Energy vs food resource ratios for alternative energy technologies

EncrqgVol.8.No. 4.pp.TL16S. I%3

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8 1983Puswlon Plus Ltd

ENERGYVSFOODRESOURCERATIOSFOR ALTERNATIVEENERGYTECHNOLOGIES WILLIAM DRITSCHILO, MIGUELMONROY,ELIZABETH NASH, BARRY SCHUYLER, BARRYR. WALLERSTEIN, JOSEPH DE VITAand RICHARD L. PERRINE Environmental

Scienceand Engineering, University of California/Los Angeles, LOS Angeles, CAggg24, U.S.A. (Receioed 10 August 1982)

Abstract-Alternative energy technologies, particularly solar-based ones require large amounts of resources such as land and water that are also required for food production. ContIicts in resource use by energy and food production systems can be estimated quantitatively by a resource use ratio based upon the number of people that can be provided with either food or energy using the resources in question. Example analyses of selected alternative energy technologies demonstrate that alcohol from corn and eucalyptus farm technology have high potential, while wind and dry geothermal energy systems have low potential for contIict with food production. The approach presented provides a quantitative measure for assessing the issues arising when food resources are used for energy production.

I. INTRODUCTION

H. Odum has emphasized the relationship between fossil energy and food.’ Modern agriculture has made impressive gains in increasing the yields of crops, both by harvesting more per hectare and by bringing more land into production, but it has done so largely through use of increasing amounts of fossil energy.” Concern over the limiting effects to agricultural production of diminishing fossil energy supplies has lead to examination of more energy efficient production systems,‘-’ more energy-efficient diets’ and has contributed to the need for alternative energy sources to replace fossil fuels. Less attention has been given to the possibility that development of some sources of alternative energy can result in a loss of agricultural productivity, even as they increase the supply of energy available to agriculture. We now face the prospect of making oil fuel, not food from soy beans.9 Several authors have suggested that biomass sources produced by organized agricultural operations will result in more efficient harnessing of solar energy than through use of more sophisticated technologies such as photovoltaics or central receiver solar collection devices.“,” Indeed, even in a country in which food production has fallen behind population growth such as India, biomass is seen to be a preferred method of harvesting energy.” Some proposed alternatives to fossil fuels can potentially affect food production through direct competition for agricultural resources or indirectly through such action as increased soil erosion or loss of soil carbon. Although the greatest concern is over biomass energy technologies, particularly ethanol production from grains,‘* other technologies, due to large land and water requirements, can potentially compete with agricultural resources or result in similar indirect effects on agricultural production. Although energy is required to support food production, the form that this energy is to take may paradoxically serve to decrease food supplies or drive up their prices. One bar to analyzing the conflicts between new, land-intensive alternative energy technologies and food production systems is that a proper accounting system has yet to be formulated that can quantify the magnitude of any such conflict or be used to evaluate technology alternatives. In this article, we review some of the major issues in the food vs fuel dilemma. We then present estimates of resource use by a selected set of technologies and attempt to quantify, through use of an energy-food resource ratio, the amount of competition for resources between food production and energy production. 2. FOOD OR FUEL?

The clearest case of a conflict betwen food and fuel production is the use of grains to produce liquid (alcohol) fuel, particularly corn grain for gasohol. The raw material for alcohol production is an unambiguous source of human food. Although less than one-tenth of the grain in

