By Susan Kraemer

Onsite energy storage and frequency regulation by wind farms is expected to be a growing requirement in wind farms in the US, just as solar has increasingly been pressured to supply its own storage to get utility PPAs.  

Founder David Marcus of ARPA-E award winner General Compression puts the current situation succinctly. “I can’t imagine running a data network without servers to store data. Or running a highway system without parking lots to store cars. And yet that’s what the grid has been trying to do.”

Like General Compression, both SustainX and Khosla-backed Berkeley startup, LightSail Energy improve on the low cost, low emissions and long lifetime benefits of classical Compressed Air Energy Storage (CAES).

“We believe that our storage technology can act like a dam in a hydro project,” says Marcus. “It can capture that energy, store it, regulate it and let it out in such a way that its useable and valuable for the production of electricity.”

FERC chairman Jon Wellinghoff describes General Compression’s storage as a technology that “can turn wind farms into coal plants.”

“We’re very pleased that FERC is going ahead and creating market frameworks for storage to add value on the grid,” says Richard Brody, Vice President, Business Development at SustainX. “Rule 755 is a big breakthrough for storage and will help bring it into the regulation services market.”

Travis O'Guin, business development analyst of LightSail Energy agrees. "We're still R&D, under the radar, but FERC Order 755 stands to be a significant boost to the economics of the LightSail Energy storage system due to the fast responding nature of our technology."

By contrast with traditional CAES, and General Compression, SustainX and LightSail Energy make pumped storage possible anywhere, in containers or pipelines. 

“The number of places on planet earth that we can do pumped storage are extremely limited,” Brody explains “New opportunities are limited and not necessarily near places where the electric load can benefit.”

Technology

The SustainX process is cleaner than traditional CAES because they don’t have to burn gas on the expansion cycle, because the process is 95% thermally efficient in both directions.

The thermal efficiency comes from compressing the air at near constant temperature isothermally. “With traditional compressed air you can get very large changes in temperature - up to 1,000 °C by going to the kind of pressures we’re going to - but we’re able to limit that temperature change by using water injection.”

The power unit, inside a building, compresses air and on the reverse cycle it takes the compressed air and generates electricity.

The compressed air is stored in underground pipelines like those built for transporting natural gas. “The piped storage is buried about a meter underground so you can farm above it or do other things,” explains Brody. You can run a utility line, so there’s not a footprint issue.” 

High energy, long duration storage

The company is aiming at high energy applications involving hours of storage, up to hundreds of megawatts. The ideal is pairing with wind, which typically is in need of a larger and longer time shift than solar.

“We believe we’re the first of the storage techs to do high energy, long duration in a way that’s not restricted by geology or requires the burning of fossil fuels,” Brody says. “So we think its disruptive.”

Non-geology-dependent mechanical ICAES storage - like LightSail Energy and SustainX are working on - should turn out to be more robust over time than battery storage.

“For large numbers of megawatts for many megawatt hours batteries are intrinsically just too small to be practically useful,” Brody points out. “You need tens of thousands of cells to do anything meaningful in size, and the complexity and the vulnerability of the batteries to thermal issues, the limitations on cycle and calendar life and the decline in the capacity of the batteries all produce a product that doesn’t meet the need.”

“In bulk energy storage we’re able to do things that electrochemical technologies cannot do because they have inherently limited cycle lives,” he explains. The lifetime maintenance costs are similar to other mechanical systems.

Value to wind farms 

Steven Chu, the U.S. Secretary of energy has said that it will be impossible to get more than 20% renewables on the grid without storage. Yet it is not a simple matter to ascribe a dollar value to the service “in terms of determining the value for kilowatts generated or kilowatt hours stored on the grid,” says Brody, because of the different mix of grid assets, owners, taxes and regulations in each electricity market.

“In some markets there might be a very low value for stabilising the wind,” he explains, “because the grid that they’re generating into has high excess capacity, or very high mandates for renewable energy.”

“In other areas, grids are much more constrained, and to be effective, wind needs to be much more schedule-able. In that case, the cost of that energy (the value of the storage) is much higher.”