About Dish/Engine Concentrating Solar Power

Dish/engine concentrating solar power uses a mirror in the shape of a dish to collect and concentrates the sun's heat onto a small area where a receiver is located.  The receiver transfers the sun's energy to a heat engine, usually a Stirling cycle engine, that converts the energy into power.  Of all the solar technologies that hve been demonstrated on a practical scale the solar dish has the highest efficiency, 30%.   The electricity needs of the entire U. S. could theoretically be met by such a system, in the desert, in an area 100 miles on a side. 

The six dish system, shown at left, was installed by Stirling Energy Systems (SES) at Sandia National Laboratories in early 2005, the largest array of dish/Stirling systems in the world. Each unit operates automatically. Without operator intervention or even on-site presence, it starts up each morning at dawn and operates throughout the day, tracking the sun and responding to clouds and wind as needed. Finally it shuts itself down at sunset. The system can be monitored and controlled over the Internet. Experimental models of the Stirling dish technology have undergone more than 26,000 hours of successful solar operation. The cost for each prototype unit is about $150,000. Once in production SES estimates that the cost could be reduced to less than $50,000 each, ($2.00 per watt) which would make the cost of electricity competitive with conventional fuel technologies.

Southern California Edison (SCE) and Stirling Energy Systems have announced an agreement that could result in construction of the world’s largest solar facility, capable of producing more electricity than all other U.S. solar projects combined.  The SCE-SES project represents the first major application of Stirling dish technology in the commercial electricity generation field.  Initially, Stirling would build a one-MW test facility using 40 of the company’s 37-foot-diameter dish assemblies.  Subsequently, a 20,000-dish array would be constructed near Victorville, Calif.  The 20-year power purchase agreement signed August 9, 2005, which is subject to California Public Utilities Commission approval, calls for development of a 500-megawatt (MW) solar project 70 miles northeast of Los Angeles using innovative Stirling dish technology.  The agreement includes an option to expand the project to 850 MW.

Development of modern dish/engine systems began in the late 1970s and early 1980s. This technology used directly illuminated, tubular solar receivers, a kinematic Stirling engine developed for automotive applications, and silver/glass mirror dishes. Systems, nominally rated at 25 kWe, achieved solar-to electric conversion efficiencies of around 30 percent. Eight prototype systems were deployed and operated on a daily basis from 1986 through 1988.

Current dish/engine efforts are being continued by three U.S. industry teams - Science Applications International Corp. (SAIC) teamed with STM Corp., Stirling Energy Systems (SES), and WG Associates with Sunfire Corporation. SAIC and SES together have five 25kW systems under test and evaluation at utility, industry, and university sites in Arizona, California, and Nevada. WGA has two 10kW systems under test in New Mexico, with a third off-grid system was developed in 2002 on an Indian reservation for water-pumping applications.

Dish/engine systems utilize concentrating solar collectors that track the sun in two axes. A reflective surface, metalized glass or plastic, in the shape of a dish, reflects incident solar radiation to a small region called the focus. The thermal receiver, located at the focus, is the interface between the dish and the engine/generator. It absorbs the concentrated beam of solar energy, converts it to heat, and transfers the heat to the engine/generator. A thermal receiver can be a bank of tubes with a cooling fluid, usually hydrogen or helium, which is the heat transfer medium and also the working fluid for an engine.  The most common type of heat engine used in dish-engine systems is the Stirling engine.

A Stirling engine uses heat provided from an external source (like the sun) to move pistons and make mechanical power, similar to the internal combustion engine in your car. The mechanical work, in the form of the rotation of the engine’s crankshaft, is used to drive a generator and produce electrical power.  Working gas temperatures of over 700ºC (1292ºF) and as high as 20 MPa are used in modern high-performance Stirling engines. In the Stirling cycle, the working gas is alternately heated and cooled by constant-temperature and constant-volume processes. Stirling engines usually incorporate an efficiency-enhancing regenerator that captures heat during constant-volume cooling and replaces it when the gas is heated at constant volume.  The best of the Stirling engines achieve thermal-to-electric conversion efficiencies of about 40%.

The collectors track the sun in two axes.  In larger systems the the dish rotates in a plane parallel to the earth (azimuth) and in another plane perpendicular to it (elevation). This gives the collector left/right and up/down rotations. In the polar tracking method, used in some smaller systems, the collector rotates about an axis parallel to the earth’s axis of rotation at a constant rate of 15º/hr to match the rotational speed of the earth. The other axis of rotation, the declination axis, is perpendicular to the polar axis. Movement about this axis occurs slowly and varies by +/- 23½º over a year.

According to a 2001 "Sun-Lab Snapshot" the Boeing/SES system, for which SES has obtained rights and is very similar to the module being marketed, incorporated the following components:

• Collector: 82 facet mirror made with 0.7 mm thin glass with 87.7 m² area, relectivity 0.91
• Engine: Kockums 4-95, 4 cylinder stirling engine 380 cc, working temp 720ºC (1328ºF), with variable pressure control

Rating and performance:

• Module rating: 25 kW at 1000W/m² solar input, Electrical: 480 v, 3 phase 50 or 60 cycle
• Module performance: Peak power 24.9 kW, peak efficiency 29.4%, Annual efficiency 24%

There may have been changes since that time, but that is the best information available.

