A supply-side approach to energy policy

cussed in the thermodynamics literature4, s the concept of exergy is considerably more general and applies to thermodynamic systems far more complex than that shown in Figure 1. Since the user temperature can never exceed the fuel temperature (T ~< T/), Equations (1) and (2) imply that the exergy of Q decreases as the heat crosses the fuel-user temperature gap. The exergy loss is:

Communications on energy A supply-side approach to energy policy

El°st=El - E = T o ( Q - T f ) ~ O (3) Existing energy policy proposals are approached from a demand-side perspective to solve the immediate problem of meeting existing demands defined by existing technologies. However, a constructive forward-looking The loss of exergy in the temperature policy requires a supply-side perspective. The purview of energy policy is gap is illustrated graphically on the ultimately the efficient allocation of our scarce supply of available energy or right side of Figure 1. Therefore, our ability to conserve 'exergy'. The authors outline a proposal for efficient exergy management. This supply-side orientaUon is based upon basic thermodynamic principles, thus energy hinges on our ability to avoid offering a foundation for formation of consistent criteria for policy-oriented the one-way destruction of exergy in critical areas such that the fuel-user decision making. Keywords: Energy; Policy; Supply The scientific community is showing a growing interest in the basic laws of thermodynamics and in the relationship between these laws and the quest for energy sufficiency. Specifically, this interest is directed towards the Second Law of Thermodynamics which expresses the unidirectional (irreversible) character of real processes of the type encountered in energy systems. Engineers have known for some time that through proper application of Second Law principles it is possible to design and build engineering components and systems which are thermodynamically very efficient. The engineering progress in this area was summarized in 1979 during the Second Law of Thermodynamics Workshop sponsored by the US Department of Energy. 1 The applicability of Second Law principles is not restricted to designing engineering components and systems. These principles may be applied to the more general problem of managing our fuel supply efficiently.

The loss of exergy Perhaps the simplest way to analyse the dissipative phenomenon associated with the use of a given fuel is to introduce the concept of exergy. However,

E N E R G Y P O L I C Y June 1982

as the terms exergy and entropy receive increasing exposure in the literature, they have become the subject of considerable misconceptions. To clarify what we mean in this discussion, consider the schematic of Figure 1. The user (eg the working fluid in a power cycle) receives heat at an absolute temperature T. The heat Q is released by a fuel which burns at an absolute temperature 7~ The second law of thermodynamics requires Tf >I T, in other words, heat cannot pass spontaneously from a body of lower temperature to a body of higher temperature. 2 If the heat Q which leaves the fuel at temperature Tf were to drive a Carnot engine operating between Tf and To (the ambient temperature), the work output of the engine would be: 3

Ef = Q [1-(To/rf)]

End-use matching As summarized recently by Lovins, 6 the energy policy community harbours two contrasting views of the energy problem. One sees the problem as that of 'expanding energy supplies from secure and affordable sources in order to meet projected homogeneous demands'. The alternative view of Taylor, 7 Lovins, a and others, which is gaining considerable popular support, capitalizes on the obvious nonhomogeneity of energy demand. It describes the energy problem as one of meeting 'heterogeneous end-use needs with a minimum of energy supplied in the most effective way for each task'. This view assumes that appropriate

(i)

The Second Law of Thermodynamics states that, given the (Q, Tf) combination relative to the ambient (To), the maximum amount of work Ef is available. Likewise, the heat O received by the user at temperature T has the maximum work-producing potential:

E = O [1-(To/T)]

temperature gaps. This paper uses this principle to focus on the proper management of the total exergy inventory of all known fuels.

Tf_. ~ : " " ~

°6

.......

.

.

.

.

.

.

I

Ef

.

(2)

In this paper we will refer to the maxi- Figure 1. The one-way destruction of mum work content (defined by Equa- exergy in a fuel-user temperature gap tion (2)) as exergy. However, as dis- with heat transfer,

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' m o d e r a t e ' temperature energy sources exist and proposes their immediate match to moderate temperature users.

