STIRLING SOLAR TECHNOLOGY.

Stirling engine, recuperation of waste heat is a key to achieving high efficiency. Therefore, waste heat exhausted from the turbine is used to preheat air from the compressor. A schematic of a single-shaft, solarized, recuperated Brayton engine is shown in Figure 5. The recuperated gas turbine engines that are candidates for solarization have pressure ratios of approximately 2.5, and turbine inlet temperatures of about 850oC (1,562ºF). Predicted thermal-to-electric efficiencies of Brayton engines for dish/Brayton applications are over 30% [9,10]. The commercialization of similar turbo-machinery for various applications by Allied Signal, Williams International,Capstone Turbines Corp., Northern Research and Engineering Company (NREC), and others may create an opportunity for dish/Brayton system developers.

Ancillary Equipment

Alternator: The mechanical-to-electrical conversion device used in dish/engine systems depends on the engine and application. Induction generators are used on kinematic Stirling engines tied to an electric-utility grid. Induction
generators synchronize with the grid and can provide single or three-phase power of either 230 or 460 volts. Induction generators are off-the-shelf items and convert mechanical power to electricity with an efficiency of about 94%. Alternators in which the output is conditioned by rectification (conversion to DC) and then inverted to produce AC power are sometimes employed to handle mismatches in speed between the engine output and the electrical grid. The high-speed output of a gas turbine, for example, is converted to very high frequency AC in a high-speed alternator, converted to DC by a rectifier, and then converted to 60 hertz single or three-phase power by an inverter. This approach can also have performance advantages for operation of the engine. Cooling System: Heat engines need to transfer waste heat to the environment. Stirling engines use a radiator to exchange waste heat from the engine to the atmosphere. In open-cycle Brayton engines, most of the waste heat is rejected in the exhaust. Parasitic power required for operation of a Stirling cooling system fan and pump, concentrator drives, and controls is typically about 1 kW.


Figure 6. Schematic of the United Stirling

Kinematic Stirling engine.

Controls: Autonomous operation is achieved by the use of microcomputer-based controls located on the dish to control dish tracking and engine operation. Some systems use a separate engine controller. For large installations, a central
System Control and Data Acquisition (SCADA) computer is used to provide supervisory control, monitoring, and data acquisition.

History

Dish/engine technology is the oldest of the solar technologies, dating back to the 1800s when a number of companies demonstrated solar powered steam-Rankine and Stirling-based systems. Modern technology was developed in the late
1970s and early 1980s by United Stirling AB, Advanco Corporation, McDonnell Douglas Aerospace Corporation (MDA), NASA’s Jet Propulsion Laboratory, and DOE. This technology used directly-illuminated, tubular solar receivers, the United Stirling 4-95 kinematic Stirling engine developed for automotive applications, and silver/glass
mirror dishes. A sketch of the United Stirling Power Conversion Unit (PCU), including the directly illuminated receiver, is shown in Figure 6. The Advanco Vanguard system, a 25 kW nominal output module, recorded a record e solar-to-electric conversion efficiency of 29.4% (net) using the United Stirling PCU [1,11]. This efficiency is defined as the net electrical power delivered to the grid, taking into account the electrical power needed for parasitics, divided by the direct normal insolation incident on the mirrors. MDA subsequently attempted to commercialize a system using the United Stirling PCU and a dish of their own design. Eight prototype systems were produced by MDA before the program was canceled in 1986 and the rights to the hardware and technology sold to Southern California Edison (SCE).
The cancellation of the dish/Stirling program was part of MDA’s decision to cancel all of their energy related activities, despite the excellent technical success of their dish/Stirling system. The MDA systems routinely converted sunlight incident on the concentrator’s mirrors to electricity with net efficiencies of about 30%. Southern California Edison
Company continued to test the MDA system on a daily basis from 1986 through 1988. During its last year of operation,it achieved an annual efficiency of about 12%, including system outages and all other effects such as mirror soiling. This is also a record for solar energy systems. Without outages, an annual efficiency of over 23% was determined to be achievable In the early 1990s, Cummins Engine Company attempted to commercialize dish/Stirling systems based on free-piston Stirling engine technology. The Cummins development efforts were supported by SunLab through two 50/50 cost shared contracts. (SunLab is a “virtual” laboratory composed of the solar thermal programs at Sandia National Laboratories and the National Renewable Energy Laboratory.) The Dish/Stirling Joint Venture Program (DSJVP) was started in 1991 and was intended to develop a 5 to 10 kW dish/Stirling system for remote power applications
The Utility Scale Joint Venture Program (USJVP) was started in late 1993 with the goal of developing a 25 kWedish/engine system for utility applications. However, largely because of a corporate decision to focus on its corediesel-engine business, Cummins canceled their solar development in 1996. Technical difficulties with Cummins’ freepistonStirling engines were never resolved.

