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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.

PV Sensor: The meter uses a polycrystalline silicon PV cell as the sensor. The cell is mounted on the top end of the meter, perpendicular to the display. The sensor responds to a spectum bandwidth of approximately 0.3-1.1 microns. A generic spectrum for a silicon PV cell is here The meter is intended for outdoor measurements of natural sunlight. The PV sensor is located behind a plastic diffuser.

Meter Calibration: Meters are calibrated on clear days in natural sunlight and adjusted to a reference cell periodically calibrated with pyranometers at Sandia National Laboratories. Meters are pointed directly at the sun for calibration with the plastic protection cover in place. Off-angle calibration is not done. However, empirical data indicate meter-to-meter performance remains consistent up to 40 degrees off-angle from the direct normal. Beyond 40 degrees the readings start to diverge and may reach 10 - 15% when pointed 70-80 degrees away from the sun. The meters are calibrated in groups and records for individual meters are not maintained.

Care of your Meter: The meters are designed for use in the field but you should treat them as you would your voltmeter; avoid dropping them, do not leave them out in the rain. They are not sealed for continuous exposure to weather. The LCD display may darken if exposed to direct sunlight for a prolonged period.

Meter Repair: We stand behind our products. If your meter is damaged or malfunctions, contact Daystar for instructions about repair or return. A repair charge may assessed if your meter is more than one year old.

Using Your Meter: 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.

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