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Austin Meares
English 101
Professor Bolton
11 April 2012
Stirling Engines: A Logical Alternative
In the past several decades, energy production has become one of the largest problems
facing America. Built on fossil fuels, namely coal and oil, industrial America is now struggling
to maintain its lifeline of these vital commodities. The energy crisis is not constrained to heavy
industry; it affects everyone. Fossil fuels, the staple foods of modern society, are becoming
increasingly scarce and will not last indefinitely. As the nation’s power supplies have begun to
falter, the cost of living has increased. Clearly, a solution to the nation’s fossil fuel addiction is
in tall order. Much work has been done to find an alternative to America’s current energy
sources, and one such alternative appears to be particularly promising. Though disregarded by
some as a valuable energy source, heat engines, especially the Stirling engine, hold the potential
to relieve the energy crunch gripping the country.
Despite their immense potential, heat engines are often met with skepticism because
many people are not familiar with them. In the words of James Walker, a physics professor at
Washington State University, “[a] heat engine, simply put, is a device that converts heat into
work” (585). To narrow Walker’s definition to the context of energy production, heat engines
such as the Stirling engine can be described as external combustion, fluid cyclic engines. In
other words, such a heat engine is one that utilizes environmental heat to create a repetitive
motion. Though the Stirling engine is the predominate form of such heat engines, it should be
kept in mind that other, similar designs exist.

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Though they may sound complicated, Stirling engines are, in principle, very simple. In
both styles of Stirling engine, alpha and beta, a chamber is filled with gas (a third style, gamma,
is similar, but is fairly uncommon). One end is heated, while the other is kept at a cooler
temperature, usually room temperature. Cyclic expansion and contraction of the gas within the
engine causes a piston, or two, in the alpha design, to move back and forth, producing
mechanical work. Because Stirling engines utilize ambient heat, they are mechanically primitive
when compared to similar-sized internal combustion engines. Also, Stirling engines have no
need for fans, electrical systems, or other such parasitic systems that degrade the efficiency of
other engine types. Because they have so few moving parts, Stirling engines are simpler than
most believe.
Stirling engines, when compared to other alternative energy sources, are quite efficient.
Much research shows that Stirling engines are capable of operating more efficiently than other
systems, especially photovoltaic systems. One study notes that the “theoretical limits of
photovoltaic conversion efficiency for a multi-junction [photovoltaic] cell predicts an efficiency
of about 90%, but in practice not even half of that value has been obtained” (Vorobiev 170). In
addition, the same study points out that “practically 80% of solar radiation [striking a
photovoltaic cell] will be transformed into heat” (Vorobiev 173). The latter statement suggests
that Stirling engines, which run off of heat itself, are the best choice for harnessing solar energy.
This advantage of the Stirling engine can be attributed to the range of electromagnetic radiation
utilized by each technology. Whereas solar cells can make use of only a specific range of solar
rays (photovoltaics are wavelength specific), heat engines absorb the energy of any type of
electromagnetic wave. The evidence concerning the high efficiency of the Stirling engine and its
relatives contradicts the views of those who affirm that systems other than heat engines,

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especially photovoltaics, are the future of alternative energy. From an efficiency standpoint, the
heat engine emerges as the obvious victor among the various systems vying to replace traditional
fossil fuels.
The advantages of the Stirling engine are not limited to simple efficiency, as Stirling
engines are highly affordable. Compared to the costs of other types of alternative energy, such
as nuclear power, wind power, and photovoltaic power, the cost of producing Stirling engines is
extremely low. Because of their mechanical simplicity, it takes little specialized equipment to
produce a Stirling engine. Some may point out that a fairly high degree of precision is required
to produce a properly sealed Stirling engine, and they are correct. However, any machine shop
or factory would possess adequate equipment to do so. Moreover, Stirling engines can be
constructed without utilizing the state of the art materials that systems such as wind turbines and
solar arrays require. In fact, Stirling engines make use of only common, everyday materials.
The body of the engine may be nothing more than steel, and the gas inside can be common,
atmospheric air. Another common critique of the Stirling engine points out that the engines wear
out quickly. As one group of evaluators puts forth, “because the engines are sealed, the internals
of Stirling engines cannot be lubricated, which makes achieving such long lifetimes very
challenging… [what] is not clear is that they have demonstrated the longevity required for
[residential use]” notes one article (Brodrick, Kurt, Roth, and Targoff 47). Though it is true that
Stirling engines have comparably short life spans, their low cost negates the economic
disadvantage of frequent unit replacement. To employ the hypothetical, one could say that it is
cheaper to replace a $1000 Stirling engine once a year than to replace a $5000 wind turbine
every other year. Also, the inability to access the internal components of a sealed Stirling engine
may be advantageous, because such a situation would all but eliminate maintenance costs.

