"Over the 25-year time frame considered here, energy efficiency makes the greatest impact when seen against indicators of sustainable development. Industrial efficiency, in particular, shows significant savings in energy and costs, with reductions in air pollution. Commercial energy shows a similar pattern, although at a slightly smaller scale. Residential energy efficiency is particularly important for social sustain-ability. Even small energy savings can be important for poorer households. In the short-term – the 2006 to 2015 decade – we can conclude that energy efficiency will be critical to making South Africa’s energy development more sustainable. In the longer-term –the next several decades - transitions which include the supply-side will become increasingly important. To achieve greater diversity there will need to be a combination of policies, since single policies on their own will not change the share of coal in TPES by very much. The various alternative electricity supply options show potential for significant emission reductions and improvements in local air quality. However, they will require a policy of careful trade-offs in relation to energy system costs, energy security and diversity of supply. The global costs (discounted total energy system costs) for the combined scenario are lower than for the base case by some R16 billion over the full 25-year period (2000-2025). Thus the savings due to the combined efficiency measures more than justify the additional costs of investing in a diversified electricity supply."