China will soon be home to the world's largest battery. The massive power facility will provide peak shaving, grid stability, emergency power, and load management to the Dalian peninsula in northeastern China.
According to the US Department of Energy, the largest battery-based energy storage system currently in operation is a 50 MW (300 MWh) sodium-sulfur battery in Japan. The largest one in development is the 100 MW (400 MWh) peaker plant in California, which will use a battery technology that's yet to be determined. And now, UniEnergy Technologies announced a partnership with Rongke Power, which will build and deploy a 200 MW (800 MWh) energy storage system featuring Rongke Power vanadium flow batteries.
Flow Battery Technology
Unlike lithium-ion and other types of "enclosed" batteries, in which all the chemical elements are held inside the battery itself, flow batteries use a pair of external tanks to store the electrolytes and slowly pump the electrolytes into a stack of electrochemical cells where the chemical reactions create electricity.
The benefits of this design are numerous: first, the storage capacity can be scaled up simply by using larger electrolyte tanks. Second, and perhaps more important, is that under a fault condition, the flow can be stopped, preventing a catastrophic thermal event. Third, flow batteries can be recharged over 15,000 times, compared to just 1,500 cycles for Li-ion batteries. The initial cost of flow batteries is around $300 - $500 per kWh, which is comparable to Li-ion.
In general, flow batteries have a round-trip efficiency of 70% to 80%; Rongke claims that theirs are at least 75% efficient, which is less than the 85% round-trip efficiency that's typical of Li-ion batteries. On the other hand, flow batteries can withstand 100% depth of discharge (DoD) without degrading their performance or shortening their lives. Li-ion batteries can tolerate a deep discharge now and then, but repeatedly going beyond 50% DoD will decrease their storage capacity and curtail their lives.
Flow batteries have trade-offs, of course, such as the need for two pumps to generate electrolyte flow. The pumps add complexity and moving parts which are susceptible to failure, and they use a small amount of power. Nonetheless, for stationary large-scale storage applications, flow batteries are gaining acceptance in the field.
Rongke's modular flow battery storage systems are housed and delivered to the site in standard sized shipping containers. The largest model is a 20 MW (80 MWh) battery, so the entire energy storage system for the Dalian project will use ten of these units. The flow batteries can operate within a temperature range of 10C to 40C (50F to 104F), so the containers include climate control, allowing them to function even when the outside temperature drops to -30C (-22F).
Peak Shaving
When the facility is fully operational in 2020, officials expect it to provide up to 8% of the region's peak power, reducing cost and decreasing stress on the grid. The local utility will purchase energy during inexpensive off-peak times and use that stored energy during costly peak demand times.
Emergency Power and Black-Start Capabilities
Adverse weather conditions cause frequent power outages in the Dalian area. Occasionally, a storm will force a power plant to shut down its generators. Restarting a generator - known as a "black start" - requires a source of electricity to energize the electromagnetic field coils inside the generator. Portable generators (like the one in my garage) often have a "pull start" cable; automobiles use a starter motor powered by the car's battery. Power plants usually get this energy from the grid, but when the grid is down they need a backup, and it's usually in the form of a small generator. But why use a generator when there's an energy storage unit on hand? Indeed, one of the services provided by the Dalian energy storage system is black-start capability.
Support for Renewable Energy
With an installed capacity of over 145 GW, China is a world leader in wind energy and is planning to increase its renewable energy production. However, the country's limited distribution network makes intermittent sources a less desirable electricity option. In order to achieve its renewable energy goals, China plans to expand energy storage in parallel with its wind and solar initiatives.
In 2012, energy storage was a $200M industry. By 2017, it could grow to $19B - almost a 100-fold increase. Li-ion batteries seem to be the choice for behind-the-meter storage, largely due to their portability and zero-maintenance. Do you think flow batteries will dominate the grid and microgrid storage market? Please comment below.
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