Land requirements for the solar and coal options pasqualetti copy (2)

Land Requirements for the Solar and Coal Options Author(s): Martin J Pasqualetti and Byron A Miller Source: The Geographical Journal, Vol 150, No (Jul., 1984), pp 192-212 Published by: Blackwell Publishing on behalf of The Royal Geographical Society (with the Institute of British Geographers) Stable URL: http://www.jstor.org/stable/634998 Accessed: 13/02/2009 17:19 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use Please contact the publisher regarding any further use of this work Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=black Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission JSTOR is a not-for-profit organization founded in 1995 to build trusted digital archives for scholarship We work with the scholarly community to preserve their work and the materials they rely upon, and to build a common research platform that promotes the discovery and use of these resources For more information about JSTOR, please contact support@jstor.org The Royal Geographical Society (with the Institute of British Geographers) and Blackwell Publishing are collaborating with JSTOR to digitize, preserve and extend access to The Geographical Journal http://www.jstor.org The Geographical Journal, Vol 150, No 2, July 1984, pp 192-212 LAND REQUIREMENTS FOR THE SOLAR AND COAL OPTIONS MARTIN J PASQUALETTI AND BYRON A MILLER The absolutequantityof landcommittedas a functionof variousenergydecisionsis an emerging issue of significancein energy planning.Since the 1973 Arab oil embargo sensitized us to the need to develop renewableenergy resources, the attentionwhichconsequentlandcommitmentshasreceivedhasoftenbeen directed at varioussolaroptions This paperreportsthe approachand resultsof a land-use comparisonover the entireenergy-supplycyclebetweencentralizedsolar-basedand centralizedcoal-basedelectricitygenerationfacilitiesin Arizona.In thisregard,the especially significant considerations for coal generation were found to be reclamationpotential,transmissiondistances,andcoolingwatersources.For solar generation,the most significantconsiderationswere packingand trackingfactors, and storage strategies.The comparisonincludes photovoltaicand power tower systems, in terms of hectare/MWe*,as well as MWh/hectareover the life of the plant Contraryto commonimpression,the amountof land requiredby coal and solar electricalgenerationwas found to be comparable.Thus, as long as coal is considereda future energy choice, the issue of absolute land needs should not renderthe solaroption at an automaticdisadvantage N RESPONSE TO clear national need and a generally heightened level of awareness and curiosity over the past ten years, we have witnessed a significant increase in the level of scientific interest and research into energy issues The response within geography is illustrated by an increasing number of publications and presentations on the topic (Blue, 1982) and the formation of an Energy Specialty Group within the Association of American Geographers Geographers' involvement in energy research has been largely directed toward threats to environmental quality, partly because land use is at the foundation of the discipline as well as most energy-related environmental problems (Pasqualetti, 1981) Within this environmental sphere lies the issue of the actual land committed to various technology-specific energy decisions and options The low level of attention to this problem heretofore has resulted presumably from the cognitive view that the commodity of open space is plentiful in comparison with the land needed for energy development As the quantity of untampered space has decreased, however, the absolute quantity of land committed by our energy decisions has become a more significant matter The issue of energy-related land commitments is a natural concomitant to an energy future which would rely to a large degree on naturally diffuse sources such as solar energy Although there are many relationships between solar energy development and land use (e.g., solar rights, street patterns, zoning), the most often mentioned (though misunderstood) relationship has been with regard to the land required for large centralized solar-electric systems; this land requirement is the topic of our paper Solar energy requirements are often mentioned as an environmental barrier to its widespread use in centralized power plants As examples: Solar energy 'suffers from an insoluble defect: it is a diffuse source of energy and requires a great deal of land surface for solar collectors' (Sutton, 1979 : 54); 'Because solar energy is so diffuse, "large" surface areas are required to collect it' (Landsberg et al., 1979 : 498); 'The environmental impacts associated with solar thermal conversion need not be severe The large amounts of land needed for large-scale, solar-electric generating plants would be the most serious' (Kendall and Nadis, 1980: 132); 'The most significant environmental impacts of large solar thermal conversion plants would be their * A key to the abbreviations used in this paper is included before the list of References Dr Pasqualetti is Associate Professor of Geography at Arizona State University in Tempe, Arizona 85287 Mr Miller is an Associate Planner for the City of Scottsdale, Arizona 85251 This paper was submitted for publication in October 1982 0016-7398/84/0002-0192/$00.20/0 ( 1984 The Royal Geographical Society LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS 193 land requirements' (National Academy of Sciences, 1979 : 366); 'The negative environmental effects of solar energy [include the] land use requirements which could compete with other, more attractive uses of land near populated areas ' (US Office of Technology Assessment, 1977 : 1-19) General comments such as those above stimulated us to seek more specific studies on the land-use needs of solar energy We found several Some of these studies are comparisons with other technologies (e.g., Caputo, 1977a, 1977b; DiNunno and Davis, 1976; Newsom and Wolsko, 1980; General Electric, 1976) Others give the amounts calculated for solar energy only (e.g., US DOE, 1977; Ouwens, 1976; Kash et al., 1976) Each of these studies suffers some shortcoming For example, DOE, Kash, and Ouwens not compare the findings for solar energy with those of any other technology and thus their numbers tend to be isolated from the sense of reality which comparative analysis would offer The DiNunno and Davis studies not indicate methodology One of the studies (Newsom and Wolsko (1980)) actually points out many of the deficiencies in some of the studies It said (p 7) that Caputo identifies 'only land for transmission and the total land for other purposes for each technology'; and that the General Electric study gives only a 'single figure for the total land use of each [technology]' However, the Newsom and Wolsko paper itself still cites from the others, is incomplete in methodological data, and does not itemize the land requirement for each energy phase for each technology Although some of the authors might have considered factors they not mention, none of the papers explicitly addresses the wide variety of factors necessary for such an evaluation (e.g., load displacement, dispatch logic, capacity factors) To muddle the issue further, the estimates offered in the papers cited above are given in a variety of units, are based on vastly differing assumptions, and (not surprisingly) are significantly different from one another For example, the US Office of Technology Assessment (1977) indicated that photovoltaic arrays sufficient to satisfy 75 Quads of electricity would need 105 km2 of land The US DOE (1977) paper stated that a 1000 MWe peak output plant would require 11.7 x 106 m2 of land for cells of per cent efficiency, 8.8 x 106 m2 for 10 per cent efficiency, and 5.8 x 106 m2 for 16 per cent efficiency Assuming a capacity factor of 0.3 and a 