Long-Term Energy Storage: What are the Options When Lithium-ion Falls Short?
Lithium-ion batteries are best positioned to meet the demand for energy storage over the next five to 10 years, but in the long run, other battery storage technologies will be needed for long-term energy storage and larger- scale applications.
That’s the word from Lux Research, which recently outlined up-and-coming battery storage technologies in a teleconference.
Right now, the need for storage is prompted by the growing use of renewable energy on the grid, said Chris Robinson, an analyst for Lux.
The amount of wind and solar on the grid has doubled, he said. Half the electricity added last year was wind or solar, driven largely by cost reductions. “Even just in the last 15 years, we have seen a big drop in the cost of solar modules. We don’t expect this trend to change,” he said.
However, the large amount of renewable energy being added to the grid is causing grid instability, Robinson said. With solar, there’s instability in the morning when there’s often too much solar coming online. And in the evening, the grid becomes unstable when the amount of solar decreases.
“Energy storage can play an important role,” he said.
The use of Lithium-ion batteries is growing quickly because prices have dropped due to increased economies of scale and larger production capacities. But Lithium-ion batteries can’t solve all problems, and are often not appropriate for large-scale and long-duration applications, he said.
For example, a large solar project in China capable of powering 2,000 homes would need massive-scale storage, in the gigawatt-hour range, a task not suitable for Lithium-ion batteries, Robinson said.
Intermittency, caused by, for example, cloud cover over solar arrays, also creates a need to store energy for longer time periods.
“We need to store energy for longer days; maybe you’re operating a wind farm and have some some cloudy days or have rain for solar. You need tens of hours to days of storage,” said Robinson.
To provide long-term energy storage, Lithium-ion is often not the best choice, according to Robinson.
“You can, and the industry does, optimize different cells for power and energy–for hybrid or full-electric vehicles. But you can’t extend this to tens of hours or even days (with Lithium-ion),” he said.
It’s expensive to try to scale Lithium-ion batteries to meet this scenario, Robinson said.
Pros and cons of long-term energy storage alternatives
Robinson described the advantages and disadvantages of a number of storage technologies that are better suited to meet large-scale, or long- duration storage needs.
Flow batteries, for example, allow for the decoupling of power and energy and can utilize different materials, including vanadium. The material costs are lower, Robinson said, and the batteries are less complex than Lithium-ion.
“Flow batteries decrease in costs as you increase in duration. You can add larger tanks and more fluid, but compared with Lithium-ion, after four hours flow batteries can be more appealing. They’re also effective in larger system sizes,” Robinson said.
Zinc-air batteries, he said, offer different advantages. They have low material costs, a high degree of flexibility, can stay at a zero state of charge with no degradation, and are most cost-effective after eight hours of storage. “But you can’t put them at very high power,” said Robinson.