From Finland to China, storage seeks simple materials and long-lasting systems to manage a grid increasingly powered by sun and wind.

A thirteen-meter-high silo filled with approximately two thousand tons of crushed stone, refractory blocks heated to nearly a thousand degrees Celsius, and heavy masses lifted and then lowered. Some of the technologies being developed to address one of the most complex problems of the energy transition have one thing in common: they use physical principles known for centuries and materials far less sophisticated than those found in modern electrochemical batteries.

The question to be resolved is the variability of renewable productionA photovoltaic system generates electricity when solar radiation is available, a wind turbine when enough wind blows, while consumption follows different curves. The greater the share of intermittent sources, the greater the need to shift some of the energy produced over time, as well as to upgrade grids and make their management more flexible.

The batteries to the lithium ions Today they represent the dominant electrochemical technology, thanks to their rapid response, progressive reduction in costs and the ability to be installed practically anywhere.International Energy Agency He calculated that to support the goal of tripling global renewable capacity, global storage would need to reach approximately 1.500 gigawatts by 2030In the agency's Net Zero scenario, 1.200 gigawatts would consist of batteries. But a power grid with increasing amounts of solar and wind doesn't require just one type of storage: durability, power, response times, cost, availability of raw materials, and the final destination of the energy vary radically from one application to the next.

Sand conserves energy by converting electricity into heat

A concrete example comes from Finland, Where Polar Night Energy has developed a high-temperature thermal storage system known as Sand BatteryThe name might lead one to imagine a conventional electric battery, but the operation is different: electricity is converted into heat and the latter is stored inside a suitably insulated solid mass.

The largest installation built by the company to date went into service in June 2025 in Pornainen, for the district heating network operated by Loviisan Lämpö. The unit measures approximately 13 meters high and 15 meters wide, develops a thermal power of one megawatt and can store 100 megawatt hours of thermal energy. Contrary to what the term “sand” might suggest, the plant uses approximately two thousand tons of crushed steatite, material recovered as an industrial by-product.

The principle remains that of storage in a granular material: when electricity is available, the system heats the storage medium through a closed air circuit; the thermal energy is retained in the insulated tank and subsequently transferred to the heating network. In this case, therefore, the capacity expressed in thermal megawatt-hours should not be confused with that of a battery designed to directly return electricity to the grid.

The first year of operation of the Pornainen plant already provides an operational benchmark. In June 2026, Polar Night Energy reported that the system had met its performance targets and that greenhouse gas emissions associated with the local district heating network had decreased by 70 percentThe data concerns a specific application and cannot be automatically transferred to other energy systems, but it shows how thermal storage can take on an industrial role when the final demand is precisely heat.

This distinction determines the scope of application. Converting electricity into heat and then using it directly avoids the need to constantly reconvert thermal energy into electricity. District heating and high-temperature industrial processes are therefore natural candidates for systems based on sand, rock, or other abundant solid materials. The availability of the storage medium also reduces dependence on lithium, nickel and cobalt, although the overall impact must be assessed taking into account construction, insulation, auxiliary systems and the origin of the electricity used.

Refractory blocks bring accumulation inside factories

The same physical logic can be applied to refractory bricksInstead of storing charges through chemical reactions, these systems transform electricity into heat and store it in materials capable of withstanding high temperatures. The concept recalls technologies long used in the steel, ceramic, and glass industries, but is reinterpreted for an energy system in which renewable electricity can be available in quantities exceeding instantaneous demand.

When wind or photovoltaic generation is abundant, resistive elements can convert electricity into heat and heat ceramic or refractory blocks to several hundred degrees, up to temperatures approaching 1.000 gradi Celsius In some configurations, the stored energy can be subsequently transferred in the form of hot air, steam, or other heat carriers and used in production processes.

The difference compared to electrochemical batteries is substantial. To quickly stabilize grid frequency and voltage or to shift electricity for a few hours, lithium batteries have characteristics that are difficult to replace. thermal storage, however, it can be interesting when the energy required by the end user is industrial heat, avoiding further conversion and allowing the use of relatively cheap and available materials.

The lifespan of the storage medium is another factor to consider. A refractory block does not undergo the same chemical reactions that cause aging as an electrochemical cell. This does not mean that a thermal system is free from wear and tear: heating elements, fans, heat exchangers, insulation, and mechanical components require maintenance. However, the part intended to physically store the heat can be designed for a very high number of cycles, altering the cost structure over the life of the infrastructure.

This feature is particularly important in industrial sectors that are difficult to decarbonize. Cement, steel, chemicals, paper, and food industries use large amounts of thermal energy, and part of this demand is still met through the combustion of natural gas, coal, or other fuels. Electrification combined with thermal storage can allow factories to generate heat when renewable electricity is available and consume it later, at least partially separating electricity production from industrial processes.