30-year plant lifetime, this translates to 1300, 980 and 660 m2/MW-yr, respectively, it was stated Caputo (1977a) estimated 2000 m2/MW-yrfor a centralized solar-thermal electric plant (compared, he indicated, to 3000 m2/MW-yr for coal), and 3800 m2/MW-yr for photovoltaics (1977b) In an attempt to classify and improve the accuracy and comparability of quantitative results, our analysis explicitly discusses, coordinates, and justifies all pertinent factors and assumptions It also standardizes the results, both in terms of unit of area per megawatt and in terms of megawatt-hours per unit of area per 35 year period (i.e., the presumed lifetime of the plant) Each step in the energy development process is included (i.e., exploration, extraction, processing, generation, transportation, distribution, disposal), as applicable Inasmuch as the primary near-term competitor of the expanded use of solar energy will probably be coal, and also to keep the evaluation of solar energy in perspective, this paper compares the land-use requirements of solar-electric plants with coal-based facilities However, even though coal is the logical comparative resource, genetic and technical differences between the use of the two fuels not allow the comparison to be completely analogous For example, coal is used both for base load and intermediate load electrical generation, while solar may offset electrical generation in base, intermediate, or peak loads, depending upon several factors such as those related to storage and dispatch Further, solar electricity generation in the short-term will be targeted to displace expensive peak and intermediate load generation, although a significant amount of base load capacity will be displaced as well (e.g., the Saguaro power tower's 1986 displacement is 39 per cent of oil and 61 per cent of coal (Weber, 1980)) As solar penetration becomes more significant, an increasing proportion of solar electricity generation will satisfy base load demand Thus, while the use of coal in our comparisons with solar energy is not absolutely ideal, no resource can be; nevertheleless, it can be used to help evaluate solar-electric strategies over the short and long terms 194 LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS Before we begin our actual comparison, two additional introductory statements are needed: (1) Our comparison assumes that the amount of land necessary to provide the materials for solar electricity generation is comparable to the land necessary to provide the materials for coal mining, railroads, and coal-fired power plants*; (2) we address the land requirements of centralized power plants only Of the three types of solar power plants that would qualify under this heading (i.e., photovoltaic arrays, power towers, and solar satellite receiving stations), only photovoltaic arrays and power towers hold near-term promise for large-capacity utilization.** Arizona is used as the site for our comparison for several reasons: it has large coal mines and several new coal-fired generating stations complete with substantial environmental documentation, ample open land for possible solar system siting, large and rapidly growing load centres, high rates of insolation, and keen interest and hopeful expectations regarding the future use of solar energy Our comparison begins from the perspective of the quantity of land needed in terms of generating capacity (hectares/megawatt) Comparison of capacity-based land requirements Land-userequirementsof coal-firedpowerplants Calculations in this paper have been based on 4965 MWe of coal-fired generating capacity located entirely within Arizona About 60 per cent of this capacity is on line and the remainder is under construction Environmental documentation pertinent to our evaluation is available for the entire 4965 MWe Calculations of coal land commitments include six of the seven phases of electricity development: exploration, extraction, transportation, generation, transmission, and waste disposal (Coal processing/beneficiation, while important in eastern coal mining, is not as significant in Arizona or most other western states The land required for breaking and sizing is part of the figure given for the mines.) Coal supplied to Arizona power plants originates at several mines, and it varies widely in terms of ash, heat content, seam thickness, and sulphur content The mined land varies in reclamation potential The only commercial coal mining operations in Arizona are the two large mines on Black Mesa (Fig 1) Approximately 12 million tons a year are mined on Black Mesa, two-thirds of which is taken from the Kayenta Mine to supply the Navajo Generating Station near Page, Arizona, and one-third of which supplies a power plant out of the study area The Cholla, Coronado, and Springerville Generating Stations are supplied from mines in west central New Mexico, just across the Arizona border One of the key ingredients in calculating the amount of land which must be committed to coal-fired electrical generation is the reclamation potential of mined land This is a very site-specific matter, and it rests heavily upon one's definition of 'reclamation' In an oft-cited work on reclamation, the National Academy of Sciences * Our assumptionis basedon a comparisonof the materialrequirementsof the Saguaropower tower proposed for a site near Tucson (111 MWe), the existing power tower near Barstow, California(10 MWe), and the Palo Verde NuclearGeneratingStationnearPhoenix.A nuclear plant was used in the comparison because nuclear data were more available and precise, and because a recent well publicized book on energy (Anderer, 1981) states that nuclear plants use even less concrete and steel than coal plants Thus, if solar and nuclear plants are relatively close on their materials requirements, presumably coal plants and solar would be even closer The comparison indicates that solar energy material needs are greater than for coal-but not so much greater that the assumption of comparability becomes unreasonable In this regard, one should point out that the amount of material used in solar technology is declining rapidly (Weber, 1982; Brown, 1982) ** The factors discussed thus far are of significance to a determination of 'direct' land use only Several other, indirect, land-use factors are not considered: (1) concurrent land use: in some arrangements land beneath and between solar arrays may be usable; (2) socioeconomic impact: personnel needed for several phases of power development will require land for housing, schools, etc.; (3) indirect land use: vast areas of land are owned, leased, or reserved for rights of way for power plants and their related facilities LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS 195 Fig Coal-fired power plants and coal mine location in Arizona (NAS) differentiates between 'reclamation' and 'rehabilitation' The former implies that 'the site is habitable to organisms that were originally present or others that approximate the original inhabitants' (NAS, 1974 : 11) 'Rehabilitation' implies that the land will be 'returned to a form and productivity in conformity with a prior land-use plan including a stable ecological state that does not contribute substantially to environmental deterioration and is consistent with surrounding aesthetic values' (ibid.) In applying these definitions, the NAS concluded that rehabilitation of western coal lands which receive less than 250 mm (10 in.) of annual rainfall or which have high evapotranspiration rates pose a difficult problem because these lands require major sustained inputs of water, fertilizer, and management If rehabilitation of the drier sites is allowed to occur naturally, it may be on a time scale that is 'unacceptable to society' (ibid., p 2) 196 LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS Thus, the matter of reclamation and rehabilitation is difficult to determine We assume that post-mining use