Resources:

Solar/Concentrating Solar Power/Dish Engine Systems, US DOE Energy Efficiency and Renewable Energy
"Solar Dish Engine", solarpaces.org/solar_dish.pdf (very slow link) 
"Sandia, Stirling to build solar dish engine power plant", Sandia press release, 10/9/04
"Major New Solar Energy Project Announced by Southern California Edison and Stirling Energy Systems, Inc.", Edison International press release, 8/9/05
Stirling Energy Systems Inc., Phoenix, AZ, www.stirlingenergy.com/
"The Boeing/SES DECC Project", Sun Lab Snapshot, August 2001

Technocrati tags: solar power, renewable energy, dish-Sterling systems

Comments

[Robert McLeod]

With a reflectivity of 0.91 they are probably using Aluminium mirrors, rather than the Silver referenced in the 1970s prototypes.

It's interesting that they can get +40 % efficiency out of test units. The theoretical maximum for a single junction Si-cell is 44 % [Shockley, 1961]. Of course, due to entropy limits solar-electric will eventually thrash solar-thermal, even in the Southwest desert, but it could take a long, long time.

I made a post about the efficiency of parabolic mirrors under clouds at my blog the other day that is relevant.

http://entropyproduction.blogspot.com/2005/08/solar-concentrators-under-clouds.html

Unfortunately, these concentrator systems are geographically limited to the Sahara and the Arizona desert.

[Engineer-Poet]

I can't help but notice that the collector area (37 m^2) is considerably less than the roof area of many homes. Also, the az-el mounts required for steering rigid dishes are expensive. This hints that it may be cheaper to cover a roof with individually steerable mirrors (a la Energy Innovations) directing light at a fixed receiver. Control of heat input could be achieved by steering individual mirrors on or off axis as required; an excess of mirrors could be used to compensate for e.g. infrequent cleaning of the mirror array.

If the same $2.00/watt price could be maintained, individual homes could produce power far in excess of their use and at less than retail cost (plus all the hot water anyone could want). The consequences would be earth-shaking.

[JesseJenkins]

"The consequences would be earth-shaking"

I agree with E-P. Energy Innovation's Sunflower solar collectors are very promising. IF (and there's the catch) they can provide aproximately $2.00/watt prices and these suckers can go on people's roofs this could be a very disruptive technology and preferable to the industrial-scale solar farm model being built by SES. However, right now, the sunflower 250 is designed for flat roofs not the angled ones on your typical house limiting them to commercial and industrial applications for now. There's still plenty of room for use in these locations but they need another model for houses (which they say they are working on now). If they can pull it off at low enough cost, these solar collectors and/or thin film pvs could revolutionize distributed solar power. And if equal in price, distributed generation is preferable to power plant-scale generation as making power where it is used is much more efficient (cuts down on costs and energy losses of transmitting power over a transmission line system).

Thanks for another good post. Cheers,
Jesse Jenkins aka WattHead
watthead.blogspot.com

[Jim from The Energy Blog]

I havn't been convinced that the Sunflower is a viable product, but it would be good if it was. If anyone has a link to some real information on it, please let me know. Distributed energy will be great when we get it. I doubt if SES can get anything close to $2.00 a watt for a lower output module that might be affordable for a homeowner. However their is a lot of industry that has enough flat roof space for these units. Even then we will need central power plants. SCE is going to put these in California, not Arizona, so we will see how their efficiency holds up. Their is a lot of power used in CA, AZ, NM, & TX, for a very large market for SES, if these could be put close enough to send the power over the grid. The only information I have is that they are using glass for the collector as I stated in the end of my post.

[Engineer-Poet]

It does not necessarily matter if these units are affordable for individual homeowners. Consider the amount of power available from the premises of:
- Multi-family condominiums.
- Apartment buildings.
- Shopping centers and malls.
- Commercial buildings.
- Municipal buildings.

Worst case, the four homeowners whose property meets at a corner give an easement for a dish on a post there; each one owns a quarter and gets 1/4 of the power. Outlay would be about $12,500 per household and production in good sunlight would be something like 37 kWh/household/day, more than the national average consumption.

(Ye GODS, this blog software is hideously intolerant! It doesn't even allow escaped characters, forget lists.)

[emely]

does anyone kno the bibliography for this website?

[Jim from The Energy Blog]

The bibliography is listed under Resources: at the end of the post. Some of the very minor sources may have been left out.

[Z2010]

Stirling engines are difficult to build (tight tolerance)and have to many moving parts for long MTBE even free piston designs. If they could build a thermalacoustic generator, possibly a cascaded regenerator stack design with linear generator then you would have a 30-40,000 hr MTBE. With the advances being made in self pumping designs (no internal heat exchangers) the technology is available.

