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SOLAR INSOLATION

Insolation (Incoming Solar Radiation) is the amount of solar radiation incident on any surface – for our purposes, we will be comparing insolation levels on the surface of the Earth. The amount of insolation received at the surface of the Earth is controlled by the angle of the sun, the state of the atmosphere, altitude, and geographic location.

The values of solar insolation are commonly expressed in kWh/m 2/day. This is the amount of solar energy that strikes a square meter of the earth's surface in a single day.

Insolation levels are used to determine what size solar collector is needed to efficiently provide adequate levels of hot water. Geographic locations with low insolation levels require larger collectors than locations with higher insolation levels.

For comparison, consider the average annual insolation levels of these two extreme locations:

  • Oslo , Norway = 2.27 kWh/m 2/day (very low)
  • Miami , Florida = 5.26 kWh/m 2/day (very high)

See the table below for insolation levels of major cities throughout the United States or Click here to determine insolation levels for a specific location.

 

State
City
Latitude
Longitude
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year Avg
AL Birmingham 33' 34" N 86' 45" W
2.29
3.31
4.04
5.14
5.92
5.98
5.81
5.7
4.8
3.93
2.96
2.25
4.34
AK
Anchorage
61' 10" N
150' 1" W
0.21
0.76
1.68
3.12
3.98
4.58
4.25
3.16
1.98
0.98
0.37
0.12
2.09
AR
Little Rock
32' 25" N
94' 44" W
2.36
3.39
4.01
5.32
5.71
6.19
6.15
5.85
5.25
4.17
2.95
2.25
4.46
AZ
Phoenix
33 ' 26" N
112' 1" W
3.25
4.41
5.17
6.76
7.42
7.7
6.99
6.11
6.02
4.44
3.52
2.75
5.38
CA
Los Angeles
34' N
118' W
3.09
4.25
5.09
6.58
7.29
7.62
7.45
6.72
6.11
4.42
3.43
2.72
5.4
CA
San Francisco
38' 31" N
121' 30" W
2.35
3.33
4.42
5.95
6.84
7.39
7.55
6.51
5.75
3.92
2.65
2.06
4.89
CO
Denver
39' 45" N
104' 52" W
2.25
3.2
4.32
5.61
6.11
6.71
6.5
5.86
5.47
4.01
2.59
1.98
4.55
CT
Hartford
41' 44" N
72' 39" W
1.7
2.43
3.48
4.07
5.14
5.58
5.38
5.04
4.13
2.91
1.81
1.42
3.59
DE
Dover
39' 8" N
75' 28" W
1.85
2.62
3.6
4.33
5.44
5.91
5.64
5.3
4.38
3.23
2.21
1.66
3.84
FL
Miami
25' 48" N
80' 16" W
3.72
4.61
5.42
6.4
6.61
6.29
6.26
6.08
5.47
4.84
3.96
3.46
5.26
GA
Atlanta
33' 39" N
84' 26" W
2.31
3.37
4.08
5.2
6.02
6.01
5.81
5.59
4.76
3.95
2.98
2.33
4.37
HI
Honolulu
21' 20" N
157' 55" W
4.38
5.15
5.99
6.69
7.05
7.48
7.37
7.07
6.51
5.46
4.41
4.01
5.96
IA
Dubuque
42' 24" N
90' 42" W
1.64
2.58
3.34
4.57
5.54
6.06
5.81
5.26
4.33
3.03
1.72
1.35
3.77
ID
Boise
43' 34" N
116' 13" W
1.73
2.72
3.77
5.22
5.9
6.57
7.17
6.12
5.28
3.29
1.74
1.46
4.24
IN
Indianapolis
39' 44" N
86' 17" W
1.67
2.59
3.28
4.67
5.46
6.11
5.79
5.37
4.76
3.33
1.97
1.46
3.87
IL
Chicago
41' 53" N
87' 38" W
1.5
2.45
3.2
4.48
5.56
6.07
5.68
5.27
4.51
3.07
1.69
1.26
3.72
KS
Kansas City
39' 12" N
94' 36" W
2.06
2.89
3.62
4.92
5.58
6.17
6.21
5.59
4.9
3.49
2.2
1.75
4.11
KY
Louisville
38' 11" N
85' 44" W
1.71
2.65
3.32
4.73
5.38
6.08
5.79
5.35
4.8
3.42
2.1
1.56
3.9
LA
New Orleans
29' 37" N
90' 5" W
2.64
3.73
4.67
5.8
6.6
6.15
6.09
5.7
5.13
4.48
3.49
2.68
4.76
MA
Boston
42' 22" N
71' 2" W
1.66
2.5
3.51
4.13
5.11
5.47
5.44
5.05
4.12
2.84
1.74
1.4
3.58
MD
Annapolis
38' 35" N
76' 21" W
