Which of these roofs for solar? 25 August 2022 at 11:42AM edited 25 August 2022 at 2:48PM in Green & ethical MoneySaving 19 replies 625 views

Brimble

I thought I'd got my solar plan all sorted, including detailed analysis of usage and potential production, but then having taken photos of various roofs over the course of a few days, I'm now rethinking based on shadowing caused by other parts of the roof / house...   Please can someone tell me what they think of these 3 possibilities (of which I could go ahead with all, some of none - though options 2 and 3 without at least some of 1 probably wouldn't make sense):


1. 'MAIN' ROOF

https://www.dropbox.com/sh/989a5zupq3srvqy/AADmtnt96TP4hrM0NgKYzrLsa?dl=0

I did originally think I'd put 12-14 panels on this SSE-facing roof, but I'm concerned by the shading from the roof 90 degrees to this one. In the pics you can see the following:
 - 1pm: Both surfaces totally unshaded (though I'm only proposing to use the one on the right side of the picture).
 - 2pm: Other bit of roof on left totally shaded - no problem, I'm not intending to use that
 - 2.30pm: Shading just starting to creep onto my preferred roof
 - 3pm: Creeping a bit more
 - 3.30pm: ...and a bit more
 - 4.30pm: Half my preferred roof is now shaded
 - 5pm: Maybe 75% now shaded

How big a problem would this be? Should I just have panels on the bit that remains unshaded until about 4pm? That would be about 6/7 panels I think. Or should I go ahead with panels on all of that surface, so maybe 12-14 panels, knowing that 75% will be shaded by 5pm? (How will that change in the winter - will it be comparatively worse or better)?


2. GARAGE ROOF

https://www.dropbox.com/sh/s1s3qpzr031geb0/AACi0p5sjttzL3KlptBO8PHaa?dl=0

This SSW-facing roof is on a garage, so considerably lower down. Nevertheless, it gets sun from about 9am this time of year - however I'm concerned about the impact of the shade coming from the chimney of my house:

 - 1pm: You can just see the chimeny shade starting to come across from bottom left.

 - 2pm: Chimney is shading the middle bottom bit of roof.

 - 3pm: Now shading bottom right.

Shortly after that it's gone, and the roof remains unshaded until about 6.30pm, after which it's lower position means the sun is quickly obscured by trees.

Roof space is about 570cm x 210cm. If I go with this roof, I reckon I can fit 5 panels in portrait orientation if they are right size (say max 185 x 105, of which plenty exist, for example Qcells 390w are 184 x 103cm).

3. 'SIDE' ROOF

https://www.dropbox.com/sh/s5ktvila2vcyqcs/AAAPxuPkgXXQLIcFqaCYQwk_a?dl=0

This WSW-facing roof is a bit frustrating as it sees sun from about 9.30am this time of year right through to well gone 7pm, so would be a great compliment for 'Roof 1' above, BUT as you can see in the pic, space for panels is minimal. Originally I hoped to be able to have line of them 'landscape' orientation right along the top (there are 3 more windows like that in a line), so maybe 8 panels, but the space between the top of each window and the top of the roof is only about 90cm or something like that, so a panel won't fit even in landscape orientation. The horizontal distance between the edge of the window gutter and the edge of the roof is about 130cm, and the roof 'diagonal height' is about 560cm, so I could probably have 3 panels in portrait orientation down the edge - would it be worthwhile doing that? Is such a small array - only 3 panels (albeit potentially 450w each) - ever going to be financially viable? Can several small different-sized arrays use the same inverter, or would a separate inverter be needed for each? 

Happy to answer any questions that might help further. Thanks as always to anyone willing and able to assist.

Magnitio

Main Roof - You will get good results for the majority of the day, with output dipping in the evening due to shading, but output would be lower at that time of day even without shading.

Garage Roof - this will be more of an issue when the sun is lower in the sky (October to March), but may not be an issue at all in June. Will it be completely in the shade of the house in Winter?

