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California Flexes Its Solar Muscles

At 1:41 PM on Saturday March 8, California hit a new record of solar energy output of nearly 4.1 GW. That narrowly beat out the previous record of 3.9 GW, which was set the day before. It's also more than double the peak solar output from last June, and quadruple the output from the summer of 2012. Coincident demand for the new record was about 22.6 GW, meaning at that peak solar served about 18 percent of demand, roughly enough to power three million homes. All of that data is from California ISO (CAISO), which reported the new mark earlier this week.

That record solar output, paired with a boost of wind energy, also caused spot-market electricity pricing to slip into negative pricing for a time last weekend, something that happens occasionally when renewable energy ramps up heavily and drives down market prices for other generating sources. In such a situation, it might make more economic sense for baseload plants that can't easily ramp up and down to just pay money for a short period of time in order to stay online.

Many factors go into how much solar output is churned out in a given day: how many plants are online and contributing, how many *stay* online, favorable weather conditions. In this case, the driving factor in this peak was new facilities coming online, according to CAISO spokesperson Steven Greenlee. Likely that reflects contributions from the big Ivanpah concentrated solar (CSP) plant that came online last month. Note that these two new solar output records also occurred in early March -- expect them to be short-lived as spring and summer approach with higher irradiance, even more facilities come online, and demand spikes. Those hotter summer days are, of course, precisely when the boost of daytime solar output is needed most.

CAISO now has about 11.1 GW of combined wind and solar resources interconnected to its grid, and roughly 15 GW for all renewables in its mix. And it'll continue to add more as the state pushes toward and looks beyond its current 33 percent renewable portfolio standard. On top of that, the California Public Utilities Commission (CPUC) just authorized utilities to procure more renewable energy (and other sources like natural gas, plus more energy efficiency) to help offset the lost generation from the shuttered SONGS nuclear plant. Bringing more solar and wind into the grid increases the challenge in meeting demand when they aren't producing, i.e. when the sun doesn't shine or wind doesn't blow, so CAISO stresses more flexible technologies on the grid that can start and stop frequently and quickly, such as storage and natural gas. "We have seen production drops of over 300 MW in less than 30 minutes," Greenlee noted. (Here we invoke the infamous Duck Curve showing the steepening ramping needs and overgeneration risk -- illustrating a potential ramp need of 13 GW within three hours.)

"Duck curve" showing steep ramping needs and overgeneration risk, representing net load on March 31, 2013. Credit: CAISO

Another tool that CAISO is developing to help manage its growing renewables fleet is the Energy Imbalance Market (EIM), which opens CAISO's real-time market for last-minute balancing of supply and demand to non-ISO entities on a pay-per-use basis, broadening the pool of energy that entities can offer and buy from beyond their own balancing areas, Greenlee explained. The market will go live this October, with Oregon-based PacifiCorp as the first customer. "If the sun blocks the Southern California solar facilities, utilities can tap into the EIM and buy energy from non-ISO generators," Greenlee explained. "Or if PacifiCorp has an excess of energy, it can offer it in the EIM."

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