1.96
2.8
3.71
4.55
5.54
6.03
5.77
5.34
4.48
3.4
2.37
1.81
3.98
ME
Portland
45' 36" N
122' 36" W
1.38
2.33
3.49
4.57
5.46
6.09
6.64
5.78
4.8
2.79
1.41
1.1
3.82
MI
Detroit
42' 25" N
83' 1" W
1.43
2.33
3.19
4.34
5.44
5.98
5.64
4.99
4.25
2.73
1.52
1.14
3.58
MO
St.Louis
38' 45" N
90' 23" W
2.02
2.82
3.52
4.97
5.56
6.21
6.05
5.63
4.91
3.55
2.21
1.73
4.09
MN
Minneapolis
44' 53" N
93' 13" W
1.6
2.61
3.3
4.55
5.44
5.86
5.77
5.12
4.12
2.9
1.62
1.34
3.68
MS
Jackson
42' 16" N
84' 28" W
1.47
2.41
3.22
4.33
5.46
5.93
5.57
4.99
4.3
2.78
1.55
1.17
3.59
MT
Billings
45' 48" N
108' 32" W
1.55
2.57
3.52
4.82
5.63
6.45
6.39
5.75
4.67
3.19
1.77
1.3
3.96
MT
Great Falls
43' 33" N
96' 42" W
1.3
2.36
3.41
4.84
5.56
6.18
6.44
5.53
4.4
2.9
1.53
1.11
3.79
NC
Charlotte
35' 13" N
80' 56" W
2.22
3.17
3.95
4.98
5.8
6.01
5.76
5.27
4.58
3.75
2.76
2.21
4.2
ND
Fargo
46' 54" N
96' 48" W
1.44
2.39
3.36
4.79
5.62
5.82
5.94
5.14
4.01
2.83
1.59
1.31
3.68
NE
Omaha
41' 18" N
95' 54" W
1.92
2.76
3.45
4.74
5.6
6.14
6.11
5.46
4.74
3.34
2
1.57
3.98
NH
Manchester
42' 56" N
71' 26" W
1.66
2.5
3.51
4.13
5.11
5.47
5.44
5.05
4.12
2.84
1.74
1.4
3.58
NJ
Trenton
40' 13" N
74' 46" W
1.71
2.39
3.43
4.04
5.26
5.67
5.39
5.14
4.18
3
1.98
1.48
3.63
NM
Albuquerque
35' 3" N
106' 37" W
2.92
3.97
4.92
6.3
6.68
6.94
6.66
5.8
5.68
4.18
3.16
2.5
4.97
NV
Las Vegas
36' 18" N
115' 16" W
3.02
4.13
5.05
6.57
7.25
7.69
7.37
6.42
6.08
4.26
3.18
2.6
5.3
NY
New York
41' N
74' W
1.67
2.37
3.41
3.93
5.11
5.48
5.26
5.01
4.05
2.85
1.82
1.4
3.53
OH
Columbus
39' 16" N
85' 54" W
1.64
2.57
3.26
4.63
5.4
6.08
5.73
5.29
4.74
3.29
1.96
1.45
3.83
OK
Tulsa
36' 12" N
95' 54" W
2.33
3.22
3.9
5.25
5.58
6.32
6.4
5.8
5.08
3.8
2.62
2.06
4.36
OR
Portland
45' 32" N
122' 40" W
1.38
2.33
3.49
4.57
5.46
6.09
6.64
5.78
4.8
2.79
1.41
1.1
3.82
PA
Philadelphia
39' 53" N
75' 15" W
1.85
2.62
3.6
4.33
5.44
5.91
5.64
5.3
4.38
3.23
2.21
1.66
3.84
PA
Pittsburgh
40' 27" N
79' 57" W
1.59
2.4
3.26
4.07
5.05
5.53
5.27
4.94
4.05
2.88
1.86
1.41
3.53
RI
Providence
41' 44" N
71' 26" W
1.7
2.46
3.53
4.2
5.17
5.67
5.48
5.08
4.21
2.97
1.8
1.43
3.64
SC
Columbia
38' 58" N
92' 22" W
2.14
2.91
3.62
5.03
5.56
6.22
6.13
5.64
4.95
3.57
2.25
1.82
4.15
SD
Sioux Falls
45' 27" N
98' 25" W
1.72
2.71
3.31
4.65
5.61
6.1
6.04
5.42
4.47
3.2
1.78
1.43
3.87
TN
Nashville
36' 7" N
86' 41" W
1.94
2.9
3.54
4.76
5.57
5.9
5.86
5.62
4.63
3.53
2.45
1.82
4.04
TX
San Antonio
29' 32" N
98' 28" W
2.57
3.7
4.43
5.54
5.94
6.62
6.49
6.28
5.7
4.67
3.43
2.62
4.83
TX
Houston
29' 59" N
95' 22" W
2.47
3.5
4.4
5.59
6.03
6.45
6.36
6.07
5.46
4.61
3.3
2.44
4.72
UT
Salt Lake City
40' 46" N
111" 52" W
2.23
3.15
4.09
5.57
6.26
6.98
6.86
5.98
5.39
3.68
2.29
1.97
4.53
VA
Washington
38' 51" N
77' 2" W
1.95
2.8
3.66
4.46
5.42
5.88
5.63
5.22
4.38
3.36
2.34
1.79
3.9
VT
Montpelier
44' 16" N
72' 35" W
1.58
2.54
3.5
4.05
5
5.24
5.37
4.92
3.79
2.46
1.52
1.28
3.43
WA
Seattle
47' 32" N
122' 18" W
1.14
2.04
3.23
4.26
5.19
5.75
6.27
5.46
4.43
2.5
1.21
0.9
3.53
WI
Milwaukee
42' 57" N
87' 54" W
1.43
2.41
3.29
4.48
5.6
6.09
5.74
5.21
4.34
2.9
1.6
1.2
3.69
WV
Charleston
38' 22" N
81' 36" W
1.75
2.64
3.34
4.26
5.2
5.67
5.49
5.19
4.26
3.19
2.15
1.62
3.73
WY
Casper
42' 55" N
106' 28" W
1.93
2.8
3.79
5.13
5.9
6.68
6.5
5.9
5.13
3.59
2.06
1.65
4.25

 

Data provided by NASA