Green Living

By Sarah Lozanova

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Solar Thermal Electricity: Can It Replace Coal, Oil, and Gas? Twice the Energy for One Third of the Carbon

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The American Southwest has some of the richest solar resources on the globe, it yet remains largely untapped. This trend may be changing as solar technology matures, market forces shift and concern for climate change mounts.

     One of the most common arguments against large-scale use of renewable energy is that it cannot produce a steady, reliable stream of energy, day and night. Ausra Inc. does not agree. They believe that solar thermal technology has the potential to supply over 90% of grid power, including future demand increase for electric vehicles.

     “The U.S. could nearly eliminate our dependence on coal, oil and gas for electricity and transportation, drastically slashing global warming pollution without increasing costs for energy,” said David Mills, chief scientific officer and founder of Ausra.

     You may be wondering, how will we have electricity at night or during cloudy weather if solar power is generating a majority of our electricity? Will we use large banks of batteries or burn candles?

Solar Thermal with Storage Capacity
     The ability to utilize solar thermal technology after the sun sets is made possible by a storage system that is up to 93% efficient, according to Ausra’s executive vice president John O’Donnell.

     High efficiency is achieved because solar thermal plants do not need to convert energy to another form in order to store it and do not rely on battery technology. Flat moving reflectors or parabolic troughs focus solar energy to generate heat. This heat generates steam that turns turbines, thus generating an electric current.

     If you want to generate electricity at 3 am, heat from the sun can be stored for later use. This gives solar thermal technology the ability to not just produce peak power, but also generate base load electricity.

     Heat storage is not a new technology, having been used for plastic manufacturing and petroleum production for a long time. Solar thermal plants have a cost advantage compared to photovoltaic technology because energy can be stored as heat without being converted to another form or relying on batteries.

     “My favorite example in comparing energy storage options is on your desktop,” said John O’Donnell. “If you have a laptop computer and a thermos of coffee on your desk, the battery in your laptop and the thermos store about the same amount of energy. One of them costs about $150 and the other one costs maybe $3 to $5. On the wholesale level, storing electric power is at least 100 times more expensive than storing heat.”

Peak Power: Low Hanging Fruit for Solar Thermal Energy
     The maximum amount of electricity demand on the power grid occurs during weekday afternoons and evenings in the summer months in most regions of the United States. This is largely caused by air conditioning loads, which gobble up electricity. Solar energy availability however starts to drop in the late afternoon, before peak load has started to wane.

     Because the electric grid needs to be able to handle these peak loads, capacity is built to specifically handle these loads. Natural gas typically comes to the rescue to produce this electricity. Although these plants are expensive to operate, they are cheaper to construct than most of the alternatives. They are fast to start, producing power in 30 minutes or less.

     Additional power plants are constructed just to generate electricity for the times when it is needed most. This causes peak electricity to be more expensive. A kilowatt hour of electricity at 3 pm and 3 am does not come with the same price tag to the utility company.

     Now add the uncertainty of the price of natural gas. “No utility can tell you what the cost of power will be from a gas plant, five or ten years from now,” said Frederick Morse, senior advisor for the U.S., Abengoa Solar. “From a solar plant, the price is fixed. There is no fuel component to alter it.”

     This is where solar energy can truly shine. “Adding solar plants that reliably generate until 10 pm displaces the highest cost alternative power,” said John O’Donnell. “That is the first wave of solar thermal plants. The daily and seasonal variation in grid load in the United States matches solar availability.”

Base Power: Eventually Replacing Coal

     Base load is the minimum amount of electricity demand placed on the power grid over a 24 hour period. Coal and nuclear plants commonly supply this energy. These plants can take hours or even days to heat up to operating temperatures and are run more continuously than peak power plants. Due largely to the lower cost of fuel, these plants can produce electricity at a lower cost. If a carbon tax is implemented in the future, this will increase the cost of electricity generated from coal.

     Due to cost, infrastructure and technology hurdles, it will be a while until we see solar energy generating large-scale base load capacity, thus replacing nuclear and coal power plants. Some of the factors that will push this along are a strong national high voltage transmission system, solar technology advances, high fossil fuel costs, a longer-term extension of the commercial solar tax credit, and a carbon tax.

Twice the Energy for One Third of the Carbon

When generating electricity, roughly two-thirds of the energy is lost. Heat is created as a byproduct to spin turbines and later wastes away in cooling towers. Considering the environmental impact of mining and burning fossil fuels, it is certainly advantageous to increase the usable energy output. As fossil fuel prices increase, efficiency will increasingly become more and more lucrative. Chicago has committed to produce 1.5 billion kilowatt hours of electricity by 2010 with a process called combined heat and power or cogeneration, which finds use for the generated heat. This process can be over 90% efficient.

     Excess heat can be used for dehumidification, heating water, and process heat. Ideally, the electricity and heating loads for the given application are similar to maximize the use of both the generated electricity and the heat byproduct. Savings are increased when the electricity and the heat can both be utilized throughout the year. These two factors maximize the financial and environmental benefits of cogeneration.

     The most common applications of cogeneration are usually on a smaller scale compared to large power plants. It is inefficient to pipe heat for long distances and it has infrastructure requirements. Hospitals, prisons, paper mills, oil refineries, waste water treatment centers, and even large towns can be good candidates for this technology. Your car can even be an example, with waste heat from the engine being used to warm the interior. There are several example of cogeneration right here in the Chicago region that are national examples of innovation.

Antioch Community High School

     Twelve micro-turbines are powered by landfill gas (LFG), producing .36 megawatt hours of electricity and heat for the 250,000 square foot school. This was the first high school in the country to utilize LFG for this purpose and savings are an estimated $100,000 annually in energy costs.

     LFG is pumped from an adjacent landfill and consists mostly of methane and carbon dioxide. Methane is one of the most potent greenhouse gases, with a greenhouse potential tewnty times greater than that of carbon dioxide. Burning methane gas reduces its detrimental effects, creating carbon dioxide and water and byproducts. The annual greenhouse gas reduction of the cogeneration facility in Antioch Community High School is equal to removing 3,000 cars from the road.

Chicago Museum of Science and Industry

     Since 1933, the museum has been one of the largest tourist attractions in the city and now has another noteworthy feature. A 1.75 megawatt cogeneration system was installed that produces electricity, heat, and dehumidifies the museum.

     The dehumidifiers can treat an impressive 10,000 cubic feet per minute and operate approximately 3,380 hours a year. Because the heating season in Chicago is about seven months of the year, the dehumidifier provides value to the museum during the cooling months as well. The more use the heating and dehumidification systems can get throughout the year, the more benefit the system can provide, both financially and environmentally.

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After earning an MBA in sustainable management from the Presidio School of Management in San Francisco, Sarah Lozanova joined Solar Service Inc. She is a writer for Green Options Media and co-founder of Trees Across the Miles, a non-profit urban reforestation project. Sarah can be contacted at Sarah.Lozanova@gmail.com.

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