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SOME MORE ELECTRONS, PLEASE —


REPORT DETAILS CAUSES OF RECENT CALIFORNIA ROLLING BLACKOUTS


SUPPLY WAS DOWN WHILE DEMAND WAS UP, WHICH IS MATHEMATICALLY INCONVENIENT.

Scott K. Johnson - 10/10/2020, 12:00 PM

Enlarge / August 14 and 15 saw a heatwave drive rolling blackouts. And then on
August 16, a station in Death Valley hit 130°F...
NASA EO

READER COMMENTS

199 with

In mid-August, just before dry lightning storms ignited a series of fires that
would break records in California, an intense heatwave resulted in rolling
blackouts on two consecutive days. The trouble came in the evening, when solar
generation drops off, leading some to claim this was the consequence of relying
on renewable electricity. But it’s not that simple, as the outages could have
been avoided. A new “preliminary root cause analysis” report from two state
commissions and the California Independent System Operator that runs the grid
presents a clearer picture of what went wrong.

The rolling outages affected a few hundred thousand people starting around
6:30pm on both August 14 and 15. They were actually the result of the grid's
rules: once the remaining reserve generation falls below six percent of current
demand, the grid operator is required to institute rolling blackouts.

The report blames the need for outages on three things: extreme and widespread
hot weather, a failure to update peak-demand forecasting practices as solar
generation grows, and mistakes on the grid market that led to some plants
exporting power when it was actually needed in-state.

First up, the weather that precipitated the shortage: It was indeed remarkably
hot, which drove demand up to power air conditioning from the afternoon into the
evening. The report puts it at about a 1-in-35-year heatwave. Grid planning
accounts for extremes to an extent, but oversizing potential supply for every
possible event can push costs to astronomical levels, so there are limits. And
those limits are changing, as the report describes this as a “climate
change-induced extreme heat storm.” There has not been a formal scientific study
of this weather event, but trends in extreme heat are clear in a warming
climate.

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Enlarge / Average temperatures on August 14 and 15 (and so electricity demand
for cooling) were exceptional.
CAISO/CPUC/CEC

Equally important is that most of the West was in the same hot, high-pressure
weather system. With demand up everywhere, there wasn’t enough available
generation in neighboring states to import extra (more on that in a moment). Hot
weather also imposes limitations on combustion plant operations—they just don't
work as efficiently—and transmission line capacity.

The second item on the report's list relates to demand forecasting. Grid
operators have historically focused on lining up supply to meet the peak of
demand, since that should handle the rest of the day. But the pinch came after
the peak in this case, at a time when solar generation was dropping off its high
point for the day but air conditioners were still rumbling. The report refers to
this as the “net demand peak”—that is, the peak of total demand minus solar and
wind generation. As solar generation grows as a share of generation in
California, this point has increasing importance, but it hasn’t been
front-and-center in planning practices.

On August 14, for example, peak demand was 46,800 megawatts just before 5:00. By
7:00, demand had dropped by about 4,600 megawatts, but wind and solar generation
had dropped by 5,400 megawatts.

There’s more going on here. Solar and wind production in this window were a
little lower than expected, owing to a dip in winds and high cloud cover. Due to
drought conditions, hydroelectric generation is down this year. Natural gas
plants also generated 1,400-2,000 megawatts less than expected because of heat
impacts and other problems. What’s more, 400 megawatts of pre-planned gas plant
outages hadn’t been substituted for.

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Enlarge / Demand (blue) and demand minus solar and wind generation (yellow) over
August 14 and 15. The periods of rolling blackouts are shown in the gray bars.
CAISO/CPUC/CEC

Imports from out of state were also lower than usual, of course, even though
some extra supply came through when an emergency request went out. Apart from
the demand elsewhere, this was also due to a transmission line connecting
California to the Pacific Northwest going down, limiting transfers.

Another important strategy for these tight supply events is to reduce demand.
That includes specific agreements that can be called upon as well as the general
calls for public conservation that went out in California and some neighboring
states. In total, utilities got about 80 percent of their coordinated demand
reduction to come through, shaving around 1,000 megawatts off early evening
demand.

The report’s third focus is the way the market behaved in the lead up to the
rolling blackouts. In several ways, the market messed up where it could have
helped. The demand forecast made on the previous day underestimated peak demand
by about 3,400 megawatts, for one. And the bidding process by which generators
sell their electricity told some California plants they could export their power
to other markets.

A rare failure like this typically requires many problems to stack up at the
same time, and that seems to have been the case. The report notes that when
California’s weather cranked up the heat again on August 17-19, blackouts were
avoided. This was in part due to some temporary alterations of the bidding
process, greater availability of imported electricity, and greater demand
reduction.

Looking ahead longer term, the report highlights some things that need to
improve. The planning process needs to adapt to current grid conditions. The
daily forecasts and bidding procedures could use tightening up, as well. But
adding grid-scale storage would make everything a lot easier by smoothing out
supply through the evening hours. That will only become more true as the share
of renewables grows—and not just in bad-luck weather extremes.

Listing image by NASA EO



READER COMMENTS

199 with
Scott K. Johnson Scott has written about geoscience and energy at Ars as a
freelancer since 2011.

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