Trains rolling through the San Joaquin Valley chug along on diesel power, hauling freight and passengers at speeds that range from a seeming crawl -- especially if you're stuck at a crossing -- to upward of 75 mph.

But the 220-mph passenger trains proposed by the California High-Speed Rail Authority would run on electricity, with overhead power lines providing juice along the 800-mile route connecting San Francisco, Sacramento, Los Angeles and San Diego.

If the system is ever built, it's going to take massive amounts of electricity to make those trains fly, raising questions about the power grid's ability to meet the demand. If you think your electric bill is high -- just be thankful you're not the Rail Authority.

Deep within environmental-impact reports for the system's Valley sections is a tossed salad of kilowatts, megawatts, gigawatts, BTUs and passenger miles. When combined, they form a picture of a train system that could use more than 3 billion kilowatt-hours (kWh) a year by the time it's fully operational statewide.

The average California home uses about 6,960 kWh in a year. At that rate, it would take more than 430,000 households to use what the train system would consume.

The Rail Authority believes actual demand will be less than that, spokeswoman Rachel Wall said.

"The draft EIRs have to analyze the largest possible impacts," Wall said. "That's certainly more than we anticipate using, but it ensures that we account for the most robust needs of the system."

Where will that electricity come from? How much will it cost? And in a state where summer heat forces people to crank up their air conditioners and utilities ask customers to watch their consumption, could the extra demand from trains create power shortages elsewhere?

Huge demand, cost

The 3 billion kWh needed to power California's high-speed trains by 2035 represents a little more than 1% of the state's current total electricity consumption, according to the California Energy Commission.

The trains would get their electricity from power stations plugged into the lines every 30 miles or so, pulling electricity from the same power grid that feeds California's homes, farms, businesses and cities.

The largest share of California's electricity -- about 49% -- comes from power plants that burn natural gas or coal. But in 2008, the California High-Speed Rail Authority set a goal of using 100% renewable energy -- electricity from wind, solar, biomass, small hydroelectric plants or geothermal sources -- to power the trains.

All of those renewable sources combined added up to just under 14% of California's electricity production in 2010.

But they represent about 30 billion kWh a year -- more than enough to juice the trains. And it's a number that's likely to grow as more solar, wind and other projects are developed.

Going green, however, doesn't come cheap. The Rail Authority expects to pay a premium for renewable power.

The agency estimates it will pay 17.5 cents per kilowatt-hour for electricity -- a figure that Wall said includes a surcharge of 3.5 cents for using all-renewable sources.

If the trains reach their full ridership potential and require the maximum 3 billion kWh of electricity, the bill adds up to about $531 million a year. The Rail Authority estimates that electricity will represent nearly 30% of its annual operation and maintenance cost.

The price per kilowatt-hour, Wall said, is based on studies of what several other transportation agencies in the state have paid for electricity in the past couple of years, and allows for rate increases in years to come.