World distribution of solar radiation

1965 Conference Paper

World Distribution of Solar Radiation George O. G. Liif, J. A. Duffle, a n d C. O. S m i t h Solar Energy Laboratory, The University of Wisconsin, Madison, Wisconsin A series o f 12 m o n t h l y world m a p s o f t h e daily m e a n s o f t o t a l solar r a d i a t i o n i n c i d e n t o n a h o r i z o n t a l surface h a s b e e n prepared. I s o l i n e s o f c o n s t a n t r a d i a t i o n h a v e b e e n d r a w n at i n t e r v a l s o f 50 l a n g l e y s per d a y ( c a l / s q era, day). D a t a for t h e c o m p u t a t i o n o f m e a n r a d i a t i o n levels were c o m p i l e d f r o m m a n y s o u r c e s , i n c l u d i n g w e a t h e r reports a n d s u m m a r i e s , p e r s o n a l communications from weather and research o r g a n i z a t i o n s , a n d I G Y a n d IGC reports. For areas in w h i c h few or n o r a d i a t i o n d a t a were available, s u c h i n f o r m a t i o n was s y n t h e s i z e d b y use of sunshine-hours data and approximation f o r m u l a e a p p l i c a b l e to t h e p a r t i c u l a r c l i m a t e t y p e . R a d i a t i o n d a t a were o b t a i n e d for 668 stat i o n s , w h e r e a s s u n s h i n e - h o u r s v a l u e s were u s e d in e s t i m a t i n g r a d i a t i o n f r o m 233 a d d i t i o n a l locations. T h e m a p s are r e c o m m e n d e d for g e n e r a l u s e in a p p r a i s i n g t h e c o l l e c t o r area r e q u i r e m e n t s for solar a p p l i c a t i o n s in b r o a d r e g i o n s . T h e y do n o t , o f c o u r s e , reveal t h e i n f l u e n c e o f m i c r o c l i m a t i c f a c t o r s o n local s o l a r - r a d i a t i o n levels. In a d d i t i o n to t h e m a p s , t h e paper c o n t a i n s a n explanation of the various radiation instruments, t h e m e t h o d s for d a t a h a n d l i n g , t h e e s t i m a t i o n of radiation values from sunshine-hours data, and the limitations and utility of the radiation maps.

N APPRAISING the economies of a proposed solar-energy application in a particular area and in designing a solar-energy conversion device to meet a potential demand, knowledge of the solar radiation obtainable at the place in question is essential. There are, of course, other uses for such information, including forecasts of evaporation from lakes and reservoirs, agricultural potential, and meteorological forecasting. I t is evident that the utilization of solar energy, as with any other natural resource, requires detailed information on availability. Some past surveys of solar incidence have been based

I

Presented at the Solar Energy Society Conference in Phoenix, Arizona, March 15-17, 1965. Vol. 10, No. 1, 1966

on very linfited world-wide data on solar radialion, somewhat more exlensive world data on hours of sunshine, and on fairly comprehensive solar radiation dala in a few selected countries such as the United States and J a p a n TM. The scarcity of radiation data throughout the world has limited the usefuhless of these compilations, except in the few locations where meteorological networks have been extensive. The wider availability of sunshilm records has not solved the problem because of uncertainties in the relationship between hours of sunshine and total energy received. Finally, in some eases, the results of the radiation surveys have been reported on an annual basis only, thereby precluding use of the information for rational design in most areas where seasonal variability of radiation is large. During the past ten years, however, m a n y new solarradiation stations have been placed in operation throughout the world, and niore data have become available, hi addition, lhe intensive effort in the Inlernational Geophysical Year (July, 1957 to December, 1958) greatly increased lhe number of radiation-measuring stations and the availability of data. M a n y of these stations have continued to record solar radiation, and longer term averages are becoming available. In view of the substantial increase in solar-radiaiion measurements, in recognition of the importance of reliable world-wide solar intensities, and as a part of a broader study of solar-energy economies, this survey and compilation was undertaken. The results of lhe solar-radiation survey will be published in a detailed report 12; this paper summarizes the report. There are several types of solar-radiation data, each of which has its particular utility. These include direct radiation at normal incidence, direct plus diffuse radi:t tion at. normal incidence, direct radiation on a horizontal surface, direct plus diffuse radiation on a horizonlal surface, and each of these on tilted and on vertical surfaces. For each type of measurement, there are also the possible choices of m a x i m u m and minimum vahIes in selected periods of time. Finally, it is necessary to decide on what sort of averaging should be employed; seasonal, monthly, daily, or hourly. For devices employing focusing systems, normal incidence of direct. 27

