It certainly does depend on what you want to do with the numbers. Like you, I have solar panels, and, also like you, I monitor them separately from my weewx installation. If all you want to do is keep a check on total (potential) energy influx, then 24-hour averaging and using the sort of calculation you suggest, will work perfectly well, though it won't take account of the fact that solar panels are generally tilted and face in a specific direction (ideally between SE and SW), while most standard weather station radiation sensors are designed to be pretty much equally sensitive to radiation coming from anywhere in the sky. OTOH, if you want to get total energy from daytime-only averages, you just need to make sure that you have counted how many samples you have, so you haven't really lost any information. My problem with simple 24-hr averaging is that if you want to know 'how bright it was' on a past date, and you use simple averaging, winter days won't get a fair shake, because, even if the sun was shining out of a clear sky all day, there will be a lot more zeroes contributing to the average and the average radiation number will be disproportionately lower than I feel it 'should be'. I suppose that the question I am asking and answering is: "What was the average radiation level *during the day*?". I know it was zero at night!
For UV, I think you are right about showing minutes per day above a specified level (or perhaps two different ones) being more useful than any sort of average, though here, too I think there is an argument for averaging (if that is what you are going to do) only during the day. On Tuesday, March 28, 2023 at 3:43:26 AM UTC-4 Cameron D wrote: > The obvious question is what you need to do with the numbers. > I have solar panels and I log the values separately so I don't use weewx > for that - I got the weather station partly to help understand my PV > output. The important long-term values to me are total energy over the > day/month/etc. So, if I was needing to use weewx values of max or mean to > plot how things were going then I suppose I would go for the 24-hour > average. The summation of W/m2 over the day scales to the total energy > generated - assuming your time interval is fixed and every value is > recorded. So for a 5 minute interval, multiply the W/m2 value by 300 will > give you J/m2. > In the same way, because you should have a fixed number of samples per > day, the 24-hour average also scales to total energy. However, if you only > use daylight or non-zero values then you are adding another variable and it > carries less meaning - if total energy is important to you. > > As for UV, since I live in skin cancer central, I would be mainly > interested in the high values. Any average would be pretty useless to me, > unless it is, for example, an average between 9:00 and 15:00 (or 3 hours > either side of solar zenith.) A better long-term value might be minutes > per day above index 10, 11 or 12. > I was not even sure an arithmetic mean of a UV index was valid, but having > had a quick look at the derivation of the index, I think it is OK. > > On Tuesday, 28 March 2023 at 12:37:18 am UTC+10 Peter Fletcher wrote: > >> I'm trying to start a discussion - not an argument! The fact that no-one >> has come up with a way of displaying historic radiation readings that a >> consensus of weather experts thinks is better than a simple average >> strongly suggests either that no-one thinks that the issue is that >> important, or that there is no one right answer - probably a bit of both. >> You can and should use whatever approach is most meaningful for you. In >> fairness, however, your temperature analogy really does not fly - maximum >> daily temperatures correlate much better with mean temperatures that is >> true for radiation values, but max temps are independently more 'important' >> than max radiation values. This is, of course, partly because it is very >> rare for a max temp to be a single isolated value in the way a max >> radiation reading may frequently be. >> >> I have switched my annual charts of both UV and Solar Radiation to show >> 'daytime averages', as previously described. I have attached images of both >> pairs of charts - 'old' uses simple averaging; 'new' uses daytime >> averaging. The maximum values are substantially higher in the latter, but >> the overall patterns are not hugely different. The higher maxima 'feel' >> better to me, but I certainly