LONDON Serious entrenchment of wind and solar in the world's power supply looks decades off unless China and India can beat already ambitious targets, through cost cuts, as meteoric growth in developed countries slows.
The renewable energy sector has been on the back foot in the past 12 months, as the financial crisis and falling subsidies created over-capacity in solar panels and wind turbines.
For a more representative view it makes sense to look at 2006-2010.
Annual global growth in installed capacity then was an impressive 28 percent for wind and 54 percent for solar, according to data from the Global Wind Energy Council and the European Photovoltaic Industry Association.
The problem for the sector is impact: this growth comes from a small base.
At the end of 2009 (the latest year for global International Energy Agency data), wind power accounted for 3.2 percent of world installed power generation capacity, and solar for less than half a percent.
Naturally as the installed base rises percentage growth slows, begging the question: when will wind and solar capacity reach a serious level, say a quarter of the world total?
Alongside nuclear and hydropower that would pull low-carbon power level with fossil fuels.
Assuming 10 percent compound annual growth rate (CAGR) for wind and 15 percent for solar, they only reach a quarter of global capacity (assumed to rise 2.3 percent annually in line with IEA forecasts) in the year 2030.
That's still a much more ambitious finding than an outlook by the oil company BP (BP.L) which on Wednesday saw fossil fuels continuing to play "a critical role", and renewables at just 11 percent of power generation in 2030.
What will growth in renewables be? It's useful to see growth and targets at the national level.
If there's a group of countries which defines renewable energy targets it's the European Union.
The bloc has a binding goal for renewables to reach one fifth of all energy consumption (heat, power and transport) by 2020.
The European Environment Agency (EEA) estimated last November that would see renewables account for a third of power generation.
However, the EEA saw a sharp slowdown in percentage annual growth over the coming decade, in line with the 2020 target, summarised in the following table:
EU wind and solar power generation, growth (PCT)
2005-2010 2010-2015 2015-2020
Wind 18.5 pct 13.4 pct 9.9 pct
Solar 70.7 pct 23.4 pct 11.2 pct
Source : EEA
Such slowing growth rates are consistent with the estimate above for a quarter or less of the global power mix by 2030.
In the United States, the latest review by the U.S. Energy Information Administration (EIA) showed combined power generation from wind and solar shot up 27 percent in the first nine months of last year compared with the same period in 2010.
Despite the U.S. shale gas revolution, wind and solar beat rising natural gas power generation both in percentage (27 percent versus 2 percent) and absolute terms (18,866 million kilowatt hours versus 12,114 mln KWh).
But wind power still accounts for less than 3 percent of U.S. power generation, despite a CAGR of 34 percent over the past 10 years.
And the United States has no federal targets for renewable energy, while it's main support system for wind power expires at the end of December, suggesting slower growth this year and possibly next.
By contrast China and India each have ambitious deployment targets and their roaring economies will account for most added capacity globally over the next quarter century.
China's National Energy Administration last week said its grid-connected wind power grew by half again while solar capacity trebled in 2011.
Beijing has guidance to connect some 200 gigawatts (GW) of wind power by 2020 from 47 GW now (CAGR 17 percent).
But that growth rate will slow after 2020 to an installed 400 GW by 2030 - a CAGR of 11.3 percent from 2011-2030, almost identical to the global assumed growth rate above.
China also has guidance to install 50 GW of solar power by 2020 compared with 3 GW now (CAGR 40 percent). India has a target to install 20 GW of solar by 2022 compared with about 0.5 GW now (also CAGR 40 percent).
The message? A rapid entrenchment of renewable energy in the world's electricity supply may depend on solar power maintaining its meteoric rise through 2020 and beyond, and major emerging economies beating their national targets.
There is a history of such out-performance in China, whose National Energy Administration has in the past raised its 2020 guidance for wind by a third and solar by 150 percent.
(Reporting by Gerard Wynn; editing by Jason Neely)