Energy storage

How to conserve renewable energy for when it is needed

Hydraulic pumping and large-scale battery storage are the two already available technologies that will allow us to conserve wind and photovoltaic energy and recover it when there is more demand.

Solar and wind energies have increasingly more weight in electricity generation, but the sun doesn't always shine and the wind doesn't blow whenever we want. Their intermittence makes it necessary to have storage systems to ensure the supply and stability of the electricity grid. It is about conserving energy when renewable production surpasses demand, in a way that it can be recovered and used at peak consumption times.

0:00

The International Energy Agency (IEA) estimates that global energy storage capacity must increase fivefold, from 272 GW available in 2023 to 1,503 GW in 2030, to complement a deployment of renewable energies consistent with the aim of achieving climate neutrality by mid-century.

The International Energy Agency estimates that global storage capacity must increase fivefold by 2030 to achieve climate neutrality by mid-century

Hydraulic pumping, which uses the difference in height between two reservoirs to generate electricity and then restart the cycle by returning the water to the upper reservoir, and electrochemical battery storage are the two most developed technologies. The IEA states that "in the future, electricity systems will need both technologies: batteries for short-term storage (of less than four hours) and pumped hydro for their long-term capacity." Pumping is already implemented on a large scale and represents over 90% of the capacity available in the EU, but, with the rapid development of lithium-ion batteries, the latter option is expected to take the lead in storage in the coming years.

Like in other fields of the energy transition, the combination of technologies according to their potential will be one of the keys for storage to achieve sufficient implementation and to combine the growing weight of renewable energies in electricity generation with the guarantee and quality of supply.

How does a hydropower plant work?

Storage in Spain

In Spain, the latest update of the National Integrated Energy and Climate Plan (PNIEC 2023-2030) establishes as a new goal that renewable sources should represent 81% of electricity generation by the end of this decade, "a very ambitious scenario, which needs to be accompanied by a substantial increase in storage capacity for everything to work," Luis Marquina considers, president of the Business Association of Batteries, Cells, and Energy Storage (AEPIBAL). This is reflected in the PNIEC itself, which aims to go from the current 6 GW to 22.5 GW of storage by 2030.

In order to continue with the rapid expansion of renewables, Spain needs to develop resources to store energy on a large scale. Currently, excess generation that can't be injected into the network is lost. They are known as "spills", which Red Eléctrica (Spanish electricity grid operator) calculates could reach 7 TWh annually in Spain by 2030. By that year, the sum of wind and photovoltaic production will surpass consumption for 20% of the hours of the day.

Storage, as well as providing flexibility to the electricity system to adjust production and demand, is also for Marquina "a necessary protection for the business model of renewable assets." Solar generation is the one that suffers the most from the gap between its peak production periods, the central hours of the day, and peak consumption hours, from seven in the evening, when we all get back home and turn on our lights and household appliances, but the sun is already setting. If a solar power plant has a storage system "it can accumulate electricity during the day, when it has lower prices because there is surplus production, to sell it at the time when, with the increase in consumption, it costs more."

Hydraulic pumping: water as a potential energy storehouse

Batteries for large-scale energy storage

Other technologies that add up: thermal storage and hydrogen

Although batteries and hydraulic pumping will be the predominant solutions in the midterm, there are other mature technologies with potential in Spain such as thermal storage in solar thermal power plants, which produce electricity from the sun's heat. The excess heat in the peak generation hours can be conserved in large tanks by using molten salts at high temperatures, which have the quality to retain that heat. That heat energy can be transformed again into electricity when the demand requires it or be used in industries and urban heating systems.

The production of renewable hydrogen is another alternative with potential to store large amounts of energy

Using excess renewable generation for hydrogen production is another alternative for large-scale and long-term storage. Renewable hydrogen works as a chemical storehouse of that energy, which can be released when necessary, and is also an energy vector with multiple applications in the decarbonization of industries such as metallurgy and refining or mobility, used for example as a raw material to manufacture synthetic fuels.

Battery storage for photovoltaic self-consumption facilities also has a very significant presence in Europe. According to data from the IEA, in 2023 it represented almost 90% of the new installed battery capacity in the EU, highlighting the impact of the residential sector. Its principle is the same as in large-scale storage: to accumulate the energy produced during the day to use it at the hours where there is no longer any solar resource but families need that electricity.

Likewise, the possibilities of Vehicle-to-grid (V2G) technology are being explored to make the most of electric vehicle batteries as a form of distributed storage. It is estimated that, on average, electric vehicles are parked and plugged into the grid for more than 90% of the time. Their owners could sell part of the electricity accumulated in their batteries in those periods and act as a support for the electricity system.