Fill your roof with in-roof PV panels instead of pantiles?

[Alan Ambrose]

>>> Are installers doing this?

 

No, think it'll be me as I want it done right.

[-rick-]

10 hours ago, LnP said:

Guidance here https://www.thefpa.co.uk/advice-and-guidance/free-documents?q=RE3 - Rooftop Mounted PV Solar Systems

 

I've come across this guidance talked about many times, but every time I look at it I can't help walk away thinking its not really aimed at domestic properties. It's all about installing big commercial systems.

 

1 hour ago, Dillsue said:

The FPA report that LnP posted says its DC isolators that account for 50% of fires. These are generally easily accessible as they're not on the roof so we'll worth a night time check that connections are tight??

 

Yes, when I said MC4 connectors it was because that is the most likely thing to fail *on the roof*. Isolators are usually elsewhere, but not really supposed to be installed on modern domestic systems any more (the inverter should come with a built in isolator and that is sufficient).

 

1 hour ago, Dillsue said:

I have limited experience of PV Installs but a used inverter I bought a few years ago came with some cut off cables terminated in MC4 connectors. With a bit of a tug the cable pulled out of one of them and when I dismantled it you could see it had been crimped with pliers rather than the correct crimping tool. If you're getting an install done double check that your Installer has the correct tools!!

 

And knows how to use it!

[Dillsue]

1 hour ago, Alan Ambrose said:

 Gus's maintenance point is a good one, but I guess if a panel fails in the middle of a big array, it's always going to be hard to sort out.

With a scaffold tower up, removing a panel or 2 below a failed panel is only 10-15mins work. I wouldn't worry about accessing an array 3 or 4 rows deep as the bulk of the time in replacing a panel is getting to site and getting access.

[-rick-]

1 hour ago, LnP said:

Getting back to the OP question about economics of tiles vs panels, according to the guidance I posted, you should include the cost of a fire resistant covering:

 

Ensure roofing materials are non-combustible* OR if installation on a combustible or partly-combustible roof is unavoidable, then apply a fire resistant covering.
* Class A1/A2 s1, d0 to BS EN 13501-1

 

In practice what would be the best way to achieve this? Fibre cement sarking boards?

 

Fibre cement is one way, I've seen a fire blanket on advertised. A layer of mineral wool would be a good option and provide insulation as well, though mineral wool formulated be used above rafters is pricey and has other complications. I wouldn't be shocked if mineral wool between rafters is enough.

 

All the above relevant to in-roof systems. On-roof systems is easier. Metal roof or tiled roof covers you. If you have a single-ply roof may need to take extra steps.

 

Quote

Are installers doing this?

 

That's my question too. I've seen a lot of talk about it but not found any hard and fast rules. Obviously GSE trays are fairly commonly used without the extra steps above but I get the impression things have changed fairly recently and I'm not sure where things currently stand.

[-rick-]

4 minutes ago, Dillsue said:

With a scaffold tower up, removing a panel or 2 below a failed panel is only 10-15mins work. I wouldn't worry about accessing an array 3 or 4 rows deep as the bulk of the time in replacing a panel is getting to site and getting access.

 

True for most systems. Some of the integrated systems might be more tricky. So something to pay attention to.

[Dillsue]

3 minutes ago, -rick- said:

 

True for most systems. Some of the integrated systems might be more tricky. So something to pay attention to.

With an in roof system a couple of roof ladders either side of a failed panel gets you access. I don't think access for panel/optimiser/micro inverter replacement should be a particular worry.

[-rick-]

1 minute ago, Dillsue said:

With an in roof system a couple of roof ladders either side of a failed panel gets you access. I don't think access for panel/optimiser/micro inverter replacement should be a particular worry.

 

It was more that I thought I've seen that some of these systems overlap/interlock the panels. Saw something showing panels being riveted in place (didn't look hard enough to see whether the panel was still removable with rivets in place but if not looked like a bit of a job to remove).

[Dillsue]

22 minutes ago, -rick- said:

Yes, when I said MC4 connectors it was because that is the most likely thing to fail *on the roof*. Isolators are usually elsewhere, but not really supposed to be installed on modern domestic systems any more (the inverter should come with a built in isolator and that is sufficient).

