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Solar Energy

Published on March 10th, 2008 | by Michelle Bennett

22

Clean Energy Intro: Solar Thermal



That’s hot! Solar Thermal at work.What if you could produce clean solar energy night and day, rain or shine, and never hit the bank for a single P.V. solar panel? Photo voltaic panels can be pricey, so the solar industry is always trying to lower costs and boost efficiency in the quest to compete with coal. One fast-growing, cost-effective solar technology uses heat to generate energy 24 hours a day, and it can store energy without batteries. In this post I’m going to investigate solar-thermal technologies.

It’s called “Concentrated Solar Power” or C.S.P. The idea is simple; no complex chemistry or fancy silicon wafers required. Glorified mirrors shaped like satellite dishes (or parabolic troughs) direct the sun’s rays towards a reservoir. The concentrated solar heat boils water into steam, and steam powers a turbine. When the water cools off it’s collected and cycled back through the system. The mirrors can even track the sun across the sky to maximize efficiency. Water is not the only fluid that can be used, but its unique properties have made it popular. More on that below.

If you remember your history, the industrial revolution was powered by steam – factories, trains and boats boiled water by burning coal. Eventually we moved on to the internal combustion engine because you got more bang for you buck – literally. These ubiquitous engines convert controlled explosions into propulsion or electricity. The problem with combustion is the waste products and their effects on our health and environment. With solar thermal, the only waste would come from building the power plant.

So how does C.S.P. produce electricity at night? It takes advantage of a unique property of water: very high specific heat capacity. That means it takes a lot of energy to increase the temperature of water. It also means that water stores heat energy for a long time. Think of a pool, lake, or the ocean. It stays warm long after the sun goes down and even through cooler days in autumn. Water has the second-highest specific heat capacity of any known substance, which makes it perfect for storing large amounts of heat energy, just as a battery stores electricity. In the form of steam, water can continue to generate electricity when the sun is down and recharge the heat “battery” when the sun is up.

Another way to store that heat is with salt – molten salt. Sandia National Laboratories is experimenting with molten salt as a storage medium because of its heat-transfer and economical properties. It also removes the heat storage process from your dynamo so you can recharge your heat batteries and generate electricity separately. The benefit to this system is that if the sun doesn’t shine for days at a time you have a strong back-up “battery”. Their system can store 2-12 hours of energy for a week. We’ve heard from Sandia before, read about their “energy from air” scheme or their solar efficiency world record – both use C.S.P.

A lot of exciting news has been emerging about solar-thermal. It’s been demonstrated as reliable for over twenty years, and new plants are coming online, or being planned, across the world. Energy is not the only benefit of Concentrated Solar Power; it also creates jobs and can use otherwise unproductive land. Empty desert is ideal for this technology – abundant clear, bright days. Some estimates even claim that we could power the entire USA with C.S.P. or even the world (1% of the world’s deserts to be exact). Regardless of such high hopes, the future looks bright for C.S.P.

For …

An animation explaining how C.S.P. works, check out Ausra.

A useful fact sheet, surf Solar Developments.

Hard data, try the Department of Energy.

DIY action, swing by Treehugger.

Solar ovens and more, see this post.

(Image courtesy of Treehugger)

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About the Author

is an environmentalist who loves to write. She grew up across the southeastern USA and especially love the Appalachian mountains. She went to school in the northeast USA in part to witness different mindsets and lifestyles than those of my southern stomping grounds. She majored in English Lit. and Anthropology. She has worked as a whitewater rafting guide, which introduced her to a wilderness and the complex issues at play in the places where relatively few people go. She also taught English in South Korea for a year, which taught her to take nothing for granted.



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  • Cliff Deane

    How does pricing compare with solar/wind in the 1megawatt range?

  • Cliff Deane

    How does pricing compare with solar/wind in the 1megawatt range?

  • http://www.yesonsolar.com Fireofenergy

    America is watching the icecaps melt (and our economy too). This is because we are sending billions of dollars overseas every week!

    Please consider Concentrated Solar Thermal as America’s main power plant. Why? Because CST stores the suns energy as heat for ON DEMAND electricity.

    CST works by using lots of mirrors that reflect sunlight to heat a fluid which fills a resevoir.

    CST is the only energy source that can provide the USA with unlimited clean energy!

    CST would be cheaper than complete CO2 sequesteration needed for clean coal if governments help support its massive deployment. (All energy options have recieved government help)

    CST would also be cheaper than nuclear (they both need help).

    CST only uses desert land, not forests. And can supply the world with unlimited energy.

    Since all renewable energy is labor intinsive, millions of jobs and millions more of secondary jobs would boost the economy such that governments would probably get more taxes back.

    And finally, CST would be much welcomed by most people, unlike “clean coal” and nuclear. There are very few emissions associated with solar.

  • http://www.yesonsolar.com Fireofenergy

    America is watching the icecaps melt (and our economy too). This is because we are sending billions of dollars overseas every week!

    Please consider Concentrated Solar Thermal as America’s main power plant. Why? Because CST stores the suns energy as heat for ON DEMAND electricity.

    CST works by using lots of mirrors that reflect sunlight to heat a fluid which fills a resevoir.

    CST is the only energy source that can provide the USA with unlimited clean energy!

    CST would be cheaper than complete CO2 sequesteration needed for clean coal if governments help support its massive deployment. (All energy options have recieved government help)

    CST would also be cheaper than nuclear (they both need help).