of the land will be feasible, but it is impossible to state categorically how the land will compare in all ways to the pre-mined condition In order to allow readers to insert their own impressions, we made our calculations based on both zero and 50 per cent reclamation of mined lands (We adhere to the term 'reclamation', along with its NAS definition, rather than the more restrictive term 'rehabilitation'.) The area physically occupied by Arizona's power plants includes land for the powerhouse, cooling apparatus, coal storage and blending areas, laboratories, parking and other usual equipment and needs The amount of land needed for cooling exhibits the greatest variation At the Navajo site, cooling water is piped one mile (1.6 km) from Lake Powell Blowdown is discharged to lined ponds where it evaporates The Coronado and Springerville power plants will use well-water, cooling towers, and evaporation of blowdown The Cholla plant uses well-water to fill a 138 hectare cooling lake for Units 1-3 Arrangements for the disposal of waste ash vary from plant to plant All coal plants must dispose of ash, and each Arizona plant has land set aside for this purpose, although the plants might not actually use all such designated land Some of the ash is sold as pozzolana for the manufacture of concrete Sale is most economic when total transportation distances are low The Cholla plant currently sells virtually all of its ash, although it still maintains a site for ash disposal A large parcel of land near the more isolated Navajo plant has been dedicated to the dumping of ash The coal-burning power plants in Arizona have all required the construction of several hundred km of transmission lines to link the plants with the principal load centres of the state A small percentage of the transmission rights of way are 'consumed' by tower pads and switching equipment Reasonably precise figures are available for the amount of land directly affected by the coal-fired power plants in Arizona (Table I) In large part these figures have been taken from environmental impact statements, although some have been derived from base data presented in those documents The remainder have been estimated Footnotes to the table identify the source of each figure The 4.03 ha/MW (9.96 ac/MW) of Table I is a total of the land disturbed directly For the generation site this includes the land actually occupied by the power plant operations The figure given for the transmission lines represents only the land disturbed by the towers and the access roads over the distance necessary to tie into the existing grid In the case of the Navajo power plant, transmission lines were not connected to the existing grid; rather, because the station was isolated and the nearest transmission lines did not have excess capacity, new transmission lines were built directly to the Phoenix Metropolitan Area The figures for the mines are for the land which will be disturbed directly during the lifetime of each power plant The figure for well fields and pipelines represents the land actually occupied by the pumps and pipelines The railroad figure is for land disturbed by railroad spurs built to connect the coal mines with the power plants The figures in Table I represent the amount of land actually disturbed over the lifetime of the power plant The figure for coal mines is obviously large and includes all the land disturbed during the plant's lifetime Since our focus is on the long-term land-use impacts of electricity generation, and since the land disturbance which accompanies solar conversion is at a steady rate, we have elected to compare the final totals for each system before factoring in the reclamation aspect, rather than try to maintain a running total which would include factors for the amount of land to be mined, being mined, and reclaimed Land-use requirements of solar power plants Solar energy possesses characteristics which complicate the calculation of the land area required for a given electrical generation capacity Unlike coal, the land area required to intercept a given amount of solar energy is a direct function of basic earth-sun relationships: insolation variation with latitude, photoperiods which change diurnally and seasonally, and the continuous daily movement of the sun across the sky In addition, daily and regional variations in incident solar radiation occur due to 197 LAND REQUIREMENTS FOR SOLAR AND COAL OPTIONS TABLE I Land area directly disturbed by activities related to coal-fired power plants in Arizona (ha(ac)) Land use Generating station site Ash disposal area Evaporation pond Well field and pipeline Station access road Railroad Transmission lines Mines Limestone source ha/MW (ac/MW) Area/MW SpringerCoronado ville Cholla Totals ha/MW Navajo (1050 MW)(1050 MW) (2250 MW) (615 MW) (4965 MW) (ac/MW) 1012 (2500) 364a (900) 243a (600) 850 (2100) 170 (420) 109h (268) 413 (1021) 310 (765) 81o (200) 174 (430) 154 (380) 138u (340) 1515* (3743)* 998 (2465) 570 (1408) 30b (74) 6c (16) 213d (526) 777e (1920) 3652f (9020) 29g (71) 21i (52) 39j (97) 131k (324) 271 (67) 3239m (8000) 29n (71) 3p (7) 4q (11) 602r (1488) 1296s (3200) 3401t (8400) NA 259v (640) None 96w (237) 579x (1474) 2468y (6095) 17z (41) 313 (773) 50 (124) 1043 (2575) 2697 (6661) 12759 31515 74 (183) 06 (.16) 01 (0.2) 21 (.52) 54 (1.34) 2.57 (6.35) 02 (.04) 5719 (14127) 4506 (11131) 6029 (14892) 3764 (9297) 20019 (49447) 4.03 (9.96) 5.45 (13.45) 4.29 (10.60) 2.68 (6.62) 6.12 (15.12) 4.03 (9.96) 30* (.75)* 20 (.50) 11 (.28) * Does not include area for evaporation ponds and ash areas that are inside plant grounds as mentioned in footnotes a, h, o, and u Figures in hectares not always sum because of necessary rounding from the acre units in the original documents Notes to Table a Including in generating station figures of 1012 (2500 ac) b 51.5 km (32 mi) of pipelines at ha/km (2 ac/mi) disturbed plus 4.0 (10 ac) disturbed for roads, reservoirs, etc c 4481.7 m (14700 ft) x 14.0 m (46 ft) wide (based on average width of disturbance at Springerville generating station) d 69.2 km (43 mi) spur; 95.5 (236 ac) disturbed by cuts; 117.4 (290 ac) disturbed by railroad bed e 230 kv Silverking to Goldfield (27.4 km (17 mi) with 500 kv Coronado to Kyrene line) (17.4 km (17 mi) alone) 230 km Silverking to Hayden (51.5 km (32 mi) alone) 500 kv Coronado to Kyrene (27.4 km (17 mi) with Silverking to Goldfield 230 kv line) (114.3 km (71 mi) with Cholla to Saguaro 500 kv line) 500 kv Coronado to Cholla (41.9 km (26 mi) alone) (80.5 km (50 mi) with Coronado to Kyrene 500 kv line) based on 507.2 km (315 mi) of transmission corridor x 1.6 ha/km (6.4 acres/mi) disturbed by construction activities, construction roads and tower pads (shared corridors are counted 1/2) f Salt River Project has negotiated contracts for the provision of 24.1 million metric tons (26.6 million tons) of coal from the Fish Lake Mine, Utah (1980-1984) Additional contracts must be negotiated to supply coal needs beyond 1984 At McKinley Mine, 17.8 are disturbed per 198 LAND REQUIREMENTS FOR SOLAR AND COAL OPTIONS million metric tons (1 million tons) of coal mined McKinley Mine coal characteristics: 5072 Kcal/Kg (9130 Btu/lb); 14.8% ash content, 0.6% sulphur content (Department of the Interior and Department of Agriculture, Final Environmental Statement-Coronado Project, August 1977) Coal characteristics and rate of land disturbance for Fish Lake Mine are not stated in the Coronado EIS Assuming the same rate of land disturbed per ton coal mined, 735.6 (1817 ac) will be disturbed at McKinley Mine and 69.2 (171 ac) will be disturbed at Fish Lake Mine During 1984, Coronado power plant will use no more than 1.4 million metric tons (1.5 million tons) of coal each year Springerville power plant (1050 MW capacity) will use 3.3 million metric tons (3.6 million tons) of coal per year at full operation Adjusting for the higher heat content of McKinley Mine coal, this is