Current Activities

In 1993, another USJVP contract was initiated with Science Applications International Corporation (SAIC) and Stirling.Thermal Motors (STM) to develop a dish/Stirling system for utility-scale applications. The SAIC/STM team successfully demonstrated a 20-kW unit in Golden, Colorado, in Phase 1. In December 1996, Arizona Public Service e Company (APS) partnered with SAIC and STM to build and demonstrate the next five prototype dish/engine systems
in the 1997-1998 time frame. SAIC and Stirling Thermal Motors, Inc. (STM) are working on next-generation hardware including a third-generation version of the STM 4-120, a faceted stretched-membrane dish with a face-down-stow capability, and a directly-illuminated hybrid receiver. The overall objective is to reduce costs while maintaining demonstrated performance levels. Phase 3 of the USJVP calls for the deployment of one megawatt of dish/engine systems in a utility environment, which APS could then use to assist in meeting the requirements of Arizona’s renewable portfolio standard. The economic potential of dish/engine systems continues to interest developers and investors. For example, Stirling Energy Systems (SES) has purchased the rights of the MDA technology, including the rights to manufacture the Kockums 4-95 Stirling engine. SES is working with MDA to revive and improve upon the 1980s vintage system. There is also interest by Allied Signal Aerospace in applying one of their industrial Brayton engine designs to solar power generation. In response to this interest, DOE issued a request for proposal in the spring of 1997 under the Dish Engine Critical Components (DECC) initiative. The DECC initiative is intended to encourage “solarization” of industrial engines and involves major industrial partners.
Next-generation hybrid receiver technology based on sodium heat pipes is being developed by SunLab in collaboration with industrial partners. Although, heat-pipe receiver technology is promising and significant progress has been made, cost-effective designs capable of demonstrating the durability required of a commercial system still need to be proven. SunLab is also developing other solar specific technology in conjunction with industry. 2.0 System Application, Benefits, and Impacts Dish/engine systems have the attributes of high efficiency, versatility, and hybrid operation. High efficiency contributes to high power densities and low cost, compared to other solar technologies. Depending on the system and the site, dish/engine systems require approximately 1.2 to 1.6 ha of land per MW . System installed costs, although currently e over $12,000/kW for solar-only prototypes could approach $1,400/kW for hybrid systems in mass production (see e e
Section 4.0). This relatively low-cost potential is, to a large extent, a result of dish/engine system’s inherent high efficiency.

Utility Application

Because of their versatility and hybrid capability, dish/engine systems have a wide range of potential applications. In principle, dish/engine systems are capable of providing power ranging from kilowatts to gigawatts. However, it is expected that dish/engine systems will have their greatest impact in grid-connected applications in the 1 to 50 MWe power range. The largest potential market for dish/engine systems is large-scale power plants connected to the utility grid. Their ability to be quickly installed, their inherent modularity, and their minimal environmental impact make them a good candidate for new peaking power installations. The output from many modules can be ganged together to form a dish/engine farm and produce a collective output of virtually any desired amount. In addition, systems can be added as needed to respond to demand increases. Hours of peak output are often coincident with peak demand. Although dish/engine systems do not currently have a cost-effective energy storage system, their ability to operate with fossil or bio-derived fuels makes them, in principal, fully dispatchable. This capability in conjunction with their modularity and relatively benign environmental impacts suggests that grid support benefits could be a major advantage
of these systems.

