The book "Solar Electricity" by Simon Roberts has some usable solar insolation maps in the appendixs'.

Came across some in SAP appendix U while looking at something else today... There's also formulae to convert to inclined surfaces
https://www.bregroup.com/sap/sap10/

AIUI it used to be quite expensive to measure solar irradiation so many climate stations measure 'sunshine hours' series instead. There's some empirical conversion methods.

This may mean that the only person who is measuring solar irradiation at your location, is you ...

But you might be able to get sunshine hours records from your nearest met station (airports are good) and sunshine hours forecasts for that location from a forecast agency (might have to pay).

Forgot to say that the forecast generation figures given to us before PV install are a little away from reality as we generate noticeably more. Not sure if that inaccuracy applies to all industry data but the figures our installers used were wrong for our locality

The Metoffice keeps all kinds of data, from historical data from weather stations that have run for a long time as well as more recent data on -amongst others- sunshine hours:
https://www.metoffice.gov.uk/research/climate/maps-and-data/uk-temperature-rainfall-and-sunshine-time-series

I think that the variation in solar PV production compared to PVGIS really depends on where you are in the country. My data is surprisingly consistent: annual averages vary only a few %, the biggest excursions over the last 8 years all fall within 10% of the total. Monthly averages correlate really well with the Metoffice data/maps:
https://www.metoffice.gov.uk/research/climate/maps-and-data/uk-actual-and-anomaly-maps

Posted By: philedgeWith our Solaredge PV inverter connected via wifi to the Solaredge web portal, generation was logged every 15 mins but I stopped using it a while ago so cant verify that for you.

I cant remeber if the portal allows you to download data

It does.

Despite myself I'm in the habit of checking mine daily and there's a csv download option that changes granularity depending if you are looking on a Day/Week/Month/Year basis.

OK, now I understand that you want a specific forecast not a generic prediction.

I do something very very crude to bias use of my off-grid storage (I allow it to discharge it a little further if tomorrow looks like it will get recharged)...

The line from my RPi crontab is:

57 4,11,21 * * * if [ "sunny" != "`wget --retr-symlinks -q -O - https://weather-broker-cdn.api.bbci.co.uk/en/forecast/rss/3day/kt1 | awk '/<title>.*emperature/ { if(++count==2) {if($0 ~ /[Ss]unny/){printf("sunny");}exit;} } '`" ] ; then rm -f /var/run/FORECAST_PV_GEN_GOOD.flag; else touch /var/run/FORECAST_PV_GEN_GOOD.flag; fi

Basically I regard the forecast tomorrow as 'good' if I can find the word 'sunny' in the the appropriate line of the BBC forecast.

Rgds

Damon

The BBC feed seems pretty formulaic, indeed may be autogenerated, and when I've been paying attention this seems to work reasonably well, to drive a SMALL change in my maximum depth of discharge.

There hasn't been a lot of opportunity over the last couple of months to see if it's doing what I expect, but it seems OK. The forecast fell back from 'tomorrow looks good' to 'not' in the last few hours and the new value lines up with the forecast page that I normally look at.

Yes, the needing to pay thing is not hugely astonishing, because orgs such as National Grid and others (farmers, outdoor events organisers, etc) probably are prepared to...

Rgds

Damon

PS. I think that for a while when the BBC was changing forecast providers the URLs were bouncing around. Anyhow, if it works for now I'm not touching it!

Thanks, Paul. Very useful post. Yes, I agree that clear night sky will have an effect, but I suspect that with my roof being somewhat shiny aluminium, the effect will be down in the noise at least at this stage. Ditto for wind chill. At the moment I'm just trying to account for factors that are big enough that I have noticed them having an effect with my animal brain.

Yes, my plan now is to scrape the met office website*. I spent yesterday evening setting up cron jobs to capture forecasts from DataHub and the website, because I realized as you say that forecasts are transient. I'm currently taking snapshots every three hours, and will do that until I work out exactly what data I do need. I've been collecting observations from the nearest weather stations for quite a while now and should start to have my own temperature and humidity data soon.

I plan to parse the website snapshots and extract the icons and store their raw details. Then I can experiment with possible weightings to get a number - my initial thought is +1 for a Sunny Intervals and +2 for a Sunny Day from the hourly forecasts of the next day's weather, but I'll have to see how well those factors work out in practice.

And then at some point I'll use it to control the heating, but I suspect that will have to be next winter now, since we're coming towards the end of the heating season.

* I might have another go at the Met Office to publish the data. It seems to me that both Damon and myself want the data to experiment to reduce our energy usage to help save energy and the planet. The data, or rather proxies for it in the shape of the sunny icons, is already published in a human-readable form, so it seems reasonable to me that they should also publish it in machine readable format, which would also make experiments more repeatable and comparable.

Is this is close to what you are after - although it goes regional at best:

https://carbon-intensity.github.io/api-definitions/#get-generation-from-to

Posted By: djhThanks for the ideas, chaps, but I'm looking for much more fine-grained data than that.



And the much easier question:
How much solar radiation was there each day last year where I live?

As I say, I can estimate an answer to the second question from my solar generation records, but how to answer the first question? And ideally compare it with historical data from the same source.

Quite a lot of personal weather stations record solar Radiation if thats any help. Try Wundermap for a local station

@djh did you see this post on OEM

https://community.openenergymonitor.org/t/ev-charging-solar-demand-shaper-agile/13159/13

Pulling forecast off Darksky.

Posted By: djhBut darksky doesn't have an irradiation forecast, or even 'sunniness'.

There is the "UV index and cloud cover". There is a fair correlation it seems between the 2. How accurate do you want it?