Passage Two Installing solar panels on the roof of your home is a big project ?but it pays off in more ways than one. There's the obvious environmental benefit, but for many homeowners, the joy comes with a dollar sign attached. An average, 5-kilowatt system will cost about $15,000 to $20,000, depending on where you live in the US. So it pays to find out if your state offers rebates(退还款) or other incentives to help lower the cost of going solar. Here is a sure bet: the federal government offers a 30% tax credit. You can start your research with this federally funded, comprehensive database that lists all sorts of incentives and policies for renewable energy by state or contact the state agency that regulates utilities. Some states with strong policies to promote solar energy use have created their own websites listing incentives, financing options and tips for hiring a contractor to install the solar panels. Your utility might offer a similar helpful guide. As with any major home improvement project, finding a good contractor is crucial. A trustworthy installer will secure the necessary permits, properly connect the solar energy system to your home and the local electric grid, and apply for incentives for you. Some states ---or local utilities--- post a list of certified solar service companies. Many consumers ask friends and neighbors for recommendations. Googling works just as well. Another big decision is how to pay for the equipment and services. You can pay for them outright, of course. A solar energy system lasts about 20 years, so paying for it upfront will be a cheaper option over time than to lease it. As an owner, you get a bonus incentive if you live in a state that allows you to sell excess solar electricity to your utility. The money you earn will show up as a credit on your bill. Another popular option is to leave the ownership and maintenance of the solar panels to your installer and pay only for the electricity produced from the rooftop system. This arrangement is done through a power purchase agreement, which can last 15 years or more. Your solar company typically sweetens the deal by charging you a lower electric rate than your utility would. Be sure to read the contract to see how your installer sets the electric rates over time. Those rates are likely to change because the average price for solar energy systems has fallen much in the past years. 29. Which is the cheapest option for a solar system?