When you look at the report roof top faults only attributed to around 25% of the fires they looked at. They only looked at 46 fires and there's tens of thousands of systems installed in the UK.  Whilst there is a risk, if you ensure a quality install the risks seem very low to me and certainly low enough to focus on quality of design/install rather than spending £££s on supplementary fire protection.

[JohnMo]

34 minutes ago, -rick- said:

Isolators are usually elsewhere, but not really supposed to be installed on modern domestic systems any more (the inverter should come with a built in isolator and that is sufficient).

Sorry have never bought in to that. The inverter DC isolator is fine for working on the PV array. But not fine to allow replacement of the inverter. You really need to be able to positively isolate the array, and AC sides to safely remove the inverter. I have 3 arrays and each has a dedicated DC isolator for the array as well as a DC isolator in the Inverter.

[-rick-]

The point of the isolator is to break the circuit. Once the circuit is broken the MC4 connector should be relatively safe to handle. Otherwise, installing solar would be a much riskier job. An isolator on a broken inverter can still break the circuit and once broken it should be safe to remove/replace and the new inverter will be installed with the isolator in the off position, ensuring no current flows during install.

[JohnMo]

10 minutes ago, -rick- said:

MC4 connector should

The word should is what makes people nervous, "should" and "is" are very different. Plus all the talk about fires starting from the MC4, it's more likely a "should" than "is", for safety. I prefer to be on the safe side and know when I come to pull the inverter, it can be completed without live high voltage DC kicking about.

[-rick-]

26 minutes ago, Dillsue said:

Whilst there is a risk, if you ensure a quality install the risks seem very low to me and certainly low enough to focus on quality of design/install rather than spending £££s on supplementary fire protection.

 

I agree, though my main concern is not really the fire risk itself, it's concern that insurers or mortgage providers will turn round at some point in the future and say that the roof represents a big risk now and therefore either bump the price or refuse to engage. Obviously this would be a wider problem affecting a wide variety of installs. But living in a flat I'm currently unable to sell due to cladding issues (which as far as the surveys go was installed in a fully compliant manner at the time of install) makes me especially touchy on this subject.

[-rick-]

31 minutes ago, JohnMo said:

The word should is what makes people nervous, "should" and "is" are very different. Plus all the talk about fires starting from the MC4, it's more likely a "should" than "is", for safety. I prefer to be on the safe side and know when I come to pull the inverter, it can be completed without live high voltage DC kicking about.

 

Definitely a trade off, but the data shows that isolators are the most common cause of fire (at some random point years after install) so that seems like the bigger risk to manage vs the need to take suitable precautions handling connectors in the once every 10-15 year activity of changing an inverter.

Edited 13 hours ago by -rick-
typo

[Beelbeebub]

My inverter has a big rotary dc isolator set built in - you turn that and the panels are disconnected therefore no load, then the mc4 connectors into the inverter can be removed with no issue (arcing) even though they are still at high voltage. 

 

I can't see how an external isolator helps there except that there will be zero voltage. 

 

 

Ultimately at some point with solar, unless you work at night or cover the panels completely you will have to work with live HV.  The MC4's are crimped onto live wires at some point (yes, doing as much work on the disconnected system as possible is best practice, but you can't avoid some work on live bits) 

[Nickfromwales]

You have to grab hold of both the negative and the positive of the same string of the DC feed to get zapped btw.

 

But if you do get zapped then there's no coming back from that, as it will be a one-time pass to Jesus-land.

 

Fitting the aux rotary isolator will always be my default, but it is also handy for changing cable disciplines; from strings off the roof into SWA for eg, where the DC needs to travel some distance internally to get to the plant room / inverter location. We have these in attic / eave spaces on most installs.

 

In the real world, this is a very isolated risk we are discussing here, and you pay less attention to the tumble drier which is more likely (statistically) to burst into flames sporadically.

[Dillsue]

1 minute ago, Nickfromwales said:

In the real world, this is a very isolated risk we are discussing here, and you pay less attention to the tumble drier which is more likely (statistically) to burst into flames sporadically.

