Combining component parts into hybrid systems to reap the benefits has always been an attractive prospect. In the past years, successful projects have come online for both solar-plus-storage and wind-plus-storage — the resiliency of battery energy storage combined with the financial boost from power generation.
So what does hybrid refer to in the world of energy storage? While the idea isn’t new, the technology is still in an early phase, only really being explored for grid applications in the past couple of years. Hybrid energy storage systems (HESS) can refer to several different types of set up; the point in common is that two or more types of energy storage are combined to form a single system.
There is no single energy storage solution that is ideal for every grid-scale application. As explained by Greentech Media, they “are typically designed for high-power applications (i.e., “sprinter” mode that provides lots of power in short bursts) or energy-dense applications (i.e., “marathon” mode that provides consistent lower power over long durations), and there are lifetime, performance, and cost penalties for using them in unintended ways.”
HESS typically combine both “sprinter” and “marathon” storage solutions to fulfill applications that have diametrically opposed requirements; e.g. fast response vs peak shaving. The potential for value stacking immediately jumps to mind.
Hybrid storage offers other avenues for cost reductions; two or more systems can share much of the same power electronics and grid connection hardware, reducing both upfront and maintenance costs. Three types of hybrid storage have started to appear past the pilot stage:
A utility in Bremen, Germany has contracted AEG Power Solutions to design and build a 20 MW hybrid battery/power-to-heat storage solution for frequency regulation. Storing energy as heat is much cheaper than storing electrochemically, which translates into a much smaller required battery capacity; AEG estimates up to 50% smaller.
Many arguments have been had as to which technology will ultimately prevail for the stationary energy storage — flow batteries or lithium-ion? Flow batteries’ low cost and long lifespan against the fast response and energy density of lithium-ion.
UK vanadium flow battery manufacturer RedT thinks the answer will combine them. In October 2017, it supplied a 1 MW hybrid energy storage system to Australia’s Monash University. RedT envisage a system where the vanadium-flow “workhorse” provides 70-80% of energy, while lithium-ion provides bursts of power for demand surges.
Similar in concept to the batter/battery HESS, supercapacitors or ultracapacitors can be used to provide fast responding bursts of electricity to complement the batteries that provide lower intensity, longer duration power. Ultracapacitors can survive an order of magnitude more cycles than most batteries, and have faster charging times.
In 2016, Duke Energy, the largest investor-owned utility in the U.S., installed a hybrid ultracapacitor/battery system which includes a 100kW/300kWh Aquion Aqueous Hybrid Ion “saltwater” battery bank. This technology clearly hasn’t reached the commercial maturity of the other hybrid types mentioned here, but it’s one to watch.
While the benefits are appealing, hybrid storage systems still face downsides. A combined system will inherently have more complex power management requirements — although the rapid advances in smart technology help assuage that worry.
More concerningly, current models such as Lazard’s Levelized Cost of Storage or costing research from the Rocky Mountain Institute do not yet have figures for such systems. In fact, there are so few examples currently in operation that accurate sample sizes are not yet possible. The business case must be proven during on an individual basis, with foggy future forecasting — excitingly challenging or unacceptably risky?
Will we be able to accurately forecast costs and revenues for hybrid solutions in the near future? Could HESS be the key to profitable value stacking? Is the increased complexity of a combined system a liability? Give your opinion at the Energy Storage World Forum Group on LinkedIn with our community of 12,300 members
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