256

W. DIUTSCHILO et 01.

the U.S. is for human consumption, the remainder is fed to livestock, which in turn is consumed by humans.‘The fact that gasohol feedstock is a human food source has received more attention in the popular press than in technical articles. Technical articles generally ignore this issue, discount its importance,‘” or propose ingenious ways to circumvent it. Lipinsky’” suggests that corn stillage and stover be substituted for feed grains consumed in alcohol production to produce 10to IS x IO9liters of alcohol annually, while obtaining the same quantity of beef production as if the grain were fed to cattle. Arguments produced to support the concept that gasohol will not compete with food production are as follows.‘5 (1) Surplus grain is to be used, (2) Economic incentives related to gasohol production will serve to spur greater grain production, (3) Grain for fuel alcohol will be produced from marginal land only, and (4) Fuel alcohol will be produced from distressed crops. Counter-arguments are that surpluses do not exist on a global basis and that local surpluses will become increasingly uncommon in the future, that economic incentives to farmers for fuel-alcohol production will result in higher food costs for consumers, and that marginal land should not be planted in grains or would require such high energy inputs for production that the gasohol system would be a net energy drain rather than gain. The net energy characteristics are discussed by Chambers and coworkers.‘6 The key to the controversy, aside from economic or net energy arguments and extending to other biomass energy resources, is whether there is surplus food production capacity or the necessary agricultural resources are available to produce surplus food. Although favourable conditions may still produce bumper crops and grain surpluses in the developed countries, world hunger is expected to increase in the coming decades as the undeveloped nations fall further behind their projected grain needs.” On a global basis, arable land is already in short supply and is being converted to non-agricultural uses.‘a’o On a localized basis, supplies of fresh water are being depleted or diverted to competing usesI On the basis of these considerations, it is difficult to argue that grain converted to fuel in one region of the world might not reduce the food supplies available to another. Conversion of biomass to energy can indirectly affect food production. Crop and forest residues have a gross heat equivalent of about 12% of the fuel consumed annually in the United States, but conversion of al! such residues into biomass energy poses severe environmental consequences from soil erosion, water runoff and nutrient loss.” Unless compensated by increased energy use in farm production practices, the resulting erosion, runoff and nutrient losses will lead to reduced soil fertility and decreased crop yields. The increased energy inputs would tend to reduce the net energy available from biomass conversion, so that use of crop residues on a large scale will either reduce crop yields or fail to yield as much net energy as envisioned. Biomass energy technologies that do not use food crops as a feed source also pose indirect threats to crop production. Use of forest residues for energy production can harm crop production through increased flooding and siltation of irrigation reservoirs and conveyance structures.” Intensive silviculture can affect forest humus, potentially serving to increase atmospheric carbon dioxide concentrations.*’ Soil humus is the major store of terrestrial carbon,‘3 loss of which to the atmosphere would further aggravate carbon dioxide build up, possibly resulting in climatic changes detrimental to food production.24 Any intensely cultivated biomass crop has the potential to result in increased soil erosion and loss of soil carbon. Biomass and other alternative energy technologies may also serve to increase air pollution locally, which in turn may damage or detrimentally influence crop production. The magnitude of this effect will depend on specifics of the technology and its location. Geothermal development can result in emissions of H2S with low ambient concentrations that are nonetheless capable of affecting crop production through chronic effects.” Accidental releases of geotherma! fluids could also damage crops if the geothermal source is located within an agricultural area.26 Large-scale wind and solar energy facilities can potentially affect local climates,” possibly to the detriment of crop production. In genera!, these effects will be minima! and localized, as compared to competition over resources. Food production requires the basic resources of land, water and energy. Interestingly, energy production requires the same basic resources: land on which to site facilities or that will be disrupted by the technology, water for cooling or for land rehabilitation and energy

Energy vs food resource ratios for alternative energy

technologies

‘;_.

to collect raw materials and convert them to usable form (or to mitigate environmental impacts). The net result of an energy technology should be to yield more energy than it

consumes, resulting in more energy becoming available for agricultural production. Quantities of arable land and fresh water are essentially limited, however. These two resources, if used to a large extent for energy production, cannot feasibly be replaced to offset losses to crop production. For example, Harte and Socolow~s give as a practical minimum an energy requirement of 170kjlliter of desalted water. Corn requires 12-14 x IO6liters of water per hectare, so that use of desalinated water to grow corn would increase the energy required to grow an acre of corn in the U.S. (given in Ref. 4) by a factor of 80. Similarly, the use of marginal land for crop production results in decreasing yields and increasing energy inputs.

l?.I9-21.29

3.

