Archive for solar thermal

Concentrating Solar Power: An In-Depth Look

I recently interviewed several industry participants and research scientists about Concentrating Solar Power (CSP) and associated thermal storage. 
Several articles came out of these interviews:

Why Concentrating Solar Power Should not Try to be Coal

The Solar Projects that Won’t be Built

What the Future of Concentrated Solar Power Might Look Like (This one made the folks at Ausra uncomfortable, and so they asked to respond.)

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Heating a building with heat from a road

The December 6 Technology Quarterly from The
Economist
magazine profiles
a Dutch office building which is both heated and cooled using heat (or cold) from the asphalt of the road outside the building
, as opposed to the more conventional use of solar thermal panels on the building’s roof.  The article optimistically ends,

The result is cheap heating in winter and cheap cooling in summer. And there is a bonus. Summer heating softens asphalt, making it easier for heavy traffic to damage the road surface. Dr de Bondt’s system not only saves electricity, but also saves the road. Expect to see more examples of it, in other countries, soon.

While this is a very elegant solution, the author fails to grasp that,
because the road is essentially an unglazed thermalOoms collector, and only gets
warm in the summer or cool in the winter, requiring that seasonal heat be stored.   Summer heat from the asphalt is used to heat the building in winter, while the chill of the inter road cools the building in summer. 

In this particular case, seasonal storage is accomplished with heat exchangers placed in not one, but two separate natural aquifers near the building.  The fortunate proximity of two such aquifers is extremely rare.  While this is a very elegant way to heat and cool a building, the lack natural aquifers in which to store seasonal heat will likely prevent widespread adoption of this
technology, no matter what the author believes.

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Transport Fuels and Solar Technologies: Bird’s Eye View

For my last couple AltEnergyStocks Columns, I’ve been taking a step back and looking at how we can get an understanding of the broad trends of energy technologies. Last week, I added to the Visual comparison of Electricity Generation Technologies I did last spring with a new Visual Comparison of Transport Fuels.

Following up, today I published a look at the varius solar technologies through the lens of their applications.

Before we go back to looking at trees, I hope you enjoy this look at the forest.

(and don’t miss the National Tour of Solar Homes next Saturday)

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Denver Tour of Solar Homes Sneak Peak; links to National Tour

Preview the Denver Tour of Solar Homes Online


The Denver area Tour of Solar Homes takes place in less than a month, and this year you can preview some of the buildings involved online. 
Check out the Sneak Preview on the right-hand side of the
Tour of Solar Homes page on the CRES Web site

.

 

The 2007 Tour of Solar Homes will take place on Saturday, October 6 in Denver and most locations around the state.  However, some of the activities are slightly different. 
The Boulder tour will take place on Saturday, September 30. 
And the tour in Pueblo will span two days: October 6 – 7. 
See a complete listing of solar home tours in Colorado on the American Solar Energy Society Web site.

 

National Solar Tour

 

Outside of Colorado, people you can find tour in your own community by visiting the National Solar Home Tour website.

 

Volunteers Needed for the Tour of Solar Homes October 6

CRES needs volunteers to help with the Denver Metro-Area Tour of Solar Homes on Saturday, October 6.  If you step forward, you will assist homeowner with visitors.   

There are two shifts: morning from 8:30 a.m. to 12:30 p.m., and afternoon from noon to 4 p.m.  

Volunteers are welcome to spend the half-day they are not working touring homes themselves. Volunteers are also invited to attend a workshop free of charge from 6 – 8 p.m. Thursday, Oct. 4 titled "Solar Photovoltaics and Xcel Energy’s Solar Rewards Program" and presented by Jeff Scott of SolSource and Juliea Gauthier of Xcel Energy.  The
workshops take place at the National Renewable Energy Laboratory (NREL) Visitor’s Center at 15013 Denver West Parkway in Golden, which is two blocks west of the Denver West Marriott at I-70 and Denver West.

