The sun can help coal fired power plants burn less coal by pre-heating the water used to make high pressure high temperature steam during periods when the sun is shining. In other words the sun would do part of the work of producing high pressure/ high temperature steam and in this manner the overall hybrid solar/coal power plant would use less coal than a coal only power plant would need to produce the same amount of electric power.
A significant cost of any solar thermal plant is the complex of boilers, steam generators, condensers and cooling towers in which water is boiled to produce high pressure steam that drives turbines transforming mechanical energy into electric energy and that recovers as much of the low pressure low temperature steam as possible in order to re-cycle it through the power cycle again. Roughly forty percent of the upfront capital cost of a standalone solar thermal electric power facility is in building the steam powered thermal electric portion of the facility that is critical in transforming the concentrated thermal energy that has been produced by the solar arrays into electricity. Maintaining and operating this portion of the power producing facility is also a significant part of the on-going operating costs.
In comparison the large arrays of solar troughs (or mirrors focused on a solar tower) that collect and concentrate the sun’s heat amount to around 50-60 percent of the total cost of a standalone solar thermal plant.
Leverage the Existing Electric Energy Producing Infrastructure of Current Coal Fired Thermoelectric Power Plants to Lower the Cost of Solar Thermal Power
By pairing solar thermal collecting arrays with existing or proposed coal fired thermoelectric power plants this very large cost – that would be necessary in a standalone solar thermal plant — can be avoided, in this manner significantly reducing the per kilowatt hour cost of the solar portion of the hybrid solar/coal plant. Various estimates have calculated that solar thermal energy could be between 30 to 50 percent cheaper by hitching a ride on existing thermoelectric power plants. This would bring the cost of solar thermal electric energy below 12 cents per kilowatt- hour or even lower making it competitive with existing grid power.
Another advantage is that because coal fired thermoelectric power plants operate at a higher temperature the overall efficiency of energy conversion from thermal energy into mechanical and hence electric energy operates at this higher level of efficiency. Existing solar thermal designs operate at around 400°C versus 500°C or higher typical in large thermoelectric plants. By pairing solar power with the existing power plant the solar contribution to the overall energy output also operates at this higher energy conversion efficiency of around 45% versus the 38% typical in existing solar thermal electric plants.
As Hank Price, director of technology at Abengoa Solar said, “It’s potentially the most cost-effective way to get significant solar power on the grid”.
The energy contributed by the sun reduces the amount of coal that the power plant needs to burn and in fact achieves a comparable reduction in green house gas emissions as would be achieved by a standalone solar power facility of similar size, but at a much lower initial cost.
Abengoa Solar and Xcel Energy Announce Solar/Coal Hybrid Power Project
Abengoa Solar, a large Spanish utility scale solar power producer and Xcel Energy, Colorado’s largest electrical utility, have begun modifying the Cameo coal plant near Grand Junction in Colorado so that portion of the energy needed to heat water is provided by the sun. This is a demonstration project and the solar contribution will be small (somewhere around 3%), but could easily be scaled up by adding more mirrors. As much as ten or fifteen percent of the total energy needs of existing coal fired power plants that are suitably sited in sunny regions and with enough surrounding land to build the arrays could come from the sun.
Not a Panacea, but it is a Low Hanging Fruit that Can Help Build out the Solar Thermal Industrial Base and Help Reduce Global Greenhouse Gas Emissions in the Meantime
Anything to do with the continued mass burning of coal is anathema to many environmentalists and many find it hard to pair the notion of renewable energy with these green house gas spewing fossil fuel dinosaurs. But once one gets past the initial instinctive distaste it is an idea that makes good sense for those coal fired plants that are sited in sunny regions and that have enough surrounding area to support the solar collecting fields. This will not change the world by any stretch of the imagination, but it can help at the margins making some of our country’s (and the world’s) coal fired power plants somewhat less polluting and fossil fuel consuming than they currently are. Additionally these solar-coal hybrids could help sunny regions meet their greenhouse gas reduction targets.
Additionally, because of the major cost savings – in the solar portion of the total power system — of these solar-coal hybrids, it will make it easier to justify adding solar power to the grid. If major utilities begin to retrofit existing coal fired power plants in suitable areas with solar power assists then the entire solar thermal industry manufacturing base will be propelled from a marginal small scale position into becoming a much larger producer.
As this happens, economies of scale and attendant improvements in the manufacturing process and solar thermal technology (such as in the glass for the mirrors and so forth) will help to create a strong solar thermal industrial base that will then be able to stand on its own and lower its own costs to grid parity for stand alone systems.
In addition in areas where there are abundant low grade geothermal resources, in many places in the American West for example, a geothermal-coal hybridized power plant could use less coal. As with the solar-coal hybrid the geothermal resources would be used to preheat the water for the boilers saving coal.
© 2009, Chris de Morsella. All rights reserved. Do not republish.