(Photo by Chuck Tidd) ^The Maricopa Solar LLC (Sterling Energy Systems, Tessera Solar) SunCatcher array in Peoria, Arizona. Shown are the sight and sound of 59 (one is under repair) SunCatcher solar collecting electric generators. Each 38' tall dish collects the sun's rays and focuses them on a hydrogen engine. The resultant heat drives the engine which powers a generator to produce 25kW max. The total array of 60 dishes can produce up to 1.5 megawatts of electricity. Each engine also produces about 55dB of noise. See the YouTube video: (http://www.youtube.com/watch?v=vG0xIBc3l9U)
Site Visit to Maricopa Solar LLC, Arizona
By Chuck Tidd
SLV Renewable Communities Alliance
Saguache, Colorado
Report on the SES Maricopa Solar SunCatcher Installation
On a bright and sunny Monday, March 22, 2010, my wife, Barb, and I visited the Tessera Solar concentrated solar electricity generation station, Maricopa Solar, in Peoria, Arizona. At ths station there are 60 25kW SunCatcher collectors generating a maximum 1.5 megawatts. The installation lies in an area that is in transition from agricultural to industrial. Just south of the installation is an electricity substation which is part of a gas electrical power generating plant which is owned by the Salt River Project, a water and power utility company operating in the Phoenix area. The installation is bordered on the west by a 4 lane roadway which separates some of the few remaining irrigated croplands. To the north and east are other warehouse and manufacturing businesses. There is a building for parts and repair (I assume) on site. The main offices and storage yard are located about a block away at 8707 N. 77th St. (See the accompanying file Maricopa Solar Installation (unfinished).jpg. [see below] This was pulled from Google maps and shows the unfinished installation and the surrounding area.)
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We observed the installation from several locations around the site and from just south of the main offices .37 miles away. (DSCN0801.JPG and see the line on Maricopa Solar Installation (unfinished).jpg) At that distance, the collectors are plainly visible and clearly audible over the city noise as a hum in the background. I regret that I didn't think to find out how far away we needed to get before we could no longer hear the sound, but my sense is that at one half mile the sound would be barely audible over the sound of the city, if at all. File DSCN0823.jpg is a video of the installation from the north. It speaks for itself.
(Photo by Chuck Tidd)
Tessera executives did not feel that their staff could be bothered, so we did not get a tour. We were also unable to get most of our questions answered with the stock answer being “That's what we're studying [at the MS installation].” Hard to believe after 12 years (I think) of operation at Sandia that they don't have some basic information. I think I will try writing their PR people again and see what they tell me. What we did learn is that they have a staff of 12 doing maintenance in shifts. Most of the maintenance is done at night for obvious reasons. However, one of the SunCatchers did go down while we were there (DSCN0817 and 18). It was turned to the north and lowered. I don't know what was removed or why it was down. The remaining 59 seemed to be in full operation.
(Photo by Chuck Tidd)
We spoke to a couple who came to see the installation while we were there. They live in the area and had watched the entire construction process. They were fascinated with the technology and just stopped by as part of their walk. They did not seem disturbed by the noise and they did not report any glare coming from the collectors.
Our feeling was that this is the appropriate location and size for this kind of an installation - in a city industrial park near the point of distribution. If sufficient land were available, up to a couple hundred could probably be built without major disruption. There is already plenty of traffic and other noise and local residents did not seem bothered.
(Photo by Chuck Tidd)
(Photo by Chuck Tidd)
(Photo by Chuck Tidd)
(Photo by Chuck Tidd)
(Photo by Chuck Tidd)
Maricopa Test Facility
Salt River Project (SRP) utility and Tessera Solar constructed a 1.5 MW Maricopa Solar Plant with Stirling Energy Systems SunCatcher Technology in the west Phoenix area, Arizona. Maricopa Solar will be the first commercial‐scale solar facility using these solar thermal dishes. The project will consist of 60 SunCatcher dishes.