Following the workshop, veteran volunteer John Avenson will give a brief orientation for volunteers about the duties the day of the
Tour of Solar Homes
. To volunteer, contact Patty Roberts via email at: patty at pacificmillimeter dot com

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CSP for Dictators

When I heard
France had offered to provide a nuclear reactor
to power a desalinization
plant in Libya, it knocked me for a loop.  I do believe in carrots to show
countries that we don’t always get along with that there is some reason to be on
our good side, but I fail to see any circumstances under which adding one more
batch of radioactive material (even if not bomb-making grade) in a troubled
region of the world is going to aid our long term security.

If we want to help Gaddafi (or
perhaps pay him off for returning hostages
,) wouldn’t it make more sense to
give him something just a little less dangerous?  Concentrating Solar Power
(CSP) is ideally suited for Libya’s hat and dry climate, and it works well for
desalinization… why not use this opportunity to advance CSP technology, and
not have to worry about proliferation to boot?

That’s the question I ask in my most recent Alternative
Energy Stocks
article.  And while I’m at it, I ask similar questions
about our relations with Iran and North Korea. 

Click
here to read the entire article.

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Visual Comparison of Electricity Generation Technologies

I just put together a couple graphs for a talk I’m giving on Monday to give people a visual feel of the various technologies for generating electricity.  These come with a gigantic caveat: the numbers are far from precise.

With changing technologies, it’s impossible to represent any of this with a single number anyway.  I’m trying to show how the technologies compare to each other, and I used four parameters:

  • Cost ($/MWh),
  • Availability (better the closer the profile of the technology matches a normal demand curve (wind is bad, baseload is okay, dispatchable is best, solar),
  • Emissions (and I count waste storage when it comes to nuclear),
  • Bubble sizes represent the size and durability of the resource (I’ve tried to combine in one number how much power we can get from the resource, but also how long supplies of fuel will last.) 

In both charts, the “best” technologies are in the upper left (low cost, low emissions, and available when we need them.)

I know that I’m going to upset a lot of people because I was too harsh with their favorite technology, so feel free and comment on the numbers I’m using, but also please provide references for where you get your numbers.  Most of these are off the top of my head, so their accuracy is admittedly questionable.   Here are the numbers I used to make the graphs.

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Holistic Approaches to Energy Problems

H. L. Mencken said, “For every human problem, there is a neat, simple solution; and it is always wrong.”  When it comes to solving the problems of peak oil and global warming, I also think that the loudest barking is up the wrong tree.  We look for the quick fix, trying to find a substitute energy source that allows us to change the way we do things little as possible, when the real problem is actually what we’re doing, not how we’re doing it.   We need holistic solutions, not quick fixes.

Too abstract?  Here are some concrete examples:

 Problem: Peak Oil

Quick fixes: Ethanol and slight increases in vehicle efficiency standards.

Holistic solutions: Change our driving culture and infrastructure, by changing the way car use is priced from fixed charges to a per mile basis (“Pay as you drive”).   Removing subsidies to use cars when other forms of transport are available, and redesigning our cities to make them easier to get around on foot, bike, and public transport.  Like other holistic solution, all these steps increase safety and reduce congestion, reduce obesity and associated health problems, as well as reducing the use of gasoline.

Problem: Wind and Solar are intermittent resources, but coal produces too much CO2 and natural gas prices are rising rapidly.

Quick Fixes: Nuclear power and “Clean” Coal.

Holistic Solutions: Shift our demand for electricity to times when it is available, by using time of use pricing, energy storage and demand alignment, and distributed energy storage such as plug in hybrid vehicles.

Investing opportunities:On thing that’s striking about these examples is it’s much easier to find investment opportunities in the quick fixes than in the holitistic solutions.  To invest in ethanol, you can just buy ADM or one of the multitude of ethanol stocks that have been going public recently, but I have yet to come up with a satisfactory way to invest in better urban planning (except buy a house in a walkable community, which is something I’m planning on doing this summer.   Stapleton is the community.  I currently live there, but I’ve been renting and waiting for the end of the housing bubble.  I actually don’t think that housing is going to go up again any time soon, but I’m tired of waiting.) 

The investment landscape is a little better when it comes to energy management.  Itron and Siemens both have divisions that help utilities manage their grids better, and there are many battery and other energy storage companies to choose from.  Still, it’s a lot harder to pick through battery companies than to just buy a nuclear powered utility or uranium miner.

