The array of solar panels recently installed on Ian Bowles's slate roof in Jamaica Plain should pay off for him in less than a decade, but the green power the state's former top environmental official generates may cost other utility customers for many more years. Massachusetts now generates enough wind and solar energy to power 38,000 homes. It produces 118 megawatts of solar energy, up from 3 megawatts in 2007 and nearly half of the state’s goal of 250 megawatts by 2017. The state also produces 61 megawatts of wind energy, up from 3 megawatts in 2007 but far from the goal of 2,000 megawatts by 2020.