Meares 1Austin MearesEnglish 101Professor Bolton11 April 2012 Stirling Engines: A Logical Alternative In the past several decades, energy production has become one of the largest problemsfacing America. Built on fossil fuels, namely coal and oil, industrial America is now strugglingto maintain its lifeline of these vital commodities. The energy crisis is not constrained to heavyindustry; it affects everyone. Fossil fuels, the staple foods of modern society, are becomingincreasingly scarce and will not last indefinitely. As the nation’s power supplies have begun tofalter, the cost of living has increased. Clearly, a solution to the nation’s fossil fuel addiction isin tall order. Much work has been done to find an alternative to America’s current energysources, and one such alternative appears to be particularly promising. Though disregarded bysome as a valuable energy source, heat engines, especially the Stirling engine, hold the potentialto relieve the energy crunch gripping the country. Despite their immense potential, heat engines are often met with skepticism becausemany people are not familiar with them. In the words of James Walker, a physics professor atWashington State University, “[a] heat engine, simply put, is a device that converts heat intowork” (585). To narrow Walker’s definition to the context of energy production, heat enginessuch as the Stirling engine can be described as external combustion, fluid cyclic engines. Inother words, such a heat engine is one that utilizes environmental heat to create a repetitivemotion. Though the Stirling engine is the predominate form of such heat engines, it should bekept in mind that other, similar designs exist.
Meares 2 Though they may sound complicated, Stirling engines are, in principle, very simple. Inboth 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 coolertemperature, usually room temperature. Cyclic expansion and contraction of the gas within theengine causes a piston, or two, in the alpha design, to move back and forth, producingmechanical work. Because Stirling engines utilize ambient heat, they are mechanically primitivewhen compared to similar-sized internal combustion engines. Also, Stirling engines have noneed for fans, electrical systems, or other such parasitic systems that degrade the efficiency ofother engine types. Because they have so few moving parts, Stirling engines are simpler thanmost 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 othersystems, especially photovoltaic systems. One study notes that the “theoretical limits ofphotovoltaic conversion efficiency for a multi-junction [photovoltaic] cell predicts an efficiencyof about 90%, but in practice not even half of that value has been obtained” (Vorobiev 170). Inaddition, the same study points out that “practically 80% of solar radiation [striking aphotovoltaic cell] will be transformed into heat” (Vorobiev 173). The latter statement suggeststhat 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 radiationutilized by each technology. Whereas solar cells can make use of only a specific range of solarrays (photovoltaics are wavelength specific), heat engines absorb the energy of any type ofelectromagnetic wave. The evidence concerning the high efficiency of the Stirling engine and itsrelatives contradicts the views of those who affirm that systems other than heat engines,
Meares 3especially photovoltaics, are the future of alternative energy. From an efficiency standpoint, theheat engine emerges as the obvious victor among the various systems vying to replace traditionalfossil fuels. The advantages of the Stirling engine are not limited to simple efficiency, as Stirlingengines are highly affordable. Compared to the costs of other types of alternative energy, suchas nuclear power, wind power, and photovoltaic power, the cost of producing Stirling engines isextremely low. Because of their mechanical simplicity, it takes little specialized equipment toproduce a Stirling engine. Some may point out that a fairly high degree of precision is requiredto produce a properly sealed Stirling engine, and they are correct. However, any machine shopor factory would possess adequate equipment to do so. Moreover, Stirling engines can beconstructed without utilizing the state of the art materials that systems such as wind turbines andsolar 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 wearout quickly. As one group of evaluators puts forth, “because the engines are sealed, the internalsof Stirling engines cannot be lubricated, which makes achieving such long lifetimes verychallenging… [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 thatStirling engines have comparably short life spans, their low cost negates the economicdisadvantage of frequent unit replacement. To employ the hypothetical, one could say that it ischeaper to replace a $1000 Stirling engine once a year than to replace a $5000 wind turbineevery other year. Also, the inability to access the internal components of a sealed Stirling enginemay be advantageous, because such a situation would all but eliminate maintenance costs.
Meares 4 The real potential of the Stirling engine lies in its versatility. Stirling engines run off of aheat differential, which may be produced any number of ways. One article discusses theirversatility, 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 eithergeothermal or solar heat. The possibility of using solar energy is especially interesting. Stirlingengines could replace more expensive and less efficient photovoltaic arrays. Also, there are anumber of ways solar energy can be harnessed for use by a Stirling engine. Simple heatabsorbers, dark-colored panels through which a liquid flows, can be laid in the sun such that thesun’s rays will warm the fluid. The heated fluid could flow to a Stirling engine to act as the heatsource. Perhaps more intriguing is the ease with which photovoltaic arrays could be converted torun Stirling engines. In his doctoral dissertation, Artin Der Minassians notes that “Stirlingengines have a potential for high efficiency and external heating makes them easily adaptable tosolar dishes” (18). Parabolic solar dishes, which can concentrate the sun’s rays at 2000 timesnatural strength, are ideal for producing the high heat Stirling engines run on. However, thisnovel adaptation of existing solar technology has yet to be adopted on a significant scale, due tohigh expense. Critics of heat engines who point this out as a shortcoming make a viable argument, butin 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 andversatility of Stirling engines makes them a good choice for residential application. In theirpaper, “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
Meares 5sector, saying that the Stirling engine “has good potential because of its ability to attain highefficiency, fuel flexibility, low emissions, low noise/vibration levels and good performance atpartial load” (35). Furthermore, the aforementioned panel-type heat absorber is a convenientsource of heat to fuel a Stirling engine. Such heat absorbers, which circulate a fluid such aswater through a panel exposed to the sun’s rays, are easy to construct, maintain, and use. Unlikeparabolic solar concentrators, panel-type heat absorbers do not require careful aiming to stayaligned with the sun. Also, such heat absorbers are already being used successfully by someindividuals to provide hot water or wintertime heating. Though heat absorbers are less effectivethan parabolic reflectors, their lack of operational cost makes them an attractive option. Throughuse of heat absorbers in conjunction with Stirling engines, households and businesses in allclimates and locales could utilize the virtually cost-free electricity of heat engines. Despite the obvious benefits of electrical generation via the Stirling engine, it isunrealistic to assume that Stirling engines could totally replace the use of fossil fuels. For themajority of individuals, heat engines would merely offset fossil fuel consumption. Most scholarsagree that technologies such as the Stirling engine are promising, yet currently unable to totallyreplace the nation’s traditional energy supplies. While they may be adopted for use generatingresidential power, it would be difficult for Stirling engines to become the primary source ofelectricity 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 usedby 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 verypromising. Widespread use of Stirling engines, which have been around in principle for over
Meares 6200 years, would be both beneficial and simple. The practical, affordable, and simple nature ofheat engines makes them an attractive possibility of escape from the downward spiral of fossilfuel dependence.
Meares 7 Works CitedBrodrick, 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.