Sunday, November 22, 2015

Flexible Coal: Better to Wear Away Than Rust Away

"Flexible Coal" with current base-load power stations converted to peaking plants, may provide a way to increase the use of renewable energy and reduce greenhouse gas emissions. Photo-voltaic and wind generated power are intermittent: when the sun stops shining, or the wind stops blowing, the energy production stops. Conventional wisdom has been that these renewable sources could not make up more than a small fraction of energy generation, until an affordable way to store that energy was found.

The problem was that coal fired power stations, now used to provide the base-load in countries such as Australia, could not be simply switched on when needed. However, the report "Flexible CoalEvolution from Baseload to Peaking Plant", from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, indicates that with some limited hardware modifications and changes to  operational practice, coal fired power stations can be cycled on and off and run at lower output than previously thought (less than 40% of capacity). Cycling the plant does damage equipment and limit its life expectancy, but may be preferable to scrapping a working plant and having to replace it with an alternative such as gas power.

Modifying coal power stations to provide a backup for renewable energy could significantly reduce greenhouse gas emissions far quicker than storage options, such as batteries. Instead of coal providing the base-load and renewable energy supplementing this, PV and wind could provide most of the energy on most days of the year. Coal power would just be switched on when needed: on cloudy windless days, at peak times during the day and at night. Also excess renewable power could be used to heat the coal station's equipment, so it is ready to start more quickly and also reduce damage from cooling.

The conversion of coal stations to peaking plants would provide a political solution for the Australian Government, needs to find a way to reduce greenhouse gas emissions, while not being seen to be damaging the Australian coal industry. Obviously off-peak coal power stations are not a long term option, as they still will emit significant amounts of carbon dioxide pollution. However, this could be a useful interim measure for the decade or so it takes for storage of renewable energy to become practical.

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