Side Roof - I wouldn't bother from an aesthetic point of view.

Screwdriva

My thoughts are similar in that I would mount as many panels as possible on the main roof. I would also mount a minimum of 5 panels on the Side Roof to take advantage of that highly profitable 4pm onwards solar generation. 

I'd ignore the garage roof for several reasons. I also wouldn't worry about shading too much with an optimizer setup.

Brimble

So with the main roof, are you both saying stack it as full as possible, and completely ignore shading, or leave the left corner free so as to at least avoid the very worst shading? (Perhaps the former but with 'optimisers' to ensure no deterioration in production of the 'best' bit - in which case I'll need to learn about, and cost, 'optimisers'... are they straightforward or will I need lots of research on them too?)

With the 'Side' roof, @Screwdriva says to mount at least 5 panels, but I can only fit 3 - does that make it more effort / cost than the value I'll get from it? @Magnitio wisely mentions the aesthetics - I just spoke to the wife about this, as she uses that part of the garden far more than I do (it's not visible from the road, so only we would see it). She's not bothered, she said if there are 3 in a straight line down the edge, it won't look terrible. But is 3 worth doing?

As for garage, I suspect you're both right, the lower winter sun will make that less productive. On that one, think I'll wait a few months and take some pictures of the shading through the winter, can always add panels there next year if I want to.

So, options are now refined to:

Main Roof - cover say 80% with panels - should get 8 x 450w that way
OR
Main Roof - cover 100% - say 12 x 450w

...and then

Side Roof - 3 panels (all I can fit) OR don't bother

Screwdriva

Brimble said:

So with the main roof, are you both saying stack it as full as possible, and completely ignore shading, or leave the left corner free so as to at least avoid the very worst shading? (Perhaps the former but with 'optimisers' to ensure no deterioration in production of the 'best' bit - in which case I'll need to learn about, and cost, 'optimisers'... are they straightforward or will I need lots of research on them too?)

With the 'Side' roof, @Screwdriva says to mount at least 5 panels, but I can only fit 3 - does that make it more effort / cost than the value I'll get from it? @Magnitio wisely mentions the aesthetics - I just spoke to the wife about this, as she uses that part of the garden far more than I do (it's not visible from the road, so only we would see it). She's not bothered, she said if there are 3 in a straight line down the edge, it won't look terrible. But is 3 worth doing?

Optimizers are required to install a SolarEdge inverter (which I recommend). In your installation, they'd be a must have because of the shading. 

If you believe you can only fit 3 panels on the West roof aspect, then go ahead. As many as the installer says you can is what I would suggest. 

Which panels have you shortlisted? 

Brimble

Screwdriva said:

Brimble said:

So with the main roof, are you both saying stack it as full as possible, and completely ignore shading, or leave the left corner free so as to at least avoid the very worst shading? (Perhaps the former but with 'optimisers' to ensure no deterioration in production of the 'best' bit - in which case I'll need to learn about, and cost, 'optimisers'... are they straightforward or will I need lots of research on them too?)

With the 'Side' roof, @Screwdriva says to mount at least 5 panels, but I can only fit 3 - does that make it more effort / cost than the value I'll get from it? @Magnitio wisely mentions the aesthetics - I just spoke to the wife about this, as she uses that part of the garden far more than I do (it's not visible from the road, so only we would see it). She's not bothered, she said if there are 3 in a straight line down the edge, it won't look terrible. But is 3 worth doing?

Optimizers are required to install a SolarEdge inverter (which I recommend). In your installation, they'd be a must have because of the shading. 

If you believe you can only fit 3 panels on the West roof aspect, then go ahead. As many as the installer says you can is what I would suggest. 

Which panels have you shortlisted? 

Great, thanks - I'll research SolarEdge inverter & optimiser at the weekend.