equivalent to 3.188 million metric tons (3.507 million tons) of coal per year for the Coronado power plant Assuming Coronado will be in full operation after 1984 and will operate for 35 additional years, 2847.0 (7032 ac) will be disturbed at an undetermined coal mine Of the 111.4 metric tons (122.5 million tons) of coal needed after 1984, 18.2 million metric tons (20 million tons) will come from McKinley Mine, 93.2 million metric tons (102.5 million tons) from an undetermined mine Land disturbed at undetermined mine assumes rate of land disturbance at McKinley Mine g 45.3 (112 ac) will be disturbed for limestone mining for the Coronado and Cholla power plants combined Land disturbed for limestone mining for Coronado based on the ratio of the MW capacity of the Coronado power plant to the combined MW capacity of the Coronado and Cholla power plants h Included in generating station figure of 850.2 (2100 ac) i 41.9 km (26 mi) of pipeline disturbed at ha/km (2 ac/mi) (disturbance rate based on Coronado EIS estimate) j 18.3 km (11.4 mi) x 14.0 m (46 ft) average width of disturbance plus 5.6 km (3.5 mi) ash haul road with 23.8 m (78 ft) average width of disturbance k 43.1 km (26.8 mi) x 30.5 m (100 ft) average width of disturbance of railroad and service road Springerville Corridor (to New Mexico) (3 sets of towers 345 kv lines) 17.7 km (11 mi) long Coronado Corridor (to Coronado power plant) (1-345 kw line) 33.8 km (21 mi) long Coronado Corridor is serviced by railroad service road which runs parallel to transmission lines Land disturbance for the Coronado Corridor is included under 'railroad' Land disturbed for Springerville Corridor is based on 17.7 km (11 mi) x 2.5 (6.1 ac)/mi (rate of land disturbed for transmission corridors for Coronado power plant) m Gallo Wash Mine, New Mexico Coal characteristics: 4941 Kcal/kg; (8894 Btu/lb); 14.63% ash content; 0.534% sulphur content: 4.5 cu m (5.9 cu yds) of overburden removed for each metric ton (1.1 ton) of coal mined (Westinghouse Environmental Systems Department, Springerville Generating Station: Applicant's Environmental Analysis, June 1, 1977) Springerville power plant will use 115.5 million metric tons (127 million tons) of coal over its 41 year lifetime; 25.5 (63 ac) are disturbed per 91 metric tons (1 million tons) coal mined n Based on area to be mined for limestone for Coronado power plant o Included in generating station figure of 413.4 (1021 acres) p Water source is Lake Powell Water is pumped approximately 4.8 km (3 mi) at ha/km (2 ac/mi) disturbed (disturbance rate based on estimate for pipeline disturbance at Coronado power plant) plus (1 ac) disturbed at pumping station q No station access road; road to ash disposal area approximately 1.9 km (1.2 mi) x 23.8 m (78 ft) average width of disturbance (width of disturbance based on road at Springerville power plant) r 125.6 km (78 mi) x 30.5 m (100 ft) average width of disturbance (disturbance width based on railroad for Springerville power plant) 382.6 (945 ac) + 219.8 (543 ac) for areas, reservoirs, construction camps, and subballast area s 1-500 kv line, to Boulder City, NV 442.8 km long (275 mi) long 1-500 kv line to Phoenix 402.5 km long (250 mi) long disturbance based on 1288 km of transmission lines x 1.0 ha/km (4 ac/mi) disturbed t Kayenta Mine on Black Mesa, AZ, coal characteristics: 5944 Kcal/kg (10700 Btu/lb); 7.93% ash content; 0.51% sulphur content (US Bureau of Reclamation Generating station; 97.2 ha/yr (240 ac disturbed/yr) x 35 years (Plant uses 5.6 million metric tons (6.2 million tons) of coal/yr) u Included in generating station figure of 174.1 (430 ac) v Based on estimate of area which will undergo accelerated change from meadow to xeric community due to groundwater pumping No estimate of area disturbed by pipelines is given in Cholla EIS w Approximately 35.4 km (22 mi) railroad spur at McKinley Mine with 27.1 m (89 ft) average width of disturbance LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS 199 x 500 kv Chollato Saguaroplant 225.4 km (140 mi) alone 114.3km (71 mi) with Coronadoto Kyrene(500 kv line) 230 kv Chollato Coconino(nearFlagstaff) 310.7 km (193 mi) alone based on 593.3 km (368.5 mi) of transmissioncorridorx 1.0 ha/km(4 ac/mi) disturbedby constructionroadsand towerpads (sharedcorridorsare counted 1/2) 2429.1 (6000ac) will be y McKinleyMine, New Mexico,see note f for coal characteristics: disturbedover 35 yearsto supplycoal to the Chollapowerplant(plantwill require2.3 million metrictons (2.5 milliontons) of coal/yr)plus 16.2 (40 ac) disturbedby mainhaulageroad (8.9 km (5.5 mi) by 18.3(60 ft) widedisturbance),10.1ha (25 ac) disturbedby servicefacilities, 12.1 (30 ac) disturbedby coal processingplant site (Dames and Moore, Environmental Report:ChollaPowerProject, 1974) z See note g Area disturbedfor limestoneminingfor Cholla based on the ratio of the MW capacityof the Chollapowerplantto the combinedMWcapacityof the ChollaandCoronado powerplants atmospheric conditions Use of the sun to generate electricity must consider these irregularities Solar energy use does not involve as many phases as coal 'Exploration' can be excluded because solar monitoring stations are small The 'extraction' and 'transportation' phases not apply to solar energy The 'generation' phase requires consideration of the size of the array, insolation, conversion efficiency, energy storage, packing factors (i.e the ratio of collector area to land area), coverage factors (i.e percentage of collector area occupied by collection materials), tracking systems, topography, and other occupied land within the fence of a generating station The 'transmission' phase is required for solar electricity as it is for coal-fired electricity 'Waste disposal' does not apply to solar electricity Land quantities required for solar conversion are not established as clearly as they are for coal, but the data needs are generally well known for each type of conversion In this paper, we have considered two conversion types: photovoltaic cells and power towers (Plate I) In order to make the necessary calculations, data are needed on solar insolation, conversion efficiencies, packing factors, coverage factors, tracking factors, storage, power conditioning, transmission lines, and additional land Insolation.-The design point for solar facilities in the Phoenix area is noon on the summer solstice with a reference direct normal insolation of 1000 W/m2 (317 BTU/ft2/hr) (Weber, 1982) This is equivalent to 100 ha/MW (.246 ac/MW) It is from this insolation level that the related capacities of solar facilities in Arizona are currently derived While rated capacity can range between peak and average capacity depending on the power conditioning and dispatch arrangement, it should be noted that rated capacity is usually significantly greater than the average capacity, as Figure illustrates Efficiency.-The term 'efficiency' represents the percentage of captured insolation converted to electricity For photovoltaic arrays, we use 11 per cent (Kelly, 1978); for power towers, 20.8 per cent (Weber, 1980) Packing factor.