unlike the solar heat concentrators, photovoltaic panels convert sunlight directly to electricity. although sunlight is free, solar panels cost a lot of money to make and have only a 10-20% conversion efficiency. until recently, photovoltaics were most commonly used in remote sites where there is no access to a commercial power grid, or as an extra electricity source for individual homes and businesses. recent advances in manufacturing efficiency and photovoltaic technology, combined with subsidies driven by environmental concerns, have dramatically accelerated the deployment of solar panels. installed solar capacity is growing by 30% per year in several regions including germany, japan, california and new jersey.