tanks for short-term storage and in underground geological formations for seasonal storage.

Hydrogen is already used in many industrial processes, and can be used in virtually any process that today requires oil or natural gas. In Spain, about 500 kt/year of grey hydrogen is already being generated, produced from natural gas and therefore emitting CO2. The 2023 National Integrated Energy and Climate Plan (PNIEC in Spanish) calls for the construction of up to 11 GW of electrolysers and the replacement of at least 74% of this grey hydrogen, which is consumed by industry, with green hydrogen.

To put it very simply, electrolytic hydrogen can reach where electricity is unable to. A number of studies by international organisations such as the IEA and IRENA estimate that in the long term, by 2050, if the climate change targets are to be achieved, the energy mix should consist of at least 50-55% electricity, 15-20% green H2, and 15-20% end-use renewables.

Endesa has submitted several green hydrogen projects to the Next Generation funding programmes, as well as other projects to adapt turbines used for generation to run on this fuel in a number of declarations of interest related to European and Next Generation projects.

Other innovative storage modalities

Endesa also has other innovative storage projects, including a Compressed Air Energy Storage project proposed for the Canary Islands, consisting of a 60 MW LAES (Liquid Air Energy Storage) installation that occupies an area similar to a football pitch and which, despite being a pilot project, is an alternative to other technologies as it is a more compact solution with minimal environmental impact.

At the Son Orlandis solar plant in Mallorca, Endesa has also recently commissioned the largest renewable energy storage installation with vanadium flow batteries in Europe, with a power of 1.1 MW and a maximum storage of 5.5 MWh, making this the company's first plant in Spain not to use lithium.

It should also be pointed out that Endesa is going to build the largest solar power plant with battery storage in the Canary Islands, on available land within the Barranco de Tirajana power station, in the municipality of San Bartolomé de Tirajana, with an installed capacity of 9.3 MW. This hybridised photovoltaic plant, "El Matorral", will use the latest technology available on the market and will have 15,000 state-of-the-art photovoltaic modules.

Over the next few years, storage will play a central role in the electricity system, but a solid regulatory framework needs to be established to make its development possible and with it, the success of the energy transition process.