-The packing factor is the ratio of collector area to land area It is dependent on the type of tracking system, sensitivity of the collector to shading, the angle and direction of topographic slope, and latitude A packing factor of 1.00 would indicate that the collectors occupy all of the land with no spacing The packing factors we use with regard to photovoltaic cells are taken from Masden (1978) He cites a range from 178 to 539, depending on the system In our calculations, we have incorporated three packing factors for photovoltaic systems: 300 was used for a vertical axis tracking system tilted 50? with respect to horizontal on flat land; 340 was used for a two-axes tracking system on flat land; and 539 was used for a two-axes tracking array positioned on a south-facing 33.4? slope (equal to the latitude of Phoenix) The packing factor used for heliostats in a power tower arrangement is 230, based on design engineering conducted by Arizona Public Service Company for the repowering power tower under study at a site near Tucson, Arizona (Weber, 1980) 200 LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS PLATE I Worker reflected in one of the 222 heliostat arrays at the power tower test facility at Sandia Laboratories, Albuquerque, NM The receiver tower itself, constructed here of concrete, is visible in the mirrors; receivers at other locations (e.g Barstow) will have concrete confined largely to the foundations of each heliostat with relatively little in the receiver (Source:US Departmentof Energy) LAND REQUIREMENTS FOR SOLAR AND COAL OPTIONS 201 Power Peak Peak^ ' Array output later use Rated '- ':" Average II 12 24 Time of Day Fig Relationship between peak, rated, and average plant output power Energy intended for use after sunlight hours must be stored earlier in the day (Source: DeMeo and Bos, 1978) Coverage factor.-For photovoltaic arrays, the unused space between the circular photovoltaic cells must be considered We refer to the percentage of the array actually covered by photovoltaic cells as the coverage factor (Cf) Currently about 75 per cent of an array is covered with the cells New techniques for the manufacturing of the cells should increase this to 95 per cent Tracking factor.-The use of direct normal insolation assumes a two-axes tracking system which maximizes the insolation incident on the collector The cost of land, however, dictates that collectors be packed tightly, so tightly that some shading takes place The tracking factor accounts for this shading and for the decreased incident insolation when a single-axis tracking system is used For vertical axis, two axes, and two axes on a 33.4? slope system, the tracking factors we use are 900, 929, and 933 respectively (Masden, 1978) Energy storage.-For a solar project, the need for storage and the amount necessary will depend on whether the unit is to provide base, intermediate, or peaking power, the penetration of solar energy in the generating capacity of a particular utility system, the incidence of inclement weather, economic considerations, the type of dispatch which is planned (e.g., immediate, delayed), and whether the facility is designed for stand-alone operation or is a repowering plant tied to an existing non-solar facility The storage type, capacity and function will affect the efficiency of electricity generation since all electricity which passes through storage will suffer loss This in turn affects land requirements; as efficiency is lowered, more land is required for a given output Power towers will have storage arrangements different from those of photovoltaic systems The Saguaro power tower, for example, will utilize a molten salt storage system all the time as a means to decouple the systems which interface with it: that is, 'storage acts as surge capacity which allows the receiver to operate independently from the salt/steam heat exchangers and vice versa' (Weber 1980 : 120) This prevents insolation variation from affecting the power output of the plant Used as storage per se the molten salt system will serve to shift the peak output to a time in the day when it will offset more expensive types of fuel The overall plant efficiency used in our calculations integrates this factor; we, therefore, have not included a separate storage phase in the calculations for power towers LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS 202 In contrast to the power tower with its built-in storage, photovoltaic arrays can operate with no storage Electricity may be dispatched immediately into the grid to displace whatever part of the load it can While this may be the case with decentralized rooftop arrays, centralized utility arrays are likely to include storage As with power towers, centralized photovoltaic arrays are currently designed to offset expensive peak facilities in order to improve the comparative economics; to this to a significant degree, storage must be included Preliminary photovoltaic array designs of the Electric Power Research Institute (EPRI) (DeMeo and Bos, 1978) call for six hours of storage with a battery round trip efficiency of 78 per cent With slightly more than half the electricity generated going to storage, 88 per cent of the potential output of the array (if there were no storage loss) is actually available for use Figures prepared by Evans et al (1981) for Sandia National Laboratory differ from the EPRI calculations The Sandia document does not assume displacement of peak facilities for different levels of solar penetration (or 'monthly solar fraction'); instead, it allows one to estimate the effect of various quantities of storage Once the monthly solar fractions are matched with the appropriate constant, sinusoidal, unimodal, or bimodal average daily load curve, optimal storage requirements (in terms of maximizing solar penetration) may be calculated Since utilities in the south-western US typically use the summer solstice as the 'design day' for solar facilities, we matched the typical summer load curve of Arizona Public Service (Figs 3, 4) (peak: 1500 hours; ratio of amplitude to mean: 0.4) to the appropriate summer load curve in the Sandia document Storage requirements were then calculated based on the summer season performance curves, an assumed 10 hour battery storage capacity, and hypothetical monthly solar fractions To illustrate, for a ratio of daily potential output to daily load (QE/L) of 1.2, the fraction of the load actually met by the solar system (F) would be 60 if no storage were used (The loss would be due to the non-coincidence of demand and insolation.) If 22 Wh/(m2 per cent) of storage (B/Arl) were assumed, the monthly solar fraction (F) would be 95 per cent, an increase of 35 per cent In this case, 50 per cent of the electricity generated would go into storage, of which 35 per cent would be retrieved This yields an efficiency of 70 per cent for that energy going into storage Overall, 79 per cent of the potential output is actually available for use The same type of calculation was used to derive the other figures of Table II 2800- 2600 - Peak day for Summer Month 2400- 2200 - 2000' 1800 Peak day 1600 12 i 10 11 12 noon for Winter Fig.3 TypicaldailyloadcurvesforArizonaPublicServiceCo (Source:ArizonaPublicService) LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS 203 SUMMER o oC) QE/L I 0.8 0.6 0.4 0.2 Fig System performance graph (Source: Evans, 1981: p A-67) It should be noted that the figures in Table II are not based on an assumption of load-specific photovoltaic electricity generation Rather, it is assumed that photovoltaic electricity is dispatched immediately into the grid to displace whatever part of the load curve it can; storage is only utilized when the electricity generated by photovoltaic arrays would be greater than the demand This dispatch arrangement implies that photovoltaic electricity will be less expensive than electricity generated at conventional base load facilities While this is not implausible, it is likely only in the long term The preceding discussion allows us to evaluate land-use requirements for two scenarios: (1) the short term, in which solar facilities will be used to displace expensive peak and intermediate load facilities, and (2) the long term, in which solar facilities may displace less expensive base load facilities The long-term scenario has two parts: solar penetration less than approximately 40 per cent (requiring no storage) and solar penetration above 40 per cent (requiring storage).