ENERGY-FOOD RESOURCE RATIOS

Brown” compared the number of drivers whose transportation energy needs could be met through corn grain used for gasohol to the number of people whose dietary energy needs could be met through corn grain used for food. This provides a useful framework for comparison for several other energy technologies. In Tables 1 and 2, we have calculated a similar ratio for a number of technologies, namely, the number of people in the U.S. whose average energy use could be met by an energy technology to the number of people in the U.S. whose average protein use could be met by converting the resources used by the energy technology to beef production. The technologies chosen represent choices available to an area of the U.S., California, that has natural resources to support a variety of new technologies. All the technologies are alternatives to conventional fossil fuel, hydropower, and nuclear technologies that comprise most of California’s energy use. With the exception of methane from water hyacinths, all the technologies have reached some level of pilot stage in development, rather than being strictly conceptual. The water hyacinth technology was included because it represented an interesting type of possible alternative technology. All systems were analyzed at a commercial size of development preferred by the utility industry, because this is the size at which conflicts between energy and food might be the most severe, in our judgement. Passive solar, roof-top photovoltaics, and wood-burning stoves, to give a few examples, may or may not conflict with food production, but the conflicts would be much more indirect than for the facilities analyzed here. Established international conventions were followed for the net energy calculations, requiring an accounting of direct and indirect energy inputs.30 System boundaries were chosen to correspond with the general boundaries in Fig. 1. Energy systems can be depicted as having 5 major component processes: (1) feedstock production, including exploration and mining activities or, for biomass systems, agricultural production; (2) transportation of feedstocks to conversion facilities; (3) conversion to electricity, liquid fuels, etc.; (4) delivery of the energy to place of end use; and (5) end use. In this analysis, direct fuel and embodied energy inputs crossing system boundaries at processes (l), (2), and (3) were tabulated from published analyses given in the footnotes to the tables. For solar and wind systems, processes (1) and (2) in Fig. 1 are unnecessary; for geothermal energy production, processses (1) to (3) are greatly telescoped. Delivery and end-mode use processes (4) and (5) have been excluded from our analysis. Beef protein production was chosen to quantify the food portion of our analysis as a necessary and convenient method of comparing (or combining) the two diverse agricultural production systems of interest to this study: low-quality range production and intensively managed irrigated crop production. Although irrigated cropland can be used for human food-crop production directly, rangeland cannot be without substantial improvement, such as irrigation. Pimentel and coworkers4.7.8 provide informative discussions of the advantages and drawbacks of various protein production systems and diets. Beef protein production possible from the resource use of the energy technologies was calculated by estimating the amount of rangeland beef that could have been produced by range used for energy production and by assuming that the water used for energy production could have been used instead to produce irrigated crops in one of California’s crop production regions. The irrigated crop and corn grain for alcohol production were assumed to be capable of being used for feedlot beef production.

W. DRITSCHILOet al. Table I.Energy analysesfor some alternative energy technologies

T 1output Gross

I

I I

/

I

I ~

I I

Technology

T IllpUt

;

sergv r

:

Caoacity

/:10'2lcj)i ratio

](lO"Kj)

i

(a)

(A) T-

Solar Centra: ReceiverC

I

!A+51

/ ;

16

Vapor-Gomina'ed Geothermala

100 we

’

2.35

0.11

) 21

Geothermale

100 MJe

1

: ; I Liquid-CominatedI

2.08

0.18

112

Oil-Bearing Plantsf

/ 2x106kg/day,I 7.08

2.75

1

kind Farmg

1

Ethanol from Corn Grainh

i1.5x106ga1,yr/0.134

,

Tree Farm' Methane'from Water HyacinthJ

a.

100 We

j

150 We

0.048

1.07

2.93

eauivalent1l orovided

I

(10'2Kj) I 'energyb

I-

1

0.10

1

Net a ; OUtpl,t (fossil 1 Population :

2.6

22

/ 4.73

16,000

:

5.3:

24,0C0

:

6.06

21,000

4.33

15.000

3.15

11.000

I :

3

j (

0.125

1 .l

0.008

3.13

0.3

5.30

'

18,000

/ I

L2L

2x108ft3/da

!

230,000

(Gross output x 3) - (input) for technologies producing electricity, (gross output) - (input) for ethanol, oil. and methane producing technologies..

b.