TABLE 1--I)[STllIBUTION OF RADIATION ANI) SUNSHINE INSTItUMENTS* l

Radiation Data

Continent Total

Epi)ley

137 49

128 0

Kipp

GunnBellani

Sunshine Data

I

i Robitzsctl

Other or Unspecified

Total

CampbellStokes

Other or Unspecified

0 0

9 68

0 33

40

2 0

67 2

I

North America . . . . . . . . . . . . . . . . . Sou! h America . . . . . . . . . . . . . . . . . Europe • . . . . . . . . . . . . . . . . . . . . . . . Africa. . . . . . . . . . . . . . . . . . . . . . . . .

Ii

I

I

Asia . . . . . . . . . . . . . . . . . . . . . . . . . . . Australia . . . . . . . . . . . . . . . . . . . . . .

25

0 47

9

68

219 71

65

107 16

43 17

40

30

142 10

17

89

29 2

69

1

7

42 2

9

I

Anaretica . . . . . . . . . . . . . . . . . . . . . . i Oce,ms 'rod Islands . . . . . . . . . . . . . 1

14 2(;

8

2

13

0

3 13

0

0

* Used in this compilation. radiation would of course be preferred, li'or flat-plate systems, it, would be preferable to have total (direct plus diffuse) radiation on a sloping surface if the eolleetor is lo be used in that position. Some design purposes would besl be served by use of maxinmm radiation values; whereas, performance over :t period of time might be delermined most readily by an appropriate mean radial ion fgure and a distribulion parameter. No single type of data or method of compiling will serve all needs. The form of the data most awfilable and most frequently reported is total radiation (direct plus diffuse) on a horizontal surfaee received each day or in some eases eaeh hour. This is, moreover, probal)ly the most generally useful form of radialion data, as methods are available for estimating other types froln these figures. After eonsideration of various time periods for averaging, monthly averages were chosen as a praetieal compromise between averages on a seasonal basis (four per year) and on a weekly basis (fifty-two per year). Thus, the data are finally presented as monthly means of lhe daily totals of solar radiation (direct plus diffuse incident on a horizontal surfaee) and averaged over the period of reeord used in the analysis. Solar radiation is measured by several different types of instruments having various characteristics and degrees of aeeuraey. With few exeept.ious, radiationmeasuring instrument s in use are of two main types: the thennoeleetrie type and the bimetallie expansion type. Each of these has variations. The thermoelectric types include the Kimball pyranomeler (manufaetured by Eppley) and the Moll-Gorezynski pyranomeler (manufaetured by Kipp and Zonen). A difference in temperalure of black and while surfaces in a glass-enclosed chamber is eaused by solar-radiation absorption; the eleetrie output from therlnopiles in these units is usually recorded on some type of ehart or totalled by means of an integrator. If well calibrated and maintained, these instrumenls can provide daily totals of solar and sky radiation usually within three percent of true values~a; most reeorded data are probably less aeeurate. The prineipal radiation meter of the bimetallic ex29;