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The real potential of the Stirling engine lies in its versatility. Stirling engines run off of a
heat differential, which may be produced any number of ways. One article discusses their
versatility, pointing out that “their combustors can be designed to operate using multiple fuels,
such as natural gas, propane, heating oil, and diesel fuel, over a wide heat input range”
(Brodrick, Kurt, Roth, and Targoff 45). Moreover, Stirling engines can take advantage of either
geothermal or solar heat. The possibility of using solar energy is especially interesting. Stirling
engines could replace more expensive and less efficient photovoltaic arrays. Also, there are a
number of ways solar energy can be harnessed for use by a Stirling engine. Simple heat
absorbers, dark-colored panels through which a liquid flows, can be laid in the sun such that the
sun’s rays will warm the fluid. The heated fluid could flow to a Stirling engine to act as the heat
source. Perhaps more intriguing is the ease with which photovoltaic arrays could be converted to
run Stirling engines. In his doctoral dissertation, Artin Der Minassians notes that “Stirling
engines have a potential for high efficiency and external heating makes them easily adaptable to
solar dishes” (18). Parabolic solar dishes, which can concentrate the sun’s rays at 2000 times
natural strength, are ideal for producing the high heat Stirling engines run on. However, this
novel adaptation of existing solar technology has yet to be adopted on a significant scale, due to
high expense.
Critics of heat engines who point this out as a shortcoming make a viable argument, but
in doing so they unknowingly endorse the use of Stirling engines in small-scale applications.
While large-scale deployment of heat engines requires further development, the affordability and
versatility of Stirling engines makes them a good choice for residential application. In their
paper, “Residential Cogeneration Systems: Review of the Current Technology,” H.I.
Onovwiona and V.I. Ugursal discuss the advantages of the Stirling engine in the residential

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sector, saying that the Stirling engine “has good potential because of its ability to attain high
efficiency, fuel flexibility, low emissions, low noise/vibration levels and good performance at
partial load” (35). Furthermore, the aforementioned panel-type heat absorber is a convenient
source of heat to fuel a Stirling engine. Such heat absorbers, which circulate a fluid such as
water through a panel exposed to the sun’s rays, are easy to construct, maintain, and use. Unlike
parabolic solar concentrators, panel-type heat absorbers do not require careful aiming to stay
aligned with the sun. Also, such heat absorbers are already being used successfully by some
individuals to provide hot water or wintertime heating. Though heat absorbers are less effective
than parabolic reflectors, their lack of operational cost makes them an attractive option. Through
use of heat absorbers in conjunction with Stirling engines, households and businesses in all
climates and locales could utilize the virtually cost-free electricity of heat engines.
Despite the obvious benefits of electrical generation via the Stirling engine, it is
unrealistic to assume that Stirling engines could totally replace the use of fossil fuels. For the
majority of individuals, heat engines would merely offset fossil fuel consumption. Most scholars
agree that technologies such as the Stirling engine are promising, yet currently unable to totally
replace the nation’s traditional energy supplies. While they may be adopted for use generating
residential power, it would be difficult for Stirling engines to become the primary source of
electricity for large-scale industry. The widespread adoption of heat engine technology would,
however, reduce domestic consumption of fossil fuels enough that the surplus fuel could be used
by heavy industry while a suitable alternative is being developed.
Though the energy crisis is becoming a formidable obstacle, it is not insurmountable.
The presence of numerous alternatives to fossil fuels, including the Stirling engine, is very
promising. Widespread use of Stirling engines, which have been around in principle for over

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200 years, would be both beneficial and simple. The practical, affordable, and simple nature of
heat engines makes them an attractive possibility of escape from the downward spiral of fossil
fuel dependence.

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Works Cited
Brodrick, Kurt, Roth, and Targoff. "Using Stirling Engines for Residential CHP."
ASHRAE Journal 50.11 (2008): 42-47. Academic OneFile. Web. 29 Mar. 2012.
Minassians, Artin Der. "Stirling Engines for Low-Temperature Solar-Thermal- Electric Power
Generation." Diss. University of California at Berkeley, 2007.
http://www.eecs.berkeley.edu. 20 Dec. 2007. Web. 29 Mar. 2012.
Onovwiona, H., and V. Ugursal. "Residential Cogeneration Systems: Review of the Current
Technology." Renewable and Sustainable Energy Reviews (2004): 1-43. Elsevier. Web.
29 Mar. 2012.
Vorobiev, Y., J. Gonzalezhernandez, P. Vorobiev, and L. Bulat. "Thermal-photovoltaic Solar
Hybrid System for Efficient Solar Energy Conversion." Solar Energy 80.2 (2006): 170-
76. Elsevier. 2 Aug. 2005. Web. 29 Mar. 2012.
Walker, James. Physics. Upper Saddle River: Prentice-Hall, 2002. Print.