This paper addresses the impact of environmentally based market failure constraints oil the adoption of renewable energy technologies through the quantification in financial terms of the externalities of electric power generation, for a range of alternative commercial and almost-commercial technologies. It is shown that estimates of damage costs resulting from combustion of fossil fuels, if internalised into the price of the resulting output of electricity, Could lead to a number of renewable technologies being financially competitive with generation from coal plants. However, combined cycle natural gas technology Would have a significant financial advantage over both coal and renewables under current technology options and market conditions. On the basis of cost projections made under the assumption of mature technologies and the existence of economies of scale, renewable technologies would possess a significant social cost advantage if the externalities of power production were to be "internalised". Incorporating environmental externalities explicitly into the electricity tariff today would serve to hasten this transition process. (c) 2005 Elsevier Ltd. All rights reserved.