Malcolm Turnbull's claim regarding replacing incandescent light globes with florescent lighting is based on a calculation that assumes that coal-fired power production would reduce in accordance with the lower demand created by more efficient lighting. As I have pointed out, this assumption is wrong. Coal-fired production would not decrease.

And as I have already pointed out, SHW would not reduce greenhouse gas emissions for the same reason that fluorescent bulbs do not reduce GHG emissions. Both are technologies used primarily at night, ie not during peak load.

However it is correct to say that by consuming less power through the use of fluorescent globes and SHW will reduce electricity bills. For this reason, it is a very good idea to make the change. Of course, it is important to remember that the extra capital outlay for the more expensive SHW system would need to be taken into account when determining whether SHW is more cost effective than off-peak electric or continuous gas. It isn't necessarily cheaper to use SHW, and certainly not in the short-term.

Geothermal hot rock energy in Australia definitely offers continuous supply. However it is not a sustainable resource, it is finite. The resource is also limited to certain places (eg in the Cooper Basin) and these are typically a long way from transmission grids. Connection to the grid will be costly in $s and in GHGs. It cannot be assumed that geothermal can scale up to supply a large portion of our energy capacity.