Almost all of us know the legend of Daedalus and Icarus. To escape from Crete Daedalus built two pairs of wings by tying feathers together with twine and using wax to fasten them to their bases. The wings worked, and the two left the island in flight. Daedalus warned his son to be careful: too close to the waves and the sea foam would wet the wings, making them too heavy. Too close to the sun, on the other hand, the wax would melt. All went well until Icarus, caught up in the excitement, flew upward. The sun melted the wax on his wings, and he fell into the sea.
This ancient story finds to this day a relevant parallel in the world of energy.
The present goal, namely “the flight to freedom,” is represented by the need for safe, competitive, and sustainable energy. The feathers in our wings are renewable sources, connected and held together by an electrical infrastructure (twine and wax). Exactly as Daedalus recommends, flying too close to the sun melts these. Exactly as happened to Icarus, we flew too high and our (infra)structure did not hold. I am talking about the episode that occurred on January 22, 2023, in Spain.
During that Sunday, in fact, Red eléctrica (Spanish electricity system operator), had to cope for 8 to 9 hours with the problem related to a very low power demand, while production from renewable sources was in excess. Even though “baseload” technologies such as combined cycle and coal were already at their lower limit, and other 98 GWh were already exported (see the graphs on Mtech below), the operator unfortunately had to recall and shut down several wind and photovoltaic farms, preventing the production of a total of 25 GWh of energy, broken down into 14-15 GWh of wind, and 9 GWh of photovoltaics, respectively.
Figure 4: source M•Tech.
Figure 5: source M•Tech.
And this was not the only dumping episode: there are increasing problems with the integration of renewable energy into the electricity system, leading to the “waste” of clean energy. For reasons related to supply stability, nowadays it is complicated to reduce nuclear power, or make combined cycle and coal go beyond certain limits. One of the main issues is related to the fact that the power grid does not currently have the infrastructure for massive, long-term storage of energy. On the other hand, just as with the wings built by Daedalus, during the night, when it is bad or the wind falls, these sources cannot give us energy to “fly.”
So, what can we do to strengthen our wings, i.e., the power grid to enable renewables not only to realize their full potential, but also to enable greater penetration into the electricity market, overcoming their intermittent nature? Long-term storage is certainly one of the most credited answers.
But let’s start with the definition. Long Energy Duration Storage (LEDS) includes all those technologies that can store energy for at least 10 hours (definition from the U.S. Department of Energy, DOE). The most important current applications are as follows.
1. Hydraulic, air-powered, and similar pumping systems
Technology: This family of applications uses a height to transform potential energy into kinetic energy. In terms of water pumping, this is the classic technology that is already widely exploited and mature in the market, which pumps water from a downstream reservoir to an upstream reservoir, and then drops it back downstream at times of high demand. Alternatives to this technology include systems that use compressed air (CAES) or solid masses (Energy Vault) in place of water. Systems that exploit water and air included possess technological (large spaces) and geographical (mountains or underground caverns) requirements that limit their potential, while solid mass technologies are promising but still underdeveloped.
Duration and energy cost: over 10 h for about 20 euro/kWh.
2. The “sand batteries” Energy from the sand
Technology: this is a high-temperature, sand-based fluid bed storage. Both electrical and thermal energy can be stored and then released as steam at high temperatures (from 150 – 400 degrees). The system has: large thermal storage capacity (up to the order of GWh); high thermal efficiency; fast response time; is modular and replicable; has a very low environmental impact due to the use of natural materials. Attention must be paid to maintenance and removal of moisture from the sands.
Durability and cost: energy storage for a range of 4 to over 10 hours to weeks, with installation costs of less than 10 euros per kWh.
3. Flow batteries
Technology: this is a device in which liquid electrolytes are circulated through battery cells to generate electricity through a redox reaction. Abundant (usually Vanadium) and low-cost chemicals are used to store energy in large reservoirs. Despite efforts, the technology is not yet fully competitive.
Durability and cost: performance is intermediate. It has an estimated cost of 100 euro/kWh. To reduce costs, an aqueous sulfur flow battery is being developed that could cost 10 euros/kWh.
4. Iron batteries
Technology: this is an iron-air exchange battery, which uses iron granules that oxidize in the presence of oxygen and revert to iron when the oxygen is removed. The technology is not yet mature as it is totally new.
