The results of financial viability studies are mixed, although stand-alone projects in isolated areas in developing countries seem currently to be the most attractive. As is the case for most emerging technologies, DG technologies are typically not yet commercially viable without support, and tend to have greater costs than conventional technologies, though many authors acknowledge the potential for future cost reductions through technological advancements. We believe there is scope for wider application here of the ‘learning curve’ analyses that have been applied to other emerging technologies. Furthermore, recognition that DG will inevitably form only part of a portfolio of generating technologies suggests that levelised cost comparisons reflect a limited perspective (even if these do incorporate wider electricity system impacts), since DG may reduce risks for any given cost level because it is likely to reduce correlations with fuel prices, and to enhance security of supply.31 This perspective also suggests that there is scope for the application of portfolio theory to incorporate DG. At the aggregate level this would focus on the benefits of diversified technologies; at the spatially disaggregated level account should be taken of the benefits of geographic diversification.