Remote Application

Dish/engine systems can also be used individually as stand-alone systems for applications such as water pumping.While the power rating and modularity of dish/engine systems seem ideal for stand-alone applications, there are challenges related to installation and maintenance of these systems in a remote environment. Dish/engine systems need to stow when wind speeds exceed a specific condition, usually at about 16 m/s. Reliable sun and wind sensors are therefore required to determine if conditions warrant operation. In addition, to enable operation until the system can become self sustaining, energy storage (e.g., a battery like those used in a diesel generator set) with its associated cost and reliability issues is needed. Therefore, it is likely that significant entry in stand-alone markets will occur after the technology has had an opportunity to mature in utility and village-power markets. Intermediate-scale applications such as small grids (village power) appear to be well suited to dish/engine systems. The economies of scale of utilizing multiple units to support a small utility, the ability to add modules as needed, and a hybrid capability make the dish/engine systems ideal for small grids.

Hybridization

Because dish/engine systems use heat engines, they have an inherent ability to operate on fossil fuels. The use of the same power conversion equipment, including the engine, generator, wiring, switch gear, etc., means that only the addition of a fossil fuel combustor is required to enable a hybrid capability. For dish/Brayton systems, addition of a hybrid capability is straightforward. A fossil-fuel combustor capable of providing continuous full-power operation can be provided with minimal expense or complication. The hybrid combustor is downstream of the solar receiver, Figure
5, and has virtually no adverse impact on performance. In fact, because the gas turbine engine can operate continuously at its design point, where efficiency is optimum, overall system efficiency is enhanced. System efficiency, based on the higher heating value, is expected to be about 30% for a dish/ Brayton system operating in the hybrid mode. For dish/Stirling systems, on the other hand, addition of a hybrid capability is a challenge. The external, high temperature, isothermal heat addition required for Stirling engines is in many ways easier to integrate with solar heatthan it is with the heat of combustion. Geometrical constraints makes simultaneous integration even more difficult. As a result, costs for Stirling hybrid capability are expected to be on the order of an additional $250/kW in large scale production. These costs are less than the addition of a separate diesel generator set, for a small village application, or a gas turbine for a large utility application. To simplify the integration of the two heat input sources, the first SAIC/STM hybrid dish/Stirling systems will operate on solar or gas, but not both at the same time. Although, the cost of these systems is expected to be much less than a continuously variable hybrid receiver, their operational flexibility will be substantially reduced. System efficiency, based on higher heating value, is expected to be about 33% for dish/ Stirling system operating in the hybrid mode.

