Solar Meter Special Features
G&R Labs has developed a solar meter that measures the suns energy in the same spectrum (.3 to 1.1 Microns) as the solar panel. The measurement in watts per square meter (W/M2) is traceable to NIST. The meter is linear to better than 0.1% over its full range. The case of the meter is extruded aluminum which shields the electronics from noisy electrical environments and is very durable.
The probe is cosine corrected to match the panels ability to pick up off-axis light. The spectral response being the same as the panel ensures that the watts per square meter (W/M2) measured is the full value of a 100% efficient panel. If you take the meter reading and multiply by the panel area in M2 then you will have the full wattage the panel should be producing at 100% efficiency. Taking the panel output wattage (volts x amps) at the same time as the meter is reading and divide by the suns wattage (100% value) then this number x 100 is the panels efficiency in %.
The calculations are as follows:
| W/M2 | Meter reading |
| A | Area of panel in M2 (feetL/3.3 x feetW/3.3) |
| Wo | Watts out of panel (volts x amps) |
| W/M2 x A = W (watts from sun) | |
| Wo/W x 100 = % efficiency of panel | |
Solar Meter Operation
Put the probe on the edge of the panel in a steady light condition. Read the meter reading W/M2. Put the Hold switch up into the On position to hold the reading. Move out of the Hold position before turning off the meter or to get new reading.
Measure the panel area in M2 (feetL/3.3 x feetW/3.3).
The meter reading W/M2 x M2 (panel) = watts from sun. Read the watts from the panel (volts x amps). Divide the watts from the panel by the watts from the sun and multiply by 100. This is the % efficiency of the panel.