9 ~10

The first view is clearly vulnerable to attack as it ignores the thermodynamic inefficiency (irreversibility) of the path linking fuel resources to users. The continued expansion of demand in the future will require us to improve our ability to use the existing (limited) fuel supply efficiently. And, as an attempt to incorporate efficiency concepts, the second view falls far short of proper management of our fuel exergy inventory. Technically, end-use matching as propounded fails because the fuels under consideration are inevitably high temperature fuels and therefore high exergy resources. And, as a fuel is matched to a use, a potential is dissipated between fuel and user temperature. The sun, for example, the resource endlessly touted for low temperature applications,11,t2 has a 'flame' temperature higher than that of fossil fuels. By concentrating on low temperature applications for solar-generated exergy, we continue to squander valuable high temperature fuels on uses that could be adapted to solar power though such fuels may be irreplaceable in some other applications and processes. In addition, and more fundamentally, end-use matching as a paradigm represents nothing new. Indeed, we will argue it has always been used and is a major contributor to our existing energy crisis. The object of the end-use approach is to tool a specific user to meet its energy d e m a n d in light of today's fuel supplies. To illustrate, an excellent example of end-use matching is the car. The demand for exergy is related directly to overcoming friction and a possible height differential while transporting an individual over a given distance, with travel time as a constraint. In places and under circumstances in which petrol was more competitive than other fuels, the family car took over as the primary mode of transport. In other places coal proved more competitive, hence the steam locomotive and an entire network of public transport, driven electrically by

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coal-fired power stations, developed. But in all cases, the dominant technology survived fierce competition among inventions based on different fuels. The energy problem we are debating today is the inevitable result of previous end-use matching. The car, which today represents a technology locked in by an economy and lifestyle highly dependent upon it, only 20 years ago was a perfectly 'end-use-matched' technology. In conclusion, what today's proponents of end-use matching are saying differs little as a decision making criterion from what man, on both individual and corporate levels, has been using for years and will doubtless continue to use.

(destroys) exergy when he travels by car and when he reads by an electric light. Given that (scarce) fuel is a source of exergy, we will evaluate the exergy content of each available fuel as a first step toward the efficient management of energy supply. Then we ask the questioni Who are the most appropriate users we can match to this fuel? O u r proposal, like end-use matching, aims at a better match between fuel and user. However, unlike end-usematching, we will not ignore any temperature difference between user and fuel remaining after the lowest temperature fuel is chosen for each job. To clarify the difference between our supply-side philosophy and the demand-side approach of end-use matching, consider the numerical example constructed in Figure 2. The The best user for a given fuel example consists of two users and two F o r a long-term energy policy to be potential fuels. The two users are a sound, it must recognize that what man power plant taking in 100 MW of heat demands, consumes, and has a limited at 850K (557°C) and rejecting 60 MW supply of is exergy. He consumes of heat at 373K (100°C), and a housing Demand - side

Supply- side

O

Fossil fuel

Energy policy

Solar

100 MW power plant

I

I

A housing

A

I

Solar: 4 3 5 0 K i Fossil

fuel: 2300 K

i iI

19.51 MW ! 85O K

293 K

i I

24.9 MW 19,51MW I

! 50.23 MW l i

Power plant 37'3 K

i

i I

11.55 MW

11.55 MW

69.74 MW

31.06 MW

36.45 MW

Housing

Total exergy loss

F i g u r e 2. A comparison of supply and demand side approaches to energy policy.

ENERGY

POLICY

June 1982

Communications on energy

district requiting 60MW at a temperature of 293K (20°C), while the ambient temperature is 263K ( - 10°C). As fuels we consider a fossil fuel with a 2300K flame temperature, and the sun (as shown in the next section, the sun's temperature as an exergy supply is at least 4350K). The first column of Figure 2 presents the result of end-use matching: the proponents of this approach have argued that the (low temperature) d e m a n d for domestic heating should be met with heat drawn from low temperature solar collectors, x3 As shown in the lower half of the same column, there are two fuel-user temperature gaps in which exergy is being destroyed steadily. The 'exergy loss' figures shown in Figure 2 have been calculated using Equation (3). The second column of Figure 2 shows the two alternatives available from the supply-side or fuel-side perspective. The starting point in the decision-making process is the fuel: for example, the best user for the fossil fuel is the power plant, because this choice minimizes the fuel-user temperature gap. The exergy of the fossil fuel is not used entirely in the power plant. The heat rejected by the power plant (60 M W at 373K) represents a new fuel, and the best user for this new fuel is the housing district. In the lower half of the column we show the calculated exergy loss and the actual location of the two temperature gaps on the temperature scale. The best first and second users for the solar fuel can be determined in the same manner. The important difference between the two design philosophies is reflected numerically in the total exergy loss calculated at the bottom of each column. In the present example, focusing on the 'best user for a given fuel' leads to total exergy losses which are approximately half of the exergy loss registered when the domestic heating demand is matched to low temperature solar collectors. In physical terms, the superiority of the supply-side approach is measured by the fact that on the right side of Figure 2 a single fuel accommodates both demands. A n o t h e r important aspect of the supply-side approach is that it identifies the exergy losses present even after the