Environmental Impacts

The environmental impacts of dish/engine systems are minimal. Stirling engines are known for being quiet, relative to internal combustion gasoline and diesel engines, and even the highly recuperated Brayton engines are reported to be relatively quiet. The biggest source of noise from a dish/Stirling system is the cooling fan for the radiator. There
has not been enough deployment of dish/engine systems to realistically assess visual impact. The systems can be high
profile, extending as much as 15 meters above the ground. However, aesthetically speaking they should not be
considered detrimental. Dish/engine systems resemble satellite dishes which are generally accepted by the public.
Emissions from dish/engine systems are also quite low. Other than the potential for spilling small amounts of engine
oil or coolant or gearbox grease, these systems produce no effluent when operating with solar energy. Even when
operating with a fossil fuel, the steady flow combustion systems used in both Stirling and Brayton systems result in
extremely low emission levels. This is, in fact, a requirement for the hybrid vehicle and cogeneration applications for
which these engines are primarily being developed.
3.0 Technology Assumptions and Issues
Dish/engine systems are not now commercially available, except as engineering prototypes. The base year (1997)
technology is represented by the 25 kW dish-Stirling system developed by McDonnell Douglas Aerospace (MDA) e
in the mid 1980's using either an upgraded Kockums 4-95 or a STM 4-120 kinematic Stirling engine. The MDA
system is similar in projected cost to the Science Applications International Corporation/Stirling Thermal Motors
(SAIC/STM) dish/Stirling system, but has been better characterized. The SAIC/STM system is expected to have a peak
net system efficiency of 21.9%. The SAIC/STM system uses stretched-membrane mirror modules that result in a lower
intercept fraction and a higher receiver loss than the MDA system. However, the lower-cost stretched-membrane
design and its improved operational flexibility are projected by SAIC to produce comparably priced systems [19].
Solar thermal dish/engine technologies are still considered to be in the engineering development stage. Assuming the
success of current dish/engine joint ventures, these systems could become commercially available in the next 2 to 4
years. The base-year system consists of a dish concentrator that employs silver/glass mirror panels. The receiver is
a directly-illuminated tubular receiver. As a result of extensive engineering development on the STM 4-120 and the
Kockums engines, near-term technologies (year 2000 and 2005) are expected to achieve significant availability
improvements for the engine, thus nearly doubling annual efficiency over the base year technology (from 12 to 23 %).
For the years 2010 and on, systems are anticipated to benefit from evolutionary advances in dish concentrator and
engine technology. For this analysis, a 10% improvement, compared to the base-year system, is assumed based on the
introduction of heat-pipe receiver technology. The introduction of advanced materials and/or the incorporation of
ceramics or volumetric absorption concepts could provide significant advances in performance compared to the
baseline. Favorable development of advanced concepts could result in improvements of more than an additional 10%.
However, because there are no significant activities in these areas, they are not included in this analysis.
SOLAR DISH ENGINE
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The system characterized is located in a region of high direct normal insolation (2.7 MWh/m2/yr), which is typified by
the Mojave Desert of Southern California. Insolation is consistent with desert regions throughout the Southwest United
States.
Research and Development Needs
The introduction of a commercial solar engine is the primary research and development (R&D) need for dish/engine
technology. Secondary R&D needs include a commercially viable heat-pipe solar receiver for dish/Stirling, a hybridreceiver
design for dish/Stirling, and a proven receiver for dish/Brayton. All three of these issues are currently being
addressed by SunLab and its partners, as part of the DOE Solar Thermal Electric Program. In addition, improvement
in dish concentrator components, specifically drives, optical elements, and structures, are still needed and are also being
addressed, albeit at a low level of effort. The solar components are the high cost elements of a dish engine system, and
improved designs, materials, characterization, and manufacturing techniques are key to improving competitiveness.
Systems integration and product development are issues for any new product. For example, even though MDA
successfully resolved many issues for their system, their methods may not apply or may not be available to other
designs. Issues such as installation logistics, control algorithms, facet manufacturing, mirror characterization, and
alignment methods, although relatively pedestrian, still need resolution for any design. Furthermore, if not addressed
correctly, they can adversely affect cost. An important function of the Joint Ventures between SunLab and industry
is to address these issues.
Advanced Development Opportunities
Beyond the R&D required to facilitate commercialization of the industrial derivative engines discussed above, there
are high-payoff opportunities for engines designed exclusively for solar applications. The Advanced Stirling
Conversion System (ASCS) program administered by the National Aeronautics and Space Administration (NASA)
Lewis Research Center for DOE between 1986 and 1992, with the purpose of developing a high-performance freepiston
Stirling engine/linear alternator, is an example of a high-risk high-payoff development [20]. An objective of
the ASCS was to exploit the long life and reliability potential of free-piston Stirling engines.
Thermodynamically, solar thermal energy is an ideal match to Stirling engines because it can efficiently provide energy
isothermally at high temperatures. In addition, the use of high-temperature ceramics or the development of
“volumetric” Stirling receiver designs, in which a unique characteristic of concentrated solar flux is exploited, are other
high-payoff R&D opportunities. Volumetric receivers exploit a characteristic of solar energy by avoiding the inherent
heat transfer problems associated with conduction of high-temperature heat through a pressure vessel. Volumetric
