Wednesday, November 14, 2012

2.7 million kilowatt hours is a lot of power, but …

There's a good* article on California's high speed rail plans in the LA Times. I'm not going to focus on the questions of how to engineer a high speed rail system through mountain passes (it's interesting, though), but look at one number which is put forth in the article:
When completed and fully operational, the bullet train will need an estimated 2.7 million kilowatt hours of electricity each day — about a quarter of Hoover Dam's average daily output.
2.7 million kilowatt hours! That's a lot. That's … 2.7 gigawatt hours! A big scary number! A quarter of the Hoover Dam! A number worthy of exclamation points! What a power-hungry system this will be. Why not shelve it, and have everyone drive and fly between San Francisco and LA?

Because as far as transportation goes, this is pretty darned efficient. Transportation uses a lot of power, and high speed rail is one of the more efficient ways to move people from one point to another. How much power does a car use? One gallon of gas has the equivalent of about 34 kWh. Now, let's assume that the average vehicle, being driven at highway speeds, gets, oh, I'll pick a number out of the air: 34 miles per gallon. This yields the very convenient measure of 1 kWh per mile. If the average vehicle has two occupants (a reasonable estimate for long-distance drives), it yields 0.5 kWh per mile. (Airplanes have a similar fuel efficiency.)

It's about 400 miles from San Francisco to Los Angeles. So the average person will use 200 kWh for that trip. 2,700,000 (2.7 GWh) divided by 200 yields—13,500. 2.7 million kWh is enough power to transport, using current technologies, 13,500 people each day between Los Angeles and California, or about 5 million per year.

The current HSR plans call for 1000-passenger trains (approximately—this is what is run in many other HSR systems) running every 9 minutes between San Francisco and Los Angeles at peak hours (7-10 a.m., 4-7 p.m.). That yields a peak-hour capacity of about 6.5 trains in each direction, or 13,000 passengers.

In other words, 2.7 million kWh would be enough to power the entire California High Speed Rail system—or enough to get one hour's worth of high speed rail passengers to make the same trip by car or plane. To put it another way, 2.7 million kWh in it's equivalent of gasoline will move about 5 million people between LA and San Francisco. It will move 20 to 30 million Californians along the same route by high speed rail—six times the efficiency!—with power left over for another 30-50 million shorter, interregional trips.

And this doesn't address where the power comes from. For vehicles and air travel, it is from fossil fuel. For electricity, it can come from renewable sources in a state blessed with hydro, wind and solar. Right now, 20% of California's power is from renewable sources; by 2020 the mandate is for 33%. With high speed rail drawing power from the grid, some of it's power will probably come from the Hoover Dam.

( * if slightly concern-trolling—yes, crossing faults is a worry but it's not like Japan's Shinkansen runs through a seismically-inactive region)

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