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The Pacific Northwest gets about two thirds of its electricity from renewable sources -- and in some areas it's as much as a hundred percent.

The Chelan County PUD in Washington state has plenty of experience with renewable energy. I asked whether they think solar power could help solve the problem of peak power demand for utilities.

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Solar can shorten peak periods and help make peak demand more manageable, says PUD engineer Jim White, but solar peaks at the wrong time to help offset peak demand.

What about the utility-class renewables, like wind? Too variable, White says, but with diversification of sites it becomes more predictable.

Chelan County PUD isn't predicting a peak capacity crisis any time soon. Time-of-use pricing is the only form of demand management it's using. That's because it owns its own hydroelectric dams.

With hydro, White says, capacity is not an issue. As long as there is water in the reservoir, output can be turned up or down to meet demand. But most utilities don't have that luxury.

Electricity and time are the ultimate perishables. Is there a viable energy-storage technique on the horizon?

White points to a nascent concept for a plug-in electric hybrid vehicle -- specifically one that can sell power from its batteries back into the grid. The concept calls for the roof of the garage to be covered with solar modules, which help to charge the car's batteries.

"If enough of these were installed, you would see the lowering of daytime peaks due to the solar, and the filling in of the valleys at night because of the charging."

Researchers are working on it, but it won't happen fast enough for most utilities.