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Sunday, March 30, 2008

Solar Thermal Electricity: Can it Replace Coal, Gas, and Oil?

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 can supply over 90% of grid power, while reducing carbon emissions.

“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?
Will we use large banks of batteries or burn candles?

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 recflectors or parabolic mirrors 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, say, 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.

Peak Power: The First Wave of Solar Thermal Plants
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.

Because the electric grid needs to be able to handle these peak loads, capacity is built to specifically handle these loads. Natural gas and oil 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.

“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 Load: Replacing Coal Power
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.

Generating electricity around the clock with solar thermal technology relies on storage systems that run turbines long after the sun sets. “Ausra has a very active energy storage R & D group and we will be prototyping a couple of systems this year here in the US,” said John O’Donnell.

Solar Energy Storage
This 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.”

The future certainly looks bright for solar thermal technology as concern over climate change increases. Global demand for electricity is growing rapidly, requiring clean solutions.

Original here

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