To determine whether this is so we need to assess the likely impact of significant DG penetration on economic activity as a whole. This is likely to be of interest in its own right (since economic activity is typically one of the wider goals of government policy,and in Scotland – for example – is one of the goals of energy policy per se), but also because this is a key determinant of the level of GHG emissions. Furthermore, we are also likely to be concerned with the sectoral composition of any changes in economic activity because we know that energy demands (and the emissions intensity of output) vary significantly across sectors. To assess the system-wide environmental impacts of significant DG penetration we have to understand its effect on sectoral and aggregate economic activity. In addition, such changes invariably have uneven impacts across household groups, and if we wish to track effects on fuel poverty, for example, we again need to adopt a system-wide perspective. We consider the system-wide economic, environmental and social impacts of significant DG penetration in turn.