Exactly......no point in scaremongering over what is a negligible risk

[Crofter]

Going back to the original question- why should I pay £50/m² for tiles when bare PV is only £30- has got me thinking. 

If you didn't want to use trays and therefore be locked in to a system, could you batten over e.g. EPDM and just not bother with the trays?

 

The only roof I've built comprised OSB sarking, non tented membrane, battens and counter-battens, then steel sheeting.

 

For a shed etc I'd have zero hesitation in doing the same idea but using panels instead of the steel sheeting. Some thought needs to be given to waterproofing the joints between panels but there are various ways of dealing with that.

 

For a house I'd want to have something more robust than simply breather membrane, hence the idea of using EPDM.

 

Thoughts?

[-rick-]

11 minutes ago, Crofter said:

Going back to the original question- why should I pay £50/m² for tiles when bare PV is only £30- has got me thinking. 

If you didn't want to use trays and therefore be locked in to a system, could you batten over e.g. EPDM and just not bother with the trays?

 

This is similar to the idea I had when I first started thinking about it. I'm pretty sure it would work. Wouldn't meet MCS standards though (they require you to use an approved mounting system - and recently removed the ability to deviate with SE signoff). If you used MCS approved mounting and there weren't issues with fire (as discussed above) then should be fine.

 

My most recent plan is do as you propose but with cheap metal roofing instead of EDPM with closed cell foam + sealant between the panels on the frame to stop the bulk of water (doesn't have to be 100% as the metal roofing is a barrier) and then metal trim (likely backed by OSB for strength) around the edges and joined to the mounting system to present a continuous roof without it technically being an integrated one. Ventilation at ridge and gutter line under the panels with mesh to stop nasties setting up home underneath the panels.

 

Edited 10 hours ago by -rick-

[Crofter]

15 minutes ago, -rick- said:

 

This is similar to the idea I had when I first started thinking about it. I'm pretty sure it would work. Wouldn't meet MCS standards though (they require you to use an approved mounting system - and recently removed the ability to deviate with SE signoff). If you used MCS approved mounting and there weren't issues with fire (as discussed above) then should be fine.

 

My most recent plan is do as you propose but with cheap metal roofing instead of EDPM with closed cell foam + sealant between the panels on the frame to stop the bulk of water (doesn't have to be 100% as the metal roofing is a barrier) and then metal trim (likely backed by OSB for strength) around the edges and joined to the mounting system to present a continuous roof without it technically being an integrated one. Ventilation at ridge and gutter line under the panels with mesh to stop nasties setting up home underneath the panels.

 

I don't know what current prices are like but when I built my roof in 2017 it was about £7/m² for corrugated steel 

 That was the higher spec 0.7mm with plastic coating rather than paint.

0.5mm galv finish is obviously the cheapest option. 

 

I've got some experience of waterproofing between panels. I built an array on my boat and had the panels mounted on a tubular steel frame, which left about 50mm between each panel. I used twin wall polycarbonate sheeting cut in to thin strips, with a larger flange on the upper side, and simply held in to place with CT1. It lasted a couple of years including an Atlantic crossing and be when I came to dismantle it I could barely get the strips off. I think the UV exposure would eventually weaken the polycarbonate.

If you're butting the panels up against each other, you've got it much easier. I would probably use a T-profile aluminium strip bonded on. Or use butyl tape.

I'm not sure how much thermal expansion you'd need to allow for but I presume that information is readily available.

[Beelbeebub]

2 hours ago, -rick- said:

 

This is similar to the idea I had when I first started thinking about it. I'm pretty sure it would work. Wouldn't meet MCS standards though (they require you to use an approved mounting system - and recently removed the ability to deviate with SE signoff). If you used MCS approved mounting and there weren't issues with fire (as discussed above) then should be fine.

 

My most recent plan is do as you propose but with cheap metal roofing instead of EDPM with closed cell foam + sealant between the panels on the frame to stop the bulk of water (doesn't have to be 100% as the metal roofing is a barrier) and then metal trim (likely backed by OSB for strength) around the edges and joined to the mounting system to present a continuous roof without it technically being an integrated one. Ventilation at ridge and gutter line under the panels with mesh to stop nasties setting up home underneath the panels.

