Which of these roofs for solar?

Martyn1981

Hiya Brimble. Can I ask, looking at the side roof, what is the distance between the bottom of those windows, and the bottom of the roof? I'm wondering if you could have a row of panels below, rather than above the three windows?

I think the other two roofs look great ..... from my perspective, which is one of shading and Solaredge systems. An added benefit of a Solaredge system is that you can easily have more than two different aspects, such as using all 3 roofs, but running through a single inverter.

That chimney shade on the garage roof is a great example, it could have a significant impact on that whole roof's generation, by shading one or two panels at a time, but with Solaredge the impact will only be on the shaded panels(s).

Regarding shading in the winter, things change a bit. You no longer need to worry about shading before east and after west, since there won't be any generation anyway, with the sun rising in the SE and setting in the SW (ish). So that gen is lost regardless. But you will be impacted by shading from trees and structures more as the sun will be much lower, and no longer able to 'see over' obstructions. Once you get PV, you really appreciate just how low the sun is in Dec and Jan.

If you are limited, say by the DNO, on how many panels you can install, then you could omit areas that are shaded a lot, as you asked, but might just be better to get the panels on the roof, with shade mitigation (Solaredge or other) and maximise annual gen. Also remember that with 3 roofs, of different orientation, pitch and shading, they won't all be peaking at the same time of day/year, which will reduce any capping if you have to go down that route.

[Edited - loads of gromatical orrers.]

Brimble

@Martyn1981 that's incredibly helpful, thanks for your continued input, it really is appreciated.

Aha it seems great minds think alike - I had the same idea yesterday about putting panels beneath the windows, but the distance from the metal panel beneath the window to the bottom of the roof is only 130cm, so once you consider advised clearance at both ends, it probably wouldn't be sufficient space (?). In any case, that low I suspect they would get too much shade from trees immediately opposite, certainly in the winter anyway.

I know this might be costly in terms of losing several months, but I'm tempted to hold fire until December and see how the sun and shading changes then - that might well determine whether or not I decide to use the garage roof.

With regard to optimisers, are you aware of any data explaining the benefit vs the cost? I mean obviously they improve production, but at what cost? For example if they only improved production by a few percent, but added 10% to the install cost, then in my position (i.e. trying to get financial benefit from each component added) that wouldn't be sensible...

Martyn1981

Morning Brimble. First off, I think you'd be able to fit panels landscape on the side roof. The panels can butt up close to the windows, without any issues. The roof fixings and rails will be set further in again. For the bottom edge of panels, the consideration, is to avoid rain overshooting the gutter, so leaving 200mm should be enough. So the crucial issue there will be shading.

I'm kinda with you on the wait and see side. It's a such a shame that the boom in PV interest, naturally ties in with high inflation and transport costs, plus the peak pricing that installers are now charging (understandably). No idea when things will calm down, and higher prices now will be offset by higher savings, for a while, but if you have reasonable concerns, such as monitoring shading through the 3 PV seasons (summer, winter and spring/autumn) then observing and learning a bit more is a good compromise.

Regarding the benefits of shade mitigation? Well that's a how long is a piece of string question. It could be a lot of shading on a very basic PV system, that has huge impacts, all the way to minimal shading on a well set up system, with strings of panels designed to reduce the impact, and panels with bypass diodes, and even split panels (almost like two panels in one), all helping to reduce the impact of shading.

But at a very (very) loose guess, I'd suggest 5% to 15% improvement for moderate shading, especially given the extremely high efficiency of Solaredge systems at nearly 99%. Though tbf most inverter efficiencies are getting higher. There is also the benefit of each panel being able to work at its best (since a batch may have varying outputs), rather than a string operating at the lowest panel level (the highest common denominator). But, I don't think panels will vary much these days, to be fair.

I think the photos of your garage roof are a great example for shade mitigation like Solaredge. For a simple/basic/normal PV system, that chimney shadow, even in the summer, will be an absolute pig! But with mitigation it'll be a good roof, so long as you accept that it will always generate less than an unshaded roof.

ispookie666

I'd wait for DNO confirmation for export limitation.  Even if they refuse G99, you could go for a G100 export limitation.  This does not mean your generation is limited to 3.68. 
I'd probably get the maximum number of solar panels installed (finances permitting), especially with split roofs as you get a much flatter generation. 
String inverters are not ideal for split roofs and roofs with significant shading.  I'm the very few  members who have an enphase system 

Brimble

@Martyn1981 thanks for the further advice. Yes, it seems as though waiting a few months to gain knowledge and understanding will probably be my plan, even if it means missing out on the solution for a few more months. I would have gone ahead now if it were simply a single PV array, inverter and battery, but now we are talking 2 or 3 different roofs, shading impacts, and therefore optimisers of some kind, I feel I'm a bit exposed again knowledge-wise, so have a lot of reading and research to do. In the mean time, of course in the next 3-4 months I will see with my own eyes the real impact of the changing sun position...

@ispookie666 - I did send a general enquiry to DNO, explaining what I wanted to do, my postcode, potential size of my PV system etc, but they replied on Friday afternoon to say that they can't advise even on high-level principles until I have the details, and need to fill in a formal application for that - so that's a bit disappointing, but hey ho. If and when it all happens, G100 is likely to be fine for me - on my Excel models, once I've taken account of my live usage, my battery storage, and my iBoost (or similar) diverter, I'd be exporting very little to the grid anyway, so their limit would not constrain me in any meaningful way. I'll read up on your Enphase systems when I'm researching optimisers...

Solarchaser

Personally I'd fill the main roof and the garage roof, I definitely wouldn't be going for premium panels as the output graphs most folk show don't show premium output.

You have a good amount of space so I'd fill it with 300-350w panels which will likely be the standard these days.
With solar panels it seems to be buy cheap, save money.

Due to the shading I'd agree about solaredge, but would if it was me go for the tigo variant and only put it on the ones that will be shaded meaning you have a larger choice of cheaper inverters.

With the two aspects you will have a house that benefits in the morning to mid afternoon and a garage that benefits afternoon to evening.

Brimble

Solarchaser said:

You have a good amount of space so I'd fill it with 300-350w panels which will likely be the standard these days.
With solar panels it seems to be buy cheap, save money.

Thanks - more food for thought! Quick question though - any reason you say 300-350w rather than 380-450w, many of which appear to be readily available these days. Are they not as good value, or is it the likely dimensions that would put you off them?

Screwdriva

Solarchaser's approach is the way to go if you're on a budget. Personally, I find Hyundai or Sharp 400W panels to be an excellent value and would never put a 'cheap' inverter in my home. 

Solarchaser

As screwdriva says, it's about money.
If you are paying big money for premium panels or medium money for smaller panels, id go with the medium money.

The reason? You have alot of roof space, so you don't need premium panels. 
If you had small rooves that you could only fit 10 panels on id say pay the premium, but you have good space for plenty of panels, so no need to pay extra.

For me personally I've worked in a few different industries including TV and video, and see what's inside the premium brands, often it's very very similar to what's in the cheaper brands.
The whole premise of you get what you pay for, doesn't stand up to scrutiny when it comes to electronics based products 9 times out of 10.