Hybrid battery systems: The best of both worlds

By Published: Wed 18 Sep 2019 for Engerati
Lithium-ion batteries make up the lion’s share of installed non-hydro storage systems so far, but flow batteries have some benefits that can provide complementary services when the two are co-located.

“By combining the two technologies, you can utilize the relative strengths of both,” says Ed Porter, Commercial Director, redT energy. “There will never be one single technology when it comes to energy storage.”  For example, a 1MWh lithium/vanadium hybrid energy storage system installed by redT in Melbourne, Australia, is at the heart of a pioneering net-zero microgrid.

RedT energy’s machines use vanadium redox flow technology to store energy in liquid form, “like pumped hydro in a box”. This technology relies on the ability of vanadium to exist in four different oxidation states, each of which holds a different electrical charge. They don’t degrade with use so are ideally suited to heavy use stationary applications, and are considered 20-year infrastructure assets, rather than short term, disposable batteries.

The flow machine element is designed to be the ‘first port of call’ for the system essentially picking up the heavy utilization work and able to store up to 6 hours of excess solar power or run through 3-4 cycles per day. The lithium battery then covers the final power requirements – minimizing the amount of times you need to call on them, whilst maximizing the use of the heavy-cycling asset, the flow machines.

The key economic value of flow machines comes from the ability to run them flat out all day every day, Porter says. Whereas you might typically see a lithium battery providing only a single service such as firm frequency response (FFR), flow machines are set up to deliver multiple revenue and savings streams, which are then ‘stacked’ together. For example, a flow machine coupled with solar generation and an export grid connection could perform the following:

  • Store excess solar power and discharge this into evening peaks, reducing site electricity costs
  • Provide FFR (or other ancillary services) to the grid to generate revenues for the site
  • Engage in wholesale market trading to take advantage of arbitrage opportunities in the energy markets
  • Provide back-up for essential site loads to improve resilience

While lithium batteries are compact, and cell costs have come down significantly, the marginal cost per cycle for flow machines is nearly zero as the system does not degrade. The electrolyte in flow machines is about 70% water, which greatly reduces the potential for thermal runaway where heat increases in a positive feedback loop or fires. Vanadium is more abundant than common metals like copper, zinc or tin and can be recycled for use in another machine after the system reaches the end of its life.

As more renewable, non-synchronous generation comes online in favor of older, thermal power plants, the level of system inertia will decrease. RedT’s flow machines can help provide synthetic inertia and were the first vanadium flow battery systems to qualify for National Grid’s dynamic FFR market in the UK. Their machine in Dorset is connected via Open Energi’s AI-driven Dynamic Demand 2.0 platform. “Using cutting edge technology like this allows our systems to optimize its activity second by second and respond to new opportunities that present themselves on the electricity markets,” Porter says.

RedT will soon deliver the first of its new 3rd generation machines, to Anglian Water in the UK. “We’re very excited to get it out in the field and show the market what it can do,” Porter says.

RedT is currently engaged in activity relating to a proposed merger with US-based vanadium redox flow battery firm Avalon, which will give it access to North American and Asian markets as well as its existing footprint in Europe, Africa and Australia. “There are a lot of obvious synergies between our two businesses. Together, we have the potential to become a truly global player in the flow battery space who can compete with the big lithium-ion giants like BYD and LG Chem,” Porter tells Engerati.

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