would not go to the wall for 'my' way of >> doing things. >> On Sunday, March 26, 2023 at 11:33:09 PM UTC-4 [email protected] wrote: >> >>> Where I live, with the hardware I use, in my understanding, it is >>> useful: in addition to the information how much energy from solar radiation >>> your location got over the day, you can tell if was clear at least for some >>> time that day, or not. So if you say "where I live, fairly high spikes on >>> otherwise cloudy days are common, and days with light to moderate cloud >>> cover with significantly lower maxima are also fairly common" that's just >>> the point: that's the extra information you get. The fact that you know >>> that because you live there is proven with data and if your station is on >>> the internet, everyone can know. >>> What would you reply to me, if I said: "I not convinced daily maxima are >>> particularly useful for temperature. At least where I live, fairly high >>> maxima on otherwise pretty cold days are common, and days with moderate >>> averages, and maxima not significantly above average, are also fairly >>> common"? Probably you'd say: "That's different", which is true, because >>> radiation changes are very like to be more radical than temerature changes >>> often, but it is not so much different one might think. >>> >>> Peter Fletcher schrieb am Sonntag, 26. März 2023 um 22:32:13 UTC+2: >>> >>>> I'm not convinced that daily maxima are particularly useful for solar >>>> radiation. At least where I live, fairly high spikes on otherwise cloudy >>>> days are common, and days with light to moderate cloud cover with >>>> significantly lower maxima are also fairly common. Simple averages are, at >>>> least, somewhat meaningful, and I don't think showing the daily maxima >>>> adds >>>> anything to them. Only counting as maxima values that are sustained for >>>> more than a specified time might make them more so. >>>> >>>> On Tuesday, March 21, 2023 at 1:16:48 AM UTC-4 [email protected] >>>> wrote: >>>> >>>>> For myself, I found that for a yearly chart, using a bar chart with >>>>> the daily averages, and a crosshair to display the daily maximum, a >>>>> comprehensive way to display solar readings. >>>>> >>>>> Peter Fletcher schrieb am Donnerstag, 16. März 2023 um 00:29:26 UTC+1: >>>>> >>>>>> In order to look at different ways of presenting solar and UV >>>>>> radiation data, I dumped the contents of weewx.sdb to a csv file and >>>>>> used >>>>>> Excel to manipulate and chart the relevant data. The attached charts >>>>>> show >>>>>> daily averages for solar and UV radiation for four-month summer and >>>>>> winter >>>>>> periods in 2021 and 2021/22. More (probably 'simple') averaging would >>>>>> probably be done in producing yearly charts for a website, but I thought >>>>>> it >>>>>> helpful to get a somewhat more granular picture of the processed data. >>>>>> For >>>>>> all the charts and both types of data, 'Avg ...' uses the current >>>>>> calculation (simple averaging of all readings for the 24 hr day), 'NZ >>>>>> Avg >>>>>> ...' represents the average of all non-zero readings acquired during the >>>>>> 24hr day, and 'Day Avg ...' represents the average of all readings >>>>>> (including any zeroes) recorded between sunrise and sunset (calculated >>>>>> for >>>>>> my location and the date by the standard NOAA method). >>>>>> >>>>>> For solar radiation, in both seasons, the non-zero and daytime >>>>>> averaging methods produce almost identical results (there are only a few >>>>>> places where the two lines do not coincide), and the numbers generated >>>>>> are >>>>>> a bit more than 1.6 times the simple average numbers in the summer and >>>>>> well >>>>>> over twice the simple average numbers in the winter. This additional >>>>>> seasonal difference is, of course, a result of the non-zero winter >>>>>> averages >>>>>> not being 'diluted' by the zero values from the longer nights. The >>>>>> results >>>>>> of the two more complex averaging methods make more sense to me as a way >>>>>> to >>>>>> present solar radiation readings for long time-periods. Non-zero >>>>>> averaging >>>>>> is computationally simpler and would probably be my preferred way to go. >>>>>> >>>>>> For UV radiation, the picture is rather different. Here, the simple >>>>>> average numbers are again lowest, but the other two averaging methods >>>>>> produce substantially different results, with non-zero averaging giving >>>>>> (particularly in the winter) results