What do apple waste, garden rhubarb, concrete balls or even parts of an entire city have in common? They all inspire researchers to come up with unusual ideas for better batteries. Because not only the one super battery is necessary for the energy turnaround and the Internet of Things, but also a lot of specialized storage that best suits the respective application. Here is our selection of ten exotic and bizarre ideas that have already passed the first feasibility tests.
1. Battery with acrylic glass
An almost unlimited battery life is a desirable goal for laptop and smartphone users. The researcher Mya Le Thai and her colleagues from the University of California discovered the necessary material for this . It has coated nanowires that store and release electrons with the plastic polymethyl methacrylate (PMMA) – the main component of acrylic glass. Apparently, the substance in the form of a tough gel stabilizes the thin wires: with PMMA, the batteries suddenly withstood up to 200,000 charging cycles. The researchers used gold nanowires with a manganese dioxide coating for this.
Conventional nanowire batteries fail because the two materials separate too quickly. This type of battery also suffers from the fragility of the wafer-thin wires. After around 5000 to 7000 charging cycles, they are usually over, according to researchers. Your new material combination is far superior to this, but unfortunately not yet ready for commercial use.
2. A rhubarb juice battery?
They are among the secret stars of the energy transition: Redox flow batteries can be built in almost any size because they store electrical current with the help of a liquid, the electrolyte. More liquid also means more stored energy, which is why underground cavities are soon to be turned into tanks of gigantic batteries.
The problem with this is that expensive vanadium salts have been driving up costs so far. That is why a team led by Michael Aziz from the Harvard School of Engineering and Applied Sciences has searched a library with around 10,000 organic molecules in search of alternatives. The researchers found what they were looking for in the class of anthraquinones, which are used as laxatives in plant medicine. You could take on the role of vanadium in the electrolyte. “They are very cheap,” Aziz says. For example, the substance they tested occurs in a very similar form in rhubarb and can also be obtained from plants.
According to Aziz, the build-up of the storage capacity with 20 euros per kilowatt hour should only cause a third of the usual costs. However, the team still has to overcome one disadvantage: the rhubarb-quinone is not as stable as the vanadium metal salts. So far, the scientists have only been able to demonstrate 100 charging cycles without measurable deterioration, but 10,000 cycles would be necessary for a commercial version.
3. An entire city as a store
Everyone knows that in the big city everyone does their own thing – also when it comes to energy supply. Some operate a photovoltaic system on the roof, others have an unused electric car and battery in the garage, and the authority next door is working with a cogeneration unit in the basement for their own use. Why not combine all these systems and others into a gigantic virtual battery and manage them centrally? In 2017, researchers simulated whether this would work in a one-year field test for two cities in the Ruhr area and then tested it in practice. A software decided who should be able to deliver electricity, where a store still needs to be filled or whether it is worthwhile to switch on an additional combined heat and power unit.
Such a “city battery” benefits from the flexibility of these small systems and does not require any major investments, because the energy generators and storage systems are already available and connected to the grid. The aim is to cushion fluctuations in electricity requirements. The need for large batteries and new power lines is reduced accordingly.
According to the team’s studies under the direction of TU Dortmund, the two cities in the Ruhr area had a storage potential of three and five megawatt hours. Upscaled to Germany, it even calculated a potential that would exceed that of the existing pumped storage systems.
4. Hollow Spheres on the Seabed
On the stormy October 28, 2017, Germany’s wind turbines with a production of 40 gigawatts topped the output of all eight nuclear power plants here on land – almost four times as much. Unfortunately, the wind turbines still have to be switched off too often in such wind conditions so that the power grid does not collapse. Scientists at the Fraunhofer Institute for Wind Energy and Energy System Technology in Kassel want to prevent this by storing the energy from offshore wind turbines on site using hollow spheres on the ocean floor.
They are based on the principle of classic pumped storage systems: if there is excess energy, they pump the balls empty deep down. If there is a need for electricity, let the water flow back in and generate electricity using turbines.
An efficiency of 80 percent is possible. In a pilot project at the end of 2016, they tested the process in Lake Constance with three small hollow concrete balls. To be economical, the balls would have to be at least 30 meters in diameter and placed at a water depth of 500 meters or more. Then up to 20 megawatt hours could be saved per sphere.
An entire storage park with many of these spheres, ideally at greater depths off the coasts of Norway, Spain, Japan or the USA, could make a substantial contribution to electricity storage.
5. Lime as storage
Excess electricity can also be stored in the form of heat. But as everyone knows, who has already poured lukewarm coffee from the thermos, it is difficult to prevent the hot from cooling down. Researchers at the German Aerospace Center are now treading a way of storing heat indefinitely and practically without loss .
They use the chemical behavior of hydrated lime (calcium hydroxide). If it is heated to temperatures of around 500 degrees Celsius, for example with electrical energy or industrial waste heat, the water bound in it separates. Burnt lime (calcium oxide) is created – and with it the sought-after heat storage. If you add water to it, it reacts back to hydrated lime and releases the stored energy in the form of great heat.
Both materials are inexpensive, easy to transport and have been familiar to the construction industry for thousands of years. However, the DLR scientists are still working on methods that can be used to convert the two substances into one another as efficiently as possible without wasting the heat converted.