* If we made a highly optimistic long-term assumption of 88 per cent solar penetration, the loss due to the inefficiency of storage is, coincidentally, identical to the loss in the short-term scenario (88 per cent * No storageis needed below 40 per cent becauseother sourcesof generation(e.g., base load coal) can providebackupin spinningreservemore economically.See Evans et al (1981), and Table III for more detail 204 LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS TABLE II Photovoltaic arrays: Relationships between potential output, solar fractions, and storage % Collected retrieved from storage 35 Efficiency of storaged 70 F QEIL 71 78 78 88 94 97 QEILa 1.20 Fb 95 B/Ac 22 % Collected sent to storage 50 1.00 80 60 88 75 58 25 27 18 42 29 15 30 23 12 39 39 0 79 1.00 a The ratioof the dailypotentialpowerconditioningelectricalouput(forthe fullarray)to the daily load Monthlyaverage daily values are used This is a potentialsolar fractionthat would be realizedwith infinite, loss-freestorage.b Monthlyaveragesolarfractionor fractionof the load that is met by the solar system The back-upenergysourcesmust meet (1-F) of the load c A dimensionalratio of storage capacityto the productof arrayarea and monthlyaverage array efficiency.Units are in Wh/(m2%).d The efficiencyof the storagebatteriesgoes downas the time allowedfor the charginggoes down Source:Derived from Evanset al (1981) efficient) We therefore include evaluation of two cases: (1) no storage (long-term with solar penetration less than 40 per cent), and (2) storage (short-term or long-term with solar penetration of 88 per cent).* Power conditioning.-Power conditioning for our purposes connotes the conversion of DC power to AC power and any required voltage transformation It is needed for photovoltaic arrays, but not for power towers Its efficiency is approximately 90 per cent the land disturbed by transmission lines from our Transmission.-Although individual coal-fired power plants is well documented, no comparable documentation exists for the solar option Thus, the land required for transmission lines must be estimated The amount could fluctuate sharply depending on assumptions, and we have made our estimates after detailed discussion with local utility personnel who have also been working on the problem The critical factors which influence transmission distances are essentially those same factors which restrict the siting of coal-fired power plants in Arizona: land availability, water availability, and air quality These factors are of particularimportance in Arizona because of its large parcels of federal and Indian land, its aridity, and its high natural concentrations of airborne particulants Because solar conversion does not involve the common problems of air pollution, the location of centralized solar stations is not influenced by the severe siting restrictions which have resulted from compliance with the provisions of the Clean Air Act and its Amendments of 1977 Nor, in the case of photovoltaic arrays, is the siting of solar stations constrained by the need for large volumes of water In Arizona (and particularly in other western states), the siting of large centralized solar power stations will be influenced primarily by only one of the conventional siting factors, that of land, particularly its amount Thus, the proposed central solar stations could be located much closer to the existing grid than coal-fired power plants The primary constraint in determining how close to the grid solar power plants can be located are the cost and the availability of land, disturbance being calculated at 1.6 ha/km (6.4 acre/mile) of transmission line * It could be arguedthat conventionalfacilitiesrequiredto meet that partof the demandnot met by solarfacilitiesshouldbe factoredinto the solarlandrequirements.To be consistent,solar facilitiesmeetingthat partof the demandnot met by conventionalfacilitiesshouldbe factoredin the landrequirementsof conventionalfacilities.Thistypeof weightingis entirelydependentupon solarpenetrationandconfusesthe landrequirementsof solarfacilities;sincethistypeof weighting is not done when comparingthe land requirementsof gas, oil, coal and nuclearfacilities,we cannotjustifysuchweightingfor solarfacilities LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS 205 Under the constraints just mentioned, solar power plants in Arizona can usually be sited immediately adjacent to the existing grid, thereby requiring no additional land for transmission lines This, for example, is the case with the 100 MWe Saguaro repowering station (and also the 10 MWe Barstow (California) power tower) However, location immediately adjacent to the existing grid requires the existence of excess capacity in that grid, capacity which would not be available in the long term, especially for the larger solar stations To maintain a long-term perspective we consider the transmission distance not from the solar-electric plant to the existing grid, but from solar-electric plants directly to the load centres Substantial areas of vacant land are available at an acceptable cost no more than 80 km (50 miles) from the centre of the Phoenix metropolitan area Transmission lines from a solar power plant located at this maximum distance from a load centre would disturb 128 (320 acres) If it is assumed that the generation capabilities of central solar-electric facilities are similar to the generation capacities of the coal-fired power plants examined above (1241 MWe average), or that several incremental solar facilities will be located along the same transmission line, transmission lines for solar electricity will disturb an additional 10 ha/MW (.25 acre/MW) Additional land.-Finally, we must consider any unaccounted land within the fence of a solar power plant Examination of exisiting fenced-in photovoltaic arrays indicates that the land area within the fence is approximately 10 per cent greater than the area occupied by the array alone * The packing factors for power towers account for all land within the fence and include the land occupied by the cooling towers, the tower itself, the maintenance yard and other facilities.** The factors discussed so far are placed together for convenience in Table III Solar formulas and results Photovoltaic arrays.-We have derived a simple formula which will yield the land required for a photovoltaic capacity of MWe (1) L = I (Se)-l (Pf)-I (Cf)-I (Tf)-I (Ste)-I (Pc)-l (1 + Al) + T where L = amountof land requiredfor MWecapacity I = averagesolarinsolation,in hectaresor acresperMW(.100 ha/MW)(.246 acre/MW) Se = systemefficiency(per cent) Pf = packingfactor, in percentageof land covered Cf = coveragefactor(percentageof arrayactuallycoveredby photovoltaiccells) Tf = trackingfactor (mean daily insolationincidenton trackingcollectorsin an array + dailyinsolationincidenton a horizontalsurface) Ste = storageefficiency Pc = powerconditioningfactor Al = additionalland disturbedwithinthe fence (per cent) T = transmissionland requirement Power towers.-Formula (2) should be used to calculate the land requirements for the power tower; it is the same as formula (1) except that the packing factor includes all land within the fence, and there is no coverage or storage factor (2) L = I (Se)-I (Pf)-I (Tf)-I + T The use of these formulas yields the figures presented in Table IV * Thisfactoris basedon admittedlysparsedatasuchas the site conditionsof the relativelylarge arrayof photovoltaiccells whichprovideelectricityto the visitorcentreand housingfacilitiesat NaturalBridgesNationalMonument,Utah ** These numberscan vary For example, the Saguaropower tower near Tucson will be a repoweringpowerplant;thusit willutilizethe coolingtowers,maintenanceyards,andmanyother facilitiesof the oil-burningpower plantto whichit is adjacent 206 LAND REQUIREMENTS FOR SOLAR AND COAL OPTIONS TABLE III Factors incorporated in calculation la of land requirements for tracking array configurations Seb Pf Cpf 11 300 95 900 11 340 95 929 11 539 95 933 Stec Pc A If 1.00 (nostorage) 88 (storage) 1.00 (nostorage) 88 (storage) 1.00 (nostorage) 88 10ha/MW (.25ac/MW) lOha/MW (.25ac/MW) 10ha/MW (.25ac/MW) T A Photovoltaics Verticalaxis, trackingon 50? tilt Two-axestrackingon horizontal surface