The odd couple

AS world leaders continue to grapple with achieving climate goals in the wake of the recent summit in Peru, an International Energy Information Administration analyst has identified a new frontier of combining coal and renewable energy systems.

Anthony Barich

Renewables made up more than 26% of global generating capacity last year, producing 22% of the world’s electricity, and continues to increase, with hydropower and solar PV each accounting for about 33% of new renewable capacity last year, followed by wind at about 29%.

A new report from International Energy Agency senior consultant Stephen Mills has revealed that a marked increase of all types of fossil fuels has been coupled with a marked increase in the uptake of renewable energy in what Mills suggested may seem to some as “an odd partnership”

Renewables’ growth has been driven by a heavy reliance on adequate and accessible electricity supplies and continuing demand rises in nearly every country; while heightened concerns over depletion of energy resources and global climate change have prompted many western governments to lift renewables in their energy mix to 20% and beyond.

Mills said wind power had emerged as the most competitive and widely deployed renewable energy thus far, although levels of solar power were also growing steadily.

“Renewable energy technologies such as wind and solar have obvious features that make their use attractive,” he said.

“Although initial capital costs for renewables-based systems can be high, operating costs can be low; emissions generated during day-to-day operation are effectively zero.”

Yet these renewable energy systems are not replacing existing or even new coal-fired power plants, and indeed renewables and coal-fired power generation are growing simultaneously, Mills said.

Perhaps the most intriguing aspect of this trend is that a growing number of hybrid coal-renewables systems have been proposed or are being developed around the world, several of which could offer significant potential.

Combining biomass with coal is a prime example of combining renewables and coal, which is already deployed widely in the form of co-firing biomass in large conventional coal-fired power plants.

“Around the world, a growing number of power plants regularly replace a portion of their coal feed with suitably treated biomass,” Mills said. “More than 150 coal-fired power plants now have experience with co-firing biomass or waste fuels, at least on a trial basis.”

Meanwhile, the intermittency of wind and solar power often produce surplus electricity, which can be used to fill demand to electrolyse water, producing hydrogen and oxygen. Oxygen could be used for a host of commercial and industrial applications, or fed to a coal/biomass gasifier or an oxy-fuel combustion plant to generate electricity.

“Different concepts and schemes combining gasification, intermittent renewables, and electrolysis are currently being examined,” Mills said.

“Some aim to incorporate carbon capture and storage. For example, an on-going project in Germany is combining coal-based power generation with aspects of carbon capture and wind-generated electricity with trials of advanced electrolyser technology to produce hydrogen and oxygen from water.

“Success could encourage increased uptake of, for instance, electrolysis, as a component part of various coal/renewables systems. Assuming that the economics can be made to work, several schemes look promising.”

Exaggerated demise

Recent trends would also seem to deflate environmentalists’ expectations of coal’s demise.

Mills revealed that global coal consumption has risen steadily for over a decade.

In some non-OECD countries, in particular, both production and consumption have increased dramatically, with consumption lifting by nearly 60% from 4.6Gt in 2000 to about 7.8Gt in 2012.

“Despite efforts to diversify, coal remains vitally important for many economies,” Mills said in his report.

“Since 2000, apart from renewables, it has been the fastest-growing global energy source. It’s the second source of primary energy after oil, and provides more than 30% of global primary energy needs.”

Australia, along with the US, Russia, China and India, has the biggest individual coal reserves, with the principal use still in electricity generation.

Coal-fired power plants produce 41-42% of the world’s electricity, and Mills said that in the coming years, electricity will continue to be provided by many different generating technologies, but the projected combinations are highly site-specific.

The IEA World Energy Outlook 2012 suggested that, for the foreseeable future, power production from most sources will continue to increase.

“In many countries, coal and renewable energy systems are being deployed at greater percentages and, thus, there is increased interest in how to optimally integrate these systems. In fact, there are a significant number of opportunities,” Mills said.

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