Holistic solutions, by their nature, have weak boundaries… the benefits tend to be diffuse, and spread over society as a whole, so it is difficult to charge fairly for them.  This, I think, is why there are so few companies pursuing them when they can pursue a quick fix that they can charge for up front.  

Companies have an obligation to their shareholders to make money.  It’s our job, as human beings, to work towards regulations that make it easier for companies to make money with holistic solutions that actually solve the problem than it is to make money with quick fixes that just cover the problem up.

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They do it with Mirrors: Concentrating Solar Power

Note 5/3/09 Some more recent CSP articles are here.

I’ve just spent some time reviewing a pile of reports on concentrating solar power (CSP) technologies for Ratepayers United Colorado (RUC), so here is a summary of the various types.

 

Technology descriptions

        Concentrating Photovoltaic

o       This technology uses mirrors or lenses to focus sunlight on high-efficiency photovoltaic chips.  The extra sunlight makes it worth the expense of making a more efficient higher complexity chip because each chip can convert more sunlight to electricity, with conversion efficiencies often twice as high as the efficiencies of conventional soar panels.  This also has the advantage of saving silicon (which is in short supply) for making chips.  Problems are that they do not work as well as conventional panels in diffuse light through clouds (because the light cannot be focused) so they are only appropriate for areas with very little cloud cover, and the extra light heats the chips more, which lowers their efficiency, and so may require some sort of additional cooling loop.

o       Article links:

o       http://thefraserdomain.typepad.com/energy/2006/03/concentrix_conc.html

o       http://thefraserdomain.typepad.com/energy/2005/11/stellaris_conce.html

        Parabolic trough

o       The oldest CSP technology, parabolic trough plants, known as SEGS 1 through 9, have been operating reliably in theParabolic solar trough technology  -  such as this SEGS plant - will be reborn in Red Rocks, California.
California and Nevada deserts since the 1970.  Parabolic trough plants work by focusing sunlight on pipes by means of parabolic mirrors.  These pipes contain a working fluid (several have been used, from water and superheated steam to molten nitrate salts.)

o       Parabolic trough technology is currently experiencing a revival, with several new plants being built.  The using of Organinc Rankine Cycle generators allows solar trough plants as small as 1 MW to be built (such as the new Saguaro plant north of
Tucson, AZ.

o       Parabolic trough technology allows energy to be stored as heat, which is much less expensive than storing electricity.  This allows the energy from these plants to be available at times of peak demand, making the electricity much more valuable.

o       Steve Raabe recently wrote an article for the Denver Post providing a good overview of the prospects of this technology in
Colorado.  The only point that he missed is the potential for hybridization with existing coal and gas plants.  By preheating steam for an existing fossil fuel fired turbine, CSP can make an old power plant operate much more efficiently.  Arnold Leitner of SkyFuel (
www.skyfuel.com) tells me “Our preliminary engineering estimates, satellite imagery of the locations and solar data show that SkyFuel could supply 50-100 MW-electric solar steam to the Comanche power plants generating an estimated 65,700-131,400 MWh of pure solar power at the facility via the existing steam turbine. SkyFuel could deliver this solar-generated steam to the power plant at an effective fuel cost commensurate to the fuel cost of burning natural gas at a modern combined cycle power plant at fuel price of 7-8 cents/mmBtu. In other words, through a FuelSaverTM at a coal-fired power plant SkyFuel could provide solar energy at the price of natural gas generation.”

o       Considering that solar power is available during peak demand, gas ifered generation is the appropriate cost comparison (as opposed to wind power, which does not deserve (or need) a price premium due to its unpredictable timing.

o       A variant on this called Concentrating Linear Fresnel Reflector (CLFR) uses many thin mirror strips instead of parabolic

troughs to concentrate sunlight from a large field onto just two tubes of working fluid.  This has the advantage that flat mirrors are much cheaper to produce that parabolic mirrors, and also allows for a greater density of reflectors in the array, allowing more of the sunlight to be used.