 

I wanted to do the same (make a roof out of the panels for cost. 

 

I went round the houses so to speak) with things like GSE trays and even rubber stripes between the panels. 

 

In the end I used trapizodal metal roofing (think industrial unit) as the waterproof layer. 

 

It seemed the easiest way to ensure watertightness. It's light (less than 25kg including panels and mounting rails), robust, easy to work on (no cracking or knocking tiles) and pretty long lasting. Industrial metal roofs easily last 25 years, often 30 or 40 (lots of units built in the 80's are still knocking about). The primary aging mechanism seems to be UV damage to the Pvc coating (don't get the painted finish) and that will be helped by the UV shading the roof. 

 

I didn't put a roof membrane under (because it's a carport) but you could easily.

 

Then there are a number of systems that use self drilling and tapping screws (the same as used to mount the metal panels to the purlins) to mount little sections of aluminum rail or you could use full length sections (just costs a bit more). The panels then just mount as normal. The total standoff from the top of the trapizodal roof profile is about 50mm to the top of the panels.

 

Of course it depends a bit on your roof design (complex hips and valleys or curves etc are harder) and overall aesthetic (work well on a modern building, not so much on a stone cottage in thr cotswolds)

 

[Stu789]

On fire safety GSE panel MCS certification includes Fire Classification BROOF(t4) part of BS EN 13501-5 - useful explanation here but TLDR is:

• B_ROOF(t4)
  • No penetration of roof system within 60 minutes
  • In preliminary test, after withdrawal of the test flame, specimens burn for less than 5 minutes
  • In preliminary test, flame spread less than 0.38 m across region of burning

and 

BROOF(t4)

Unrestricted; can be used anywhere on the roof

 

Back to filling the whole roof with PV panels... does anyone have experience of doing this with GSE half frame system on a sloped roof?

GSE install instructions & configurator show 170mm flashing/finishing to each side + 160/150 bottom and top but then elsewhere show the detailing for straight to the gutter - a bit of a contrast to the architect glossy cover photo!

 

 

[Alan Ambrose]

@Beelbeebub - that looks very neat, how are the panels mounted to the metal roofing there?

[Beelbeebub]

32 minutes ago, Alan Ambrose said:

@Beelbeebub - that looks very neat, how are the panels mounted to the metal roofing there?

Thank you.

 

I used a mini rail system. I can't remember the exact make, but I'm very similar to this

 

https://midsummerwholesale.co.uk/buy/k2-pitched/k2-mutlirail-10-with-screws

 

Fastensol and Renusol do similar.

 

Basically short bits of rail with an epdm pad underneath.  These get screwed to the top flat bit of the roof profile allowing the standard mounts to clip in. Effectively you are using the sheet metal profile as the rail itself. It was very easy to put up, especially as the sheet metal roofing was easy to walk on.

 

I made (3d printed) some end caps to give the exposed rail ends a nice finish. I could stick some skirting round to neaten stuff up but I don't think I will have any bird/pest issues and it does allow for better ventilation.

 

Visually being able to line up with the edges makes a difference.  There was a fair bit of discussion about this as the guidelines talk of 400mm margins and the like but nobody could really find out exactly why. The best explanation was wind lift, so we took extra care to make sure everything was well fastened down and there was a good load path to the heavy foundations. 

Edited 6 hours ago by Beelbeebub

[Mike]

2 hours ago, Beelbeebub said:

There was a fair bit of discussion about this as the guidelines talk of 400mm margins and the like but nobody could really find out exactly why. The best explanation was wind lift

It's part of the Microgeneration Installation Standard (my emphasis):

 

5.8.7   Solar PV modules should not be mounted within 400mm from any edge of a domestic roof unless specific measures are taken to:
    • Resist the increased wind uplift forces in the edge zone through additional fixings and, where necessary, additional roof timbers for those fixings
    • Ensure ridge-tiles remain secure
    • Ensure rainwater run-off patterns are not affected
    • Ensure build-up and shedding of snow cannot cause injury or property damage

    • Reduce nuisance from wind noise

 

https://mcscertified.com/wp-content/uploads/2021/10/MIS-3002_Solar-PV-Systems-V4.0.pdf