# Solar Photoelectric

## 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).

## 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
(SE is the same as )

The DC to AC derating factor used in the calculations in 0.77. See Solar Derating .

## Solar Electricity (Photovoltaic, PV) (Net Metering) in the New River Valley of Virginia

This is web page http://www.roperld.com/science/SolarPhotoelectric.htm

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L. David Roper, http://www.roperld.com/personal/roperldavid.htm; roperld@vt.edu
4-apr-16