Everyone’s familiar with the need for renewable energy sources as a replacement for the fossil fuels that are still in heavy circulation. But energy production is about more than just producing the energy you need right now.
Alongside fresh sources of energy production, innovative approaches to energy storage are also required — to keep generating energy even when it’s nighttime (and the solar panels are therefore not working) or it’s not blowing a gale (and therefore powering the wind turbines). The most well-known energy storage system is, of course, a battery.
Nonetheless, there are some other fascinating solutions that are being explored and, in some cases, widely used around the world. Here are five of the most innovative. You’ll almost certainly be hearing a lot more about them in the months, years, and decades to come.
The idea of storing energy through gravity sounds, well, kind of left field. But it may also be brilliant. Just like a coiled spring is loaded with energy that can be released on command, so too does gravity-based storage work in roughly the same way — only by using weights ranging from 550 tons to 5,500 tons that can be dropped from great height on command to spin a winch that feeds power into the electric grid.
It’s a concept that is currently being explored by some pioneering players in the field, including the excellently named Gravitricity, a U.K.-based company that is currently building a demonstrator system located in Edinburgh, Scotland. The company aims to have this completed by the end of 2020, coronavirus-related delays notwithstanding. After that, it plans to build a full-scale system that will be connected to the grid by 2023.
“The main advantage [of this approach] is a cycle life 10 times or more longer than batteries,” Charlie Blair, managing director of Gravitricity, told Digital Trends. “It is a mechanical system, so the degradation is minimal compared to chemical alternatives. Alongside that, the versatility in configuration means we can provide a range of energy storage responses, such as fast frequency response, or slower discharge cycles to even out the ‘peakiness’ in renewable generation.”
Riddle me this: When is an elevated reservoir like a giant battery? Answer: When it’s being used for pumped hydroelectric storage. In essence, this form of energy storage works a lot like the Gravitricity system described above. However, while that approach involves weights lifted in a shaft to transfer grid energy, in this case water is used in place of weights.
This highly effective — and widely used — approach to energy storage involves pumping water uphill into elevated reservoirs where it is stored in the form of gravitational potential energy. As required, water from these reservoirs can then be released so that it runs downhill and can be used to power turbines.
Pumped hydro has been employed in some measure since the 1890s. Making it even more sustainable will involve ensuring that the excess off-peak grid power used to pump the water to the reservoirs is also produced in a sustainable manner.
Perhaps the most science fiction-sounding energy storage solution on this list is cryogenic energy storage. In this particular approach to energy storage, electricity is used to cool air until it liquefies at -196 degrees Celsius (-320 degrees Fahrenheit). This liquefied air is then stored in a tank. When it is needed to prop up the grid, this liquefied air can be turned back into its everyday gaseous state — either by exposing it to ambient air or else by warming it up with wasted heat produced as a by-product of industrial processes. This gas can then be used to power turbines and generate electricity.
A variation of liquid air energy storage is compressed air energy storage (CAES). Offering another sustainable alternative to batteries, compressed air storage promises longer life expectancy, lower maintenance, and technical simplicity.
There are currently two CAES plants in the world: One based in Germany and the other in Alabama. Both store compressed air in underground salt caverns. (Researchers have also explored the possibility of storing compressed air underwater.) When it’s needed, the pressurized air can be heated up and expanded, then used to drive turbines.
Both of the current CAES plants burn natural gas when generating electricity, thereby making them effectively modified gas turbines. That could change in the future, though.
“Much development in recent years has focused on making CAES plants zero carbon,” Andrew Pimm, a Research Fellow focused on energy storage and renewable energy at the U.K.’s University of Leeds, told Digital Trends. “[This is done] by removing gas combustion from the process, and introducing thermal energy storage to raise the efficiency and ensure that moisture in the compressed air doesn’t freeze as the air is expanded when the system is discharging. CAES with integrated thermal energy storage is typically known as adiabatic CAES. An adiabatic process is one in which no heat is transferred between the system and the environment.”
One final potentially important large-scale energy storage technology is hydrogen storage. A crucial part of what is called the developing “hydrogen economy,” hydrogen storage begins with the conversion of electricity into hydrogen through the process of electrolysis. This hydrogen can then be stored in underground facilities like the salt caverns used for compressed air energy storage. As required, the hydrogen can be re-electrified for use in the grid.
While current hydrogen storage has a lower efficiency than other storage solutions, interest in it is also growing rapidly. And, as Pimm said, “People often get stuck on efficiency — what really matters is the overall cost of providing a reliable supply of electricity.”
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