November 22, 2021
The 5 Most Promising Long-Duration Storage Technologies Left Standing
Long-duration energy storage holds great potential for a world in which wind and solar power dominate new power plant additions and gradually overtake other sources of electricity. Wind and solar only produce at certain times, so they need a complementary technology to help fill the gaps. And the lithium-ion batteries that supply 99 percent of new storage capacity today get very expensive if you try to stretch them out over many hours.
The problem is, no clear winner has emerged to play that long-duration role. Here at Greentech Media, we’ve spent years covering the contenders, which range from quixotic defiers of the laws of physics to understated, scientifically minded strivers. The makeup of this roster has fluctuated to the rhythm of bankruptcies and new investments.
Plenty of options technically “work.” The question is, do they work with an acceptable price point and development cycle, and can the businesses providing them stay afloat long enough to actually prove that? That last step has been hard for companies to fulfill, insofar as in previous years there were practically no places to actually sell this stuff.
1. Pumped hydro
Midcentury modern design is hot again, so why not midcentury storage technology? This gravity-based concept physically moves water from a low to a high reservoir, from which the water descends, when needed, to generate electricity. This dates from way before lithium-ion’s heyday and still provides some 95 percent of U.S. grid storage, according to the U.S. Department of Energy.
Once built, these systems boast a very low cost of storage, and they hold truly massive amounts of energy compared to even the world’s biggest battery. The problem is that it’s extremely difficult to build new pumped-hydro storage plants, due to the permitting implications of large water-based infrastructure and recent difficulty in executing massive construction projects in general.
The new school of pumped hydro focuses on isolated reservoirs that don’t disrupt river ecosystems; this simplifies permitting, but projects still face a decade-long development timeline and billion-dollar price tags.
2. Stacked blocks
What if, instead of using batteries or pumping water, you stored surplus power by automating a six-armed robotic crane to stack thousands of purpose-built, 35-metric-ton monoliths into a Babel-like tower and drop them down again when you needed to release the power?
The idea arose from iterating on pumped hydro’s gravity storage, but adapting it for greater geographic diversity and to avoid the limitations described above.
3. Liquid air
Highview Power doesn’t consider itself a startup anymore. After 15 years of refining its technology, this U.K.-based company has moved from running pilots to developing large-scale plants.
The company’s mechanism cools down air and stores it in pressurized above-ground tanks. The compression equipment and power generators come from established supply chains in mature industries. The technological innovation here is using them for grid storage.
Highview’s leaders realize they need to self-finance early projects to show the market that they work. They raised $46 million from Sumitomo Heavy Industries in February to do just that.
4. Underground compressed air
Humans have stored power in underground caverns for decades: A plant in Huntorf, Germany dates from 1978, and Alabama’s McIntosh plant opened in 1991. But those pioneering projects failed to kick off a trend. Several startups tried and failed to improve on that technique.
The basic concept is to use excess electricity to pump compressed air into a suitable underground formation that acts like a giant storage tank. Releasing the pressurized air allows the plant to re-generate electricity when needed.
5. Flow batteries
Flow batteries have been considered promising for as long as anyone’s thought about long-duration storage, but that hasn’t given them many advantages in the marketplace.
The archetypal flow battery company is either insolvent or still aspiring to its first substantial commercial deployment. But a lot of flow battery scientists swear by the technology, which circulates liquid electrolytes to charge or discharge electrons via redox reaction.