There is no such thing as a perfectly reliable power station, or electricity system, argues Energyscience. As a result all systems are already designed to handle variability in both demand and supply. The report acknowledges wind's variability is different from the variability of fossil fuel power stations; the variability of small amounts of wind power in the grid is indistinguishable from variations in demand.
Electricity supply systems consist of more than base load power stations, which (especially large coal and nuclear plant) do not have the flexibility to cope with the frequent variations in demand. Base load plant, generally with high capital costs but low fuel costs, run nearly all the time. Energyscience identifies two further categories: peak load plant, which run during daily peaks only and usually have lower capital costs but high fuel costs; and intermediate load plant, which run most of the day and have characteristics that fall between those of base load and peak load power. Ideally, power system operation is organised so that optimum combinations of these three types of plant deliver lowest cost electricity to the consumers. That optimum mix may change as a result of the introduction of wind energy.
The amount of backup required is 20-33% of the wind power capacity, according to the report, which does not say how great the proportion of wind on a system can be. But with that level of required back-up, the implication is that the presumed proportion of wind is quite high, possibly somewhere in the region of 40%. According to Energyscience, renewable energy could supply over half of Australia's electricity by 2040 and there is no technical barrier to renewable energy supplying 100% of grid electricity.