ENERGY POLICY June 1982

best user was matched to a given fuel: from the tight-hand columns of Figure 2 we conclude that in the gap between the first fuel (fossil or solar) and the first user (the power plant) there is considerable room (exergy) for accommodating a third, unspecified, demand. Especially in the case of solar exergy, Figure 2 emphasizes the need for the development of high-temperature applications to be placed in a temperature gap (4350K--850K) which promises to remain unfilled in the forseeable future. In conclusion, we propose a thermodynamic basis to develop a sound supply-side approach to energy policy, where the policy can pertain to a state, country, continent or world. Given that efficient (loss-free) allocation of scarce exergy is a goal of the 'unit' of concern, and recognizing that economically-based decisions will not accomplish this goal (because fuel prices do not reflect fuel exergy content), a pragmatic approach is then to:

temperature of any fuel resource. In particular, it is important to establish that solar energy is indeed a high temperature fuel. The effective temperature of the sun as an exergy source, Tf, can be determined by combining Equation (2) with the exergy content of solar beam radiation TM

•

Solar v natural gas

• •

•

•

on the demand side, list the jobs (demands) we consider worth doing, for economic or social reasons; order them in demand temperature cascades; on the supply side, take an inventory of our exergy supply and available technological ability to exploit it; from this inventory, assess which fuels we can best afford to consume on the basis of availability of substitutes for existing and projected necessary processes and the feasibility of development of alternative technologies; and then match user cascades to fuels, minimizing the exergy loss in the temperature gaps. The minimization of exergy loss must be started at the top of the cascade, by selecting the user closest to the fuel temperature.

E = Q F 1 - 4 T ° ( l - cos 6) ¼ 3Ts

L

3

W e conclude that the solar fuel is characterized by an extremely high temperature. In view of this conclusion, it is indeed unfortunate that some of the most influential proponents of solar energy are giving this important resource an undeserved 'low temperature' name. is The labelling of solar heat as being available at low and moderate temperatures is part of the enthusiasm associated with making ~solar energy' look good in a 'second-law efficiency" sense vis-a-vis conventional (nonsolar) fuels. Consider, for instance, Kreider's comparison TM of solar versus natural gas, as two fuel options for maintaining a building at Ta = 20°C when the ambient is at To = -10°C. The second-law efficiency is defined as the ratio of the exergy intake required by the application at hand, divided by the exergy released by the fuel source 17 "qll = (1 -

Solar exergy as a high-temperature fuel

J

where To, Ts and i5 are the ambient temperature (300K), the surface temperature of the sun (5800K) and the half-angle of the cone subtended by the sun's disc (0.005 rad). The result is shown plotted in Figure 3, as Tf versus the solar disc half angle 6. The sun fuel temperature is maximum 73000 K, when atmospheric scattering is absent (~5 = 0.005 rad). The minimum temperature Tf = 4350K, corresponds to the case of diffuse sunlight 05 = n/2).

To/TB)/(I-T,,/Tf)

(5)

In the case o f natural gas burning at a flame temperature 7"/= 2300K, Equation (5) yields TM Till ----0.116. In the case

In connection with the fuel utilization procedure outlined in the preceding of solar heating, Kreider considers a section, it is important to know the solar collector delivering heat at Tc =

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Communications on energy 30°C; using Tc as the solar fuel temperature, he calculates a second law efficiency well above the value corresponding to natural gas, Vln = 0.776. His conclusion is that the solar design is dramatically more exergy-efficient in comparison with traditional gas furnaces. The fallacy of this argument should be obvious in view of the concept of 'sun temperature as an exergy source' developed in this section and illustrated in Figure 3. Substituting the solar fuel temperature corresponding to diffuse sunlight into Equation (5), we obtain 1111 = 0.19. Our conclusion is that both alternatives, solar and natural gas, are highly inefficient from the point of view of avoiding the one-way destruction of exergy. A s illustrated in Figure 2, fuels such as natural gas and solar power should first be used in high temperature applications; the heat rejected from these first applications can then be cascaded down to applications at lower temperatures, eventually, to the job of keeping a building warm.

