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Using Solar Panel Data

Discussion and questions about Cumulus weather station software version 1. This section is the main place to get help with Cumulus 1 software developed by Steve Loft that ceased development in November 2014.
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Ken22
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Using Solar Panel Data

Post by Ken22 »

I just installed solar panels on my roof and have access to the data on the wattage being generated at any point in time.

It seems that this data could be used to tell Cumulus about Solar Radiation, UV Index and Daily Sunshine.

Is there a not too hard way to connect the two?

Ken
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steve
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Re: Using Solar Panel Data

Post by steve »

If you could periodically generate a file in the format that the Blake-Larsen solar sensor software produces, with the sunshine hours in it, Cumulus will read the sunshine hours from that. I think the file also contains the solar radiation figure, but I'm not sure whether Cumulus actually uses that. The format is very simple, but I can't remember it exactly at the moment. If that sounds like it would be useful, I could look for more details when I get a minute.

I don't think you'll be able to derive UV, I think you need a specific sensor for that.
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Re: Using Solar Panel Data

Post by PaulMy »

Here is one previous thread on the SRSunshine.dat file https://cumulus.hosiene.co.uk/viewtopic.p ... SRSunshine

The Blake-Larsen files contain additional data.

Paul
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steve
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Re: Using Solar Panel Data

Post by steve »

Thanks for that, Paul. For some reason I thought the current solar radiation figure was in there, but I was clearly confused!
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Re: Using Solar Panel Data

Post by AllyCat »

Hi,

As Steve says, the panels aren't going to measure UV but only the sum of "Visible" and "Near IR" light wavelengths (which is similar to the watts/m2 value used in meteorology). However, IMHO most amateur "UVI" values are potentially "wrong" anyway, because the low-cost UV sensors measure UVA and the official UV Index measures / predicts UVB.

But I'm afraid that I doubt if the measurements from your Solar Panels will be very useful for "Sunshine" reporting either. The "difficut" part is generally not "measuring" the light level but interpreting it! In particular, the Watt's/m2 value is based on an accurately horizontal sensor (the better sensors include a spirit level) and your panels are presumably on a sloping roof?

In principle, it might be possible to mathematically correct for the slope (provided that the time and date of every measurement is known / logged) but bear in mind that in summer, the sun can be "behind" the plane of sloping panels in the early morning and late afternoon, so is not likely to be accurately reported.

However, the light level (and thus power generated) does increase quite enormously when the sun directly hits the panels, so you might find that a simple "threshold" power (perhaps 20% - 50% of the rated power of the panels), preferably corrected for time of year and time of day, might give a moderately useful "Sunshine Hours" figure for the Cumulus Blake Larsen file.

If you're interested in more general sunshine measurements at the "hobby" level, then the "Weatherduino" project (which can provide data for Cumulus) might be of interest. See for example here, here or here.

Cheers, Alan.
Ken22
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Re: Using Solar Panel Data

Post by Ken22 »

PaulMy wrote:Here is one previous thread on the SRSunshine.dat file https://cumulus.hosiene.co.uk/viewtopic.p ... SRSunshine
Thanks for all the information.

I put a dummy SRsunshine.dat file in my Cumulus folder and turned on Extra/Sun in my display configuration, but nothing about sun showed up on my display screen. Any ideas on what I could be doing wrong?

Ken
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steve
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Re: Using Solar Panel Data

Post by steve »

If you selected "Use B/L", and you have put the SRsunshine.dat file in the data folder, then after the file has been read (once a minute) the 'sun' icon should light up yellow if the fourth line of the file is "True", and the 'tooltip' for the sun icon should show the figure from the first line of the file (sun hours so far today). If that doesn't work, and no error appears in the diags log relating to the reading of the file, then I'm stumped.
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Re: Using Solar Panel Data

Post by Ken22 »

[quote="steve"]If you selected "Use B/L", quote]
That was the problem. I missed the "Use B/L".

It is working now. My next job is to convert watts into radiation.

I hope there is a formula I can use given the angles of the panels.

Ken
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Ken22
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Re: Using Solar Panel Data

Post by Ken22 »

Ok, now that I have the little sun icon, how do I fill in the "Light" and "Solar Rad" boxes?
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steve
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Re: Using Solar Panel Data

Post by steve »

You can't, not by this method, at least. See the posts above - the SRsunshine.dat file doesn't have anything like that in it.

The only way to feed solar radiation data in to Cumulus is as part of the station data, and Cumulus will only read from one station at a time. You could create an easyweather.dat file (and put 'Lux' values in it), but one instance of Cumulus would only read data from that and not from your weather station at the same time - you would need to run a second instance of Cumulus.
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Ken22
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Re: Using Solar Panel Data

Post by Ken22 »

steve wrote:You can't, not by this method, at least. See the posts above - the SRsunshine.dat file doesn't have anything like that in it.
Any chance you would be willing to add a check for extra fields to the SRsunshine.dat file?

Ken
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Re: Using Solar Panel Data

Post by steve »

Not in Cumulus 1 - at some point I could look at doing something like that in MX.
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Re: Using Solar Panel Data

Post by Gordon-Loomberah »

Ken22 wrote: My next job is to convert watts into radiation.

I hope there is a formula I can use given the angles of the panels.
It's going to be a lot more complicated than that, there's the previously pointed out mounting angle problem, especially in summer when the sun will be behind the panels at the start and end of each day, then there's dust and bird droppings on the panels reducing output, shadows from overhead cables, trees etc. Even a TV antenna can drop the output from one string of panels by up to 20%. A tree shadow half way across one panel can just about wipe that string out completely under a clear sky, but in cloudy weather may barely be noticeable due to the diffuse nature of the radiation source.
Then there is the issue of inverter efficiency vs power level and temperature, temperature coefficient of the solar panels, typically about 0.5% less output for each degree the cell temperature rises. Panels are rated at 25C, but in the real world, it has to be much colder than that for the cell to be at 25C. It is influenced by many things including wind speed, Watts/m^2 radiation, angle of incidence of the solar rays, mounting position, type of roof, etc. I've measured it, and on a 35C day cell temperature can be upwards of 65C, meaning output can be 25% or more down on the rating.

So many variables have to be taken into account, I'd say it was almost impossible to get any sort of accuracy over an extended period by measuring a domestic PV system's output to determine W/m^2.
Loomberah Weather: http://gunagulla.com
Ken22
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Re: Using Solar Panel Data

Post by Ken22 »

Gordon-Loomberah wrote: It's going to be a lot more complicated than that...
Yes it is, but I should be able to get an approximation.

I have 34 panels each with a separate micro-inverter. The total wattage will not vary much from things like an antenna shadow.

At my latitude and South West facing, the sun is only behind the panels early in the morning. Even with the sun behind the panels, they are still generating measureable power. A program to estimate solar radiation may need a dataset for each day of the year (which can be done), of maybe it can be calculated based on all the known variables.

I have access to air temperature and wind speed.

In the end, even if I am 20% off, it may still be a fun project.

Thanks for your input.

Ken
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