Solar Thermal Electricity: Catching the Eye of Utility Companies

POSTED: Friday, March 28, 2008

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The American Southwest has some of the greatest 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, while finding solutions to environmental issues.

"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."

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.

Photo: Ausra's facility in New South Wales, Australia. Courtesy of Ausra.