How to Convert a Coal Power Plant to Solar Thermal

How to Convert a Coal Power Plant to Solar Thermal

Converting an existing coal power plant to solar thermal energy offers several potential benefits, including reducing air pollution and greenhouse gas emissions. However, this transition also comes with significant engineering and economic challenges that must be addressed. This article provides an in-depth look at the technical feasibility and steps involved in converting coal power to solar thermal.

Evaluating the Existing Coal Plant Infrastructure

The first step is thoroughly evaluating the existing coal power plant infrastructure. This includes:

  • Assessing the boiler, turbine, generator and any other key components to determine if they can be modified to work with a solar thermal system or if new equipment is needed. Older plants may need more modifications.

  • Surveying the plant site to identify areas suitable for installing solar thermal collectors like parabolic troughs or solar power towers. South-facing areas without shading are ideal.

  • Analyzing the electrical grid connection to ensure it can handle the intermittent nature of solar thermal energy. Upgrades may be needed.

  • Considering the coal plant’s age, efficiency and remaining useful life. Converting newer plants is generally more cost-effective.

  • Estimating costs for equipment modifications, additions or replacements. This early cost analysis informs overall feasibility.

Properly evaluating the existing infrastructure provides critical data to determine if conversion is possible from an engineering perspective and cost-effective based on the remaining useful plant life.

Designing the Solar Thermal System

If the coal plant is a good candidate, the next step is designing the solar thermal system:

  • Choosing parabolic trough or solar power tower technology. Power towers can achieve higher temperatures with heat transfer fluids like molten salt.

  • Determining the solar field size to provide sufficient thermal energy to replace coal. More collectors offset cloudy weather.

  • Selecting heat transfer fluids like oils or molten salt that store thermal energy. Molten salt allows higher temperature storage.

  • Sizing thermal energy storage tanks, typically enough for 8-15 hours of plant operation.

  • Integrating steam generation from the solar thermal system with the existing steam cycle.

  • Incorporating backup fuel sources like natural gas for periods without sufficient solar energy.

  • Designing a new electrical substation if transmission capacity needs upgrading.

The system must be custom-designed for the specific coal plant site and infrastructure. Thermal energy storage enables generation to continue even when the sun isn’t shining.

Permitting and Construction

Permitting a converted coal plant involves navigating regulatory requirements at multiple levels:

  • Local permits for construction, land use and environmental impact.

  • State environmental agency approvals for changes in plant emissions.

  • Regional transmission organization acceptance of grid interconnection and solar generation.

  • Potential federal permits from the Environmental Protection Agency depending on plant emissions.

Navigating the permitting process can take 1-3 years for environmental impact assessments, public hearings and regulatory approvals.

Once permitted, construction may take 1-2 years for solar equipment installation and plant modifications. Plants must often continue some coal operations until solar integration is complete.

Operating a Converted Solar Thermal Plant

Operation and maintenance of a converted solar thermal plant differ from traditional coal plants:

  • Daily startup requires carefully synchronizing the solar heat source with steam generation and turbine loading.

  • Solar collectors require regular cleaning and maintenance for optimum efficiency.

  • Thermal storage tank maintenance is crucial for storing excess daytime heat.

  • Personnel need extensive training to master solar plant operation.

  • Reliability and efficiency may suffer initially but improve with experience.

  • Burning backup fuel during extended clouds or nighttime adds complexity.

While more challenging to operate than a standard coal plant, converting to solar thermal reduces fuel costs and environmental impacts.

Financial Incentives for Conversion

Converting existing coal plants to solar thermal represents a major investment that requires extensive incentives:

  • Federal investment tax credits can offset 30% of capital costs.

  • State or utility incentives can further defray conversion costs. These vary greatly.

  • Federal clean energy grants and loan guarantees provide low-cost financing.

  • Selling excess daytime solar power to the grid can generate added revenue.

  • Potential carbon trading credits if a carbon price is in place.

Incentives can improve the economics of conversion, but costs may still outweigh benefits for plants with significant useful life left.

Case Study: The Sulphur Mountain Solar Thermal Project

One successful project is the Sulphur Mountain Solar Thermal facility in Colorado. This converted an old 25 MW coal plant to solar thermal with parabolic trough collectors. Conversion took 2 years at a cost of $62 million, offset by a $36 million DOE grant. The plant can now generate 12 MW of solar power and has reduced carbon emissions by over 40,000 tons per year. While technically and economically challenging, this project shows coal to solar thermal conversion is achievable.

Converting existing coal plants to solar thermal energy holds promise to reduce carbon emissions from the power sector, but involves substantial technical and economic hurdles. With sufficient incentives and political will, more coal to solar thermal conversions may become viable and further decarbonization.