pansion type is the Fuess-Robitzseh pyranometer or pyranograph (with self-contained recorder). In this instrument, differential expansion of a metallic d e m e n t due to solar absorption causes the movement of a stylus oil a clock-driven chart. Its accuracy is lower than the thermoelectric types, deviations of ten pereem from true value not being uncommon. Another meter of this type is the Miehelson pyranometer. Unless a pyranolneter is provided with SOlne lype of integrator, the common method for obtaining hourly and daily total radiation values is by planimetry from the chart records. Another radiation instrulnent used by a few stations is the Bellani pyranometer, which provides an indication of total solar radiation by the quantity of a liquid that has distilled from a solar-heated evaporating chamber. Periodic measurement of the distilled liquid permits estimation of the incident radiation during the imerval. In the United States, the Eppley pyranometer is most frequent ly used, whereas in Europe and Africa, the Kipp is more common. The Robitzseh bimetallic type is simpler and cheaper, and fairly widely used in South America and Asia, as well as in scattered stations elsewhere in lhe world. The other type of data used in this study is the pereentage of possible sunshine or the hours of sunshine per day as measured by the Campbell-Stokes sunshine recorder. This instrument employs a spherical lens to focus direct sunshine onto a paper chart. Discoloration of the chart occurs, due to heat, whenever the solar disc can be seen. The length of the discolored line divided by the total length of the chart corresponding to the time between sum'ise and sunset is the percent possible sunshine for the day. This instrument is widely used and is actually a standard for this type of measurement. Table 1, in addition to showing the nulnber of the more widely used instrument types, is indicative of the degree of coverage and (indirectly) the reliability of the results. Thus, in North America where a rather dense nelwork of accurate instruments exists, high confidence can be placed in the results. Conversely, a limited nun> Solar Energ!l

bet' of stations its South America and parts of Asia, coupled with the use of some pyranometers of lower accuracy, places the results for these areas at a lower confidence level. The need for use of sunshine data in many of these areas is evident, and the extent to which such observations were used in estimating radiation is indicated in the table. Since mean values of total radiation were being sought for e,mh month, a sufficient number of years of observations was desired to establish a reasonable long-term average. No fixed number can be assigned to the necessary period for all such data, there being considerably more variability year-to-year in some climates than others 14. In general, averages were computed on the basis of all the available data, no matter wtmt its duration. It, some places, records of more than twenty years' duration were used. Approximately 220 st ations can be considered to have good long-term averages, hi m a n y instances, however, data of only three years duration had to be used, and at a few stations only one year was available. In these eases, if nearby radiation records were not available, sunshine hours were also used to supplement the information. At nearly all locations, sunshine records were of sufficient duralion to be representative averages. Table 2 shows the distribution of radiation data, by continent and by duration groups. Methodology of Data Procurement Data for the computation of monthly means of daily t ola[ radiation were procured through extensive literatslre searches, through personal colnmunications with various weather bureaus and research organizations, and through use of World Meteorological Organization reports (particularly those reports and compilations resulting from I G Y and I G C programs) '5. As these data were received from the various sources they were standardized to monthly means of daily sums of total (direct and diffuse) solar radiation received on a horizontal surface in the units of gm eal per sq em per day (langleys per day). Generally, these data were provided ill the for,n of daily or monthly totals and it was then neeessa W to convert these totals to cumulative monthly means for mapping purposes. These data were also standardized to the International Pyrheliometrie Scale (IPS-1956). Data recorded on the Smithsonian (1913) scale were reduced by 2 percent and data recorded on the Angstrom (1905) scale were increased by 1.5 percent 16. Use o f S u n s h i n e D a t a for E s t i m a t i n g R a d i a t i o n The distribulion of recorded solar radiation stations on the monthly maps shows that Central American, South American, polar and ocean regions, and Asia (with the exception of Japan) are charaelerized by either a sparseness or a very limited duration of radiation data. It was therefore necessary to supplement Vol. 10, No. 1, 1966

TABLE 2--DUIIATION OF HADIATION RECORI)S Y e a r s of R a d i a t i o n R e c o r d s Continent 10 or more

5 to t0

2

1

No. America . . . . . . . . . . . . . So. America . . . . . . . . . . . . . . .