Lifting a mass to return electricity to the grid

Another family of technologies also eliminates the heat conversion and goes directly back to the mechanics. gravitational storage It uses electricity to lift a mass and convert it into potential energy. When the grid requires power, the mass is lowered in a controlled manner, and the movement activates generators that return electricity.

The principle is closely related to that of thepumped storage hydroelectricIn traditional power plants, energy is stored by transferring water from a lower reservoir to an upper one, while in new gravitational systems, water can be replaced by blocks, weights, or other solid bodies. This difference is significant, as it theoretically allows gravitational systems to be installed even where the geography doesn't permit the construction of two large reservoirs.

Among the companies that are industrialising the concept is the Swiss-American energy vault. Rudong, in the Chinese province of Jiangsu, an EVx system with an indicated power of 25 megawatts and a capacity of 100 megawatt hours, equivalent to four hours of power output at nominal power. The installation is located next to a wind farm and the Chinese national grid and uses vertically moved solid masses to store and release energy.

The project also highlights another feature of the technology: the medium that stores the energy is not subject to the electrochemical degradation typical of cells. Energy Vault indicates a designed operating life of 1000 hours for the system. 35 years and an expected round-trip efficiency of more than 80 percent. These are manufacturer-declared values, and their industrial relevance depends on actual performance during prolonged operation, required maintenance, and the overall cost of stored energy.

Other projects are studying a particularly interesting variant for the territories that have abandoned mining: using the shafts of abandoned mines As vertical infrastructures for lifting and lowering weights. The potential advantage lies in the reuse of existing underground structures, transforming an element of the former industrial system into a component of the new energy infrastructure. However, geology, depth, structural conditions, and redevelopment costs make each site unique.

A renewable grid will need different storage systems

Sand, bricks, and gravity are therefore not three universal substitutes for lithium batteries. Rather, they address different needs within the same problem: temporally decouple energy production and consumptionAnd it is precisely the diversification of functions that explains why a comparison based solely on nominal capacity can be misleading.

A lithium-ion battery can react very quickly to grid demands and is particularly effective for regulation services and storage on the order of a few hours. The IEA points out that electrochemical systems are particularly suited to providing flexibility for periods ranging from approximately one and eight hoursThermal storage, on the other hand, can retain energy for longer periods when the required end product is heat, while gravitational systems focus on the longevity of the infrastructure and the ability to repeat numerous cycles without chemically degrading the storage medium.

The need to differentiate technologies also emerges from the expected size of the market. In 2023, over 1,000 technologies were already in operation in the global electricity sector. 85 gigawatts of batteries And in the same year, approximately 42 gigawatts were added. According to the International Energy Agency, to maintain a trajectory compatible with the strong growth of solar and wind power, total global storage capacity would need to grow approximately sixfold by the end of the decade.

Lithium will therefore retain a central position. Its average costs have decreased by approximately 90 percent since 2010 and lithium iron phosphate chemistries have reduced the need for nickel and cobalt in many stationary applications. However, the geographical concentration of some stages of the production chain, the growing demand for critical minerals, and the recycling and degradation of cells remain. In 2023, according to the IEA, China had nearly 85 percent of the world's cell production capacity.

The industrial response may therefore consist not in identifying a single "battery of the future", but in building a portfolio of complementary technologies. Terna, analyzing storage alternatives in Italy, places electrochemical, thermal, and gravitational solutions within a system in which networks, new renewable capacity, and storage must evolve together.

Bitter oranges fallen from city trees become biogas

Then there are forms of energy integration that go beyond storage itself. SevilleFor example, bitter oranges fallen from city trees have been tested as a raw material for biogas transformation, destined for wastewater treatment plants and energy production. The industrial principle is different from that of a battery, but it is part of the same quest to connect urban flows, waste, and energy production and consumption.

For grid operators, the decisive criterion remains the required function. Stabilizing the system in a few seconds, shifting photovoltaic production from afternoon to evening, supplying heat to a factory for many hours, or storing energy for longer periods are technically different problems. Power, capacity, efficiency, durability, response speed, land use, material availability, and cost per cycle determine the most suitable solution.

The growth of renewable sources makes this distinction increasingly concrete. Storing energy does not necessarily mean storing it in the form of electrons inside a cell: it can mean heating two thousand tons of rock, bringing refractory bricks to a high temperature, pumping water to a higher basin or lifting a mass of many tonsThe physics underlying these solutions has been largely understood for some time. The industrial innovation lies in scaling, controlling, and integrating them into electricity grids where production will increasingly depend on variable sources.

The real comparison will therefore be based on operating data: cost of the energy actually recovered, efficiency after thousands of cycles, maintenance, system life, response speed and ability to be replicated on a large scale. energy transition It does not require sand, bricks or gravity to defeat lithium, but each technology to be used where its physical and economic characteristics allow it to best solve a specific storage problem.

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