How to Size a Grid-Connected Solar Photoelectric System
Optimum Orientation of Solar Panels
Magnetic Declination
Definition: deviation between magnetic north and geographic north. Map of deviation between geographic south and magnetic south for aligning solar panels:
Left of 0 is east, right of 0 is west.
For example, geographic south in Blacksburg VA falls between the 7 degree west and the 8 degree west lines relative to magnetic south. This means that the solar panels should be aligned 7-8 degrees west of magnetic south (using a compass).
Optimal Tilt Angle for Solar Panels
Efficiency for Facing Direction and Tilt Angle of Solar Panels for Blacksburg VA
(This calculation was made for Sacramento CA, which is 1° north of Blacksburg VA; so the numbers are also valid for Blacksburg VA.)
Solar Panels Calculator
For Roanoke VA (37.3° latitude) the calculator yields the following for a 1 kWatt array:
Tilt Angle |
Azimuth Angle |
Yearly kiloWattHours |
Ratio to Optimum |
Yearly $ @ $0.10/kwh |
37.3° |
180° (S) |
1273 |
1 |
$127 |
37.3° |
135° (SE/SW) |
1189 |
0.934 |
$119 |
37.3° |
90° (E/W) |
989 |
0.777 |
$99 |
37.3° |
45° (NE/NW) |
743 |
0.584 |
$74 |
37.3° |
0° (N) |
620 |
0.487 |
$62 |
15° |
180° (S) |
1221 |
0.959 |
$122 |
15° |
135° (SE/SW) |
1183 |
0.929 |
$118 |
15° |
90° (E/W) |
1083 |
0.851 |
$108 |
15° |
45° (NE/NW) |
975 |
0.766 |
$98 |
15° |
0° (N) |
925 |
0.727 |
$93 |
45° |
180° (S) |
1254 |
0.985 |
$125 |
45° |
135° (SE/SW) |
1163 |
0.914 |
$116 |
45° |
90° (E/W) |
945 |
0.742 |
$95 |
45° |
45° (NE/NW) |
668 |
0.525 |
$67 |
45° |
0° (N) |
529 |
0.416 |
$53 |
60° |
180° (S) |
1164 |
0.914 |
$116 |
60° |
135° (SE/SW) |
1072 |
0.842 |
$107 |
60° |
90° (E/W) |
845 |
0.664 |
$85 |
60° |
45° (NE/NW) |
542 |
0.426 |
$54 |
60° |
0° (N) |
374 |
0.294 |
$37 |
90° (vertical) |
180° (S) |
800 |
0.628 |
$80 |
90° (vertical) |
135° (SE/SW) |
771 |
0.606 |
$77 |
90° (vertical) |
90° (E/W) |
611 |
0.480 |
$61 |
90° (vertical) |
45° (NE/NW) |
369 |
0.290 |
$37 |
90° (vertical) |
0° (N) |
239 |
0.188 |
$24 |
0° (horizontal) |
Not Applicable |
1099 |
0.863 |
$110 |
The DC to AC derating factor used in the calculations in 0.77. See Solar Derating .
Optimum Orientation of Solar Panels for Time-of-Use Rate
Latitudes of Major USA Cities
Solar Roofing
Solar Electricity (Photovoltaic, PV) (Net Metering) in the New River Valley of Virginia
- Baseline Solar Solutions (Pat Bixler)
- Direct Connect Solar and Electricity (David Zachow)
- Solar Connexion (Bryan Walsh
This is web page http://www.roperld.com/science/SolarPhotoelectric.htm
L. David Roper, http://www.roperld.com/personal/roperldavid.htm; roperld@vt.edu
4-apr-16