Ret output divided by 1980 per capita energy consumption in California of 33 2.95 x 108 kjlyr.

c.

Gross output for a 100 Me to be 4.45 x lo5 Me,

solar central receiver power plant is expected

34 annually.

Input energy represents a capital energy

34 35 cost of 6.59 x lo5 iWe-hr over a 30-yr lifetime plus 25% for operations and 3.5 x '0' kj associated with turbines (not included in Ref. 34). based on information given in Ref. 36. d.

Gross output and input for a geothermal facility at the Geysers, California, with a 77.5% capacity factor, 25-yr lifetime, and 4% internal energy requirements is given in Ref. 37.

e.

Gross output and input for a flashed-steam design geothermal facility in Imperial Valley, California, 70% capacity factor, 25-yr lifetime, 25% internal energy consumption, and mechanical draft coolina. is aiven in Ref. 37.

f.

Gross output and input for a euphorbia production system described by Calvin38 that would yield 2 x lo6 kg/day, 30% oil, 70% alcohol, along with bagasse.

9.

Gross output is based on 25-4W

wind machines, operating at 34%

CapaClty.

39

The input was calculated from energy associated with materials used for 40.411.88 x 101' kj, 30-yr lifetime, and 2% of construction, 42 for operations and maintenance.

Capital

COStS

Capital costs of S600/kw43 were con-

verted to energy from the ratio of energy use to gross national product.44 h.

45 Based on a project proposed for California. Gross output represents the energy of ethanol, 84,828 8tu/ga1.46 process energy and capital equipment

Input energy includes 54,870 Etu/gal 47

plus energy required to produce

16 5.77 x lo5 bu corn at 2.6 gal ethanol per bu corn and 1.03 x lo6 kcal energy used to produce 1 ton corn grain.

48

Based upon these calculations

159

Energy Yj food resource ratios for alternative energy technologies Table 1 (Contd) the

process

produces process

heat,

to Ref.

21.

process

energy

power

27,000

to eucalyptus

2.08

protation, assumed with

surface

for a 1500

hectare,

Capital plant,

feed

56.2

have

reduced

of energy = 56 Ib,

kj/kg

dry

wood,

would

be devoted

energy

inputs:

kj

fertilizer,

for

x lo6

and be

kj

3.02

for

trans-

4'

Ue

irrigation

to be 10%

30-yr

of those

lifetime,

consumption

x

for

drying.

used

assumed

bill'on.5'

capacity

d 60%

annually.4'

2.16

would

were

a ratio of energy

through

be

1 bu corn

hectares

pelleting,

costs

According

We

kj,

4.93

x lo7

loading,

by gravity

power

and

required

3.98

be

actually

estimate

with

per-hectare 50

for chipping.

input.

can

latter

20,000

hauling,and

supplied

units

are

can

kg.

of 27%

following

x lo7 kj

energy

con-

to gross

product.44 design

hyacinth

plant

economic

feasibility.

(1 ft = 0.305

and

is given

m) and

by converting

Convertfng national

the

this

which

Btu/lb.

is assumed

efficiency

and maintenance,

MU coal-fired

A conceptual

culated

facility

per

950

production

requirement.

energy

or

= 0.454

of eucalyptus

with

water

to energy

national j.

8.05

negligible

verted

plant

energy

1 8tu = 1.0545

r,

lb, lb

1 bu corn

Btu/lb'G

heat

stover,

= 3.785

kj for harvesting, and

process

by subtracting

kg dry weight

growth

at 6000

potential corn

generating

for operations

x lo6

tons

= 2000

weight)

any

of

1 ga'

At an overall

Assuming

kj

x lo8

kj, 1 ton

kg (dry

lb stalks

kcal

However,

energy.

eliminating

requirements

= 4,184

x lo8

net

53.7

x 1013

in stalks.

factor.

lo5

of

1.585

A conventional

5.34

provide

thereby

7.187

from

available 1 kcal

not

a byproduct

recovered

i.

will

to energy product.

operating in Ref. Gross

characteristics 52.

