Have you been debating installing a solar photovoltaic system, but you don't know if your site has sufficient sun exposure (insolation) to make it worthwhile? Are you planning a solar system, but want a convenient way to figure out which potential location will provide the best exposure for your solar panel array? The Daystar Digital Solar Meter is exactly what you need!

This compact, easy to use solar meter allows you to simply walk around your planned installation site and measure potential photovoltaic output at any location. Just point the Daystar's sensor directly at the sun, and the digital readout displays the Watts per square meter.

From the manufactuer's website:

The Daystar solar meter provides an accurate reading (3%) from 0 - 1200 Watts/m2 when they are pointed at the sun. Resolution is 1 W/m2, maximum display reading is 1999. The irradiance value is presented on a 0.75" easy-to-read LCD display. The meter is (2.5" x 4.5" x 1.0" inches) (6.4 x 11.4 x 2.5 cm) and weighs (less than 5 ounces) (140 g) with the 9-V battery installed.

The Daystar solar meter measures instantaneous solar power and provides the reading in Watts per square meter. You can calculate the total power striking the PV array by multiplying the area of the active PV material by the reading from the meter. You can estimate the output power from the PV array for that condition by multiplying by the advertised module efficiency. You would have to adjust that value for losses, temperature effects, inverter efficiency, etc., to obtain the actual system output. More information is available as a .pdf download here.