Solar Radiation Readings W/m2

[geoffw]

As I can't afford to have a solar radiation reader, I have been looking around locally for a weather site that provides them. I have just found one within 15km, and I intend negotiating to include their output data on my website (obviously crediting them with a link). However looking at their output and at the Cumulus Radiation Graph I see an apparent anomaly!

http://www.milfordweather.org.uk/index.php

Cumulus seems to assume a an upper possible radiation limit of 230 w/m2, yet the readings displayed by Milford Haven Port Authority ranged up to 450 today. Today was mainly cloudy but did brighten up for while this afternoon.

[mcrossley]

Geoff, you will need a clear cloudless day to compare the readings. I have found the actual reading is strongly affected by clouds, they reflect additional light down to the sensor if the orientation is right. So you often have the situation where a perfectly clear day gives lower readings than one with broken cloud.

The spikeness of those graphs indicates lots of clouds.

[steve]

And when you do get a clear day, you can if you wish then calibrate the Cumulus settings to try to get the calculated theoretical max closer to the readings you're using. The default settings are just to get you close. Depending on the type of solar sensor they are using, you may not be able to get them to match at all.

[geoffw]

Thanks Both - I'll let you know how I get on.......