Battery technology has come a long way since the days when your granddad had to periodically peek under the hood to add water to his lead-acid battery.
Even a decade ago, the idea that battery banks would soon be “smoothing energy flow” between the electricity produced by wind and solar farms and the utility grid was almost inconceivable. But batteries are now being harnessed to regulate and store the inherently variable energy output from wind and solar projects worldwide.
In addition, batteries are increasingly being used for off-grid applications including everything from stabilizing unreliable grids in developing nations to offering independent-minded Europeans and North Americans an alternative to total reliance on utilities.
By some estimates, energy storage could help stem billions of dollars worth of wasted energy annually; with the global smart-grid market expected to top $400 billion by 2020.
“Renewables are reaching a point where there’s substantial penetration on the grid,” said Haresh Kamath, EPRI Program Manager for Energy Storage and Distributed Generation in Palo Alto, California. “California wants 1.3 GW of energy storage on the grid by 2020.”
Kamath notes that New York, New Jersey and the Canadian province of Ontario have declared similar goals.
Batteries are the key to it all. Battery capacity can help meet the needs of a renewable-energy powered grid at any given point.
A 1-MW/2.8-MWh Grid Storage Solution installation in Japan. The project was commissioned in March 2014 and is being used for peak shaving and demand charge management. Credit: A123 Energy Solutions.
In their simplest form, batteries convert electricity into chemical energy and store it. In an ordinary car battery, lead-based plates are submerged in an electrolytic mixture of water and sulfuric acid. This reactive mixture releases electrons that, in turn, flow through electrical conductors to produce energy.
When charging, the chemicals inside the battery change from a low-energy state to a high-energy state. When a battery is discharged, the materials go from a high-energy to a low-energy state.
“We think energy storage will make intermittent renewables more valuable,” said Paul Siblerud, Executive Vice-President of Marketing and Strategic Sales at ViZn Energy in Columbia Falls, Montana. “We drive by wind farms all the time and it seems like half the turbines have their blades tethered back and aren’t even turning. If we could store that energy and dispatch it at high peak times, you could use that power when needed.”
For a 100-MW wind farm, energy storage would need to range between at least 10 to 50 MW of capacity. Kamath said that such a large wind farm would need to allot as much as $50 million for an energy storage application of this size.
Depending on the system design and location, amortization on such a large storage facility might take 5 to 7 years, said Kamath.
Performance of Storage Technologies
Credit: Data from EPRI and the International Renewable Energy Agency (IRENA). This chart was modeled after the IRENA and the International Energy Association - Energy Systems Analysis Program (IEA-ETSAP)’s Electricity Storage Technology Brief released April 2012.
Solar power is also subject to the vagaries of the weather. “Solar has a tendency to drop out,” said Siblerud. “Cloud formation over your panels can cause a 30 percent drop in power.”
One key to making energy storage using batteries actually work are bi-directional inverters that convert electricity from DC power in a battery bank to AC in the household; or AC to DC when charging. Industrial scale inverters not only control battery charging for grid-scale solar and wind operations, but they also manage switching and voltage when making the transition from a wind or solar operation to the grid.
That is known as, “smoothing the grid” or taking the renewable energy that is generated and regulating it, so it can be put on the grid.
“Unfortunately the trade-off has always been that generally fossil-fuel gas peaking plants are doing the [smoothing] work,” said John Wood, CEO of Ecoult Energy in Sydney, Australia. “Yet batteries do it better, as there is essentially zero lag between signal and response. It can give full power in an instant and soak up full power in the next instant.”
Wood said that PNM of New Mexico has integrated Ecoult’s Ultrabattery into a four-acre solar farm comprised of 2,158 photovoltaic panels.
“To date, Ecoult’s most significant renewable energy smoothing project has been the PNM solar project in New Mexico,” Wood said. “The 500-kW solar plant can experience rapid ramp rates of over 130 kW per second, so it is useful to the grid operator that there is some buffer between that and the grid. Ultrabattery technology can charge and discharge quickly and continuously for long periods.”
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