For years, electricity came from a generator – such as a coal-burning plant – through the transmission system. The power was dropped off at distribution substations and then went all the way to the consumer’s outlet. The current only flowed in one direction.
Rarely, if ever, was power put back onto the distribution system. A utility engineer would say that’s the way the system was designed. And it was, in fact, designed that way. But electrons can go both ways.
Daniel Girard, director of engineering, procurement and construction business for S&C Electric Co. in Chicago, says nowadays, the current doesn’t go right to left or left to right. It goes in all directions possible. Consider Hawaii, which has a lot of rooftop solar. Every fourth home is feeding into the grid.
“With solar on the rooftop, you end up with all this electricity being put into the grid, where the control systems and the way in which they control voltage at the transformer of the substation don’t even come into play,” Girard says. “You get an injection of a lot of electricity.”
The problem is that you end up with areas that result in less load on the feeders than what was anticipated by the utility. This can cause the utility’s settings to be incorrect. It’s a failure of the system.
It can work, but it doesn’t at present. S&C is one of several manufacturers of energy storage systems that are working to incorporate energy storage into the grid infrastructure. S&C is taking what it calls a “community energy storage” approach.
There is technology available that could enable utilities and cooperatives to deploy community energy storage units. Such equipment could be put into a grid that could act as load or as generation. Because they are fairly small – 25 kVa – it could be used to assert control over the grid, at least at the local level.
During the day, for example, when most people are working and electricity is being generated on a homeowner’s roof, the power could be diverted into the storage system. The utility could release the stored power when it is actually needed.
“Most neighborhoods in the U.S. really need power between 6:00 p.m. and 10:00 p.m.,” Girard says. “That’s a big shift compared to where it used to be – it used to be more 2:00 p.m. to 6:00 p.m. But, society is changing. The grid really isn’t. Storage can provide the means to follow the demand.”
Most photovoltaic generation is fading away by 6:00 p.m. Community energy storage, in turn, can enable the diversity of lifestyles using solar generation and the existing infrastructure.
Community energy storage, deployed at the feeder level, would be controlled at the substation level. The 25 kVa units would be dispersed throughout the grid according to the requirements of specific communities. The utility would have the ability to manage the collection and distribution of the power according to customer demand.
The benefit is that storage can be incorporated into the existing infrastructure without recreating the entire grid.
“These units could be incorporated into underground or overhead distribution systems,” Girard says. “A given unit might sit near the transformer and serve a portion of a neighborhood.”
The community storage concept is not just a way to make better use of rooftop solar generation. It would also have the ability to maintain service to customers in the case of an outage. Essentially, the devices can operate as an uninterruptable power supply.
One utility – which prefers to remain nameless – is testing such a community storage configuration. Residents were not even aware there was an outage during a wind storm that saw widespread damage to poles and power lines. Because the storage provided a source of electricity, the inverters remained functioning, which enabled the rooftop PV to continue supplying electricity.
“There was so much sun during the three days of the overall outage that the batteries of the community storage system were over 100 percent charged,” Girard says. “The utility had to shut down the power collection for the safety of the battery. The homeowners didn’t know the difference.”
Another aspect of the community storage concept is that neighbors who are drawing from the same unit can work cooperatively to keep the system functioning optimally through Twitter or other social media. For example, if the batteries are in play, neighbors can inform each other not to use more electricity than they really need in order to make sure there is enough for all during the course of an outage. Such a pilot is in operation in British Columbia.
“There are numerous places where people are starting to see PV and energy storage coming together to serve a larger purpose,” Girard says. “There really is a lot of common ground between the utility, the municipality and the ratepayer.”
Michael Puttre is a freelance writer based in New York.