A SUBSTANTIAL increase in renewable energy by 2030 would result in far cheaper electricity than if SA persists in its bid to build 9,600MW of nuclear power, a study by Stellenbosch University has found.

The study, published a week ago, confirms in broad strokes the findings of two other recent expert analyses — one by the Council for Scientific and Industrial Research and another by the Energy Research Centre at the University of Cape Town — which warn that nuclear energy will be the most expensive of the options available to SA.

The Department of Energy has embarked on a process to procure six or eight new reactors. While the department says it has done comparative studies on the costs of different technologies that show nuclear power to be "competitive", it will not make these public.

The study by senior researcher Paul Gauché was commissioned by environmental lobby group the World Wildlife Fund to test the feasibility of a larger mix of renewable energy in SA.

The Integrated Resource Plan 2010, which is the government’s key planning document, proposes that renewables generate 9% of the annual electricity produced by 2030. The WWF has suggested that this be increased to 20%.

The study compares the costs of the energy mix likely to arise in each model. Mr Gauché uses a spatial-temporal methodology that predicts the energy supplied by wind and solar in 2030 based on detailed real sunlight and wind data in the year 2010.

In the IRP 2010 model, in which the energy mix includes existing coal of 34,746MW (including Medupi and Kusile); additional coal of 6,250MW; the full additional 9,600MW of nuclear power; 24,000MW of renewables; 7,330MW of open-cycle gas turbines; 2,370MW of combined cycle gas; and pumped storage of 2,912MW, the estimated cost of the energy mix is R1.50/kWh.

In the WWF model, which includes no new additional nuclear and no additional coal but 38,708MW of renewables; 7,680MW of open-cycle gas turbines and 4,000MW of combined cycle turbines and the same amount of pumped storage, the overall cost of the energy mix is R0.65/kWh.

The two models have slightly different projections of demand in 2030, but even when this is taken into account, the WWF model remains lower in cost.

"We found that a well-balanced renewable system will generate energy at a cheaper rate than the system does in any other configuration," says Mr Gauché.

The key is, says Mr Gauché, the balancing of a renewable system with the use of pumped storage, open-cycle and combined cycle gas turbines.

Renewables are able to cover the system most of the time and the largely unused emergency generators essentially doubling up spare capacity.

This system is able to cope better than a "stiff" system, which includes large amounts of nuclear and coal. Neither of these technologies can be easily turned down when there is excess and cheap energy available from renewables. Particularly in the case of nuclear, costs are fixed no matter how much energy is put into the grid, he says.

Added to this is the advantage that the cost of renewable energy is falling and will continue to do so as technology develops.

"Nuclear seems to be the bully in the room, it makes the rest of the system go up and down more than necessary. It doesn’t fit well with a flexible system or when you start to add renewables and this results in the model giving a higher cost for the whole system" he says.

While much of the world might need nuclear energy to lower carbon emissions, sunny countries like SA can build a carefully balanced system with renewable energy.

The environmental downside of such a system is that it must include the burning of diesel as a back-up and at peak times when supply doesn’t match demand.

"The most important thing is how often they get used," he says.

The main argument used by nuclear energy proponents against renewables is their variability, unlike coal and nuclear which can supply a steady base-load.

Mr Gauché says his report is a first attempt to quell this debate.

Apart from the fact data show that wind and solar are complementary in SA when aggregated over a few days, as well as months and seasons, arguing against renewables on the ground they do not provide base-load is the wrong point of departure.

"Asking whether renewables can provide unvariable power is not the right question. Instead we should see renewables as a cornerstone of our future system that in the right combination serves our national interest."