It is not that easy, we have privatised the energy markets so there are rules that need to be followed. Ignoring cost is not something governments can or should

It is not that easy, we have privatised the energy markets so there are rules that need to be followed. Ignoring cost is not something governments can or should do, there are many more factors that need to be taken into account and this combination is what should be optimized for instead of just one factor. The most sustainable way to supply power is to reduce the need to supply it in the first place, insulation and other energy saving measures are usually subsidized already.