Sparking up our electricity

Independent Weekly
Friday 23/10/2009 Page: 17

One way or another it appears Australia will have an emissions trading scheme (ETS) soon. The aim of such a scheme is to reduce carbon dioxide (CO2) emissions entering the atmosphere by charging organisations that are emitting CO2 for the right to do so. In turn that cost will be passed to consumers resulting in lower electricity usage. But this won't happen evenly for electricity, which is generated by a range of methods that emit different amounts of CO2, which means electricity charges vary under an ETS scheme.

SA remains heavily dependent on brown coal, which emits the most CO2. This is either from Leigh Creek coal burnt in the Northern and Playford power stations near Port Augusta or imported from Victorian generators by the interconnector power links. For this reason we need to re-engineer our electrical power generating system under an ETS.

Electricity companies, urged by the State and Federal governments, have started moving in this direction. The likeliest replacement option is wind energy. To bring our wind facilities up to the standard and size where they could cover the 780mW of power generated by coal would cost about $4 billion. So what else can be done? Being more efficient consumers is good but won't save 780mW. Leaving aside the politically controversial option of nuclear energy we have one major technology available. And we already have a working example right here in Adelaide at Pelican Point.

Combined cycle gas turbines offer a way to cut the cost of CO2 replacement. CCGT are really two power stations in one. The first half is just like one of the engines on the wing of a 747. It burns gas and the output turns a generator - this is the gas turbine part and it extracts about 40% of the available energy. The combined part comes from using the extremely hot exhaust gases from the gas turbine to heat water, create steam and use it to turn a second turbine where about 15% more energy is extracted.

Using this technology to replace coal electricity from the Leigh Creek stations would cost a bit less than $1 billion. Because the infrastructure is small when compared to wind farms they can be developed faster and located more conveniently to the main users. This would mean that instead of producing a kilogram of CO2 per kW/h we only produce 400g. But we still need to use a carbon-emitting fossil fuel, so we still need to buy a supply of gas and permits for the CCGT. The decision between wind turbines and CCGT will come down to the interest payments on the difference in the capital costs versus the running costs.

In householder terms, it's the interest payments on the extra $3 billion on the wind energy company mortgages versus the CCGT gas bill. We still don't really know the cost of the CO2 permits or the structure of the ETS so as a community we are working in the dark. Which way will we end up re-engineering our electricity system? It's still hard to predict. However the lower capital cost and concentrated simplicity of CCGT power plants when compared with the diffuse nature of wind turbines probably means most of the electricity supplied under the ETS will be from natural gas-fuelled CCGT for the next three decades.

Doug Gillott is President of the SA Division of Engineers Australia.