The effect of user density A key aspect of the proper manage ment of fuel exergy inventory is the decision to consider all fuels and users as an ensemble. Therefore, the optimum cascading of fuels and users must take into account their relative geographic position. In this connection, it is important to point out that the exergy concept, defined by Equation (2) assumes that the user acts alone in his environment. In reality, especially as population and energy use increase, an individual's ability to use a certain fuel is adversely affected by the presence of one or more neighbouring fuel users. Consider for example the power plant '1' operating between a fuel Tf and a lake TL, as shown in Figure 4(a). The lake rejects heat to the ambient To, at a rate Qo = UA (TL - To), where A and U are the lake surface area and a proportionality constant. Using Equation (2) it is easy to show that the exergy of the fuel (Q, Tf) relative to T Ois given by

E = Q [1 To + QoI(UA)]

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In conclusion, the fuel exergy E decreases as the lake heat rejection per unit area, Qo/(UA), increases. In the case of a single power plant, the lake heat rejection Qo is equal to the heat rejected by the power plant. However, as more and more users are connected to the lake, Qo increases and, simultaneously, the ability of each individual user to produce useful energy (E) decreases. This effect is illustrated in Figure 4(b). The fuel-user cascade described in this paper has the beneficial effect of easing the 'crowding' of exergy users. A s illustrated in Figure 4(c), by placing two or more exergy users on a vertical temperature ladder has the effect of minimizing the heat rejected to the immediate low temperature reservoir. Due to this effect, the reservoir temperature TL is lower than in the case of Figure 4(b), hence, the exergy available to and received by each user is greater.

i0 ~

k~- uo4

i05

,,,,,I

,

, ....

0.01

,,I

,

,,,,,,,I

0.1 8,

, I

rodions

Figure 3. The absolute temperature of the solar fuel, as an exergy source.

temperature gaps is minimized. Thus, to make the most of the exergy available from a given fuel, it is necessary to assemble users on the fuel-environment temperature scale so as to minimize fuel-user temperature gaps. We showed that the most promising fuel resource of the future, the sun, is in fact an exergy source of very high temperature. This conclusion contradicts the popular end-use matching view that the sun is a low temperature energy source. We showed that we can Concluding remarks harvest the most exergy from the sun by In this paper we proposed a thermo- first channelling the solar radiation into dynamic basis for the proper manage- the application of highest temperature; ment o f our limited fuel resources. This the exergy remaining from this first approach is based on the recognition application can be used downstream as that the scarce commodity we refine fuel for low temperature second from fuels, for our own consumption, is applications. In conclusion, we feel that for a exergy. We have shown that the exergy of a given fuel is utilized to its fullest future energy policy to be effective in when the loss of exergy in the fuel-user the long run, the present debate should (o)

F rz

(b)

(c)

l

r°

Figure 4. The detrimental effect of 'user clustering' on the low temperature reservoir (TL); the beneficial effect of assembling fuels and users on a vertical temperature scale (Figure 4(c)). E N E R G Y P O L I C Y June 1982

Communications on energy

not lose sight of the basic principles of thermodynamics. We must establish a dialogue, an open channel of communication and understanding, between economists, businessmen, and policy makers on the one hand, and thermodynamicists and engineers on the other.

