Calculating solar insolation

[GW@PE]

Have you ever wondered, or read about someone else's solar panel performance, and wondered how much solar energy these panels were exposed to, to make this power.  I had the desire to know how much power a 1kW solar array could produce say at latitude 50N at different times during the year.  It was unlikely I would live there to measure it.

I was able to find some seriously complicated spreadsheets that could calculate the sun angle, as well as other stuff at say, this Latitude and Longitude, on this year, on this day at this hour, minute, and second, but this is not really useful if you wanted to get a feel for how the available solar energy falling on a standard horizontal flat surface anywhere on earth changed throughout the seasons.

It would be nice to also have a visual representation in addition to a calculated value for the solar day. 

To cut to the chase, I have written a little program that runs in a Windows environment that does this. 

The program, I offer, is not a precise scientific tool, and I have made a few shortcuts to simplify the maths.  The most noticeable is, the year has 360 days, instead of 365.25. 

The about menu gives help type info on program controls.

The calculated solar energy for the approximate day number is displayed on top right of screen.  This would be for a cloud free day.  Obviously solar panel sizing, thermal specs, and orientation need to be factored to work out actual power for an array.

Gordon.

[Wolvenar]

Looks interesting

[oztules]

Good to see you here Gordon. Look forward to any projects you may be playing with.

Your program won't run under wine.... guess I'll have to fire up the windows partition.... and have a look.


................oztules

[tomw]

Your program won't run under wine.... guess I'll have to fire up the windows partition.... and have a look.


................oztules

Funny, it runs under Wine here fine on Ubuntu 11.04

Tom

[rossw]

I wrote a web-based app about 7 months ago that I will try to dust-off and finish. It's a little bit similar.

It lets you enter the alignment of your panels, your location (lat/long), and a couple of other critical variables - if your panels track the sun in 0, 1 or 2 axis, and how far it tracks (if it has limited movement).

It will then calculate the theoretical clear-sun watt-hours and lists the results month-by-month, and a yearly total.
I think I had a few more things in it, like time-of-day demand etc, but its long enough now I forget!

[oztules]

Thanks Tom.

I will try a bit harder.... not sure how, but if it runs for you then it must be able to run on Ultimate Edition.2.9

Thanks for the heads up

.............oztules

[brucedownunder]

   

   Welcome to the forum Gordon , good to hear from you again ..

  Bruce

[Watt]

Sweet, thanks very much.   

[oztules]

Gordon, nice little application.
Ross, will look forward to seeing it. The panel tilt information will be enlightening to me.

...........oztules

[GW@PE]

Thanks all for the feedback.

For those not familiar with the user interface, here is a screen shot.  <hopefully it is visible>



As the scroll bars are moved, the line drawing of the earth moves with the season, the yellow line latitude indicator moves, and the approx blue line graph indicator for incident solar changes.

I don't see any point in calculating yearly harvest, or even monthly, as there really is no way of factoring in weather data.  It is relatively easy to make allowance for fixed panel orientation and even a full 2 axis solar tracking.  My own fixed panel arrays give approx 20% more power in winter than the std pyranometer and calculated flat array power, and  10% less power in peak summer.

I use the picture display to better visualize how the seasonal earth position relative to the sun affects the day length and incident solar.  The calculated daily solar was a few extra lines of code in the loop that draws the daily incident solar graph.

I use the calculated energy harvest to check seasonal performance of my panels only.  Even with a recording pyranometer, it is useful to have a calculated number to reassure one in winter that the panels are producing expected power.  Where I live, the winter sun is a max of 2.78kWh/kW and the summer sun is 7.75kWh/kW, on a flat array.   It is relatively easy in winter to think that low yield indicates a fault, until the calculated solar is looked at.

This is a relatively small program, and to add complexity will require changes to the way the program works.  Presently for each change to the latitude, or day number, the program has to recalculate and redraw new graphs of the earth position etc, and new half hourly calculations of the incident solar, and replot it, and update the calculated integrated daily energy harvest.

Updates of the program will be available from my file server.

Gordon.