Help Me Understand How to Use Solar Radiation Weather Info

[Matrix]

I have a weather station on my roof about 25 ft from my solar array. I've had it longer than the array ... but have known it also reports and records Solar Radiation. I casually checked out what that meant last summer but at the time did not have any real use for the info so I did not pay much attention to it.

Now that i have a small 2.5k array ... is there any useful info I can gleam from knowing the solar radiation that my weather station is reporting?

Right now it is reporting 165.4 W/m^2. What are some ways I can use that info to better understand the performance of my solar array? Or perhaps any other creative ways to use Solar Radiation Reporting and Recording for understanding and comparing what my solar array is doing. (this is purely a hobbyist question ... but thanks for the input)

[J.P.M.]

I have a weather station on my roof about 25 ft from my solar array. I've had it longer than the array ... but have known it also reports and records Solar Radiation. I casually checked out what that meant last summer but at the time did not have any real use for the info so I did not pay much attention to it.

Now that i have a small 2.5k array ... is there any useful info I can gleam from knowing the solar radiation that my weather station is reporting?

Right now it is reporting 165.4 W/m^2. What are some ways I can use that info to better understand the performance of my solar array? Or perhaps any other creative ways to use Solar Radiation Reporting and Recording for understanding and comparing what my solar array is doing. (this is purely a hobbyist question ... but thanks for the input)

The short answer to your first question is yes. Lots.

The answers to your other questions are a bit more complicated, depending on what type of information you want, or PV system performance information or data you want to estimate.

For starters:

1.) Who's the mfg. of the weather station ?

2.) Read any manuals for the station.

3.) Make sure it's operating and reporting data correctly.

4.) There is a lot of useful information you can get from a weather station to help analyze PV system performance, but to get the most out of it and not be misled by what the weather station is outputting, you'll need to have some knowledge of the variables involved. The raw data won't be of the most or even much value beyond confusion value without some massaging. One example: the weather station will give you "Global Horizontal Irradiance" ("GHI") numbers. Your 165.4 W/m^2 is GHI. That number needs to be converted to something called "Plane of Array" ("P.O.A.") irradiance to be useful in evaluating array performance. Lots of other numbers such as temp. and wind vector are required for array performance estimates.

My weather station is located about 4 ft. north of my array, about 1 ft. or so higher than the high point of the array. Consider relocating yours.

The best place I know of to gain an accurate and thorough understanding of how to use solar radiation data and other weather information is: "Solar Engineering of Thermal Proceses" by Duffie and Beckman. Study/understand Chap. 1 & 2 and you'll know what to do with the weather station data. Otherwise GIGO applies.

[Matrix]

Thanks ... will check that out. The station is a Ambient Weather 1400 and it has been reporting since Jun 17. I have compared it with several other stations in the area and there seems to be good agreement about the data it is collecting.

[J.P.M.]

Thanks ... will check that out. The station is a Ambient Weather 1400 and it has been reporting since Jun 17. I have compared it with several other stations in the area and there seems to be good agreement about the data it is collecting.

Good start. What do you want to learn/monitor about your array's performance ? Options are many, depending on how much work you want to put into it.

Not a knock, but necessary to know : The Ambient Weather 1400 solar sensor accuracy is given as +/- 15 %. That's kind of wide to put a lot of faith in without some added calibration effort.

[Matrix]

Good start. What do you want to learn/monitor about your array's performance ? Options are many, depending on how much work you want to put into it.

Not a knock, but necessary to know : The Ambient Weather 1400 solar sensor accuracy is given as +/- 15 %. That's kind of wide to put a lot of faith in without some added calibration effort.

I really don't know what I want to learn/monitor. I wasn't sure what there was very much to know about that info the 1400 was giving me and how I could use it. I was looking for some guidance if indeed there was anything to gleam at all ... which, according to your previous comments, there appears there possibly could be.

So things like ... What is the 1400 reporting 165.4 W/m^2 actually telling me about the solar power available and what are some of the ways I could learn from that info for my solar generator. You gave me some ideas to google in your first post and when I get time later I will look at those.

[J.P.M.]

I really don't know what I want to learn/monitor. I wasn't sure what there was very much to know about that info the 1400 was giving me and how I could use it. I was looking for some guidance if indeed there was anything to gleam at all ... which, according to your previous comments, there appears there possibly could be.

So things like ... What is the 1400 reporting 165.4 W/m^2 actually telling me about the solar power available and what are some of the ways I could learn from that info for my solar generator. You gave me some ideas to google in your first post and when I get time later I will look at those.

There is indeed a lot to glean. It appears that, at this time, you don't know what you don't know and that's OK, as long as you stay curious and accept the idea that there are few one word, one concept or one equation/equality answers.

To your question: The 165.4 W/m^2 is the instrument's estimate of the sum (integrated) total over all wavelengths of solar radiation that the solar sensor is capable of detecting that is received on a plane that is normal to gravity - in other words, parallel to level ground. Under clear skies, that number will range from near zero at sunrise/sunset to something like ~~ 1,000 W/m^2 on a very clear day in the lower latitudes near the equinoxes around solar noon, that is, when and where the sun is close to vertical overhead. Clouds or atmospheric contaminants will reduce that number. Cloudy skies commonly produce GHI's of ~~ 150 - 300 W/m^2 and it's all diffuse solar radiation - that is, no beam radiation capable of casting a shadow.

Example: If your GHI is 165.4 W/m^2, and you translate that via correlations and irradiance models to a P.O.A. irradiance estimate on your array of, say, 140 W/m^2, and you know your array's area is, say, 10 m^2, and you array monitor says that the array output was 250 W when the P.O.A. was 140 W/m^2, you will know that your array's overall instantaneous efficiency was 250/(10*140) = 0.1786 or ~ 17.9 % (provided of course, you remembered to clean the dust/dirt off the solar sensor). And that can be just the beginning.

Many things will conspire to attenuate solar radiation on a surface, including the angle the sun makes with the receiving surface. The convention on environmental irradiance measuring/monitoring is to measure and report the GHI and then calculate/estimate P.O.A. irradiance from well established and various correlations that have been developed over many years, and from solar geometry.

Again, see Duffie and Beckman for a lot of the particulars. The more you learn and the less you think you know, the better will your information be.

Depending on how involved, persistent and how careful you may want to get, you can squeeze a surprising amount of information from the data output of a weather station, particulary when combined with monitored output of a PV array.