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Solar Probability


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After a question from @joe90, and some comments and data from @JohnMo about solar energy, I made a bit of a sweeping statement and a simple model that showed half the time it is dark, and then is roughly halves for each increase in power.

Now that was a very simple model and was in now way meant to be used for prediction.

As I wanted to know what was happening, I have spent a few hours today getting some data from WeatherUnderground stations, on in a place called Hillockhead near Inverness and another load from Redruth, Cornwall.

The data covers the whole of 2022.  The solar gauges on these weather stations are generally horizontally mounted, so do not produce the same readings that say a south facing solar module would.  To do that, so jiggery pokery with geometry has to be done.


What is interesting to me, is that even though Inverness is in the far north, and Redruth is in the far south, how similar the solar distributions are, the mean power per square metre readings are different.  Over the year, Hillockhead has a daylight men of 145 W.m-2, Redruth 178 W.m-2.


Here is a chart showing the full year.




December, while different, shows the same similar pattern.




As does June




The hours of daylight are, to my surprise, very similar, just a bit time shifted (about an hour).

I am surprised just how similar the data traces are considering the geographic locations, about 7.6° of latitude.


If I get time, I shall try and create a more accurate model of the power distribution, then see how it fits to other locations in the country.

I could also try and do another short term prediction model Ed Davies and myself tried a few years back but got nowhere, but I have a few more ideas on it now.

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Hillockhead is not far from me, on the north coast of the Moray Firth.  It's one of the weather stations I use when checking if it's good sailing weather.


Contrary to popular belief but sun does shine up here.  The reality is the main difference in the weather up hers vs down there, is here it is colder and windier.  

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The air force moved up here for good reason. Very little or no fog, very dry (rain shadow caused by rain already falling in the Cairngorms) and longer summer days, although we have quite a bit shorter days during the winter, so suppose it balances out over the year.


Think all the above make up, for being a lot further north.

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