54 1

37 2

17 13

9 9

Europe . . . . . . . . . . . . . . . . . . . Africa . . . . . . . . . . . . . . . . . . . .

19 0

38 21

26 13

11 6

Asia . . . . . . . . . . . . . . . . . . . . . . Australia . . . . . . . . . . . . . . . . .

16 2

165

84

2O

61

0 5

4 14

7 4

3 3

Antarctica . . . . . . . . . . . . . . . . Oceans "rod Islands . . . . . . . . .

these records by use of related information and approximarion formulas. Forttmalely, in nearly all countries regular measurements of sunshine duration and cloudiness are made at mnnerous weather stations. These records generally cover long periods (i.e., 20 Io 60 years) in contrast to the records of radiation. The daily sums of radiation have been shown to be functions of sunshine duration at a particular location, with the most common correlation being Q=Qo

a+b~o

Here Q is the amount of radiation received at the surface location per day; Q0 is the amount of radiation per day that is available at a point outside the atmosphere (a maximum for the location, assulning no atmospheric depletion); a and b are constants serving to correlate the radiation and sunshine; S is the nmnber of hours of sunshine instrument-recorded at the site per day; and So is the maxinmm number of hours of sunshine that are possible at the site per day, assuming an unobstructed horizon. This relationship is based on a development of AngstromS7; similar estimating procedures have been used by Fritz and MacDonald ~, 2, Black a, 4 and Maleer ~, ~ for example. The general method by which radiation was estimated froth sunshine data involved first the determination of a and b by use of the equation for a location where both types of solar data are available. Values of a and b were deterlnined for locations in several climatic types, in an effort to compensate for variations eaused by general elinmtie differences. The use of universaltype conslants and elinmtic-type constants was previously discussed by others '< ~s The resulting equations, with the computed values of a and b and with percent-of-possible sunshine data and Q0 dala, were then used in determining average radiation each month at locations in similar climates where only sunshine records were available. The calculation of Q0 and So values for specific locations and months was simplified by use of exisling ta29

bles. Values of Q0 were obtained from Page is, who had listed monthly means at various latitudes 40°S to 40°N, based on the data of Milanovitch for the northern helnisphere and those of D r u m m o n d for the southern hemisphere. The solar constant used was 2.00 ly per rain. M o n t h l y curves were then plotted as Q0 vs. latitude, so that. values for specific locations and months could be readily determined. Values of So were determined from tables of sunrise and sunset published b y the U. S. Naval Observatory ~9. The method of least squares was used for the deterruination of the constants a and b. Certain slations that offered fairly long-term radiation and sunshine records in a nmnber of different climate types were then selected and the monthly averages analyzed b y use of the relationships : a

=

EyE NEx

E E/y (Ex)

, b

NZxy-

NEx

Zx~'~y

-(Zx)

where N = the number of d a t u m points, x = S/So, and

Y = Q/Qo. A quadratic expression and one using a square-root term were also f t t e d to the data, but the results did not v a r y significantly from those obtained with the linear fit. Hence, the linear relationship was selected. Grouping the data in bimonthly, quarterly, and annual average values did not alter the constructs significantly (4-5 percent deviation at. the locations investigated), so for other than monsoon-type c]imates, where seasonal constants were computed, yearly constants were employed. For climate classification, the world climatic m a p s of Trewartha were used 2~, 22. Since these classifications are necessarily broad, differences within a given climatic classification were distinguished by reference to the vegetation maps of Kfichler 2°. After establishing a correlation between S/So and Q (by determining a and b) for each clinmtic type (Table 3), sunshine records from each station which lacked radiation data were first reduced to monthly averages of daily percent possible sunshine (if not already in that form). Long-term monthly normals were next determined b y averaging the monthly values. Each station was then classified as to climatic type, vegetation type, and the total range of variation in percentage possible sunshine. Monthly mean radiation levels were then calculated b y use of the nornml sunshine percentages and the equation derived specifically for each classification. These computed radiation values are of course approximate, but they are found to be reasonably consistent with actual radiation measurements in a number of test locations. 30

