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

[Alan Ambrose]

I was thinking along the 'fill your roof with in-roof PV panels' line of thought both for aesthetics and because panels are so cheap these days.

 

For materials (excluding labour, trays, fixings, battens etc) I'm seeing ~£50/m^2 for pantiles, ~£90/m^2 for PV panels.

 

The idea would be to pretty much ignore any excess power in the middle of summer but have better availability in the shoulder seasons.

 

My roof is about 120m^2 which suggests say ~60 panels, ~24kW peak - say 4 strings @ 500V DC each. Even if we use power for cooling in the summer, I can't see us using half that amount.

 

Is this mad, smart or somewhere in between?

 

 

 

 

[-rick-]

1 minute ago, Alan Ambrose said:

For materials (excluding labour, trays, fixings, battens etc) I'm seeing ~£50/m^2 for pantiles, ~£90/m^2 for PV panels.

 

What is included? Panels themselves should be closer to £30/m^2, double that once you include the trays. Am I missing something?

 

https://www.bimblesolar.com/solar/solar-pallets/PALLET-C455

 

 

[Alan Ambrose]

Ah, I was looking at Viridian panels for the look, but cheaper panels makes the 'PV cheaper than tiles' argument even better?

Edited Sunday at 12:41 by Alan Ambrose

[-rick-]

I'm definitely in the camp of wanting as many panels as possible (even on the north side of a roof if the roof pitch is relatively shallow). Maximizing winter production using large numbers of panels seemed more cost effective than pretty much any other energy efficiency measure (when I last sat down and did some costing on this which is a while ago).

 

The Viridian system looks good, whether it's worth the premium though idk. Proprietary panels always a concern but if doing roof trays then you are locked into a fixed size panel whatever you do (make sure you get spares/have a guaranteed ability to replace them in case you get unlucky with a hail storm or similar). The latest Viridian panel seems pretty up to date, glass-on-glass which is good to see (as last time I looked the more proprietary systems seemed to be a few steps behind the latest panels.

[Ferdinand]

You perhaps also need to apply the revenue from export - I get 15.5p from Octopus.

Plus there is the possibility of EV charging.

My house is built to ~2010 building regs, and with 2015 FITs and Octopus (35 panels on EW orientation) I now break even, with no House Battery or EV.

Ferdinand

[Alan Ambrose]

A subsidiary question is ... what will be the most likely panel size to stick around? I see there's a bunch at 1,134mm wide but then lengths from 1,686 to 1,990. Seems to me that's important if you're doing in-roof so you can replace them if needed.

[JohnMo]

8 minutes ago, Alan Ambrose said:

what will be the most likely panel size to stick around

Don't bank on any size staying around long. Just bought some 500W panels and they were actually smaller than the datasheet, things move pretty quickly.

 

If you have space to store, buy some extra panels just in case?

[Tony L]

3 hours ago, -rick- said:

The Viridian system looks good

I thought so too then I did a bit of Googling & found this review, which has made me wary.

 

[Gus Potter]

5 hours ago, Alan Ambrose said:

Is this mad, smart or somewhere in between?

Go for somewhere in between.

 

Think maintenence and roof penetrations. 

 

Where you have eaves you need to think about roof access (and gutter damage) , something solidish to stand on. Verges, keep away from them as any disruption here can cause the roof to leak. 

 

Think about what service penetrations you might want in the roof.

 

This could be a soil vent stack, any fan vents and so on. Keep a good margin around thec penetration flashings. If using tiles then think about the tile width so you don't end up with a funny width of tile.. the detailing is going to be hard and it gets harder when you have fewer tiles between the panles and the verges as there is less room for adjustment on the width as you lay them. 

 

Be careful folks as if you have not thought through the detailing and maintenence cost (risk of breaking things when you go on the roof)  then it will come back to bite you. Remember that your house will not go up perfectly plumb as it will get built to a tolerance.

Edited Sunday at 18:04 by Gus Potter

[Mike]

9 hours ago, Alan Ambrose said:

'PV cheaper than tiles'

I like the idea, but there was a recent warning over here in France against integrating panels into roofs due to a number of fires., Risk listed included lack of regular checks, faulty electrical connections, and the accumulation of material underneath the panels. The advice was to stick to mounting them on rails so that the tiles act as fire protection.

 

There's a photo of the aftermath of one recent incident here: https://www.revolution-energetique.com/actus/feu-de-panneaux-solaires-le-toit-de-ce-college-est-presque-entierement-detruit/

 

 

[SteamyTea]

19 hours ago, Mike said:

there was a recent warning over here in France against integrating panels into roofs due to a number of fires

I think this is a rather over rated problem, it is similar to BEV fires, you hear about it because it is rare, not common.

When I was in Australia, they had some huge fires. Many warnings were about getting leaves out of gutters. Apparently that is one of the major risk raisers.

 

A properly installed system should have a very low fire risk, but there are a lot of panels globally.

China alone makes about a TW of panels a year, so over 2 billion a year. A million roof top fires would be a failure rate of 0.05% on panels.

I suspect that most problems are caused by wiring, then micro inverters, but that is after leaves.

