Regenerative Fuel Cell Promises A Low-Cost HBr Battery Energy Store

A hydrogen bromine-based battery energy storage solution shows promise for long duration storage.
Published: Thu 23 Oct 2014

In concept it is a regenerative fuel cell but in operation it is a battery – this is the new hydrogen bromine (HBr) energy storage solution from Israel-based storage company EnStorage.

The solution, which is set to scale up to demonstration scale, has the potential to offer a low-cost, long-life system for long duration (>4-hour discharge) grid storage for utilities and behind the meter storage for large commercial and industrial facilities, necessitated by the integration of increasing levels of renewable energies.

“It’s the most cost-effective flow solution there is, based on the raw materials,” comments the company’s vice-president of business development Itai Karelic. [Engerati-Israeli Cleantech - Smart solutions to global challenges]

HBr battery solution

In concept the HBr solution is very straightforward, Karelic explains. HBr is electrolyzed to form HBr3 and H2, which is stored in a separate tank. During discharge, H2 is consumed, releasing energy and converting the HBr3 back to HBr.

“There is only one electrolyte tank and pump in a self-contained system with no by-products, and no active components in the hydrogen loop” says Karelic. Another unique feature is that the electrolyte flows in only one direction, whether charging or discharging, enabling instantaneous switching between the two states.

EnStorage is not the first company to investigate the use of HBr as a battery solution, but its breakthroughs have brought it to a level that should be cost effective. “There are essentially two innovations in our solution,” says Karelic. “One is on the R&D side, with the proprietary membrane and catalyst and other stack components that we have developed. The other is on the mechanical side with electrochemical compression of the hydrogen, avoiding the need for a compressor in this loop.”

Taken together these developments contribute to a system of reduced complexity and increased safety. “And this makes a big difference to the efficiency and final cost of the battery.”

O&M is low with minimal requirement to replenish the hydrogen once a year to maximize the storage capacity. “There is no perfect way to store hydrogen and there will always be a little loss,” Karelic points out. “But it’s not significant and may contribute to a reduction of a few minutes in the storage capacity.”

The nature of HBr also makes it suitable for use in all climates from very hot to very cold, and with no by-products the solution is potentially applicable for use anywhere in the world.

HBr battery demonstration

So far a 50kW prototype of the battery offering 2 hours of storage has been completed. This is now being scaled up to a 150kW, 6-hour demonstration with AREVA and Schneider Electric, with support from the KIC InnoEnergy FlowBox project. [Engerati-New HBr Flow Battery Under Development]

“These are companies with the know-how and resources that can help us to develop the supply chain. Scaling up can be very costly from a production point of view,” Karelic comments.

From a technological perspective, the process should be fairly straightforward. There is little restriction on the tank size, although a very large tank may take a year to manufacture. “We are currently playing around with the numbers to determine where we would move from a containerized to a fixed installation. For smaller installations up to a few megawatts and hours of storage, it makes sense for these to be containerized as the production process can be semi-automated and what one loses on scaling up one gains on automation. At some point for larger installations it will make more sense to build a plant than to have a large number of containers in one spot.”

HBr battery storage applications

Karelic says that typical applications of such a battery system would include:

● Levelling renewable generation output

● Storing power during weak demand

● Providing back-up power during flat spells

● Providing power during peak times

● Distributing storage across the grid and microgrids through a modular system.

As an example of a long duration storage application, Karelic cites a modelling study for a US Virgin Islands desalination plant. The 20-year cost of the lowest cost PV/wind/storage solution is US$22.5 million, which compares with US$42 million for the current diesel generation.

“It’s a no-brainer that a distributed storage application makes sense in such a context,” says Karelic. “Energy storage has focused mainly on power applications, but as more and more renewables come on line the need for longer duration energy storage becomes apparent. This is what we were forecasting when we started to develop the system back in 2008.