Mapping A cylindrical projeclion base m a p was selected f¢)r presenting the lnonthly maps of total solar radiat ion aad for a m a p showing the location of data points. Bolh actual and estimated data were posted to the m o n | h t y base maps. Color coding was utilized to distinguish between actual and estimated data, and to indicate l tie term of the actual data. The color coding system was useful in judging the location of isolines for given radia tion values. An interval of 50 ly per d a y between radiation isolines was selected. This interval had been used in previous mapping efforts by others, thus facilitating comparisons. Other considerations were aeeuraey and utility. As l he general distribution patterns became visible, this interval permitted distinguishing between isolines reasom~bly well. Moreover, the magnitude was small enough for climatic changes to be noted (i.e. as the interwfl became larger, the effects of variations in elimate and topograp h y tended to become obscured). The base nmps showing the radiation data were then used in positioning the isolines by interpolation. In addition to the radiation data, the following information was used in deternfining the final location of lhe isolines. 1--Reliability of Averages. Preference was given ~() longer-term data. Silnilarly, aetual data represenling relatively long-term periods were given greater weighl than estimated values. 2 Physical Situation. Where reasonable and possible, consideration was given to maeroelimate rather than micro-climate. T h a t is, lines were drawn in recognition of the probable location of solar-proeess equipment. For example, radiation measurements made at the top of a mountain, above normal eloud levels and atmospheric pollutants, were not weighed heavily, as they would not indieate conditions at the probable sites of solar devices.

3--Relationships Between Solar Radiation and Climate. There is an interdependanee of mean solar radiation and elimate. In an effort to provide a more rational basis for interpolating between data points, elimatie overlays (based on T r e w a r t h a ' s climate map 2L 22) were developed. Since elimatie elassifieations are generalized and broad, vegetation overlays (based on maps of Kuehler 2°) were also used. These helped, in certain eases, to provide a basis for estimating constants and interpreting differences in radiation levels within a given elimatie elassiffieation. Further assistanee in loeating the isoliues was obtained through review of various publieations on climate and meteorology. Loeal information was also provided b y personal communication with meteorologists and solar workers in several geographie areas. Upon evaluation of the data, it was deeided to exclude most of the polar regions from the nmps. Most of ~he Solar Energy

TABLE 3--CLIMATIC CONSTANTS FOR REGRESSION EQUATION Sunshine Hours in Percentage of Possible Location

Veg.**

Climate*

Range

Avg.

Charleston, S. C . . . . . . . . . . . . . . . . . . . . . . . . . . . . Atlanta, Ga . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Miami, Fla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cf Cf Aw

E M E-GI)

60-75 45-71 56-71

67 59 65

0.48 0.38 0.42

0.09 0.26 0.22

Madison, Wis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E1 Paso, Tex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Poona, Indi't (Monsoon) (Dry) . . . . . . . . . . . . .

l)f BW Ant

M DSi S

40-72 78 88 25-49 65-89

58 84 37 81

0.30 0.54 0.30 0.41

0.34 0.20 0.51 0.34

Albuquerque, N. M . . . . . . . . . . . . . . . . . . . . . . . . . Malange, Angola . . . . . . . . . . . . . . . . . . . . . . . . . . ttamburg, Germany . . . . . . . . . . . . . . . . . . . . . . .

BS BW Aw-BS Cf

GI) I)

68-85 41-84 11-49

78 58 36

0.41 0.34 0.22

0.37 0.34 0.57

Ely, Nevada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brownsville, Tex . . . . . . . . . . . . . . . . . . . . . . . . . . . Tamanrasset, Sahara . . . . . . . . . . . . . . . . . . . . . .

BW BS BW

Bzi GDsp DSp

61-89 47-80 76-88

77 02 83

0.54 0.35 0.30

0.18 0.31 0.43

Honolulu, Hawaii . . . . . . . . . . . . . . . . . . . . . . . . . Blue Hill, Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Buenos Aires, Arg . . . . . . . . . . . . . . . . . . . . . . . . . .

