In practice, therefore, achieving universal access — and still more transformational access — will be critically dependent on ODA and other official external financing, mainly in the form of grants, given most LDCs' debt sustainability constraints. Securing this financing will require a very considerable increase in such financing for the power sector (chapter 5). Official grant financing is particularly appropriate to investment in renewable electricity generation. While there are some local environmental benefits from such technologies in terms of reduced ambient air pollution, the primary reason for preferring renewable technologies to fossil-fuel generation is the reduction in GHG emissions.