receivers avoid this by transmitting solar flux through a fused silica “quartz” window as light and can potentially work
at significantly higher temperatures, with vastly extended heat transfer areas, and reduced engine dead volumes, while
utilizing a small fraction of the expensive high-temperature alloys required in current Stirling engines. Scoping studies
suggest that annual solar-to-electric conversion efficiencies in excess of 30% could be practically achieved with
potentially lower cost “volumetric Stirling” designs. Similar performance enhancements can also be obtained by the
use of high-temperature ceramic components.
SOLAR DISH ENGINE
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4.0 Performance and Cost
Table 1 summarizes the performance and cost indicators for the solar dish/engine system being characterized here.
4.1 Evolution Overview
Over the next 5 to 10 years, only evolutionary advances are expected. The economic viability of dish/engine
technology will be greatly enhanced if an engine capable of being “solarized” (i.e., integrated with solar energy) is
introduced for another application. The best candidates are the STM 4-120 and the Kockums 4-95 kinematic Stirling
engines for hybrid vehicles and industrial generators, and the industrial gas turbine/generators. Assuming one of these
engines becomes commercial, then commercialization of dish/engine systems at some level becomes likely. With the
costs and risks of the critical power conversion unit significantly reduced, only the concentrator, receiver, and controls
would remain as issues. Given the operational experience and demonstrated durability and reliability of the remaining
solar components, as well as the cost and performance capabilities of dish/engine technology, commercialization may
appear attractive to some developers and investors. The modularity of dish/engine systems will help facilitate their
introduction. Developers can evaluate prototype systems without the risks associated with multi-megawatt installations.
The commercialization of power towers and, therefore, heliostats (constructed of shared solar components), along with
the introduction of a solarizable engine, would essentially guarantee a sizable and robust dish/engine industry. The
added manufacturing volumes provided by such a scenario for the related concentrator drives, mirror, structural, and
control components would significantly reduce costs and provide an attractive low-cost solar product that will compete
in the 25 kW to 50 MW power market. e e
4.2 Performance and Cost Discussion
From the above discussion, one of three basic scenarios will happen: (1) no solarizable engine will be commercialized
and, therefore, significant commercialization is unlikely, (2) a solarizable engine will be introduced, therefore
spawning a fledgling dish/engine business or industry, and (3) a solarizable engine will be introduced and power tower
projects will be initiated. Under this scenario, a large and robust solar dish/engine industry will transpire. Of course,
numerous variations on the above scenarios are possible but are impossible to predict, much less consider. For the
purpose of this analysis, the second scenario is assumed. The cost and performance data in the table reflect this
scenario. As discussed in Section 3.0, a STM 4-120 or Kockums 4-95 is assumed to become commercial by 2000, with
a dish/engine industry benefiting from mass production. This scenario is consistent with the commercialization plans
of General Motors and STM for the STM 4-120.
Although a Brayton engine for industrial generator sets is also a potential positive development, the table considers a
dish/Stirling system. A hybrid capability has been included in the table for the year 2000 and beyond. A capacity
factor of 50% is assumed. This corresponds to a solar fraction of 50%.
The following paragraphs provide the basis for the cost and performance numbers in the table. System and component
costs are from industry sources and independent SunLab analyses. Costs for the MDA system are from [15]. The
installed costs include the cost of manufacturing the concentrator and power conversion unit (PCU), shipment to the
site, site preparation, installation of the concentrator and PCU, balance of plant (connection to utility grid). The
component costs include a 30% profit. These costs are similar to those projected by SAIC at the same
Table 1. Performance and cost indicators.
1980's Prototype Hybrid Commercial Engine Heat Pipe Receiver Higher
System Production
Higher
Production
INDICATOR 1997 2000 2005 2010 2020 2030
NAME UNITS +/-% +/-% +/-% +/-% +/-% +/-%
Typical Plant Size, MW MW 0.025 1 50 30 50 30 50 30 50 30 50
Performance
Capacity Factor % 12.4 50.0 50.0 50.0 50.0 50.0
Solar Fraction % 100 50 50 50 50 50
Dish module rating kW 25.0 25.0 25.0 27.5 27.5 27.5
Per Dish Power Production MWh/yr/dish 27.4 109.6 109.6 120.6 120.6 120.6
Capital Cost
Concentrator $/kW 4,200 15 2,800 15 1,550 15 500 15 400 15 300 15
Receiver 200 15 120 15 80 15 90 15 80 15 70 15
Hybrid ---- 500 30 400 30 325 30 270 30 250 30
Engine 5,500 15 800 20 260 25 100 25 90 25 90 25
Generator 60 15 50 15 45 15 40 15 40 15 40 15
Cooling System 70 15 65 15 40 15 30 15 30 15 30 15
Electrical 50 15 45 15 35 15 25 15 25 15 25 15
Balance of Plant 500 15 425 15 300 15 250 15 240 15 240 15
Subtotal (A) 10,580 4,805 2,710 1,360 1,175 1,045
General Plant Facilities (B) 220 15 190 15 150 15 125 15 110 15 110 15
Engineering Fee, 0.1*(A+B) 1,080 500 286 149 128 115
Project /Process Contingency 0 0 0 0 0 0
Total Plant Cost 11,880 5,495 3,146 1,634 1,413 1,270
Prepaid Royalties 0 0 0 0 0 0
Init Cat & Chem. Inventory 120 15 60 15 12 15 6 15 6 15 6 15
Startup Costs 350 15 70 15 35 15 20 15 18 15 18 15
Other 0 0 0 0 0 0
Inventory Capital 200 15 40 15 12 15 4 15 4 15 4 15
Land, @$16,250/ha 26 26 26 26 26 26
Subtotal 696 196 85 56 54 54
Total Capital Requirement 12,576 5,691 3,231 1,690 1,467 1,324
Total Capital Req. w/o Hybrid 12,576 5,191 2,831 1,365 1,197 1,074
Operation and Maintenance Cost
Labor ¢/kWh 12.00 15 2.10 25 1.20 25 0.60 25 0.55 25 0.55 25
Material ¢/kWh 9.00 15 1.60 25 1.10 25 0.50 25 0.50 25 0.50 25
Total ¢/kWh 21.00 3.70 2.30 1.10 1.05 1.05
Notes:
1. The columns for "+/-%" refer to the uncertainty associated with a given estimate.
2. The construction period is assumed to be <1year a="" br="" for="" mw="" scale="" system.="">SOLAR DISH ENGINE
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production rates [19]. These projections are also consistent with similar estimates by Cummins and with projections