output

340 operating capital units

and

through

The

plant

of a methane is the minimum

is calculated days

based

per year.

oeprating a ratio

costs

size

on 1000

Energy to '980

of energy

from

input dollars

consumption

water for

Btu/ft3 was

cal-

and to gross

44

Analysis of the solar central receiver technology will be used to illustrate our general approach and methodology. Energy inputs and outputs were obtained from published analyses. The gross output in kWhr was converted to kj for the purpose of computing an energy ratio (output to input), then multiplied by 3 to represent the energy content of the amount of petroleum-based liquid fuel that would have been consumed to produce an equal amount of electricity. This convention was employed for the other electricity generating technologies (geothermal, wind and eucalyptus farm); oil bearing plants, ethanol-from-grain, and methanefrom-water-hyacinth were credited with an output energy that represented the heat content for the fuel produced. The net output given in Table 1 represents the liquid fuel equivalent minus the input energy. Net, not gross output, was preferred because the technologies varied in their net energy characteristics. The net energy of the process was then divided by the average per capita energy use in the U.S. (2.95 x lO*kj/yr) to yield the number of people who could be provided with energy by the technology. Calculation of food displaced by the technologies considered two separate resources: land and water. It was estimated that the solar central receiver facility would displace 405 ha of rangeland. Of the other technologies considered, all except liquid-dominated geothermal recovery (which displaced cropland) and ethanol from corn grain technologies also displaced rangeland. For the solar central receiver technology, the rangeland was judged to be of low quality, capable of supporting 0.2 AUM/ha (AUM-animal unit month). The total AUM were converted to beef production, assuming that 1 AUM will result in 15 kg calf production. The live weight of beef produced was then converted to kg of protein available for consumption. In

260

W. DRITSCHILOet al.

Table 2. Food resource analyses and energy: food ratios Popula. tion provide< with energy

I/Technology

I-

PooulaFood tion Energy: I displacec prov:?ed food I tiith resourcei (kg bee1 protein) ratio I protein'

Water "se

Land use (ha)

(m3)

-.I

/

jSolar Central ! Receiverb

16,000

405

IVapor-Dominated I Geothermalc

24,000

26

'Liquid-Tbminited Geothermal

21,000

26.7

Oil-Bearing Plantse

15,000 11,000

IIWIndFarmf Ethanol from Corn Grainq

3

ITree Farmh

13,000

2.7~10~

,

/

1.4x104

550

0

2.14~10~

8

3000

j

9.8x106

5.42~16~

2,130

10

/

26,720

0

1.17x103

57

260

I

26

0

36

24.3 20,000

93

23

11000 3,600

0.008

43,000

2.1x108

0.4

230,000

2.01x107

1.300

a.

Food displacement in kg beef protein divided by 19%

5.

Land and water use were based upon the 10 we

47

per capita annual

protein consumption of 25.6 kg.33

ha

and 2.7~10~ m3,53

Earstow prototype plant.

Low quality rangeland in :he Lucerne 'Valley,

54 California. supports 0.2 AUM/ha.

We have assumed 1 AUH results in 15 kg

calf production. The number of kg protein was calculated from calf live weight according to Ref. 55 for lean beef.

Water used for cooling purposes

was assumed capable of use to irrigate alfalfa at 26,600 m3/ha to produce 18.000 kg/ha.'6 beef.57

10.95 kg alfalfa were assumed to produce 1 kg feedlot

The number of kg protein was calculated from kg live beef according

to Ref. 55 for medium fat beef.

The methods of calculating kg beef protein

from alfalfa produced and AUMs are identical for all other technologies. c.

Land use is given Geysers region

59 in Ref. 5R; cooling water is not required.

Soils in T!le

vary considerably in ability to support grazing, ranging from

0.8 to 3.7 AUM/ha.Go We have assumed 2.0 AUM/ha as typical for the region. d.

Land requirements are the high estimate from Ref. 26; water, midpoint of estimates given in Ref. 61 and 62.

Land used was assumed to be capable of

growing alfalfa; the water used, for irrigating alfalfa. e.