up to three times those generated >>>>>> by >>>>>> non-zero averaging. Here, I think daytime averaging makes more sense. As >>>>>> I >>>>>> indicated in my earlier post in this thread, I thought that non-zero >>>>>> averaging for UV radiation was likely to produce 'average' results that >>>>>> were distorted by periods of sunshine during an otherwise cloudy day, >>>>>> and I >>>>>> believe that this is a substantial contributor to what is happening >>>>>> here. >>>>>> Assuming, however, that stations which have UV sensors generally also >>>>>> have >>>>>> solar radiation sensors, it might be computationally simpler to average >>>>>> UV >>>>>> radiation readings if/when the accompanying solar radiation values are >>>>>> non-zero. >>>>>> >>>>>> Any thoughts or comments? >>>>>> >>>>>> On Saturday, March 11, 2023 at 4:05:18 PM UTC-5 Peter Fletcher wrote: >>>>>> >>>>>>> When looking at some of my 'yearly' charts (see >>>>>>> https://fletchers-uk.com/weather/index.html), the other day, I was >>>>>>> struck by how low the 'peaks' in the Solar Radiation and UV graphs >>>>>>> were. >>>>>>> On a sunny day in the summer (yes - we do have such days in >>>>>>> Buffalo!), I >>>>>>> typically see Solar Radiation numbers above 900 and UV values above >>>>>>> 7 >>>>>>> for at least a couple of hours around solar noon, but the peaks of >>>>>>> the >>>>>>> yearly graphs barely exceed 325 and 2, respectively. A (very) little >>>>>>> thought revealed the reason for this - the longer term charts >>>>>>> average >>>>>>> the raw values recorded over periods of more than 24 hours (a week, >>>>>>> in >>>>>>> my case), so the averages displayed on the charts include a large >>>>>>> number >>>>>>> of entirely predictable nocturnal zero readings. In the depths of a >>>>>>> Buffalo winter, it is dark for 15 hours out of the 24, and even in >>>>>>> high >>>>>>> summer here it is dark for a bit less than 9 hours out of 24. >>>>>>> >>>>>>> 'Straight' averages are easy to compute, and make reasonably good >>>>>>> sense >>>>>>> for displaying the majority of weather-related measurements, which >>>>>>> typically have no particular diurnal pattern - or, at least, not >>>>>>> such an >>>>>>> extreme one - but it doesn't seem totally to make sense to use them >>>>>>> when >>>>>>> you know in advance that there is such a pattern. OTOH, it clearly >>>>>>> wouldn't be very useful just to record and display the daily peak >>>>>>> values >>>>>>> for these measurements, since that would treat otherwise cloudy days >>>>>>> during which the sun appeared through the clouds for ten minutes >>>>>>> around >>>>>>> noon in the same way as days on which the sun shone out of a >>>>>>> cloudless >>>>>>> sky from dawn to dusk. Some averaging is needed. >>>>>>> >>>>>>> One possibility that might produce (IMHO) more meaningful results is >>>>>>> 'non-zero averaging' - do not count zero values in computing the >>>>>>> average. Solar Radiation rarely reads as zero during the day, so the >>>>>>> results of this calculation should correspond reasonably well to a >>>>>>> daytime-only average. Daytime UV readings, OTOH, are frequently zero >>>>>>> if >>>>>>> it is reasonably heavily overcast, so 'non-zero averaging' would >>>>>>> produce >>>>>>> misleadingly high 'average' values on days with variable cloud >>>>>>> cover. >>>>>>> >>>>>>> A second, and, I think, better, possibility would be to explicitly >>>>>>> record and average only daytime values for both readings - defining >>>>>>> daytime as being between sunrise and sunset for the date and the >>>>>>> station's location. >>>>>>> >>>>>>> It might also be of interest to record and display the average daily >>>>>>> number of minutes/hours for which the reading exceeded a particular >>>>>>> threshold, and/or the level reached for at least a certain length of >>>>>>> time - the thresholds in each case being determined in advance - but >>>>>>> computing these results on the fly would likely be more challenging. >>>>>>> >>>>>>> I am going to be playing with implementing these ideas over time, >>>>>>> but I >>>>>>> would like to hear others' thoughts. >>>>>>> >>>>>>> -- >>>>>>> >>>>>>> Peter R. Fletcher <[email protected]> >>>>>>> Home Page - https://pfletch.fletchers-uk.com >>>>>>> >>>>>>> -- You received this message because you are subscribed to the Google Groups "weewx-development" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-development/fe2f240a-6aef-4536-98e6-7a5f1a573508n%40googlegroups.com.