 

Edited Monday at 17:53 by SteamyTea

[-rick-]

It's the MC4 connectors that get most of the blame. In theory its a standard but each manufacturer has variation which can lead to tolerance mismatch and poor joints. Also, the connections from the roof to the inverter usually need to be made to fit on site and bad crimps, etc, has apparently been a problem. Arc Fault detection in inverters is now mandated by some countries to try and pick up on these dodgy connections (not yet here AFAIK).

 

This has been a problem that has got a decent amount of attention from MCS, etc, so I would expect any recent install here to be fairly robust against it, but certainly an area to pay particular attention to if DIYing. For my future plans, I'd plan to see if I can put some 1-wire or similar temperature probes next to every join as an extra layer of safety. (Obviously needs monitoring).

[SteamyTea]

1 hour ago, -rick- said:

I'd plan to see if I can put some 1-wire or similar temperature probes next to every join as an extra layer of safety

Simple thermistors and an alarm should do it.

No need for a separate processor to interpret the 1Wires, that is just adding complexity in my opinion.

[Alan Ambrose]

Ah yeah, it seems DC arc faults are harder to monitor than AC ones. I guess on-roof systems usually have a nice layer of non-flammable ceramic, concrete or slate to provide a lot of protection. Maybe in-roof needs a fire-proof layer too? Thin cement board maybe?

Edited Monday at 19:09 by Alan Ambrose

[-rick-]

5 minutes ago, SteamyTea said:

Simple thermistors and an alarm should do it.

No need for a separate processor to interpret the 1Wires, that is just adding complexity in my opinion.

 

When you are talking about a whole roof, this might be a lot of separate thermisters and wires to manage, all routed to a central point to alarms. I'm pretty sure I saw a premade cable with 1 wire thermisters spaced along the wire. Thats why I mentioned it, install would be comparitively trivial. Been a while ago though so would have to do some searching to see if something like that is still available.

[-rick-]

6 minutes ago, Alan Ambrose said:

Ah yeah, it seems DC arc faults are harder to monitor than AC ones. I guess on-roof systems usually have a nice layer of non-flammable ceramic, concrete or slate to provide a lot of protection. Maybe in-roof needs a fire-proof layer too? Thin cement board maybe?

 

Some of that might already be there depending on your roof makeup, MCS does have some requirements. Saw a company advertising a fireproof blanket to install under panels and someone posted here about GSE trays waiting for fire safety tests here and I'm going to be interested to see if the result of those tests is any change to standard install instructions. (Could cause a few problems for people who have already installed but not yet got sign off).

 

[SteamyTea]

3 minutes ago, -rick- said:

When you are talking about a whole roof, this might be a lot of separate thermisters and wires to manage

Will have to ponder it, but thermistors in series may do it, one that gives an abnormal reading could trigger an alarm.

May even work in parallel.

Won't tell you which joint, but it can shut down the system for safety.

But as I pointed out earlier, probably not a real problem if fitted carefully.

 

Should be possible to fit a firebreak under the panels if a new roof.

Extra cost, but extra peace of mind.

[SteamyTea]

 Cross posts a bit.

[-rick-]

I went googling: https://www.beadedstream.com/a-guide-to-thermistor-strings/

[SteamyTea]

26 minutes ago, -rick- said:

went googling

I am too tired to look, but shall let you do so, report back if useful please.

[-rick-]

It shows the concept. Lots of companies selling similar but all very industrial/scientific so likely stupid prices. Coming up blank on aliexpress. This feels like a diversion from Alan's thread so I will park this for now. I'm a long way away from actually needing this.

[LnP]

23 hours ago, Mike said:

I like the idea, but there was a recent warning over here in France against integrating panels into roofs due to a number of fires., Risk listed included lack of regular checks, faulty electrical connections, and the accumulation of material underneath the panels. The advice was to stick to mounting them on rails so that the tiles act as fire protection.

 

There's a photo of the aftermath of one recent incident here: https://www.revolution-energetique.com/actus/feu-de-panneaux-solaires-le-toit-de-ce-college-est-presque-entierement-detruit/

 

 

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

[Dillsue]

13 hours ago, -rick- said:

It's the MC4 connectors that get most of the blame. In theory its a standard but each manufacturer has variation which can lead to tolerance mismatch and poor joints. Also, the connections from the roof to the inverter usually need to be made to fit on site and bad crimps, etc, has apparently been a problem. Arc Fault detection in inverters is now mandated by some countries to try and pick up on these dodgy connections (not yet here AFAIK).

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??

 

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!!

[LnP]

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? Are installers doing this?

[Alan Ambrose]

>>> DC isolators that account for 50% of fires

 

That's interesting and I think the guys at eFixx are suggesting that they should not be fitted - but the Foa guidance that @LnP pointed to says 'DC isolators should be available for firefghters'. Guess we're still figuring this out.

 

DON'T Install DC Isolators On Solar, Electricians Warned

 

I think sensors (thernistor strings or whatever) are an interesting approach.

 

Also, some kind of retardant membrane (fibreglass cloth comes to mind) would be helpful as ling at it doesn't interfere with whatever membranes are there.

 

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.

 

Edited yesterday at 07:58 by Alan Ambrose