One of renewables’ biggest challenges is that their peak power generation doesn’t always align with when people use the most electricity. Storage is the answer to that problem, but renewables also have a unique set of energy storage system requirements.
Saving excess energy for later use seems straightforward enough, but it’s hard to do at scale sustainably. Lithium-ion batteries are a popular option but depend on rare metals and harmful mining practices. Some alternatives are eco-friendly but not efficient enough to support an entire electrical grid. As a result, some of the most promising emerging storage solutions may not be what you’d expect. Here are five of the best ideas.
- Pumped Hydroelectric Storage
Pumped hydroelectric storage — or, more simply, “pumped hydro” — is the most common way to store electricity in the U.S. It accounts for 94% of all energy storage capacity in the nation and has been around for decades.
Pumped hydro works by using surplus electricity to pump water to a reservoir. When people need more energy, water flows down from that reservoir through a turbine to generate electricity. Since all the motion in this system comes from water and gravity, it doesn’t produce any greenhouse gas emissions.
The biggest downside to pumped hydro is that it doesn’t work everywhere. It takes a lot of water to generate a meaningful amount of power, so it requires lots of space and is better for large-scale applications than microgrids.
- Hydrogen
Hydrogen fuel cells are another promising solution to renewables’ energy storage system requirements. This starts with using excess renewable power for electrolysis, which converts water into hydrogen. Then, fuel cells convert that hydrogen back into electricity when needed.
The only emissions from fuel cells are heat and water, so hydrogen storage is carbon-free. Fuel cells also convert energy more efficiently than batteries, making them a better storage solution, especially in applications that don’t generate as much electricity. Similarly, hydrogen is remarkably energy-dense, so it can store a lot of power in a relatively small space.
Some people worry about hydrogen storage because hydrogen gas is highly flammable. However, converting it to ammonia during storage mitigates that problem. The biggest obstacle is just a matter of cost. Right now, fuel cell technology is expensive, but that will change over time.
- Sodium-Ion Batteries
Lithium-ion (Li-ion) batteries — the kind that power EVs and most handheld electronics — are another popular storage medium but a controversial one. The technology works well, but lithium mining takes a huge toll on the environment. Sodium-ion (Na-ion) batteries have recently emerged as a promising alternative.
Sodium isn’t as rare as lithium, and mining it isn’t as damaging. Sodium-ion batteries are also much more affordable. The average Li-ion battery costs $137 per kilowatt-hour (kWh) of capacity, while a Na-ion battery costs just $40 per kWh.
Na-ion batteries are less energy-dense than Li-ion, but they’re also less prone to thermal runaway, which could help them last longer with more development. As this technology improves, it could be a helpful, low-cost way to expand renewable energy.
- Compressed Air Energy Storage
A more surprising way to meet energy storage system requirements is through compressed air. Compressed air energy storage (CAES) systems use surplus electricity to compress air and store it underground. That pressurized air can then power wind turbines for carbon-free energy when needed.
CAES can hold a much higher amount of energy than other storage methods like pumped hydro because you can compress a lot of air into a tiny space. Air compressor technology has also been around for a long time, so modern systems are both effective and cheap.
Installing CAES systems can be difficult, and it’s not possible in all areas. However, where it is possible, it’s eco-friendly, efficient and affordable, making it a tempting solution.
- Thermal Energy Storage
Thermal energy storage (TES) works similarly. Instead of using compressed air, it uses heat. Electricity either generates heat or chills a substance, and then the system stores it before using it for heating or cooling during peak energy times to reduce electrical consumption.
Home heating and cooling is one of the best examples of TES’s potential. Imagine a home used a TES system to cool a refrigerant with electricity during low-consumption times. Then, during peak consumption hours, the TES system circulates that already cold refrigerant through the house to cool it without using any more energy.
TES’s applications may be more limited than other storage options, but this category is a big one. Heating and cooling account for 46% of home energy use on average, so these changes go a long way.
Renewables Need Energy Storage Systems
The world needs to switch to renewable energy sources, and renewables need better storage to work effectively. These energy storage system requirements may be tricky to navigate, but there are plenty of options out there.
These five storage techniques are just a sample of the eco-friendly ways power grids, businesses and consumers can hold on to excess renewable energy. As they become more accessible, renewables will become a more viable option for people across the globe.
By Emily Newton, an industrial journalist and the Editor-in-Chief of Revolutionized
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