Generating electricity through clean energy sources is one thing, but storing output for later use is another. How can the country find an ideal energy storage solution?
What Is the Ideal Energy Storage Solution?
The ideal energy storage solution is predictable, dense, efficient, convenient and scalable. For the longest time, fossil fuels have met all these criteria. The downside to these prehistoric repositories of energy is that extracting and burning them have environmental consequences, which have become too severe to ignore.
Some renewables — such as wind and solar — are intermittent, while the power plants needed to harness more reliable ones, like geothermal, often face geographical restrictions. Pumped storage hydropower, accounting for 93% of all utility-scale energy storage in the U.S., only has 43 facilities since it’s viable only in areas that can hold large bodies of water at different elevations.
Finding the best solution requires understanding the largest challenges facing the energy industry.
What Are the Biggest Challenges in Renewable Energy Storage?
The U.S. Department of Energy recognizes four critical barriers to widespread renewable energy storage adoption — industry acceptance, regulatory environment, safety and performance and cost competitiveness.
To become ready for prime time, a renewable energy storage technology must:
- Demonstrate its commercial viability to attract capital from investors.
- Enjoy regulatory certainty.
- Prove its dependability when integrated into a more extensive network and compatibility with utility software.
- Be cheap enough to avoid inflating the cost of electricity.
Hitting the above criteria is exceptionally challenging, which is why the usual renewable energy storage issues persist. Nevertheless, some innovations show a ton of promise.
What Are the Most Promising Renewable Energy Storage Solutions?
The most promising renewable energy storage solutions are the following.
1. Gravity-Based Systems
Lifting heavy objects hydraulically into the air using electrical pumps can store large quantities of potential energy. It’s similar to how a spring holds energy when you stretch it. During weak renewable energy generation periods, lowering them releases kinetic energy that can go into the grid when needed.
It’s a fascinating concept, although this storage method has limited capability. It’s perfect for use cases needing to store energy for less than a day. Still, a gravity-based energy storage system’s capacity can go up to 10 gigawatt-hours, rivaling a large pumped storage hydropower facility.
2. Sodium-Based Batteries
Lithium has rightfully dominated the commercial battery world since the 1990s, but sodium may emerge as a better solution.
Lithium reigns supreme because it makes efficient, lightweight, compact, portable and long-lasting batteries. Lithium-ion batteries can reach up to 3.5 volts — 200% more powerful than their closest alternatives. Regarding storage, they can hold about 300 watt-hours per kilogram, which is four times greater than other batteries.
The problem with lithium is unsustainable. Its global estimated reserves amount to only 26 million metric tons, which can run out quickly once electric vehicles (EVs) go mainstream. Learning to recycle lithium is a good option, but switching to sodium as soon as possible is better to evade impending shortages.
Like lithium-ion cells, sodium-ion ones can reach practically similar voltages. Compared to lithium, sodium is more abundant. It’s the sixth most common element on Earth’s crust, so adopting it for commercial battery installations can avert material shortages.
Regarding energy density, sodium-ion batteries are where lower-end lithium-ion ones were a decade ago. Estimates predict that they will be able to store about 150 watt-hours per kilo by 2025. A Chinese automaker is confident enough in the technology and plans to produce the world’s first sodium-ion battery-powered EV.
Moreover, researchers at the University of Sydney have improved the sodium-sulfur (Na-S) battery’s capacity and longevity. This Na-S battery iteration promises to store energy four times as much as lithium-ion batteries. Its primary material comes from seawater, which can dramatically reduce battery production costs.
3. Iron Phosphate Batteries
Cobalt plays a vital role in lithium-ion batteries. This bluish-gray metal contributes to energy density, ensures voltage stability, slows capacity degradation, and accelerates charging speed.
However, cobalt reserves are scarce, potentially running out by 2050. About 70% of its mining occurs in the Democratic Republic of the Congo, where unethical working conditions are rampant. Even if cobalt mining activities become less hazardous, having a centralized source of such a critical battery material makes EV battery production highly prone to supply-chain issues.
Iron phosphate batteries are the key to becoming less dependent on cobalt. Compared to other lithium-ion battery chemistries, the one based on iron phosphate offers less energy density.
Still, it’s efficient enough for shorter-range vehicles. Embracing iron phosphate batteries can neutralize cobalt supply risks, freeing up more scarce resources for higher-density chemistries needed for longer-range EVs.
4. Thermal Energy Storage Methods
Thermal stores are mediums that absorb energy and release it when needed. Materials have unique thermal properties, so they can retain power for heating and cooling for various amounts of time.
Sensible thermal energy storage is when you raise or lower a medium’s temperature. The latent method occurs when a material changes phases while its temperature remains constant. Thermal energy storage can also involve a chemical reaction.
Thermal energy storage systems can be centralized and decentralized. Massive industrial facilities and concentrated solar power plants can leverage centralized systems.
On the other hand, residential and commercial properties usually benefit from decentralized ones, storing solar energy to heat water and space. Thermal energy storage systems may be different. Buildings that implemented them saw a 40% peak load reduction, leading to considerable energy bill savings.
5. Renewable Fuels
Hydrogen and methane can be instrumental in helping utilities store excess power from solar panels and wind turbines. Converting renewable energy into either fuel is an excellent way to keep carbon-free power for later use indefinitely.
Proton-conducting fuel cells can turn hydrogen into a utility-grade battery and feed electricity to the grid when needed using a single set of catalysts. Before, two separate devices performed these jobs. Electrolyzers split water into oxygen and hydrogen gasses with electricity, while fuel cells transform hydrogen back into electricity.
Although proton-conducting fuel cells still have room for improvement regarding material strength and durability, they’re already the most efficient electrochemical energy conversion devices.
Shipping container-sized methanation plants use renewable energy to convert biomass gasification outputs — carbon dioxide, carbon monoxide and hydrogen — into methane. It becomes transportable through existing natural gas pipelines to generate electricity. Although burning methane emits greenhouse gasses, biomass gasification processes can capture them.
This novel methanation concept works best when electric and gas grids link. However, it’s scalable enough for smaller facilities to work in tandem with wind and solar farms in a decentralized manner.
A More Sustainable Future Is in Store for the World
Storing green energy proves to be more problematic than generating clean electricity. Inefficient and infeasible energy storage systems have slowed the world’s shift to renewables, but progress is picking up pace.
While the above concepts are important steps, no single innovation can solve everything. It takes a combination of ingenious technologies to plug the various gaps in renewable energy waste for good.