Barriers to the adoption of an energy efficient technology

Solid state electronic ballasts promise significant energy savings in the lighting systems of large buildings. However, organizational factors and standard operating procedures may inhibit the adoption of this technology in the large, bureaucratic public and pnvate sector organizations which represent the major Mary Bejan potential users of this technology. Graduate School of Business Administration Keywords: Energy; Efficiency; Technology adoption University of California Berkeley, CA, USA Adrian Bejan In this paper, we address institutional Organizational factors, standard Department of Mechanical factors which may hinder widespread practices and procedures, and channels Engineenng application of solid state electronic of communication affect the behaviour University of Colorado ballasts (SSEBs) a technology which of large complex organizations. 2 Our Boulder, CO, USA has been developed to reduce power analysis of the attributes of potential

1A.B. Cambel et al, eds, 'Second law analysis of energy devices and processes', Energy, The Intematlbna/ Journal, Vol 5, No 8-9, August-September 1980. 2j. Kestin, A Course in Thermodynamics, BlaisdeU,Waltham, MA, USA, 1966, p410. 3W.C. Reynolds and H.C. Perkins, Engineering Thermodynamics, McGrawHill, New York, 1970, p 195. 4j. Kestin, 'Availability: the concept and associated terminology', Energy, The International Journal, Vol 5, No 8-9, August-September 1980, p 679--692. 5j.E. Ahem, The Exergy Method of Energy Systems Analysis, John Wiley, New York, 1980. 6A.B. Lovins, 'Re-examining the nature of the ECE energy problem', Energy Policy, Vol 7, No 3, 1979, p 178-199. 7V. Taylor, Energy: The EasyPath, Union of Concerned Scientists, Cambridge, MA, USA, 1979. SA.M. Lovins, Soft Energy Paths: Towarda Durable Peace, Ballinger, Cambridge, MA, USA, 1977. 9Lovins, op cit, Ref 6. ~OF.Kreith, D. Keamey and A. Bejan, 'Enduse matching of solar energy systems', Energy, The Intemationa/Joumal, Vol 5, No 8--9, August-September 1980, p 875-890.

"/bid. 12Lovins,op cit, Ref 6. ~Kreith, eta/, op cit, Ref 10. ~4J.E. Parrott, 'Theoretical upper limit to the conversion efficiency of solar energy', Solar Energy, Vo121, 1978, p 227. ~SLovins, op cit, Ref 6 and Kreith et al, op cit, Ref 10. a6J.F. Kreider, 'Second-law analysis of

solar-thermalprocesses',EnergyResearch, Vol 3, 1979, p 325. 17F. Kraith and J.F. Kreider, Principles of Solar Engineering, McGraw-Hill,New York, 1978, p 28. lSNote that in Equation (5) To, TB, and Tf are absolute temperatures, expressed in degrees Kelvin (og To = 263K).

E N E R G Y P O L I C Y June 1982

consumption by fluorescent light tubes. SSEBs operate fluorescent tubes at radically higher frequencies, resulting in a 20-25% reduction in electric power consumption per unit of light output, reduced heat loss, extended lamp life and other advantages. Solid state circuitry built into each light fixture permits these advantages to be realized in a decentralized, costeffective manner. This contrasts with earlier technology which would have required a centralized conversion facility and use of a separate, high frequency electrical circuit for all high frequency lamps in a building. The realization of these advantages may be hindered because of the organizational attributes of major prospective buyers. Governments and large private sector organizations represent the major potential market for SSEBs. Berry and Martin assert that 'marketing research on individual consumers is extensive and the methods and problems are well understood'. However, market research in which government and firms are the major adopting units, and utilities play a major role in the promotion of products, has only received recent attention from marketing experts. In situations in which these large scale public and private bureaucracies are involved, standard marketing techniques are less useful. Bureaucratic decision making processes 'are too varied and too complex to be easily reduced to the kinds of modeling techniques and marketing theory currently available for use'. 1

purchasers of ballasts is based on telephone interviews with a sample of representative users in three categories: state officials (20), city officials (12), and industrial energy managers (13).

Organizational factors State and city governments. In state

governments, purchasing is often handled by individual agencies. There is usually no central purchasing agent with a mandate to ensure that energy efficient ballasts are ordered. Cities are like states in that purchasing is decentralized. Rarely are there citywide standards for the purchase of energy efficient equipment. In one city, information is sent to departments by a central office, but departments have to be persuaded by the power of the central office's suggestion. The central department has no formal authority. In another city, mandatory use requirements are being considered, but they have yet to be approved by the proper political officials. In a third city, a committee composed of engineers and interested citizens has been studying central purchase agreements. In a fourth, an energy office is working on a comprehensive energy plan which is being designed by a large, citywide committee. Overall, organizational arrangements to carry out a conversion to energy efficient ballasts are not in place in either state or city governments.

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