1 / [ 1

/Methane from j Water Hyacinthi

40.5

1

Poor quality rangeland suitable for euphorbia production can support 0.04 AUM/ha.54 Land use assumes only 1% of land required for a wind farm is actually 42 occupied by facilities,

A wind site under development in California,

63 supports 1 AUM/ha. 45 and water required46 for the ethanol pmduction The estfmates of land use facflitles given Inthetable are neqllqlble compared to land and water used to produce grafn.

The kg beef protein qtven In the table represent the

amount of protein that could be obtained If used for feedlot beef at a COnversion proportion of 10.95 kg corn

per kg beef live weight.

The number of

1 /

Energy vs food

resource ratios for alternative energy technologies

161

Table 3Contd) kg

beef protein was calculated from kg live beef according to Ref. 55 for

fat beef. h.

Water requirements are from Ref. 64 for nonagricultural land in the San Joaquin Valley, California. Ue have assumed this water could be used instead to irrigate alfalfa. Based upon rainfall information, we assumed that range quality was 0.2 AUM/ha.

i.

Land quality was assumed to be identical to that for the solar central receiver. We have assumed the water required could be used to irrigate alfalfa. Further detials on all calculations and their inherent assumptions are given in Ref. 65.

addition, it was estimated that the solar central receiver facility would require 2.7 x IO6m’ per year of water used for cooling. We calculated the amount of alfalfa that could have been grown using this amount for irrigation water, given the recommended practices for alfalfa in the Imperial Valley (the nearest major field crop producing region). The alfalfa was then assumed to be fed to beef in a feedlot operation with 10.95kg alfalfa producing 1 kg live beef. The live beef was converted to kg protein. Water consumption by liquid-dominated geothermal, eucalyptus farm and water hyacinth systems was treated in an identical manner. The calculated food displacement by the solar central receiver system was 1.4~ 10Jkg beef protein, all but approximately 100kg resulting from water consumption. The total beef protein calculated was divided by the per capita U.S. protein consumption (25.6 kglyr), resulting in a number for people provided with protein of 550 and an energy: food resource ratio of 29 (population provided energy: population provided protein). The alcohol-from-corn-grain technology used food directly as a raw product. We calculated the beef production possible from the grain, assuming a feedlot system. The land and water requirements for the grain-to-alcohol conversion facility were negligible in comparison. The eucalyptus tree farm technology analyzed also had a substantial fertilizer requirement. We have not considered the additional food that could have been produced had the fertilizer been used for food crop, rather than tree production. 4. CONCLUSIONS A wide variation in energy-food ratio is given in Table 2. The wind farm analyzed has the least potential for conflict with food production, as the facility would supply the energy needs of 11,000 people, while displacing beef production capable of supplying the protein for only 1 individual. Ethanol from grain represents the other extreme: net production of energy would suffice for 3 people, while the food displaced could have met the protein needs of a population on 3,600. Results for the wind farm are applicable to other wind areas located within poor rangeland (this is generally true of windy regions in California) and assume that all land between wind machines would still be available for grazing. If this latter assumption turns out to be false, the calculated energy-food ratio would decrease by a factor of 10-100. The results for the ethanol-from-corn system are highly sensitive to the net energy of the process. Our analysis assumes an optimistic positive net energy balance; however, even if all input energy to the process were discounted, the resultant energy-food ratio (0.1) still suggests that the resources in question would best be used for food rather than energy production. The quality of a geothermal resource and its location will strongly affect the potential for conflicts with food production. The vapor-dominated system examined is situated on poor rangeland and requires no external cooling water, resulting in an energy-food ratio of 3000. The liquid-dominated geothermal resource examined is located in the Imperial Valley and requires cooling water, resulting in an energy-food ratio of 10. If waste-water unsuitable for agricultural use is used for cooling for the liquid-dominated case, the food production forgone is reduced by 93% and the resulting energy-food ratio is 140. Similarly,the favorable energy-food ratio for water hyacinth (47) would be increased considerably if the water needs could be met by wastewater. Indeed, the process could result in excess water produced, should water hyacinth

