Topic: Davis Vantage Solar Radiation Sensor

[Pedr057]

The units for the solar radiation sensor are W/m2. That sounds simple enough on the face of it. However, exactly what area does it relate to? Is it in the horizontal plane ie parallel to the ground? Is is a plane normal to the sun? Is it something else?!

Wy do I want to know? Well, I have an array of PV solar panels that are partially shaded, especially in winter, and I'd like to compare the solar radiation from the weather station with the apparent radiation on the PV panels. I have all the specs for the panels including the maximum power generated in W/m2 and efficiencies etc and want to estimare the percetgae losses due to shading. Knowing exsctly what the weather station is measuring is key.

[broadstairs]

The Davis sensor measures global solar radiation and not direct. If you want to measure direct you need a different sensor. Davis sensors can be affected by reflections from clouds and can reach values around 900+w/m2 or more in high summer at solar noon.

Stuart

[Mattk]

https://www.davisinstruments.com/pages/solar-radiation-an-explanation

[havtrail]

I would think you would want to mount the solar radiation sensor at the same angle and direction as the solar panels.

Rich K.

[broadstairs]

I would think you would want to mount the solar radiation sensor at the same angle and direction as the solar panels.

Rich K.

I'm not sure that will achieve the desired result since this sensor needs to be mounted level so it points straight up any other way will invalidate the readings. It measures total or global solar radiation which is direct and reflected radiation, you cannot estimate direct from global in any way.

Stuart

[johnd]

If your prime objective is to gather irradiance data for correlation with the solar panels' performance then I think mounting the sensor normal to the plane of the panels should work fine. The solar panels don't distinguish between direct and indirect irradiance, so the panel performance and sensor readings should be comparable. But, sure, as you imply, the sensor readings will no longer provide a standardised meteorological reading for global/total solar irradiance

[mcrossley]

If you want both, keep it horizontal and apply a correction factor based on the suns position in the sky and the angle of the panels. Just a bit of simple trigonometry
It would not be perfect, as the senor cannot distinguish between the diffuse and direct contributions, but it may be "good enough".

[Pedr057]

Thanks for the responses - they've given me some good ideas for further investigation. I had already built myself a spreadsheet model that I use to calculate the instantaneous power output at 15 mins intervals throughout the year (approx 35,000 points). I can use it to optimize zenith/inclination and azimuth/orientation for the panels, either for the year as a whole or a particular season eg winter. However, it can't account for weather and shading adverse impacts so I thought using my weather station might give me some insights into te weather component when the panels aren't shaded.

I hadn't considered direct and diffuse radiation. The panels and station aren't that far apart so not a prime concern for me (the station is much, much less impacted by shading though).