【单选题】

Sally Kemmerer has, so far, escaped NorthernCalifornia’s rolling blackouts.

But up on the roof for her Oakland home, workers are tapping into, perhaps, the most reliable power source, the sun. It could mean no more worries about blackouts or power rates.
Sally Kemmerer, a homeowner, says, "I hope that we’ll be able to zero out, you know, our electric bill. I mean that’s definitely our goal."
Turning the sun’s rays into electricity is, of course, nothing new.
ButCalifornia’s power crisis has cast a new light on the technology.
Gary Gerber, a solar power contractor, says, "I might have been getting three phone calls a week a couple of months ago. I’m getting six a day now, it’s completely crazy."
Alternative energy is even more attractive, thanks to a state rebate program. So far this month,California’s energy commission has received 200 project applications. That is more than the number of applications all last year.
Putting in a solar roof is still a relatively expensive proposition. This project cost around 45,000 dollars.Even taking into account the state subsidy of 12,000 dollars, that leaves a net cost to the homeowner of around 33,000 dollars.
Sally says, "We were happy to find out that, eventually, the system should pay for itself, you know 20-years, maybe."
Aaron Wellendorf has had a p-v (or photovoltaic generator) for more than a year. Like most solar systems, his is not off the grid completely and the utility still kicks in at night, or when there’s no sun.But when there is bright light, things change.
Wellendorf says, "I’m turning my meter backward with extra power that I’m generating."Backward
That’s right! Wellendorf’s meter tracks how much power goes back into the utility griD、Last year all he paid for electricity was a service charge. That charge was around five dollars a month.
In fact, even after powering his super-efficient household appliances and his converted electric track, Wellendorf generated a net surplus of more than 2,000-kilowatt hours.
Unfortunately, state law doesn’t require the utility to pay him for that. Wellendorf says, "I don’t get it in money, I just get the satisfaction of helping out the power griD、"
And, he gets the satisfaction of being energy self-sufficient.
According to the article, when a homeowner puts in a solar roof, her worries about blackouts or power rates might be over. Why might that be true
A、Solar power may be less expensive and more reliable than power supplied by utility companies.
B、Her roof won’t leak with the heavy solar panels on top of the roof.
C、Putting in a solar roof is still an expensive proposition.
D、Super-efficient appliances use less electricity than regular appliances.