Renewable energy systems, such as photovoltaic and wind-turbine energy systems, are considered to be environmentally sound from the viewpoint of carbon-dioxide emissions and resource depletion. The cost of energy supplied from renewable energy systems is higher than that of conventional fossil-fuel systems, and this hinders the wider spread of renewable-energy systems. Global environmental problems, however, are becoming more obvious. There is a movement to defray the additional cost of electricity generated in environmentally-sound processes. In this paper, we report the results of a survey using the contingent valuation method (CVM) of the willingness of Japanese households to pay more, in the form of a flat monthly surcharge, for renewable energy. The median value of willingness to pay for renewable energy by Japanese households is estimated at about 2000 yen (around 17 US$ with the exchange rate 115 yen/US$) per month per household. (C) 2003 Elsevier Ltd. All rights reserved.