Af Df Cf

G D G

57-77 42-60 47-68

65 52 59

0.14 0.22 0.26

0.73 0.50 0.50

Nice, F r a n c e

Cs

SE 1) B

49-76 55-81 34-56

61 67 48

0.17 0.36 0.28

0.63 0.23 0.39

...............................

1)arien, Manchuria . . . . . . . . . . . . . . . . . . . . . . . . . Stanleyville, Congo . . . . . . . . . . . . . . . . . . . . . . . . .

i

l)w Af

* Climatic classification based on Trewartha's elinmte map (see ref. 21, 22). ** Vegetation classification based on Kiichler's map (see ref. 20). Cf--Continental, continuously moist (;s--Continental with dry season during summer ])f--Snow forest, continuously moist 1)w--Snow forest, dry season in winter Aw--Tropical forest, dry season in winter Am--Tropical forest, monsoon rains Af--Tropical forest, continuously moist B--Broadleaf evergreen

BZ--Broadleaf evergreen, dwarf shrub form ])--Broadleaf deciduous trees l)S--Broadleaf deciduous, shrub form E--Needleleaf evergreen trees G--Grass GD--Grass and broadleaf deciduous trees M--Mixed: broadleaf deciduous and needle-leaf evergreen trees S--Semideeiduous: broadleaf evergreen and broadleaf deciduous trees

d a t a front these regions were compiled d u r i n g the I G Y I G C p r o g r a m , a n d their d u r a t i o n was t h u s l i m i t e d ~o a m a x i m u m of 2½ years. S u n s h i n e - h o u r s inform'~tion was also i n a d e q u a t e . Solar-Radiation

Maps

T h e d i s t r i b u t i o n of solar r a d i a t i o n t h r o u g h o u t the world has been compiled in the form of twelve m o n t h l y m a p s 12 four of which are reproduced here. These are for March, June, September, and December, representing solar c o n d i t i o n s for the m o n t h s of equinoxes a n d solstices. A n o t h e r m a p shows the location of r a d i a t i o n a n d s u n s h i n e recording s t a t i o n s from which d a t a were obtained. I t is seen from the s t a t i o n map, Fig. 1, that a b u n d a n t solar r a d i a t i o n d a t a are available in the U n i t e d Slates, in western E u r o p e , in J a p a n , a n d to a s o m e w h a t lesser cxtcnl in Africa s o u t h of the equator. L i m i t e d r a d i a l i o n records are available in Australia, eastern Europe, a n d in p a r t s of S o u t h America. T h e b a l a n c e of the r a d i a t i o n m e a s u r e m e n t s o b t a i n e d are widely scattered. T h e regions where s u n s h i n e d a t a were used to the greatest e x t e n t (i.e. where r a d i a t i o n d a t a were sparse) include p a r t s of S o u t h A m e r i c a a n d Mexico, China, I n d i a , n o r t h e r n a n d western Africa, a n d F r a n c e . Vol. 10, No. 1, 1966

A few o b s e r v a t i o n s on the r a d i a t i o n m a p s are in order. First, it m u s t be recognized t h a t the scarcity of d a t a in m a n y areas necessarily limits the accuracy of the results in such regions. Secondly, there can be no a t t e m p t in such a b r o a d world s t u d y to assess micro-climatic variab i l i t y in regions where high m o u n t a i n s or other local geographic conditions cause s u b s t a n t i a l v a r i a t i o n in cloud cover b e t w e e n p o i m s a few miles to a few h u n d r e d miles apart.. However, v a r i a t i o n in solar r a d i a t i o n due to m a j o r geographic factors such as large m o u n t a i n chains, ocean currents, desert regions at high a n d low altitude, etc., are seen a n d are of i n a j o r significance. Values represented b y the isolines range from fifty to m a x i m a of 750 ly pet" day. A l t h o u g h n o t shown on the m a p s (but c o n t a i n e d in the full t a b u l a t i o n of d a t a from all s t a t i o n s used in the c o m p i l a t i o n 12) the m a x i m u m average m o n t h l y value of solar r a d i a t i o n a n y w h e r e in Ihe world is at the S o u t h Pole, where D e c e m b e r averages are n e a r l y 1,000 ly per day. Isolines formed b y dashes on the m a p s indicate rough e s t i m a t e s based u p o n very little d a t a (perhaps one m e a s u r e m e n t ) a n d s y m m e t r y with a d j a c e n t r a d i a t i o n c o n t o u r s of greater reliability. I n some areas, dashes were used to c o n n e c t solid lines to facilitate reading. No (Continued on p. 37) 31

