## Monday, July 11, 2016

### Weather station's solar panels...

Weather station's solar panels... Some time ago I purchased a Weatherhawk 621 weather station, but with all the things going on around here I never got around to installing it. The technology it uses is interesting - it measures all the usual weather factors without using any moving parts. Wind speed and direction is calculated via an ultrasonic system that measures the speed of sound in both directions along three axis 120 degrees apart. Precipitation is measured via a gigahertz radar that measures reflectivity to measure the non-vapor water in the column of air over the station, and the Doppler effect to measure the rate of fall.

It's a heated model, so that no ice will accumulate on the radar antenna and ultrasonic transducers. Because of this, the power consumed by the station is much higher in the winter. The station will be mounted a long way from any power source, so I'm going to use solar panels to charge a couple of truck batteries, and a controller to give me a constant 24 volts. Those solar panels will be pointed toward true south (not magnetic south) to maximize the light they'll catch. But what angle from the vertical should they be?

I'd have guessed something like 45 degrees from the vertical. When I calculate it, though, I come up with approximately 30 degrees from vertical (closer to straight up and down than flat). We're at roughly 41.5 degrees latitude here in Paradise. Add the earth's 23.5 degree tilt to that, and mid-winter the sun's elevation at noon is just 90 - (41.5 + 23.5) = 25 degrees. The rest of the winter it's between 25 and 35 degrees. Splitting the difference to work well all winter long, we get about 30 degrees. That's what we get for living so close to the North Pole!!!