    CST only uses desert land, not forests. And can supply the world with unlimited energy.

    Since all renewable energy is labor intinsive, millions of jobs and millions more of secondary jobs would boost the economy such that governments would probably get more taxes back.

    And finally, CST would be much welcomed by most people, unlike “clean coal” and nuclear. There are very few emissions associated with solar.

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  • MichelleBennett

    Robert: I’ve never heard about this before, how interesting! Since solar thermal, and solar in general, can be limited at an industrial scale to sunny areas a technology that combines different energy collection/storage techniques could potentially make a big impact in darker latitues. I’ll have to investigate further…

  • MichelleBennett

    Robert: I’ve never heard about this before, how interesting! Since solar thermal, and solar in general, can be limited at an industrial scale to sunny areas a technology that combines different energy collection/storage techniques could potentially make a big impact in darker latitues. I’ll have to investigate further…

  • http://www.shpegs.org Robert J. Rohatensky

    SHPEGS is the Solar Heat Pump Electrical Generation System open project that takes some ideas from solar thermal, geothermal and absorption heat transformers into a new idea in energy storage for electrical power generation and structure heating. The project’s focus is to design and build a feasible location independent renewable power system for moderate climates where there is a large electrical demand in winter months, but low solar insolation.

  • http://www.shpegs.org Robert J. Rohatensky

    SHPEGS is the Solar Heat Pump Electrical Generation System open project that takes some ideas from solar thermal, geothermal and absorption heat transformers into a new idea in energy storage for electrical power generation and structure heating. The project’s focus is to design and build a feasible location independent renewable power system for moderate climates where there is a large electrical demand in winter months, but low solar insolation.

  • http://greenchemistry.wordpress.com/ James Bashkin

    This is an excellent post! Thanks for the information. Jim

    Nearly nothing but novels

    Chemisty for a sustainable world

  • http://greenchemistry.wordpress.com/ James Bashkin

    This is an excellent post! Thanks for the information. Jim

    Nearly nothing but novels

    Chemisty for a sustainable world

  • Steve Block

    A few clarifications here:

    The typical heat transfer medium for a trough-based CSP plant is an oil, which can be heated to several hundred degrees F. The oil is then used in a heat exchanger to boil water and run the steam through a turbine and power a generator.

    Solar power towers, like the photo at the top of this post, are neat but not commercial and are unlikely to be commercial. The parabolic trough plants are what has worked on a large scale in the past and what is being used in current CSP projects. As an engineer who has 30+ years of experience with solar thermal power told me this morning “I can’t imagine anyone would build a power tower today.”

    Lastly, in response to the first comment, it is not really useful to consider solar and wind to be competing energy sources. Both are highly dependent on a location-specific resource. Wind is much more widely available and generally easier to develop, and is much more cost effective. Solar CSP requires flat land but is generally more predictable of a resource and has inherence advantages in terms of generating during peak hours, but is much more expensive.

    One must also be careful about calculating how much land is required for the two technologies. For solar CSP it is basically the amount of land the plant takes up, much like a conventional power station. For wind land use can be calculated as the total footprint of land affected by the project, but this skews high as only a fraction of that total land is actually directly used by the turbines.

  • Steve Block

    A few clarifications here:

    The typical heat transfer medium for a trough-based CSP plant is an oil, which can be heated to several hundred degrees F. The oil is then used in a heat exchanger to boil water and run the steam through a turbine and power a generator.

    Solar power towers, like the photo at the top of this post, are neat but not commercial and are unlikely to be commercial. The parabolic trough plants are what has worked on a large scale in the past and what is being used in current CSP projects. As an engineer who has 30+ years of experience with solar thermal power told me this morning “I can’t imagine anyone would build a power tower today.”

    Lastly, in response to the first comment, it is not really useful to consider solar and wind to be competing energy sources. Both are highly dependent on a location-specific resource. Wind is much more widely available and generally easier to develop, and is much more cost effective. Solar CSP requires flat land but is generally more predictable of a resource and has inherence advantages in terms of generating during peak hours, but is much more expensive.

    One must also be careful about calculating how much land is required for the two technologies. For solar CSP it is basically the amount of land the plant takes up, much like a conventional power station. For wind land use can be calculated as the total footprint of land affected by the project, but this skews high as only a fraction of that total land is actually directly used by the turbines.

  • Michelle Bennett

    wow, thanks for the great comment!

  • http://www.EDF.org Lauren Guite

    Solar thermal power plants are also more efficient than wind farms (which need about six times the acreage per watt produced) and biofuels (which need 30 times the land per watt).*

    Thanks for the great post!

    Lauren Guite

    Environmental Defense Fund

    *Earth: The Sequel (www.EarthTheSequel.com), page 65.

    (Ausra is just one of the many innovative start-ups racing to reinvent energy and fight global warming that you can read more about in Earth: The Sequel!)

  • http://www.EDF.org Lauren Guite

    Solar thermal power plants are also more efficient than wind farms (which need about six times the acreage per watt produced) and biofuels (which need 30 times the land per watt).*

    Thanks for the great post!

    Lauren Guite

    Environmental Defense Fund

    *Earth: The Sequel (www.EarthTheSequel.com), page 65.

    (Ausra is just one of the many innovative start-ups racing to reinvent energy and fight global warming that you can read more about in Earth: The Sequel!)

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