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e | O l ~ Dept. U.W, A - H¢

eEOG. Oept. U,W. A - x C

dala are available over most ocean areas, but measuremenls on small islands permit inter-insular estimates. A typical application of the maps can be illustrated by choosing an area, such as northeastern Brazil, and estimating the 'm~ount of energy which can be recovered by one square foot of horizontal solar collector in a typical year. The four nlaps are representative of the seasons, and indicate 500 ly per day in the spring, 350 in the summer, 500 in the fall and 550 in the winter. Based on these figures, the ammal total radiation is 173,000 cal per sq cm, corresponding to 640,000 Btu per S(l ft. If the solar device has a meart annual efficiency of forty percent, about 250,000 Btu per sq ft could be recovered in a typical year. These figures can be refined by use of monthly maps of radiation and equipment efficiencies more representative of performance at the various radiation levels. Figures of this type can thus be used to determine the approximate size of solar equipmeat to meet specified requirements, or seasonal variat ion of solar process output. We believe that these solar-radiation maps are by no means a final or definitive set, but rather that they represer~i an effort to use the data readily available at this time ,utd to present it, in a form useful to those interested in the terrestrial applications of solar energy. As more dala become available, these maps can most. certainly be refined and improved. It is hoped that these improveme,)ls will be made as they become possible.

5.

6.

7.

8.

9.

Dnring [GY (International Geophysical }'ear 1957-1958),"

10.

11.

12.

13.

14.

ACKNOWLEDGMENTS The a u t h o r s of this p a p e r and the full report soon to be published by the University of Wisconsin are i n d e b t e d to the m a n y meterologists, solar research and d e v e l o p m e n t workers, g o v e r n m e n t officials, and others who c o n t r i b u t e d d a t a for this st udy. W i t h o u t this assistance, this report would not have been possible. We p a r t i c u l a r l y appreciate the efforts of m a n y of these people in t r a n s c r i b i n g and averaging d a t a from t h e i r own records. Special appreciation is expressed to Mr. ])ale Fester for his •~n'dysis of radiation and sunshine data. The assistance of Prof. R. 1). Sale of the U n i v e r s i t y of Wisconsin C a r t o g r a p h y Labor,~tory, and Prof. G. T. T r e w a r t h a , of the l ) e p a r t m e n t nf Geography, is acknowledged, as is the cooperation of the Extension Division of the U n i v e r s i t y of Wisconsin. Finally, the financial s u p p o r t of Resources For the Future, Inc., of Washington, D. C., is acknowledged.

1. S. Fritz,

"Solar

Radiation

During

15. 16. 17.

18.

19.

REFERENCES Cloudless

Days,"

Healing and Ventilation, ~6, No. 1, (January, 1949). 2. S. Fritz, and T. H. MacDonald, "Average Solar R a d i a t i o n in the United S t a t e s , " Healing and Ventilation, ~6, No. 7, (July, 1949). 3. J. N. Black, C. W. B o n y t h o n , and J. A. Prescott, "Solar R a d i a t i o n and the D u r a t i o n of S u n s h i n e , " Qvarterly ,lo~,rnal Royal Melerological Society, 80 (344), (April, 1954). 4. J. N. Black, " T h e 1)istributi,m of Solar R a d i a t i o n Over

