Electricity generated by rooftop solar, when it is not used at the location where it is generated, flows into the grid. From a homeowner’s point of view, that’s a good thing, because that home’s meter turns backward in sunny locations and, in regions where policy supports solar, the system could turn a profit. But from the point of view of grid operators and utilities, is it a good thing?
Grid operators have to deal with electricity coming back at them, a turn of events they have not before faced. And it will be coming back at them in highly varied waves, depending on the season, the number of clouds in the sky and other factors.
Utilities have to worry how much less electricity they are going to sell. And worry does not suit people who write business plans.
Smart Grid innovations offers potential solutions. Battery storage systems and battery electric vehicles (BEVs) connected to the grid offer other alternatives. What are the best kind and size of batteries and what is the best way to connect them?
Professor Rajit Gadh, Director of the Smart Grid Energy Research Center at the UCLA School of Engineering and Applied Science, is leading an effort to answer such questions in the laboratory and then take the answers into the real world.
Gadh talked with GTM about some questions his researchers are trying to better understand.
In his lab, a solar panel was connected directly to a lead-acid battery and a BEV charging cable was nearby. On a metal shelf across the room, an array of lithium-ion phosphate batteries were connected to an array of light bulbs. These setups pose three questions, Gadh said.
“Lead acid is cheap, if you want large amounts of power,” he explained. “The lithium-ion phosphate batteries tend to have long life. With a microgrid, a small load -- a home or a neighborhood -- can be off the grid. It’s called islanding.” The question, Gadh said, is “How much solar and how much battery?”
It is a particularly crucial question for solar, he explained, because in many places solar’s variability is extremely dynamic. One moment a system can be at full power, in the next a cloud could pass over, and in the next it could be gone.
“You may decide you want a battery that just solves the intermittency problem when cloud cover comes in, so you might need a small battery. But if you want to do islanding for three or four hours, you need a bigger battery. So the battery becomes an integral part of solar offerings.”
The economics will eventually provide the answers to these questions about batteries and variable distributed generation in grid islanding, Gadh said.
The other question, he said, was “solar to EV.” About one-third of all BEV purchasers currently also have a solar system and many more charge at public stations powered by rooftop panels.
The solar panel in Gadh’s lab that was connected directly to the lead-acid battery “goes straight from DC to DC. But if you look at the EV level one and level two charging stations, the most common today, they are AC.”
To go from the direct current (DC) of solar panels to the DC current in a BEV through the home alternating current (AC) charging systems required by regulators for safety reasons, he said, “you have to go through an inverter, and you lose power. So one of our students is trying to go DC-to-DC straight. That becomes relevant if you have a solar garage and you’re feeding power directly into the car.”
Both the DC-to-DC solar to battery setup and the battery-to-light-bulbs setup, Gadh pointed out, have smart switches built into their circuits that allow them more flexibility. It is not yet widely realized, he said, that “there are certain types of loads that you can actually run straight off of solar.”
He and his students are working hard to “push the envelope and show what can be done.” But, he added, “at the end of the day, there are policies and the economics of it. Which of these ideas is going to win,” he said, “is a very complicated equation.”
Research is about identifying the right questions to ask, he noted. “We try to narrow down what we work on based on what the economic situation looks like today and what it could look like in the near future.”
And economics, he said, is greatly dependent on policy. There must be, he said, “appropriate incentives for solar” and they must be consistent.
“One utility on one street -- an enterprise the size of UCLA -- can install solar. Five blocks down, with a different utility, the business case may not be there,” Gadh said. “We have to push that envelope hard. If you want the technology to take effect, you have to have a playing ground on which you can play, and today, I don’t think we’re there.”