by SunLab engineers. Because of the proprietary nature of cost information, detailed breakdowns of cost estimates are
not available in the public domain. Costs are also extremely sensitive to production rates. The installed costs are,
therefore, extremely dependent on the market penetration actually achieved. Operation and Maintenance (O&M) costs
are also based on [15]. They take into account realistic reliability estimates for the individual components. They are
also reasonably consistent with O&M for the Luz trough plants and large wind farms. Component costs are a strong
function of production rates. Production rate assumptions are also provided. The economic life of a dish/engine power
plant is 30 years. The construction period is much less than one year.
1997 Technology
The base-year technology (1997) is represented by the 25 kW dish-Stirling system developed by McDonnell Douglas e
(MDA) in the mid 1980s. Similar cost estimates have been predicted for the Science Applications International
Corporation (SAIC) system with the STM 4-120 Stirling engine [19]. Southern California Edison Company operated
a MDA system on a daily basis from 1986 through 1988. During its last year of operation, it achieved an annual
efficiency of 12% despite significant unavailability caused by spare part delivery delays. This annual efficiency is
better than what has been achieved by all other solar electric systems, including photovoltaics, solar thermal troughs,
and power towers, operating anywhere in the world [13,21). The base-year peak and daily performance of near-term
technology are assumed to be that of the MDA systems. System costs assume construction of eight units. Operation
and maintenance (O&M) costs are of the prototype demonstration and accordingly reflect the problems experienced.
2000 Technology
Near-term systems (2000) are expected to achieve significant availability improvements resulting in an annual
efficiency of 23%. The MDA system consistently achieved daily solar efficiencies in excess of 23% when it was
operational. The low availability achieved with the base-year technology was primarily caused by delays in receiving
spare parts and by the lack of a dedicated O&M staff. A 23% annual efficiency is, therefore, a reasonable expectation,
assuming Stirling engines are commercialized for other applications, and spare parts and a dedicated staff are available.
In addition, near term technologies should see a modest reduction in the cost of the dish concentrator simply as a result
of the benefits of an additional design iteration. Prototypes for these near-term technologies were first demonstrated
in 1985 by McDonnell Douglas and United Stirling. Similar operational behavior was demonstrated in 1995 by SAIC
and STM, although for a shorter test period and a lower system efficiency. O&M costs reflect improvements in
reliability expected with the introduction of a commercial engine. Production of 100 modules is assumed. At this
production rate, component costs are high, resulting in installed costs of nearly $5,700/kW . e
2005 Technology
Performance for 2005 is largely based on one of the solarizable engines being commercialized for a non-solar
application (e.g., GM’s introduction of the STM 4-120 Stirling engine for use in hybrid vehicles). Use of a productionlevel
engine will have a significant impact on engine cost as well as overall system cost. This milestone will help
trigger a fledgling dish/engine industry. A production rate of 2,000 modules per year is assumed. Achieving a high
production rate is key to reducing component costs, especially for the solar concentrator.
SOLAR DISH ENGINE
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2010 Technology
Performance for years 2010 and beyond is based on the introduction of the heat-pipe solar receiver. Heat-pipe solar
receiver development is currently being supported by SunLab in collaboration with industrial partners. The use of a
heat-pipe receiver has already demonstrated performance improvements of well over 10% for the STM 4-120 compared
to a direct-illumination receiver [1]. While additional improvements in mirror, receiver, and/or engine technology are
not unreasonable expectations, they have not been included. This is, therefore, a conservative scenario. A production
rate of 30,000 modules per year is assumed.
By 2010 dish/engine technology is assumed to be approaching maturity. A typical plant may include several hundred
to over a thousand systems. It is envisioned that a city located in the U.S. Southwest would have several 1 to 50 MWe
installations located primarily in its suburbs. A central distribution and support facility could service many
installations. In the table, a typical plant is assumed to be 30 MW . e
2020-2030 Technology
Production levels for 2020 and 2030 are 50,000 and 60,000 modules per year, respectively. No major advances beyond
the introduction of heat pipes in the 2010 time frame are assumed for 2020-2030. However, evolutionary
improvements in mirror, receiver, and/or engine designs have been assumed. This is a reasonable assumption for a $2
billion/year, dish/engine industry, especially one leveraged by a larger automotive industry. The system costs are
therefore 20 to 25% less than projected by MDA and SAIC at the assumed production levels. The MDA and SAIC
estimates are for their current designs and do not include the benefits of a heat-pipe receiver. In addition, the MDA
engine costs are for an engine that is being manufactured primarily for solar applications. Advanced concepts (e.g.,
volumetric Stirling receivers) and/or materials, which could improve annual efficiency by an additional 10%, have not
been included in the cost projections. With these improvements installed costs of less than $1,000/kW are not e
unrealistic.
5.0 Land, Water and Critical Materials Requirements
Land requirements for dish/engine systems are approximately 1.2-1.6 ha/MW . No water is required for engine e
cooling. In some locations, a minimal
Stirling Energy SystemsNew and Improved Solar Thermal Collection DishWhile a lot of people think about photovoltaic panels when "solar power" is mentioned, solar thermal must not be underestimated. One of the players in that field is Stirling Energy Systems (SES), who we've written about before when they set a new world record for "solar-to-grid system conversion efficiency" (31.25 percent, beating the previous record of 29.4 percent). Well, in collaboration with Sandia National Laboratories, SES has refined its SunCatcher design. Read on to find out how the new version compares to the old one