        Power Tower

o       Power Tower technology is similar to solar trough technology in that it uses mirrors to concentrate sunlight on a working fluid which is then used to superheat steam to run a turbine.  The difference is that the mirrors concentrate all the sunlight onto a single receiver at the top of a tower.  This allows for higher temperatures, but leads to engineering problems because of the high temperature at the receiver.

o       Lower price per watt is theoretically possible compared to trough technology because of the higher temperatures.

o       So far, only two pilot plants have been built and operated, called Solar One and Solar Two (actually the same facility as Solar One, but converted to use nitrate salts as the working fluid rather than superheated steam).    Both Solar One and Two incorporated thermal energy storage.  Due to the success in demonstrating the technology of Solar Two, a commercial 15MW plant Solar Tres is in the planning stations.  This station will incorporate enough thermal storage in molten salt tanks for 24h operation.

        Solar Chimney

o       A Solar chimney consists of a large greenhouse (multiple square miles of area covered by a transparent roof) which is sloped gently up to a central hollow tower or chimney.  The sun heats the air in the greenhouse which then rises up the chimney driving an air turbine (similar to the hydroelectric turbines used to generate power at dams) in the chimney as it rises.  Water filled tubes on the floor of the greenhouse serve as heat storage which allows the chimney to operate even at night and on cloudy days.  The amount of water in the tubes can be changed to alter the profile of power production and match it closely to the power demand the chimney serves.

o       The edges of the greenhouse can actually be used for agribusiness to grow plants, so not all the space taken up is solely devoted to electric production. 

o       The beauty of solar chimneys is that they are extremely low tech, and can be built without heavy equipment using simple materials.  The only exception to this is the turbine, and even that is much less complex than turbines used to generate power from wind, because the wind in a solar chimney is much more regular than naturally occurring winds and storms that wind turbines have to deal with. 

o       The first solar chimney was built in
Manzanares, Spain and ran continuously for 32 months in the late 1980s with 95% availability (considerably better than most coal and nuclear plants.)   See a video tour of this chimney I ran across on EcoGeek.

o       A 200MW chimney is planned by EnviroMission of Melbourne Austrailia for the Austrailian Outback.

o       It may be possible to build solar chimneys on south-facing slopes or simply as an extra layer of glazing on tall buildings with a turbine at the top which would make them even cheaper by avoiding the necessity of building the tall chimney (my idea).

 

        Dish Stirling

o       A Dish Stirling system is a parabolic mirror which focuses heat directly on a Stirling engine, a simple closed-cycle engine which operates simply using any heat source.  Sometimes hybridized with a fossil fuel source to provide heat when the sun is not shining. 

o       Dish
Sterling systems have the advantage of small size and scalability, because each individual mirror-engine system produces only around 25kW, but many can by linked together.

o       Because the suns rays are focused directly on the engine, there is little opportunity for thermal storage, a great advantage of several other thermal concentrating technologies.

o       Stirling Energy Systems currently has a few demonstration systems in operation.  They have signed purchase agreements with two
California utilities to build a total of around 1 GW of electric generation, but both projects are still in early testing phases.

o       According to Sandia National labs, this is the most efficient technology for converting sunlight into electricity.

CSP Technology comparisons

Technology Scale Levelized cost per MWh Pros/Cons Complexity/ deployment

Concentrating PV

Any

$15-$20

No storage option; does not work well on cloudy days

High.  Beginning to be deployed in last couple years.

Dish
Sterling

25 kW per dish

Unknown

High efficiency, modular.  No thermal storage.

Just beginning to be deploy

Parabolic Trough

Most: >50 MW for economies of scale;

Organic Rankine Cycle 1MW+

$8-$18 current

$6 potential

Can hybridize with existing fossil plants.

Storage, well understood technology, needs water for efficient cooling.

Plants operating consistently for 30 years in CA.

Solar Tower

>30 MW

$18+ current,

$5 potential,

can hybridize with existing fossil plants.

Storage.  Potentially cheaper than solar trough. Needs water for efficient cooling.

2 pilot plants with operational history.  First commercial plant now operational.

Solar Chimney

100-200MW

Not yet known.

Baseload power, low maintenance.

Low complexity, great potential for 3rd world.

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