Coal-fired power plants have been the backbone of US electricity production for decades, but 25% of them will be retired by the end of this decade. Some of their replacements will be fueled by LNG. Others will make way for a disruptive technology that can “switch from charging to discharging in less than 1 second” and has a “significantly higher capacity use factor.” Paul Siblerud, VP Marketing at ViZn Energy Systems, explained where battery storage will provide most peaking capacity in the future.
His company just commissioned a study, entitled GUIDE TO PROCUREMENT OF FLEXIBLE PEAKING CAPACITY: ENERGY STORAGE OR COMBUSTION TURBINES?, that predicts battery storage will take over many of the functions currently performed by peaker plants. They already outperform conventional plants in several areas, but need to be more competitively priced.
Chet Lyons wrote that, “Storage will be a disruptive winner against simple cycle gas-fired CTs at that point, assuming a typical mid-range cost for competing fossil-based CT generation resources.”
As the scale of ViZn Energy Systems’ manufacturing increases, the cost per unit will drop. By 2017, they expect the cost of their 4-hour battery storage unit to be roughly competitive with mid-ranged combustion turbines. By 2018, ViZn should be competitive with a simple cycle peaker.
“We have a shot at becoming the lowest cost solution,” said Siblerud. “We are not expecting to displace all peaker plants, but our strong play is when you have a feeder line for a utility or a microgrid that has a fair amount of renewables tied to it.”
Lyon’s report mentioned California’s adoption of large amounts of renewable energy, which would require an additional 4,600 MW of capacity. Lyons wrote that the “limited speed” of fossil fuel powered plants is “less suitable for … stabilizing distribution circuits negatively impacted by high penetration solar PV. [However] … with the availability of new energy storage technologies, in particular flow batteries, utilities have the means to economically meet the increasing need for flexible peaking capacity using 2 to 6 hours of storage.”
“In those circumstances, battery storage is a viable alternative to peaker plants,” said Siblerud. “Flow batteries, specifically alkaline based flow batteries like ours, can do 3 to 4 hours,” he said. “That’s the key peak time that you usually have to deal with and now you can do that economically and safely. We have an opportunity to take some of that market.”
Using a 30 MW wind farm as an example, he said generation doesn’t usually “just drop to 20 MW. It’s pretty messy on its way down and vice versa on its way up.” There are usually peaker plants idling for occasions like this and they can usually ramp up in 3 to 5 minutes. Then you kick on the other plants and that can take up to 20 minutes.
“You are burning a lot of fossil fuels” to keep this system going.
“That is an area where batteries are superior,” said Siblerud. “They are available in a millisecond, or as fast as the inverter can switch.”
Can battery storage shave off enough peak demand so that utilities no longer have to buy peaker plants that are only needed a few times a year?
“Distributed networks, in general, have the potential of an integrated battery storage for peak shaving. In many cases, a properly sized battery can handle the load very nicely,” said Siblerud. “However, in many projects, it is economically more viable to run a combination of peaker and battery.”
If everything was working in concert, utilities could shut down their “chillers” when there is a peak. This could drop the demand by a third, or whatever is necessary to stabilize the grid. After the peak was over — in maybe fifteen minutes — they could turn the chillers back on.
“Unfortunately, right now there is not a lot of coordination between load and generation,” said Siblerud. “We are having to create little distribution networks, microgrids, that just handle their own visibility.
“That’s a good start, but there are some good options between batteries that have faster response and longer energy capacity in concert with peaker plants.”
Flow batteries like ViZn Energy Systems’ zinc/iron redox flow battery, are designed for applications where they might do two or more full discharge cycles a day.
“A flow battery needs to be used. It has some parasitic losses intrinsic to the battery itself,” said Siblerud. “The chemistry is constantly flowing. You need pumps to pump this chemistry through. If that battery just sits there charged through a seven day period, you’re going to have losses on the system. A major benefit of flow batteries is that there is no material loss if you are running a punishing duty cycle or deep discharging all the way down to a zero state of charge. You can make a complete charge or discharge as many times a day as you want. A flow battery can run at full-power for 3 to 4 hours or nominal power for 8 hours or more. It likes to be used a lot and in those applications is far superior to UPS or back-up systems.”
Lead acid or lithium-ion batteries are well suited to handle periods of peak demand. They typically cannot discharge as deeply as flow batteries or be charged up and down 3 or 4 times a day, however, and they require thermal controls and protection. However, they can also sit idle for long periods without losing much charge.
It is difficult to give a rough figure for the amount of energy companies can save using battery storage to shave peak demand. Depending on their individual circumstances, he has seen it range anywhere from 10% to 60%.
Battery storage is currently more expensive than peaker plants, though it is also faster, environmentally sustainable, and more efficient for certain applications.
“At the end of 2016-2017, when we get down to the $250 kWh range, we will be very competitive and in some cases replace peakers completely,” said Siblerud.
All graphs taken from GUIDE TO PROCUREMENT OF FLEXIBLE PEAKING CAPACITY: ENERGY STORAGE OR COMBUSTION TURBINES?; headshot is Paul Siblerud, VP Marketing at ViZn Energy.