Hybrid Energy Storage System Combines Ultracapacitors and Batteries

Investment in grid-level energy storage is expected to triple over the next five years, with a multitude of players delivering a wide variety of technologies, each with its own benefits and drawbacks. Duke Energy recently installed a hybrid energy storage system (HESS) that combines high-capacity batteries with fast-responding ultracapacitors. The pilot project will provide peak demand response, load shifting, and support for a utility-owned 1.2 MW photovoltaic array.

Hybrid Energy Storage System (HESS)
Other than fuels, batteries offer the highest energy density of any energy storage system. They’re also quite versatile since they’re easily scalable and, unlike pumped hydro or compressed air energy storage, they don’t depend on local geography. On the other hand, batteries take a while to charge, they have limited lifespans, and they can’t deliver or absorb large power surges.

Ultracapacitors (or supercapacitors) can charge quickly and survive ten times the number of cycles that most batteries can handle. Ultracapacitors’ quick response times allow them to take in or dish out substantial bursts of power, but for a given size/weight, ultracapacitors can’t pack nearly as much energy as batteries can.

While batteries are the marathon runners of energy storage, ultracapacitors are the sprinters. Duke Energy decided to employ both in its HESS, pairing a 100kW/300kWh Aquion Aqueous Hybrid Ion “saltwater” battery bank with a 277kW/8kWh Maxwell Technologies ultracapacitor module.

Battery
The Aqueous Hybrid Ion (AHI) battery is maintenance-free like a Li-ion battery, but according to Aquion, the AHI is more robust than Li-ion. For example, the AHI can operate over a wider temperature range (-5°C to 40°C), it’s not susceptible to thermal runaway (even when overcharged), and it is made from recyclable and sustainable materials. AHI batteries don’t have quite as much energy density or power delivery capabilities as their Li-ion competitors, however. The 100kW/300kWh battery bank can power about 80 homes for three hours.
Read full article at Engineering.com