Vol. I0, No. 1, 1966

the E a r t h ' s Surface," Arch. Met. Geoph. Biokl. B. Bd 7, H.2: 165-189, (1956). C. L. Mateer, "Average Insolation in C a n a d a During Cloudless D a y s , " Canadian Jonrnal of Technology, 33: 12-32, (1955). C. L. Mateer, " A P r e l i m i n a r y E s t i m a t e of the Average Insolation in C a n a d a , " Canadian Journal of AgricTdtural Science, 35, N o v e m b e r D e c e m b e r 1955, p. 579-594. M. I. Budyko, " A t l a s Teplovogo B a l a n t s a , " Leningrad Glav. Geofi. Obs. in Voeikova, (1955), and revised 1964 edition. H. E. Landsberg, "Solar R a d i a t i o n at the E a r t h ' s Surface," Solar Energy, V, N u m b e r 3, J u l y - S e p t e m b e r 1961, p. 9598. Dov Ashbel, "New World Maps of Global Solar Radiation

20.

21. 22.

T h e Hebrew University D e p a r t m e n t of Climatology and Meterology, (Jerusalem 1961). K. Sekihara, " T h e Amount and Properties of Solar Radiation in J a p a n and the I n s t r u m e n t s for its M e a s u r e m e n t s , " E / C o n f . 35/S/2 10 April, 1961, paper presented at U N Conferences on New Sources of Energy, Rome 1961 I. B e n n e t t , " M o n t h l y Maps nf M e a n Daily Insolation for the U n i t e d S t a t e s , " Solar Energy, IX, No. 3 (July-Sept., 1965). G. O. G. L6f, J. A. Duffle, and C. O. Smith, "World Dist r i b u t i o n of Solar R a d i a t i o n , " Engineering Experiment Station Report No. 21, The U n i v e r s i t y of Wisconsin (Madison, 1965) To be published. A. J. l ) r u m m o n d , " I n s t r u m e n t a t i o n For T h e M e a s u r e m e n t of Solar R a d i a t i o n - - A Survey of M o d e r n Techniques and Recent l ) e v e l o p m e n t s , " E Conf. 35/S/117 25 M a y 1961, Paper presented at U N Conference on New Sources of Energy, Rome 1961 J. N. Black, "Some Aspects of the Climatology of Solar R a d i a t i o n , " E Conf. 35/S/13 10 April 1961, P a p e r presented at UN Conference on New Sources of Energy, Rome 1961. "C-~talogue of I G Y / I G C MeterologicM D a t a , " WMO/ OMM--:Vo. 135 IGY/AGI 4 (Geneva, December 1962). Ibid., B, p. 4, 11. A. Angstr6m, "Solar and Terrestrial R a d i a t i o n , " Quarterly ,lo~rnal of the Royal Meterological Society, 50: 121, (1924). J. K. Page; " T h e E s t i m a t i o n of M o n t h l y Mean Values of Daily Total Short Wave R a d i a t i o n on Vertical and Inclined Surfaces from Sunshine Records for L a t i t u d e s 40 ° N o r t h - - 4 0 ° S o u t h , '' E / C o n f . 35/S/98 16 M a y 1961, paper presented at UN Conference on New Sources of Energy, Rome, 1961. " T a b l e s of Snnrise~ Sunset and T w i l i g h t , " S u p p l e m e n t to the American Ephemeris, 1946, obtainable from Superi n t e m l e n t of l)oeuments, U. S. ( ; o v e r n m e n t P r i n t i n g Office, W',shington, D. C. Goode's World Atlas, ed. E d w a r d B. Espenshade, Jr., " l l t h e d , " (Chicago: R a n d McNally & Company, 1960). p. 16 17. G. T. T r e w a r t h a , An Introd~ction to Climate, "3rd e d , " (McGraw-Hill Book Co., 1954). (;. T. T r e w a r t h a , The Earth's Problem Climates, (Madison: The University of Wisconsin Press. 1961).

37