W. DRITSCHILO et al.

Energy

vs food resource

ratios for alternative

energ)

technologies

263

production be coupled with additional water purification (the water hyacinth itself is capable of removing certain wastes from water). Economic and technical issues remain 10 be resolved before methane from water hyacinths becomes a practical technology; their resolution could also effect the analysis presented here. Oil-bearing plants have a favorable energy-food ratio (260) despite the large amount of land required and the low energy ratio for the technology, when grown on low quality rangeland without irrigation. The anticipated yield (2.7 x IO4kg/ha) may be optimistic for poor quality land. More intensively managed Euphorbia would probably result in a lower energy-food ratio due to use of irrigation water. The solar central receiver facility, occupying less low quality rangeland than the Euphorbia plantation, has a lower energy-food ratio (29) due to the need for cooling water. Use of argicultural wastewater or once-through cooling” would increase the energy-food ratio for the solar central receiver technology. The tree farm studied also has the potential to conflict with food production. Because of requirements for a large tract of land, eucalyptus production is most feasible in marginal agricultural land, such as that with low rainfall. The lack of rainfall, however, creates a requirement for irrigation water to support the necessary level of production. This irrigation water use, along with the large amount of rangeland used, results in an energy-food ratio of 0.4, meaning that the resources used could feed more people than they can provide with energy. The energy-food resource ratios presented should be interpreted with a certain amount of caution. Uncertainties in net energy analysis, such as for the ethanol from grain technology, are capable of affecting the resultant ratios. In addition, the technologies considered are at different stages of development, which influences the ability to perform accurate energy and resource analyses. More importantly, the energy-food resource ratios are sensitive to the specifics of the sites chosen for the technologies. The clearest example is the discrepancy between ratios for the two geothermal technologies. However, even with such uncertainties, the ratios are useful “notional” indices of potential conflict between er,ergy and food technologies. At the extreme, it is apparent that wind energy technology and vapor-dominated geothermal are compatible with food production, while ethanol from grains and tree farming will produce energy only at the expense of substantial losses of food production resources. The other technologies should bear further analysis before it can be unequivocably determined that conflicts with food production would be minor. The convenient convention of using beef protein production for accounting of food production from the resources used is only a partially accurate one with respect to the U.S. diet and is a wholly unwarranted one for much of the undeveloped world. In terms of analyzing global resource use, a food-energy ratio reflecting non-beef protein, such as from grains, that could have been produced from the irrigation water would have resulted in somewhat different ratios from those presented. Energy is itself a necessary resource for food production. In our analysis, there is a tacit assumption that the average per capita energy use included energy required for food production. We therefore did not credit energy produced by a technology as capable of increasing food production. However, in certain areas of the world in which food production is indeed severely limited by lack of energy resources for land improvements such as irrigation and fertilization, certain of the above technologies could serve to increase food production, rather than complete with it. Finally, we have no clear understanding of what a socially equitable energy-food ratio should be. One argument might be that use of resources for energy production should result in more people being provided with energy than would have been fed had the resources instead been devoted to food production. In this case, all the technologies examined except ethanol from grains and eucalyptus farms are socially acceptable. However, the need for food is perhaps a more basic one than the need for energy, particularly considering some of the more profligate uses of energy, so that a ratio somewhat higher than 1.Omight be required for equitability. Conversely, in times or regions of excess food production, a ratio less than 1.0 might be socially acceptable. The difficulty encountered is one that is common when scientists attempt to enumerate what is essentially an ethical question. Science can measure; it cannot assign ethical values. Whitehead’s comment on mathematics3’ is equally true for quantitative sciences. The energyfood resource ratios provide enumeration of what to the present has been an important, but unquantified issue. The ethical and public policy implications of the enumeration deserve

264

W. DRITSCH~LO et nl.

further scrutiny, however. We cannot answer the question of whether we should put our to energy or food production, but we have answered the related question of how much food production is foregone relative to how much energy is produced by a particular technology. We have measured Whitehead’s apple, in a sense, in the hope that other investigators will be spurred by our analysis to consider the unscientific, but important questions concerning how much of our food resources can be devoted to what types of energy technologies. resources

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