Stirling Energy SystemsNot Reinventing the WheelThe new Suncatcher is evolutionary rather than revolutionary (you can compare it to the older design by looking at the photo below), but according to the specs released by Sandia National Laboratories, it seems like a significant improvement:


The new SunCatcher is about 5,000 pounds lighter than the original, is round instead of rectangular to allow for more efficient use of steel, has improved optics, and consists of 60 percent fewer engine parts. The revised design also has fewer mirrors — 40 instead of 80. The reflective mirrors are formed into a parabolic shape using stamped sheet metal similar to the hood of a car. The mirrors are made by using automobile manufacturing techniques. The improvements will result in high-volume production, cost reductions, and easier maintenance.

90% of the Suncatcher components will be made in the US, and by using automobile suppliers to make the parts, Stirling Energy Systems is leveraging their manufacturing expertise (and I bet that auto suppliers are glad to get the extra work). “By utilizing the automotive supply chain to manufacture the SunCatcher, we’re leveraging the talents of an industry that has refined high-volume production through an assembly line process. More than 90 percent of the SunCatcher components will be manufactured in North America," says Steve Cowman, Stirling Energy Systems CEO.




Stirling Thermal Motors


25 kW power conversion system under test at Sandia National Laboratories. Using STM4-120 engine incorporating variable displacement power control.



Advnco/Vanguard 25 kW dish/Stirling system installed at Rancho Mirage, California.

The Vanguard concentrator is approximately 11 meters in diameter and made of 366 mirror facets, each facet measures 18 by 24 inches. The engine used is a United Stirling AB (USAB) Model 4-95 Mark II driving a commercial 480 volt/ac 60-Hz alternator.



McDonnell Douglas/Southern of California

California Edison 25 kW dish/Stirling system. The 944 square foot concentrator consists of 82 spherically curved glass mirrors each 3 foot by 4 foot. The United Stirling 4-95 Mark II engine (4 cylinders of 95 cc displacement) uses hydrogen as the working pressure at a maximum gas pressure of 2900psi.. This engine delivered 25kW output at 1000W/m2 insolation.