The facility is admittedly an experiment: "...the 1.5 MW plant will allow SRP to have first‐hand experience with this technology, its performance and integration into the grid." (Tessera Solar August 2009 Press Release)
Stirling Energy Systems (SES) is the global supplier of the SunCatcher™ solar dish engine
system. The company is located in Scottsdale, Arizona, and has test dishes Sandia National Laboratories in New Mexico. National Toll Roads (NTR), an Irish waste management and energy company owns a controlloing interest in SES.
The sister company to SES, Tessera Solar, is the exclusive developer/owner/operator of utility-scale SunCatcher solar power facilities. Tessera Solar North America is headquartered in Houston, Texas. Its international office is in London. NTR is the parent company to Tessera.
How Does It Work?
The Stirling dish works by focusing sunlight from a parabolic mirror array through an opening in the Power Conversion Unit (PCU) where hydrogen gas is heated, expanding to push a piston, like in a car engine. Then the hydrogen cools and conracts. Pistons convert energy into a rotating mechanism which generates electricity. The mechanism operates like a solar chimney -- air rises like wind up a flu. This turns a propeller.
The solar dish would typically be mounted on a foundation consisting of a metal pipe
that is hydraulically driven into the ground, or when necessary the foundation would consist of rebar-reinforced concrete constructed below grade. The pedestal on which the SunCatcher Dish Assembly would be secured is about 18 feet 6 inches in height.
The Dish Assembly would be fitted with a trunnion that attaches to the pedestal. Each Dish Assembly would consist of a 38-foot wide by 40-foot high steel structure that supported an array of curved glass mirror facets. These mirrors would form a curved shape engineered to concentrate solar energy onto the solar receiver portion of the PCU. The Dish Assembly includes azimuth and elevation drives for tracking the sun and a PCU support boom.
The Power Conversion Unit converts the solar energy into grid-quality electricity. Hydrogen
gas is used in a closed-cycle heating/expansion – cooling/compression cycle to drive a
high-efficiency, 380-cubic-centimeter displacement, 4-cylinder reciprocating Solar
Stirling Engine. The Stirling Engine powers an electrical generator that produces 25
kWe net output after accounting for on-board parasitic loads at 575-volt alternating
current, 60 Hz of grid-quality electricity. The PCU attaches to the end of the PCU boom.
The solar receiver consists of an insulated cavity with an aperture that allows the solar energy to enter. Within the cavity are 4 heater heads. Each heater head forms a tube network for one quadrant of the engine. The solar flux, radiant energy from the sun, heats the metal tubes and the heat is then transferred through the tubes to the working hydrogen gas. The heat absorbed at the solar receiver drives the Solar Stirling Engine.
The kinematic Stirling Engine has evolved from a Kockums kinematic Stirling Engine design. A generator is connected to the Stirling Engine to produce the electrical
output of the SunCatcher. Waste heat from the hydrogen gas within the engine is transferred to the ambient air via a radiator system similar to the type used in automobiles. The SunCatcher cooling system is made up of ethylene glycol fluid, a cooler in the gas circuit, a radiator, a fluid circulation pump, and a cooling fan. The cooling fan and circulation pump are driven by electric motors. The system is used to cool the hydrogen gas before the compression portion of the cycle. The pump circulates the cooling fluid through the gas cooler and radiator. Waste heat from the hydrogen gas is transferred to the ethylene-glycol fluid in the cooler. The coolant is then pumped through the radiator where the fan forces ambient air over the cooling fins to remove heat. The heat is transferred to the atmosphere via the airflow over the radiator. (From the Calico Solar Project Staff Assessment/Draft Environmental Impact Statement.)
This technology is a "big challenge" according to one engineer we talked to. The engine is full of small parts, and has operational problems. New 4-cylinder piston engines are being tested. "Time will tell," said our consultant.
Tessera's spec sheet says the dishes do not operate in 35 mph or above winds.
The price tag of these engines is so far quite expensive, making the Stirling technology even less commercially viable than other forms of solar thermal energy.
