As many of you attending Maker Faire might recall, I mentioned the "March 27" date, where the ISO (Independent System Operator) asked solar facilities to "turn off".

Reproduced here, is an excerpt from that April 11, 2016 NPR article Stephanie Joyce and Lauren Sommer:
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Solar energy records are falling left and right in California these days, as the state steams ahead
toward its ambitious renewable energy goals.  But the success of solar has brought about a hidden downside: on some perfectly sunny days, solar farms are being told to turn off.  That’s because in the spring and fall, when Californians aren’t using much air conditioning and demand for electricity is low, the surge of midday solar power is more than the state can use.  It’s becoming a growing concern for those running the grid at the California Independent System Operator. At their Folsom headquarters, a team continually manages the power supply for most of the state, keeping the lights on for some 30 million people.  “It’s constantly solving a constant problem, meaning you’re always trying to balance,” says Nancy Traweek, who directs system operations for the grid.

Ups and Downs of Renewables
On March 27, a sunny day, some solar farms had to shut down because there was more power on
the grid than Californians were using. In the past, balancing California’s electric was fairly straightforward. The power supply was constant, coming from natural gas and nuclear power plants that put out a steady stream of electricity.

But the growth of solar and wind power has thrown a wild card in the mix. The sun and wind are
much less predictable.  “All of a sudden you have a major cloud that comes over a solar field,” Traweek says, and that causes the solar power to drop off.

“That [power] needs to come from somewhere else immediately,” she says.

So grid operators have to keep the natural gas plants running in the background. If they’re turned
off, many take four to eight hours start up again.California’s highest demand for electricity also happens right as the sun goes down, when Californians come home from work and lights turn on. Grid operators need natural gas power plants at the ready to meet that peak and to fill the gap that’s left by solar power.

But add up all those energy sources – solar, wind, natural gas, as well as hydropower, nuclear and
others – and on some days, they’re making more electricity than California needs

“When it gets really bad, now we really got to start cutting as much as we possibly can,” Traweek
says. “If that’s not done, then you could have a blackout.”

So, grid operators have to tell solar farms to shut off.

“That’s zero-carbon, clean energy,” says Keith Casey, a vice president at the California Independent
System Operator. “It would just be a travesty to curtail large amounts of it.”

Casey says the problem will only get worse as more solar and wind connect to the grid. California
plans to hit 50 percent renewable energy by 2030.

Joining Grids Across the West
California’s grid operator is developing a solution, one that is garnering controversy across state
lines.  Right now, California’s grid runs mostly on its own, like an island. But there are power lines reaching across the West.

“You’re operating your little piece of the system,” Casey says, “but if you can operate it as an
integrated whole, you can just operate the system more efficiently.”

So, Casey is proposing California join up with its neighbors. Instead of having lots of electric grids
across the West, each doing their own thing, there would be a larger regional grid, sharing power
across state lines.

When California has too much solar power, neighboring states would buy it, preventing California
from having to switch off the solar farms.

“It’s a win-win,” Casey says. “We really think we need to seize the most efficient opportunities that
are out there for integrating renewables.”