Two-axestrackingon 33.4? slope 1000 (317) 1000 (317) 1000 (317) (storage) Key I Se Pf Cf Tf Ste Pc Al T - Designinsolution-W/m2(Btu/ft2/hour) Systemefficiencyof photovoltaicarray Packingfactor Coveragefactor Trackingfactor(net increasein incidentinsolutionon a trackingarray) Storageefficiency Powerconditioning Additionalland disturbed(in percent)withinthe fence Transmissionlandrequirement B Power tower la Seg 1000 208 Pf2 23 Tfr T 929 10ha/MW (.25 ac/MW) (317) Key I Se Pf Tf T - Design insolation-W/m2(Btu/ft2/hour) Systemefficiencyof powertower Packingfactor Trackingfactor Transmissionland requirement Sources: a Weber (1982) b c d e f Kelly(1978) Masden(1978) DerivedfromMasden(1978) Pennerand Icerman(1975) Based on the site conditionsof the large arrayof photoboltaiccells at NaturalBridgesNational Monument,Utah g Weber(1980) h DerivedfromMasden(1978) TABLE IV Land requirements for solar electricity, halMW (ac/MW) Photovoltaic arrays Vertical axis, collector tilted 50? Two-axes, horizontal surface Two-axes, 33.4? slope Power towers * As provided in stations under construction Withoutstorage Withstorage 4.43 (10.91) 3.80 (9.36) 2.43 (5.97) 5.02 (12.36) 4.31 (10.60) 2.74 (6.75) Withstorage* 2.35 (5.79) LAND REQUIREMENTS FOR SOLAR AND COAL OPTIONS 207 Final rankings for capacity-based land requirements Undoubtedly, many combinations of assumptions can yield a variety of results We have chosen scenarios we consider of most widespread interest and applicability With regard to coal-fired power plants, the first combination (Table V) assumes that only the land actually allocated and directly disturbed should be included Reclamation at coal mines is assumed to be 50 per cent The second combination (Table VI) differs in that zero reclamation is assumed In both tables, we compare the land requirements of coal-fired power plants with the land requirements of power towers and photovoltaic arrays designed to a variety of specifications Comparison in terms of electricity generated A comparison of the land requirements of solar- and coal-based electrical capacity is usually given in terms of generating capacity only We have made our initial calculations in this format to facilitate comparisons with previously published figures However, solar and coal power plants of equal rated capacity will produce different amounts of electricity over an equal period of time One reason for this is that coal plants can operate at any time, while the solar plants are tied closely to hours of sunshine Thus, a more useful comparison, one which compares the actual electricity generated during a period of time, would eliminate considerations such as how well generating capacity matches fluctuating demand and differences between rated and average capacity In order to make a comparison of this sort, capacity factors must be included Capacity factors for the Navajo Generating Station and the Cholla No unit have been calculated to be 71.1 per cent and 80.2 per cent, respectively (Salt River Project, 1981; Arizona Public Service, 1981) In calculating MWh/ha/35 years for the coal-fired power plants not yet in operation, we have applied the latter figure For power towers designed on a reference direct normal insolation of 1000 W/m2 (317 BTU/ft2/hour), a solar annual capacity factor of 27.3 per cent is anticipated (Weber, 1980, 1982) For photovoltaic systems, a capacity factor of 300 is anticipated (Weber, 1982) Additionally, a normal maintenance outage factor of 94 must be factored in for power TABLE V land disturbeddirectly*,50% reclamation,ha/MW(ac/MW) Rankingof land requirements: Navajo** Centralreceiver Photovoltaic, 2-axes, 33.4? slope Photovoltaic,2-axes,33.4?,slope, storage Springerville Coronado Photovoltaic,2 axes Cholla Photovoltaic, 2-axes, storage 10 Photovoltaic, 1-axis 11 Photovoltaic, 1-axis, storage 1.92 (4.75) 2.35 (5.79) 2.43 (5.97) 2.74 (6.75) 2.75 (6.92) 3.71 (9.16) 3.80 (9.36) 4.11 (10.16) 4.31 (10.60) 4.43 (10.91) 5.02 (12.36) * Includes land actually allocated, including land physicallyoccupied by well pumps and transmissiontowers ** Obtainswaterfroman existinglake; thus, no landis dedicatedto well fieldsor coolingponds 208 LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS TABLE VI Ranking of land requirements: land disturbed directly*, no reclamation, ha/MW (aclMW) Centralreceiver Photovoltaic, 2-axes, 33.4? slope Navajo** Photovoltaic, 2-axes, 33.4? slope, storage Photovoltaic,2-axes Springerville Photovoltaic,2-axes,storage Photovoltaic,1-axis Photovoltaic,1-axis,storage 10 Coronado 11 Cholla 2.35 (5.79) 2.43 (5.97) 2.68 (6.62) 2.74 (6.75) 3.80 (9.36) 4.29 (10.60) 4.31 (10.60) 4.43 (10.91) 5.02 (12.36) 5.45 (13.45) 6.12 (15.12) * Includes land actually allocated, including land physicallyoccupied by well pumps and transmissiontowers ** Obtainswaterfromexistinglake; thus, no land is dedicatedto well fields or coolingponds towers (derived from Weber, 1980) Conservatively, we assume the same normal maintenance outage factor for photovoltaic arrays A summary of MWh/ha/35 years for coal-fired power plants in our study area is given in Table VII and a summary of MWh/ha/35 for solar power plants is given in Table VIII Rankings assuming 50 per cent reclamation at coal mines and zero reclamation at coal mines are shown in Tables IX and X, respectively To calculate MWh/ha/35 yr (MWh/ac/yr) for a power plant, MW/ha (MW/ac) must first be found by dividing by the capacity-based land requirement shown in Tables V and VI This number is then multiplied by the number of hours in 35 years (306600) Finally, this must be multiplied by the capacity factor in the case of a coal-fired power plant, and by the solar annual capacity factor and the normal maintenance outage factor in the case of a solar power plant TABLE VII Electrical production for coal-based facilities, MWh/ha/35 years (MWh/ac/35 years) Navajo Cholla Springerville Coronado Weighted average 50% reclamation 113538 (45 967) 59828 (24222) 89416 (36201) 66278 (26833) 82253 (33301) No reclamation 81341 (32931) 40179 (16267) 57586 (23314) 45118 (18266) 45055 (18241) LAND REQUIREMENTS FOR SOLAR AND COAL OPTIONS 209 TABLE VIII Electrical production for solar facilities, MWh/ha/35 years (MWhlac/35 years) Withoutstorage Photovoltaic arrays 19495 (7 925) 22724 (9237) 35627 Verticalaxis, collectortilted50? Two-axes,horizontalsurface Two-axes,33.4?slope (14483) Withstorage 17208 (6 995) 20066 (8157) 31510 (12809) Withstorage* 33429 (13589) Central receivers * As providedin stationsunderconstruction TABLE IX Ranking of electrical production per unit area: land disturbed directly*, 50% reclamation MWh/ha/35 years (MWh/ac/35 years) Navajo** Springerville Coronado Cholla Photovoltaic, 2-axes, slope Centralreceiver Photovoltaic, 2-axes, slope, storage Photovoltaic,2-axes Photovoltaic,2-axes,storage 113538 (45 967) 89416 (36201) 66278 (26833) 59828 (24 222) 35 627 (14483) 33429 (13589) 31510 (12809) 22724 (9237) 20066 (8 157) 10 Photovoltaic,1-axis 19495 11 Photovoltaic,1-axis,storage 17208 (7925) (6995) * Includes land actually allocated, including land physically occupied by well pumps and transmission towers ** Obtains water from an existing lake; thus, no land is dedicated to well fields or cooling ponds Discussion and conclusions Estimates of land requirements of coal and solar energy are sensitive to several factors; changes in any of these factors could effect changes in land dedication The two factors most critical to solar energy include cell efficiency and storage efficiency Improvements in either of these would reduce the amount of land necessary for solar facilities Use of the land beneath the solar devices or placement of photovoltaic arrays on rooftops would also reduce the commitment of land through multipurpose dedication 210 LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS TABLE X Ranking of electrical production per unit area : land disturbed directly*, no reclamation MWh/ha/35 years (MWh/ac/35 years) Navajo** Springerville Coronado Cholla Photovoltaic, 2-axes, 33.4? slope Centralreceiver Photovoltaic,2-axes,33.4?slope, storage Photovoltaic,2-axes Photovoltaic,2-axes,storage 81341 (32931) 57588 (23 314) 45118 (18 266) 40179 (16267) 35 627 (14483) 33429 (13589) 31510 (12809) 22724 (9237) 20066 (8157) 10 Photovoltaic,1-axis 19495 11 Photovoltaic,1-axis,storage 17208 (7925) (6995) * Includes land actually allocated, including land physicallyoccupied by well pumps and transmissiontowers ** Obtainswaterfromexistinglake; thus, no land is dedicatedto well fields or coolingponds With regard to coal, improvement of reclamation techniques is the most significant consideration in reducing land requirements Relaxation of pollution control regulations would allow power plants to be located nearer to load centres and would also reduce the amount of land needed for sludge disposal In addition, an increase in the number of mine-mouth power plants would reduce the land needed for coal systems Although any or all of these adjustments would affect the outcome of our study, there is no way of knowing which will occur, when they might occur, or what the precise impact of such changes would be to the amount of land required for either type of system We can, however, offer some response to our initial question as to the land demands of centralized solar power plants On a rated-capacity basis, the rankings show solar facilities to be comparable to coal in their land demands On an output basis, however, the coal facilities clearly have a lesser land demand than solar facilities, although the difference between the 'best' solar arrangement in Table X (ranked fifth) is only about 12 per cent less than the next higher ranked (coal) option The disparity between the coal and solar land requirements, calculated on an output basis, would change as a function of the type of use to which it would be put In the short term, solar facilities will primarily be peak and intermediate load facilities, and thus they will compete against conventional peaking facilities with lower capacity factors than coal-fired power plants Over the long run, solar power plants would function more as base load facilities and would thus be more land-intensive than coal-fired power plants From our examination of the several tables presented in this paper, we conclude that land commitments for solar power, though large, are often comparable to those for coal when calculations include the entire fuel cycle Thus, the amount of land required for centralized solar power stations is unlikely to retard their deployment in Arizona The criteria and approach presented here can be applied to the same problem at other sites and can adjust for the different efficencies of a changing technology LAND REQUIREMENTS FOR SOLAR AND COAL OPTIONS 211 Acknowledgements We gratefully acknowledge the comments of Tom Wilbanks, Eric Weber, Merwin Brown and Donovan Evans on earlier drafts of this paper The authors retain full responsibility for any errors List of abbreviations used MW Megawatt, one million watts MWe Megawatts-electric, the usual measurement unit for large power plants MWh Megawatt-hours, one megawatt over a time period of one hour MW-yr Megawatt generated 24 hours per day, 365 days per year Watt One joule per second, a measure of power-power measures energy over a time period Quad It is defined as 10-15 BTUs, or a quadrillion BTUs KCal Kcal (=3.968 BTU) References Anderer, Jeanne with Alan McDonald and Nebojsa Nakincenovic 1981 Energy in a finite world: Paths to a sustainable future Report by the Energy Systems Program Group of IIASA Cambridge, Mass.: Ballinger Publishing Company Arizona Public Service 1981 Personal communication Arizona Public Service 1982 Personal communication Blue, Jackalie L 1982 Geographic perspectives on energy: A bibliography Oak Ridge: Energy Division, Oak Ridge National Laboratory Brown, Merwin 1982 Personal communication Arizona Public Service Caputo, Richard S 1977a Solar power plants: dark horse in the energy stable Bulletin of the Atomic Scientists: 46-56 Caputo, Richard S 1977b An initial comparative assessment of orbital and terrestrialcentral power systems (final report) Pasadena: Jet Propulsion Laboratory DeMeo, E A and P B Bos 1978 Prespectives on utility central station photovoltaic applications EPRI ER-589-SR special report Palo Alto: Electric Power Research Institute DiNunno, J J and R J Davis 1976 Land requirements of alternate electric generating systems Report distributed at the Atomic Industrial Forum, Inc conference on land use and nuclear facility siting, 18-21 July Evans, D L., W A Facinelli, L P Koehler 1981 Simplified design guide for estimating photovoltaic flat array and system performance Albuquerque: New Mexico General Electric Company 1976 Energy conversion alternatives study (ECAS), General Electric phase II final report, volume II, advanced energy conversion systems, conceptual designs: part 3, open cycle gas turbines and open cycle MHD; and part 4, summary of results, NASA-CR 134949, G E report no SRD-76-064-2 Schenectady, NY: General Electric Co Kash, Don E., et al 1976 Our energy future Norman: University of Oklahoma Press Kelly, Henry 1978 Photovoltaic power systems: a tour through the alternatives Science 199 Kendall, Henry W and Stephen J Nadis 1980 Energy strategies: toward a solar future Cambridge, Mass.: Ballinger Publishing Co Landsberg, Hans H (Chairman) 1979 Energy: the next twentyyears Cambridge, Mass.: Ballinger Publishing Co Masden, Glenn 1978 Optimization of the geometrical parameters for arrays of tracked collectors to give minimum energy cost Proceedings, 13th IEEE Photovoltaic Specialists Conference Washington, D.C National Academy of Sciences 1974 Rehabilitation potential of western coal lands Cambridge, Mass: Ballinger Publishing Co National Academy of Sciences/National Research Council 1979 Energy in Transition 1985-2010 San Francisco: W H Freeman & Co Newsom, D E and T D Wolsko 1980 Preliminary comparative assessment of land use for the Satellite Power System (SPS) and Alternative Electricity Energy Technologies, Argonne National Laboratory, DOE/ER-0054 Ouwens, Dacy C 1976 Does solar energy demand more land surface, and more materials or energy investment than nuclear energy or fossil fuels? Electricity solair-solar electricity: 1005-14 Toulouse, France: International Conference on Solar Energy Pasqualetti, M J 1981 Energy and land use In Land use, a spatial approach, eds J Lounsbury, L Sommers, and E Fernald: 161-186 Dubuque, Iowa: Kendall/Hunt Publishing Company Penner, S S and L Icerman 1975 Energy, vol II: Non-nuclear energy technologies Reading, Mass: Addison-Wesley Publishing Co., Inc Salt River Project 1981 Personal communication 212 LAND REQUIREMENTS FOR SOLAR AND COAL OPTIONS Sutton, Antony C 1979 Energy: the created crisis New York: Books in Focus, Inc US Department of Energy 1977 Environmental Development Plan (EDP) Washington, DC: U.S Department of Energy US Office of Technology Assessment 1977 Application of solar technology to today's energy needs, Summary Weber, Eric R 1980 Saguaro power plant solar repowering project, conceptual design, final technical report Report No DOE/SF 10739-2 San Francisco: U.S Department of Energy Weber, Eric R 1982 Personal communication Arizona Public Service  ... indirect land use: vast areas of land are owned, leased, or reserved for rights of way for power plants and their related facilities LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS 195 Fig Coal- fired... when comparingthe land requirementsof gas, oil, coal and nuclearfacilities,we cannotjustifysuchweightingfor solarfacilities LAND REQUIREMENTSFOR SOLAR AND COAL OPTIONS 205 Under the constraints.. .The Geographical Journal, Vol 150, No 2, July 1984, pp 192-212 LAND REQUIREMENTS FOR THE SOLAR AND COAL OPTIONS MARTIN J PASQUALETTI AND BYRON A MILLER The absolutequantityof landcommittedas