Solar electric systems pay off most quickly for consumers who use a lot of energy because extra
charges are given for heavy use, but the solar system still makes sense for low-energy users such as
myself.
     So much of Americans' carbon footprint results from buildings-about 43%, according to the U.S.
Department of Energy. I'm in a household of 1.5 (mom and 7-year-old), and we use only about 4
kilowatt hours of electricity per day, something we've managed through behavioral changes, such as
turning off the lights in rooms after we've exited, and through in-home efficiencies (效率), such as
swapping out all my light bulbs for energy-saving ones and using power boards that can turn off DVD
players, coffee makers and other electrical equipment.
     Using less electricity means I can get by with a smaller, less expensive solar system that not only
covers my use but also produces a credit on my power bill. Going solar also meant my house was
upgraded with a time-of-use meter. This type of meter allows me to receive credit for the electricity I
produce during peak hours when electricity costs the most, but pay the least for the electricity during
off-peak hours, when I recharge my cell phone and laptop and perform other tasks requiring power.
     The downsides are that I am tied in to the grid (电网) and still affected by power failure, and I now
have solar panels (太阳能电池板) that need to be cleaned. It's a subject of debate, but REC Solar said
dirty panels decrease energy production by 6% to 8%.Many panel producers recommend cleaning
panels at least once during the summer. I wash mine whenever they look dirty or dotted with bird
droppings, which is about every other week.
     I think $6,000 is a small price to pay, not only for panels that should produce my next 20 years of
electricity, but also for the greenhouse gases I'm not creating.

1.What is mainly talked about in this article?

A. The ways of cutting power bills.      
B. The tips on reducing electricity use.
C. The benefits of using solar systems.    
D. The importance of protecting the environment.

2.Why does the writer recharge her mobile phones during off-peak hours?

A. To save credit.    
B. To save time.  
C. To save energy.
D. To save money.

3.The underlined word "downside" in Paragraph 4 is close in meaning to ______.

A. discount          
B. disadvantage    
C. disapproval      
D. disagreement

4.The author cleaned her power panels ______.

A. to make them work properly          
B. to protect the environment
C. to make them look better              
D. to avoid power failure