[Jim Mixan]

Good news in the very near future regarding Thin Film Solar PV applications and LED Lighting. Researchers in the Lab have created Quantum Dots. This is nano scale technology that can be made by chemists in almost any University. Quantum Dots are being called artificial atoms, as they are made up of groups of atoms numbering in the hundreds to a few thousand. Keyword here is (Small). Light beams shining through these Quantum dots do not behave like normal optics, ex. lenses and mirrors. LEDS and Solar cells are made of similar materials. In a Solar cell light photons strike the surface and electrons flow in a circuit. In a LED electrons flow through the junction and photons are radiated. This is a definite correlation between these technologies. Researchers are claiming that inexpensive thin films made with Quantum dots will be cheaper than current technolgies based on Silicon. Super efficient LEDS for low voltage lighting and Solar Panels that can be sprayed on to a substrate hold great promise. Do a Google search on the subject of Quantum Dots and you be the judge.

[yousef zakaria]

hi every body..
i want to ask if any one has information about the design of "solar powered heat engine"?

[esroger]

The specs and suggeted pricing of these Stirling/Solar units make very exciting converstion. If the could, would, should commentary has been acheived, I'm ready for a distributed energy installation without delay. Mine is an agricutural pumping situation, where space and orientation aned appearance are not issues.

I very much agree with Jim from the Energy Blog(8/17/05).

$2 per watt SHOULD have amazing consequences IF it WOULD deliver what the developers say it COULD.

Is there any updated info on progress of this technology?? Any real hard info would be appreciated.

[Ernest Demaray]

For the concentrator there are three things, the low cost mirror, the delta G to e- converter and the ROS. There is hope for a very low cost durable (20yr) mirror. I am doing that. The heat converter seems like the turbine engine prior to WWII. The Sterling, the so called 'bladeless' turbine (wish they would not say 'ionize'), the 'cascade' acoustic (pizo?) converter, even perhaps a high pressure direct steam electrolysis to H2 converter. Solid state G/e- It will be!

[khalid ismail naser alwali]

hello dear freinds
please send to me full offer for iraq dish grid engine solar cell
with many thanks
khalid ismail naser alwalli

[britany]

yo

in english?
im doing this for a year 11 assignment

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[Mark Blooman]

The CSP projects underway are quite exciting. Consider also the experimental systems using Ammonia as a transfer medium to produce turbine generated electricity - heated by the airconditioning no less! Heat pump efficiency coefficients in excess of 4 have been achieved.

The PV systems have a greater theoretical capacity, but solar thermal systems using a mix of new and existing technology have the lead right now. And Right now is when we need them.

Anybody know of commercially available systems now? Solar or any other heat source?

[Greg woulf]

I can't help you on commercial sources, but I think there's some action going on in California for Stirling energy.

They're ready to start construction on the two big SES plants, one in the Mojave, and one in San Bernadino.

I read a transcript from SES about their current status and it sounds like it's going well. They're finalizing production methods and repair/maintenance instructions so that they can accomplish the goals as cost effectively as possible.

California has them approved for both 800+ MW energy plants. They just need final certification to begin construction, and from that to construction is supposed to be less than a year.

Even if PV does overtake thermal in efficiency, it's got to also do it at the same cost to mean anything.

I hope they are very competitive with eachother, so that we make the best use of supplies and still get competitive prices without monopoly.

[Calamity]

Dish/Stirling engines are said to have the advantage of directly converting the heat into motion. However, it might actually be better to have a heating medium. The key is storage. Mainstream storage of electricity is problematic: it is too expensive. Flow batteries are too costly, lead acid also and ditto for every other battery in existence. Buck a watt solar panels are no good if the storage costs hundreds of dollars per kwh.
2. Pumped hydro is an exception and moreover also a mature industrial scale technology. However it is geographically limited so it cannot be economically expanded all that much (although it could technologically).
3. Flywheels are a wildcard, but right now are not feasible for mainstream electricity storage. Same for superconducting coil storage. Eestor is currently vaporware.

So, the bottom line is that some of the above problems need to be solved in a reasonable timeframe. If they do, PV might win big. If it takes much longer, then meanwhile there's solar thermal with proven inexpensive and reliable storage tech. Ready to go right now.

Dish/sterling however, competes directly with CPV, novel flat plate (e.g. Sliver Cells) and thin film schemes. This is a competition which it ultimately cannot win.

Therefore, if I was forced to choose between dish/sterling and CLFR, I'd take the latter.

[EricTheRead]

Just a thought about storing electricity. Why can't one store PV electricity using thermal storage? Electric heating is pretty efficient, is it not?

Mind you, then you need a heat based generator to extract the energy later, so you have to add that to the cost of using a PV system to collect things. A combined system like this might win on effiency grounds (unclear), but it's probably got a problem on the cost side....

[pradip]

Which companies involved in selling Dish/Stirling systems?