http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/05/04/BAGDS6F8K91.DTL
Some Southern California businesses were asked to curtail energy use Monday as a heat wave increased power demand and led to transmission problems.
Power lines near Chino became overloaded as average temperatures hovered around 101 degrees in Southern California, creating the highest demand for electricity so far this year. The unusually hot May weather came as several power plants in the southern part of the state were off-line for maintenance, and not enough power could be sent from north to south.
Statewide, the peak demand for electricity was nearly 3,000 megawatts higher than forecast. A megawatt is enough to power about 750 homes.
Northern California was not affected by the power squeeze, and the problems did not threaten a return to rolling blackouts.
However, the "transmission emergency,'' declared for late afternoon by the California Independent System Operator, forced Southern California Edison to ask several large-energy users to use less power. The customers, mostly manufacturers, pay less per megawatt if they agree to cut electricity use during high demand periods. It was the first time in nearly two years that power grid managers called on businesses that participate in the program to cut usage.
Grid operators also called on homeowners to avoid using appliances like dishwashers and washing machines until after 6 p.m.
Despite the unusually hot temperatures Monday, the state had enough power, according to Stephanie McCorkle, director of communications for the grid operator.
"It just wasn't in the right place,'' she said.
The emergency came a few weeks after the agency issued a summer forecast, warning that electricity supplies would be tight this year as the state faced record demand for electricity. Other agencies such as the California Energy Commission say new power plants must be built or the state could face serious shortages by 2006.
But along with increasing supply, experts also say transmission lines must be upgraded. Along with some shortages in 2001's energy crisis, blackouts were caused by overloaded power lines.
--snip--
This has repeatedly resulted in the ISO finding itself in a situation with no good options but to either pay outrageous prices or curtail load (i.e. load shedding of interruptible load or if load shedding doesn't solve the problem, blackouts).
I have seen a lot of power systems and been involved up close and personal in a lot of electric power load forecasting, but I am constantly amazed that California doesn't have a better forecasting program. To be surprised on short notice with a 3,000 MW error is like needing to find 3 large nuclear power plants just sitting around doing nothing that you can call on for you forecasting errors. That is a heck of a lot of extra generating reserves that the system to carry just to compensate for bad forecasting.