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/d56a46fd-fce2-4bb2-b650-760fe9b53b54n%40googlegroups.com.