Even the California Energy Commission seems skeptical:
"POWER PLANT RELIABILITY: Staff cannot determine whether the predicted power plant availability factor of 99%, as supplied by the Applicant, is achievable. Further, staff cannot predict what the actual availability might be, given the demonstration status of the SunCatcher technology and limited data on large-scaled deployments of SunCatchers. The availability factor of a power plant is the percentage of time it is available to generate power; both planned and unplanned outages subtract from this availability. Staff believes it possible that the project may face challenges from considerable maintenance demands, reducing its availability. No Conditions of Certification are proposed" (From the Calico Solar Project Staff Assessment/Draft Environmental Impact Statement page ES-27).
And the explosion danger is something to be concerned about: a small amount of hydrogen gas mixing with oxygen in the air will explode.
Tessera's Calico project has an Application for Clean Water Act 401 Water Quality Certification for Federal waters (here ephemeral flood washes). In it hydrogen tanks are described, as well as piping and compressors to supply each of the 34,000 SunCatchers. "Each high pressure supply tank will supply hydrogen gas to 360 SunCatchers via a 0.25-inch stainless tubing....If a release were to occur, personnel would be required to evacuate the immediate area then eliminate any sources of ignition..."
Our engineer consultants emphasized how small hydrogen is, the smallest molecule of all, that can leak through steel. It requires very precise machine work that has to date been impractical in assembly line production (costs will be very high). Tessera will have to continuously bleed small amounts of hydrogen into the engines. Leaks plus ignition sources would be an extreme hazard. One engineer we talked to compared a scenario to "the Hindenberg, which was filled with hydrogen. Bad idea."
Written reports from more engineers:
"The SunCatcher project was nothing more than a placeholder to justify the need for the $1.3 Billion Sunrise Powerlink," -- Bill Powers of Power Engineering. Powers was unequivocal in his opinion that the 1,525-acre Tessera Solar industrial solar facility proposed in Saguache County should not be permitted. Familiar with Tessera projects in California, Powers said the complicated SunCatcher technology is "riddled with problems and untested on a commercial scale". Powers reported that current $3.50/kW pricing for installed PV is lower than the DOE’s $4.50/kW best-case price target for proposed dish Stirling/SunCatcher. “It’s already old technology”, Powers said, “and unless there was a technician standing by each of the 8,000 SunCatchers” the project will never produce the energy that Tessera claims it will. (In, Our Renewable Future II: The Power of Distributed Generation, March 11, 2010 - http://slvrenewablecommunities.blogspot.com/)
Barry L. Butler, PhD, formerly of Sandia National Laboratory, and owner of Butler Sun Solutions. Testimony given on behalf of conservation groups in the matter of the Application of San Diego Gas & Electric Company for a Certificate of Public Convenience and Necessity for the Sunrise Powerlink Transmission Project Application 06-08-010
(Filed August 4, 2006), before the Public Utilities Commission of California:
"A 'mean time between failure' between 2,000 and 10,000 hours must be proven before
dish/Stirling can be incorporated into utility-scale installations.4 The current 'mean time
between failure' is a few hundred hours. This means a great deal of time, effort, and
money must be spent on maintenance. This drives up the cost of operating a dish/Stirling
unit. The commercial viability of the Stirling system is unproven at this time.
"My opinion is that dish/Stirling technology holds much promise. By 2020, the technology could be a significant player on a commercial scale in the concentrated solar power category. However, there is no possible way that dish/Stirling solar can move from high cost prototype models with substantive reliability concerns to large-scale production of high reliability low-cost commercial models by 2008 and full operation of a 12,000 dish, 300 MW array by the end of 2010. An entire step wise development 1MW, 10MW, 100MW with installed cost, reliability and operation & maintenance costs assessed over a year of operation at each step is necessary to move from current prototypes to the large-scale commercial plants contemplated in the power purchase agreements between SDG&E and SES."
See an article in Scientifc American:
"The systems have been criticized as being too expensive, unreliable and requiring extensive maintenance thanks to many moving parts. Also, ground has not yet been broken on either California site for which SES signed purchase power agreements in 2005, adding to skepticism that these systems will ever become commercially viable.
“'At these high temperatures, with this many moving parts, people doubted whether SES could really pull it off,' says Reese Tisdale, research director for solar power at Cambridge, Mass.-based Emerging Energy Research. The relatively small Arizona plant is intended to allay those concerns."
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