Panel angles + insolation

fclauson

As I have a low pitched roof (25 deg) I have been looking at if its worth putting some of my panels at 90 deg to capture more of the winter sun - the answer is its not

I thought the attached graph might be of interest - what is shows is that there is very little benefit of putting panels at 90deg

Comments welcome on any of the above

the legend on the chart is "number of panels @ angle" format

quentingargan

Interesting to see this. In general, the chart used in training is the one attached, which gives a misleading impression that 30 degrees is the optimum. However, this is because it gives total solar gain over the year, but that may mean far to much from May to July, and not enough at all in April and August.

But this chart would always suggest for example that it is better to mount panels on a west facing roof with 30 degree pitch, than to mount them vertically on a south facing wall.

T-Sol computer simulation gives you month by month similar to what you have shown, and allows us to have some estimation of how much energy you get and when.

Looking at December, it seems that the 90 degree gives roughly 11, while 25 degrees gives about 6.

However, 90 degrees is never the optimal angle, even in mid-winter. If you experiment at 60 degrees, you may get better figures.

If I had a choice of angles though, I would try to optimise the system around Spring and Autumn production. In winter, unless it is a passive house, the heating will provide relatively low cost hot water, and in summer you'll have too much anyhow. It is by otpimising spring and autumn that you can get the most out of the system.

By the way, tube systems that rely on a heat pipe can't be placed vertical. They need an angle of between 15 and 75 degrees usually. That rules out most tubes, whereas in winter, it is probably tubes you need to use to make anything of the small amount of heat available.

quentingargan

Oops. Attachment got lost. Trying again...

fclauson

Quentin

Attached is the spread excel sheet for insoloation I have been using to do my calcs - the "various angles" tab is the one to play around with - yellow fields can be changed to update the calculations

What seems strange is 12 panels pointing due south @say 25 degrees roof angle produce the same as 6 pointing south east and 6 pointing south west

I would have thought that the latter would have given you more as you get a but more early in the morning and a bit more late at night

May be the spread sheet is wrong

Spread sheet contains macros - please reaname on save to be of type ".XLSM" - it has been virus checked - but you use at your own risk - no warrenty implied or given :mad:

quentingargan

Thats interesting and I'll play with it a bit more. However, the spreadsheet summary table seems to give the same result - something wrong there.

However, working on pitch, by putting the panels at about 60 degrees, you get about 30% more yield in spring and autumn than having them at 30 degrees. Assuming you want maximum yield year round for a passive house, and can't use more than a certain amount in the summer, that would seem to make sense.

fclauson

Here is a new version - there was an error in the one of the formulae

The graphs now show more realistic data

remember you have to rename this to be a ".xlsm" prior to opening

again - virus check - but no warrenty implied or given