One factor driving energy policies across the world is repeated claims by activists that green energy is gaining substantial market share over its despised fossil fuel competitors.
The Californian grid is supposedly awash with green electricity, with American newspapers reporting that the state's ambitious green energy target of 33% of power from green sources by 2020 is within reach. Quick calculations with figures from the Californian Energy Commission Energy Almanac indeed show that green power accounted for about 30% of the electricity generated in 2015.
But well over half of that came from hydro power, biomass (timber waste used as fuel in small power stations), and geothermal. Those power sources have been used in California for many years and are dispatchable; that is, they can be switched on and off at command. Hydro is particularly highly valued on all networks, as it can respond very quickly to balance unexpected shifts in supply or demand.
That still means 13% of the state's power was generated by the intermittent sources of wind and photovoltaics (the latter of which make up an astonishing 6.4 % of total supply) plus a smaller contribution from the big solar power stations that excite activists. However, that still substantial proportion comes with problems. Both wind and photovoltaic output can vary from nothing to full capacity, with the average output of wind towers usually about 35 % of rated capacity. So the overall percentage figures cited above means that at times the network had very little green power coming in, while at other times well over half of its supply might have been weather-dependent green electricity.
That's fine if there is plenty of conventional capacity ticking over, ready to start up when the wind dies and the sunshine fades. But as South Australia has found out in the last few months, having lots of wind on a network without a backup conventional plant is a recipe for instability. In other words, there are limits to wind and photovoltaic power.
Activists also enthusiastically point to Chinese grids, with various reports claiming that 25% of power is clean and green. In fact, the overwhelming majority of this power comes from hydro projects large and small, including many built long before the green energy drive.
A 2014 report by the International Renewable Energy Agency estimated that about 2.5% of power on the Chinese grid at the time was from wind farms. A count of existing, proposed and under-construction projects in China in the December issue of The Resources and Energy Quarterly (produced by the Australian Office of the Chief Economist) indicates that wind power will remain a marginal player on the Chinese network for the foreseeable future.
As various commentators have noted, the Chinese network is still primitive compared to the Western grids, with a report by the US policy analysis group the Wilson Centre pointing out that the Chinese grids confusingly remain both state government-owned and largely unregulated (although prices are regulated, and electricity is generated through a quota system rather than cost of generation). Introducing large amounts of intermittent energy is not straightforward.
Variations on the same story can be told for almost every example cited by green enthusiasts of evidence that the green revolution is nigh, so don't bother to invest in coal.
One possible exception is the Danish network, but that is only because it is a small part of a large, dense European network. The Danes export excess wind energy for storage in the numerous dams of Sweden and Norway. Pumping water up hill into dams remains the only known method of bulk storage of power, pending several quantum leaps in battery technology (small scale balancing storage may now be possible). The Danes re-import the power when the wind dies away. This is expensive, but it is green.
Germany is also often cited as a green leader, but this green sheen fades on closer inspection. When the grid has a lot of wind or PV power, instead of reducing the output of their mainstay brown coal plants the grid managers take advantage of being part of a larger European grid by exporting the surplus power to their near neighbours.
What about renewable base-load plants? These have been under development for decades with little progress. Installations such as the Gemasolar pilot plant in an alpine desert region of Southern Spain have achieved 24-hour operation but, as those same reports admit in passing, cannot do so continuously. One solution would be to import green power over large distances using direct current lines from, say, desert regions to Northern Europe, but this will require extensive investment in power supply infrastructure.
Green power has certainly made considerable progress in the last few years, but that progress is far short of activist assurances and has distinct limits with present technology; a point energy policy-makers in all countries should bear in mind.
Photo: Flickr/Curtis Simmons