Durability and cost: 100 hours of storage at less than $20/kWh.
Other less high-performing, but certainly more popular technologies on the market are lithium-ion batteries. Due to their maturity, they are to date the most widely used in conjunction with photovoltaics. Unfortunately, however, the costs are high and the performance is not high. The bargain is to reach €150/MWh, and they can in fact store energy for only six hours. There are pilot projects on hydrogen. Excess electricity from renewables can convert water to hydrogen through electrolysis. However, the time is very long (10 years) due to the complexity of the system and the cost.
But what is the price that makes these technologies competitive? An MIT study led by materials science and engineering prof Yet-Ming Chiang says that for the grid to be 100 percent covered by a mix of solar and wind power, storage system costs would have to be priced as follows to compete with benchmark fossil technologies:
- 10 to 20 euros/kWh to compete with a nuclear power plant.
- 5 euros/kWh to compete with a combined cycle.
Assuming even just 5 percent were covered by other sources, storage could run at a price of 150 euros/kWh.
The 20€/kWh benchmark is a challenging target for most currently available technologies. But although battery prices are expensive, renewables are gaining competitiveness and ground day by day. This makes for a strong push on signing pilot projects. The state of California, for example, recently announced a $15 billion climate package that includes $350 million to support “pre-commercial” LDES projects.
As far as the European Union is concerned, several steps have been taken in this regard since 2017:
- The European Battery Alliance was established, which proposed a strategic plan for batteries covering the entire process.
- An investment platform involving all stakeholders was created to incentivize the interaction between the present and the development and commercialization of this technology.
- Batteries Europe was founded as the reference for battery research and innovation.
- Two major projects of common European interest (IPCEI) were launched, with investments of several billion euros, 12 EU countries involved, as well as dozens of companies and research organizations.
- About 500 million euros were allocated under the Horizon 2020 research program, with an initiative dedicated to the long-term perspective called Battery 2030+.
- The EU’s 7-year (2021-2027) Horizon Europe program for climate, energy and mobility was launched, including batteries as one of the themes.
It is certain that batteries play a key role within the 2030 climate goals, which include:
- An ambitious renewable energy target for 2030
- Stricter CO2 standards for transport
- A review of infrastructure legislation for alternative fuels
- Common rules on energy taxation.
Magnus is also moving in this direction: in fact, a study has been launched to expand a photovoltaic system from 300kWp to 1200kWp with the support of LEDs technologies. This is because we believe that in the coming years storage systems will become a complement to renewables. It is important to reach this stage because only through prolonged energy storage can we seriously begin to think about how to replace gas and coal-fired power plants. The goal would be threefold: to achieve a cleaner energy mix make us independent of some geopolitical dynamics related to fossil fuels, and to combat the cannibalization of prices during peak hours of the day.
The latter issue is increasingly important since during some hours of the day prices reach very high figures as they are set by fossil fuels, which moreover carry with them an environmental burden related to CO2 emissions. Batteries would provide further support in the transformation of the dynamics that renewables have boosted. Just think of the change that is taking place in the conception of the exploitation of pumped-storage systems. In the past they would store energy during the night and early morning hours when the electricity used to pump had a low cost and give up energy during the middle hours of the day. For the past couple of years this has been changing. Pumping systems are being operated during the middle hours of the day, to take advantage of excess photovoltaic and wind generation, and then reclaim power at the time when this fail. The reversal of this profile is also being reflected in prices, reducing the costs of the central parts of the day, once historically higher because of the extra effort required of the combined cycle in handling daily peaks in demand (see the following plot).
Figure 6: source Aleasoft – El Periódico de Energía.
LEDS clearly play a key role in strengthening our wings, but there is more. Indeed, to ensure a fully renewable mix, overcoming seasonal and daily cycling issues, seasonal storage strategies and artificial intelligence algorithms will come into play, combining both long-term and short-term storage technologies, but also integration with green hydrogen and the enhancement of more “stable” renewables such as offshore wind (less intermittent technology).
However, without starting from the base, i.e., the near-term availability of low-cost LEDS technologies, it will not be possible to “fly” toward the complete decarbonization of electric generation. It is necessary to accelerate the development and commercialization of these technologies, which nowadays are still hardly sustainable in the long term, especially from the economic point of view.
Guenda Hehmann | Energy Consultant