6. The apple battery
Sodium ion batteries would be a cheap alternative to the common lithium batteries if there weren’t a fundamental problem: there is still no good anode material that allows frequent recharging while maintaining the same battery power. Graphite, which is used in lithium batteries, was unfortunately not convincing in tests. During a walk in the Ulm Danube Park, Liming Wu could have taken decisive steps towards a solution.
The doctoral student picked some apples from the tree in the park and brought them to the laboratory for further tests, says Stefano Passerini from the Helmholtz Institute Ulm (HIU) for electrochemical energy storage. His research group then dried the apple scraps, treated them with acid and burned them over high heat. What was left was the carbon contained in the apple, which however has a special microstructure . In contrast to crystal-like graphite, carbon layers accumulate here in an unordered stack. The gaps between them offer enough space for the relatively large sodium ions.
Later, the scientists simplified the whole process by using pre-treated apple scraps from the food industry as a raw material. If it were possible to produce the electrode material from waste products, it would further improve the ecological balance of the battery. It doesn’t always have to be apple: Other green waste could also be used, experiments by various research teams show on corn cobs, banana, pomelo or peanut shells.
7. The breathing mountain
In late 2017 , employees of ALACAES tested how to store energy in a mountain with compressed air in a closed tunnel in the Gotthard massif.
They led ambient air into a 120 meter section of the tunnel and compressed it to seven bars. Two thick, steel-clad concrete plugs prevented the air from escaping. Here, too, the well-known principle of compressed air storage was used again: The energy used to compress the air can be recovered if the escaping compressed air is passed through a turbine.
Conventional compressed air reservoirs of this type are plagued by a serious problem: If air is compressed, it heats up very much and loses energy to the environment. If you release the pressure, the air cools down rapidly – sometimes so strongly that the turbines freeze. Both reduce the efficiency of the storage. The technicians around Giw Zanganeh therefore installed a heat exchanger at the end of the pressure chamber. It collects the heat generated during compression and uses it to later heat up the outflowing air. The trick with the heat exchanger allows electrical energy to be stored with an efficiency of up to 75 percent, according to the experts. A commercially used pressure chamber would, however, have to withstand significantly higher pressures and be larger and ideally spherical.
8. Salt as a battery
Liquid salt is already used today in solar thermal power plants, where it absorbs and stores the sun’s heat. The thermal energy stored in the heated salt can then be converted into electrical power in steam turbines.
Now researchers at DLR want to use this technology to capture the waste heat from energy-intensive industrial plants. Arc furnaces in the steel industry would be a worthwhile goal, the scientists are convinced.
After all, the stoves use almost as much electricity as a small town, of which 20 to 30 percent is lost as heat. But there is also enough waste heat in aluminum or glass production. And last but not least, excess electricity from wind or solar plants could be converted directly into heat and stored in the salt. For practical tests, the scientists put the TESIS (Test Facility for Thermal Energy Storage in Molten Salt) into operation at the end of 2017, in which 100 tons of liquid salt circulate.
The special thing about their system, which they call a thermal battery, is that it only needs one tank. Here, the lighter salt, which is around 500 degrees Celsius, floats above, while the cooler salt collects below.
9. Batteries according to electric eel concept
Animals also use electricity and use it when they need it. The electric eel Electrophorus electricus, for example, produces electrical currents with its body, which it stores so that it can be abruptly released during hunting or in defense. Researchers led by Thomas Schroeder from the University of Michigan have taken a closer look at the principle behind it to construct energy storage devices that may one day also be used in the human body.
In the electric eel, specialized muscle cells generate tiny voltage differences of just 150 millivolts by transporting electrically charged particles. Significant currents only emerge when thousands of such cells become active at the same time. For their replica, Schroeder and colleagues also rely on small units that generate weak electrical voltage. To do this, they produce gels made of biocompatible polyacrylamide, each with different electrical properties. For example, if you print them on two carrier foils and bring them into contact with each other, a tension arises.
The research team hopes to one day use such energy storage devices to drive small circuits that are built into sensors, for example as sensors. They could also serve as a power source in pacemakers and could theoretically even be recharged there using human metabolism.
10. Artificial atolls as energy islands
Building an entire island to store electricity – that is the visionary idea that the Danish architecture firm Gottlieb Paludan is pursuing together with researchers from the Technical University of Denmark. Their plan is to fill up a sand wall about ten meters high off the coast, so that a kind of artificial atoll is created. Electricity is stored on the same principle as in pumped storage power plants on land. If there is excess energy, water is pumped out of the middle of the island. When energy is needed, the inflowing water drives turbines and thus makes the stored power available again.
While there are hardly any suitable places for pumped storage power plants on land, there is enough space available in the sea. In addition, the energy can be generated on site: Wind turbines or solar power plants could be on the ring wall of the Green Power Island. It also makes sense to open up the newly gained place in the sea for industry or tourism. The architects have drawn up corresponding plans for China, India, Bahrain, Florida and the Kattegat off the Danish coast.
A disadvantage is the high construction costs of such an island – and the associated interference in nature. In Belgium, the government advanced a very similar project in 2015. Thousands of cubic meters of sand and gravel should have been moved for the electricity storage island in the Wadden Sea , with unclear consequences for the sensitive biotope. Ultimately, the plans disappeared into the drawer.