HERE’S an idea: Buy a house, and make money off the investment. Guaranteed. So long as the sun keeps coming up.

That is the pitch being made at River Pointe, an age-restricted community in Manchester where PulteGroup Inc. is installing, as a standard feature in each house, solar technology that earns energy credits.

PulteGroup, a company based in Bloomfield Hills, Mich., is not the only builder offering solar-equipped homes in New Jersey. But it is among the first to start offering solar units as a standard feature in every house in a development, and to tot up the ways that buyers can earn as much as $30,000 over 15 years.

Those earnings will come in four ways, according to Paul Schneier, the president of the company’s metropolitan New York and New Jersey division: savings of more than half on electricity bills, a onetime federal tax rebate of at least $6,000, an annual break on property taxes, and income from the sale of the credits back to utility companies.