Intermittent renewables and electricity supply reliability

How to deal with the intermittency of some renewable energy sources (wind, solar)? How to reconcile that intermittency with the need for reliable electricity supply? Options include limiting the contribution of intermittent energy sources such that overall electricity supply reliability can be ensured, and/or the use of energy storage systems.
Dr Mark Diesendorf (2010) writes:
“Some sustainable energy sources and measures are at least as reliable as coal power. These include demand reduction by means of energy efficiency, energy conservation and solar hot water, and renewable electricity supply by hydro with large dams, bioenergy, solar thermal power with thermal storage and geothermal power. They can all be used to reduce the demand for base-load coal without reducing the reliability of the generating system.
“What about fluctuating renewable electricity sources, such as wind, run-of-river hydro, solar without storage, and wave power? They simple add fluctuating sources to an electricity supply system that is already designed to handle fluctuations in demand and conventional supply. All base-load power stations, including coal and nuclear, are partially reliable and therefore require some back-up. Breakdowns of coal and nuclear power stations occur less frequently than fluctuations in the wind and sunshine, but when coal and nuclear do break down, they are off-line for longer periods than lulls in the wind or periods of overcast and darkness. To compare the reliability of coal and nuclear with that of wind and sun in an electricity grid, we have to compare the reliability of the whole generating system with and without the renewable electricity sources.
“Both computer modelling and practical experience show that the existing system can handle small penetrations of fluctuating renewable electricity sources into the grid. For large penetrations, wind in particular can substitute for base-load coal-fired power stations, provided either some additional peak-load plant is installed or the grid is interconnected into a larger neighbouring grid, in order to return the generation reliability to the original level. For instance, Denmark is planning to increase its wind energy contribution to 50% of total annual electricity generation by increasing the capacity of its transmission link to Norwegian hydro. Since Australia cannot do this, it will need some additional peak-load capacity, in the form of gas turbines or hydro. The amount of additional back-up increases with increasing wind penetration, but decreases as the geographic dispersion of the wind farms increases. For a geographically-dispersed wind energy penetration of 25% of total generation, the additional peak-load capacity required to maintain reliability would be a small fraction of the wind capacity. Since the back-up only has to be operated infrequently, it can be considered to be reliability insurance with a low premium. By the way, the gas turbine could be fuelled with biofuels produced sustainably.”
Click here to download Mark Diesendorf, 2010, ‘The Base Load Fallacy and other Fallacies disseminated by Renewable Energy Deniers’, EnergyScience Coalition Briefing Paper.