In this article, we examine the evaluation of the economic potentials of various renewable energy technologies. We first argue that traditional evaluation methods are fraught with shortcomings, most of which are avoided through the use of a global, integrated energy model such as MARKAL. We then provide evaluations of several technologies in the following sectors: electricity production, alternative transportation fuels and technologies, and water-heaters. The evaluations are conducted in two contrasted situations one of which ignores environmental externalities, the other which explicitly takes them into account. The two contrasted scenarios lead to quite different conclusions.