From the NYTimes:
Bees, in cardboard hives, pollinate the 550,000 plants at Backyard Farms greenhouse. Tomatoes are usually pollinated by the wind; before bees became common in greenhouses, the task was accomplished by hand with electric vibrators.
Lights allow Backyard Farms to defy geography and grow tomatoes in midwinter. When all of them are switched on, they use as much power in 32 minutes as the average American household does in a year.
Inside the Backyard Farms Greenhouse - The New York Times, 2010.