No more Lithium: 4 ways renewable energy could be stored in the future

Lithium-ion batteries are being used extensively for a wide range of applications, including those to make processes less polluting and more environmentally friendly. However, sourcing components for their manufacture is nowhere near being environmentally friendly. In July, we reported how lithium mining has a long-term impact on the hydrology of the regions where they are mined, damaging that it can take decades or more to recover from.

There are also issues of overheating that can sometimes take batteries offline for significant periods or, worse still, end up causing a fire. With the world increasingly turning to renewable sources for energy needs, there is a significant need for environmentally friendly and cost-effective energy storage solutions that will supply energy when production is low.

The move away from lithium-based storage solutions has already begun and in some cases has been in the works for 14 years. Researchers and entrepreneurs looking for sustainable storage options have turned to some basic elements like water, sand, and carbon dioxide in the air to serve as energy reservoirs. Here’s how they work.

Water based battery

The concept of storing energy in water for a long duration has been around for centuries. When available, excess energy is used to pump water up from a reservoir at a lower height to one that is much higher. When there is a demand for energy, water from the higher reservoir is let out, and energy from the flowing water is used to do work, in the modern instance, move turbines to generate electricity.

In July this year, Nant de Drance, a pumped-storage power project in the Swiss Alps, became operational. “The efficiency of a complete pumped-storage cycle is above 80% for Nant de Drance, which is one of the highest efficiencies currently available for storing electricity. This high efficiency was made possible with the use of variable speed machines and the overall design of the water system,” said a company spokesperson in an email to Interesting Engineering.

With a storage capacity of 20GWh, the ‘water battery’ easily dwarfs Tesla’s Megapacks that deliver 3MWh. However, for all its technical complications, it would be relatively easier to build a battery pack than to fight the Swiss Alps' geology, as engineers did by drilling through them for 14 years before the project became operational.

However, not all energy storage solutions are that complex to build. Some, like the carbon dioxide battery, require lots of steel and water.

Carbon dioxide battery

Built-in an industrial region of Sardina, Italy, the world’s first carbon dioxide battery appears from a distance like a big bubble about to burst. Underneath the large steel dome is carbon dioxide gas captured from the atmosphere and stored under normal temperature and pressure.

During high renewable energy generation periods, carbon dioxide is further compressed and converted into its liquid state. The heat generated during this process is stored. When power needs to be supplied, the liquid CO2 is heated up and converted back into a gas that powers a turbine, which generates power.

The company claims its battery’s round-trip efficiency (RTE) is 75 percent AC-AC. This means that a fully charged CO2 battery can discharge up to 75 percent of the energy stored during the charging phase, comparable to lithium-ion batteries.

It triumphs over Li-ion batteries, though, because it is made entirely from off-the-shelf components, and since it uses only carbon-dioxide gas, it will not undergo degradation. Building such a battery costs less than half of what Li-ion-based energy storage comes up to and is also without the risk of toxicity or fire during or after usage.

Sand based battery

Concerning using readily available materials, the Finnish company Polar Night Energy (PNE) takes a bold step. It found its answer to the energy storage problem in the humble component sand. “We were studying different kinds of solid materials and came up with sand since that is available in Tampere. It is a low-cost, bulk material that is simple and easy to handle,” said Markku Ylönen, CTO of the company, in an email to Interesting Engineering.

The battery uses resistive heating to increase the temperature of the air when excess renewable energy is available and then uses a heat exchanger to transfer the heat to the sand. Since the melting temperature of sand is high, it can be used to store increased amounts of heat and also for extensive periods of time, running into months, before it is used again.

The company claims that the company already has a commercial-scale installation that uses 100 tonnes of sand for energy storage, where the energy conversion efficiency is close to 100 percent. Ylönen also told IE that the company is ready with plans to scale this up 100 times with a 1GWh storage facility and is currently in discussions with potential clients and funders to get the project underway. Going forward, the 1GWh facility will be the company’s standard installation size for most projects.

Not all energy storage solutions need to be built anew. Julian Hunt and his team of researchers at the International Institute of Applied Systems Analysis (IIASA) in Austria have an innovative way to use existing infrastructure, such as skyscrapers, as energy storage systems.

Skyscrapers to store energy

The idea seems to combine a mix of sand and water-based batteries since it plans to use the elevator downtime in skyrises to move bags of wet sand to higher levels in the buildings. When the power demand increases, these wet sandbags will be moved down the elevators again. At the same time, a regenerative braking system will work as a mini generator and supply energy to the grid.

Hunt’s plans include the use of autonomous robots that will do the shifting and moving of the weights inside the building. The proximity of the power generation capacity with urban areas where the demand is higher, along with a claimed round trip efficiency of 70-80 percent, makes the system very attractive.

Interestingly, the team hasn’t patented its technology, so anybody who has access to an elevator system in a skyscraper could potentially try out the system. Speaking to IE, Hunt observed that the autonomous robots he suggests be used are already a regular feature at major logistics hubs and available as a service. They may cost around $100,000 today, but with scaled production in the future, this cost would come down considerably.

Apart from that, the capital expenditure for the system is around $70,000, which has a claimed installed cost of $20-120/ MWh.

Hurdles in the way of alternative storage solutions

Most of these technologies are still in their early stages of development or commercialization and are not without drawbacks.

A project like Nant de Drance might have massive potential and has already been built at scale, but it has also taken many years to materialize. Moreover, it is difficult to replicate it in different parts of the world due to differences in geology. “The machines and their components are specific to the particularities of the plant. It was sometimes difficult to obtain the desired quality and some parts had to be remanufactured,” the spokesperson told Interesting Engineering.

The team also still needs to demonstrate that the project is commercially viable in the long run. Although it has the water rights (concessions) to the facility for 80 years, the return on investment has also been calculated for this duration, and fluctuations or low prices of energy for prolonged periods can put severe dents on the profitability of the project. Currently, the promoters do not have plans on the horizon to build any other similar projects.

After demonstrating its technology in Sardinia, the makers of the CO2 battery, Energy Dome, are ready to deploy utility-scale batteries. However, the company's founder estimates estimates that these batteries have a capacity of 20MW, which roughly translates to powering 15,000-16,000 homes for a period of 10 hours.

Polar Night Energy’s next plant will have a 1GWh storage capability. The only issue is that although the technology works great when using the stored heat directly when attempting to convert it to electricity, the efficiency of the process drops to 20 percent. “Our heat storage is not suitable for small volume, quick cycles, in which Li-ion batteries excel," Ylonnen told IE, adding, “We aim for large volumes of energy, with longer cycles.”

Chris Hendon, a professor of chemistry at the University of Oregon, agrees, “Heat is a tricky beast to tame — it is constantly trying to cool down (while heating the surroundings), and hence energy storage devices which rely on heat differentials rather than electron energy differentials face an uphill entropic battle.”

The lift-based storage system sounds like quick-to-deploy technology that can be used immediately. However, the idea still exists only on paper and hasn’t been tried in an actual building yet. “The main challenge is to find a building with a regenerative braking system that would be willing to install the system and borrow some space to store the containers,” Hunt told IE.