Nor sure about panels yet, however the simple dimensions of my available spaces might well need to be a driver for that. Knowing next to nothing about panels, I was looking yesterday at JA 450w, as these are 172 x 113cm, a bit more 'square' than many others, and with the dimensions of both the main roof and the side roof, that shape works better.

To explain that in case you're interested:

Main roof 'height' (well, diagonal height, you know what I mean hopefully) is about 570cm. With those JA panels being 172cm 'long', I could fit 3 in 570cm, and still have 54cm left for clearance. If I went for more rectangular panels - say 212 x 105cm, I wouldn't be able to fit 3 that way. I know you might argue that I might find a different 'pattern' that works with that other size, but it doesn't work out as well.

Similarly on the side roof, the distance down the side is about 590cm - so again I can fit 3 x 172, plus some clearance, but not 3 x 212.

I appreciate you're probably going to say to me that dimensions are definitely not the best way to choose panels, but if it means a). it allows me to squeeze 1 or 2 more panels on, and b). the brand isn't a complete no-go, then would that not be the best solution?

Screwdriva

Brimble said:

I appreciate you're probably going to say to me that dimensions are definitely not the best way to choose panels, but if it means a). it allows me to squeeze 1 or 2 more panels on, and b). the brand isn't a complete no-go, then would that not be the best solution?

I had a feeling you were going down that route I would focus on quality and their dimensions. 

If you want the best panels money can buy, you have two options: Sunpower Maxeon or Solarwatt
If you want great panels that are excellent value for money: Sharp/ Hyundai 400W all black.

Have a look at each manufacturer's models and hone in on a panel that's right for you (dimensionally, specifications & aesthetically). I would avoid Chinese manufacturers for a multitude of reasons. 

Brimble

Screwdriva said:

If you want the best panels money can buy, you have two options: Sunpower Maxeon or Solarwatt
If you want great panels that are excellent value for money: Sharp/ Hyundai 400W all black.

Have a look at each manufacturer's models and hone in on a panel that's right for you (dimensionally, specifications & aesthetically). I would avoid Chinese manufacturers for a multitude of reasons. 

I'm primarily doing this for financial reasons tbh, so I definitely want the best value for money (not 'false economy, buy cheap buy twice" value, but genuine value). That said, how on earth does joe public like me know which panels are any higher or lower quality than others? I can check dimensions and aesthetics, but I wouldn't have a clue where to start with specifications...

Then one other question remains - on my main roof, should I stack it as full as possible (presumably with optimisers) knowing that some of it will be fully shaded by 4pm in the summer, or should I only put panels on the 'best' (say) 70%? When you consider the cost of the panels and the lost production etc, which option would be ultimately optimal?

Screwdriva

Brimble said:

Then one other question remains - on my main roof, should I stack it as full as possible (presumably with optimisers) knowing that some of it will be fully shaded by 4pm in the summer or....

Yes. With optimizers. Your West facing roof will handle the post 4pm generation. Your Main roof will do the heavy lifting till then.

Brimble

Screwdriva said:

Yes. With optimizers. Your West facing roof will handle the post 4pm generation. Your Main roof will do the heavy lifting till then.

And with optimisers, do you only put them on the panels that are impacted by shade, or do you have to put them on all panels on that array, even if well away from shade? (Just trying to do it in the most cost-effective way).

2nd_time_buyer

Brimble said:

Screwdriva said:

Yes. With optimizers. Your West facing roof will handle the post 4pm generation. Your Main roof will do the heavy lifting till then.

And with optimisers, do you only put them on the panels that are impacted by shade, or do you have to put them on all panels on that array, even if well away from shade? (Just trying to do it in the most cost-effective way).

With Solaredge you need them on all panels. With Tigo you can put them on only those impacted by shade.

Both systems offer, individual panel monitoring, which presumably is more useful if you are monitoring all the panels. However, more optimisers on the roof, also means more things to go wrong. So lots to weigh up.