Solar panels BC/roof structural survey - online options?

[ptd006]

I am planning to install solar panels on my house roof. I have a standard fink truss roof with 100mm x 35mm top chord/rafters and 70mm x 35mm posts. It's a ~8.4m span and they are 60cm apart. It's a mid-1980s build and looks in good condition. Currently I have 50kg/sq. m concrete interlocking tiles (similar to Redland Renown). It'd be 8 (4x2) 18.7kg panels at ~11.1kg/sq. m, i.e. ~22% additional dead load. About the only quirk is the pitch is relatively shallow (around 25 deg to horizontal).

This seems such a run-of-the-mill situation there's no need for a surveyor to actually visit. Has anyone used or can recommend a trust worthy surveyor I can engage online?

Thanks!

 

[^woody^]

I've seen hundreds of roofs with solar panels, traditional and trussed. None have required any internal works.

However if you are dead set on instructing someone, or need to by the installers, then its a structural engineer you need not a surveyor

 

[ptd006]

Thanks, noted!

I think it's fine too but this would be for a DIY install* so I want to take all precautions.

*At the moment for me it doesn't make financial sense to pay the MCS premium for a small array for self consumption. Many people are enthuastic about 10-15 year payback but i don't get it as that's lousy compared to many other investments. Also, looking online it's not like all MCS approved installers do an amazing job (although nearly all would be better than me, of course )

 

[^woody^]

Don't forget to allow for the weight of about 70 pigeons and various nests and their mess

 

[ptd006]

I'll get netting as pigeons have been a problem for neighbour (who has solar panels on same terraced house development as me- installed a long time ago with no support and no problems..).

 

[garyo]

*At the moment for me it doesn't make financial sense to pay the MCS premium for a small array for self consumption. Many people are enthuastic about 10-15 year payback but i don't get it as that's lousy compared to many other investments. Also, looking online it's not like all MCS approved installers do an amazing job (although nearly all would be better than me, of course )

I'm considering a similar non grid tie diy install. I'm currently thinking of dumping it all in to the hot water cylinder and the ensuite UFH circuits. I think I can get a two year payback using ex solar farm panels, depending on how future proof I go on the inverters. A decent return, as you say, particularly with the way energy costs are going (my hot water is oil fired)

What setup are you planning?

 

[ptd006]

Hey,
Sounds good! If you're only going for hot water why not get thermal panels? [Edit: the plumbing is more hassle than wiring?] I looked at the ex solar farm panels and while they would be cheaper I'm going for new panels:
(a) I can only fit 8 panels (max 1.06m x 1.78m). Actually I could increase the size slightly but I don't want to go too near my neighbours roof (I've got an end terrace) or get too near the edge due to wind noise and because I'm scared of falling off Also, being lazy, restricting to a single renusol 4.4m fixing rail would avoid any splicing. In any case, getting close to 3kW (or above) on my roof basically means using newer more efficient panels. All the ex farm panels I saw were older, max 275W.
(b) New panels have a warranty.
(c) New black panels look wayy better than scratched silver framed panels

Basically even doing it myself there's a lot of fixed costs, e.g. I still need to hire scaffolding and spend a couple of days on the roof. Electrical work is fixed (same 4mm2 DC, isolators, inverter AC side and NICEIC electrician to do final connections for Part P). BTW I think strictly speaking Part P applies to off grid systems too. Anyway, I don't think it's worth scrimping on panels. I think ex farm 250W panels are around £50? Well, you can get new black 330W panels for as low as £110. Most new panels I saw quoted 0.6% linear loss per year. So 5 year old "250W" panels could easily only be 240Wp. In £ per W adjusted terms that's only £330 extra for the warranty and smarter looking panels. Overall let's say max 15% extra. It's worth it for me. If you have more space or can get the ex farm panels cheaper I can see they make sense.

Inverter- I'm looking at the Sofar 2700TL-G3. It's definitely not the cheapest (around £400). I wouldn't mind grabbing a cheap 2nd hand inverter, as it's easy to replace. I already have a 2nd hand Sofar ME3000P battery storage inverter that has been fine.

My CU is in an integrated garage. It's a short and easy run for the DC cables directly down to the garage where I'll put the inverter. There's an old wire for a defunct burglar alarm I can (hopefully) use to pull the new cable through.

Scale mock-up (based on 340w 1m * 1.68m panels and renusol fastenings):

So far no structural engineer I've emailed has given a quote. I'll update here if they do.

 

[ptd006]

2 year paypack would be great btw! I reckon more like 8 years for me (but potentially much shorter depending on electricity prices- at the moment I have Octopus Go Faster but it's not clear how long that deal will survive..)

 

[^woody^]

So far no structural engineer I've emailed has given a quote. I'll update here if they do.

Your better off asking a truss manufacturer who can tell you for free, or seeing if there is a label somewhere on those trusses that shows the load capacity

 

[ptd006]

Your better off asking a truss manufacturer who can tell you for free, or seeing if there is a label somewhere on those trusses that shows the load capacity

Thanks for the suggestion, good idea- I'll take a look for label tomorrow.

This is partly about having "something" to show insurer, building control, future buyers (if I sell the house) etc that the matter has been properly assessed. If there's a clear label or indication that 0.785kN/m^2 (standard trussed roof design load according to the MCS doc) then it's fine. If there's any doubt though I'll probably keep chasing an engineer.

I have a hunch some MCS installers just whack panels up thinking "it'll be fine... at least till I get paid". The LABC guidance suggest 15% additional dead load as being the threshold at which a competent person to assess. Combinations like Redland Renown at 50kg/m^2 with 11.5kg/m^2 of panels (i.e. +23%) is surely very common. Yet, I don't see a lot of MCS installers claiming to part of a CPS for assessing it and also there aren't a lot of structural engineers who specifically advertise it. Anyway sorry for the tangent!

 

[ptd006]

I couldn't find a label- only for the timber itself ("EDANE M75 BS 4978 S2").

With more Googling I found a copy of the 1984 BS 6399, which should have been in force when my house was built. It already has the 0.75kN/m^2 imposed load specified for 10-30 degree roofs. The snow load here (also West Mids ) is 0.47 kN/m2. So, I think the panels are really no problem. Perhaps no structural engineers are responding because of that.

However I did notice some of the felt could do with replacing :/

 

[garyo]

Sounds good! If you're only going for hot water why not get thermal panels? [Edit: the plumbing is more hassle than wiring?] I

Yes exactly. Plus I've read that the tipping point had been reached where PV is now so cheap that even though solar thermal will capture more energy it ends up being more expensive. Also our upstairs UFH is electric, so it fits in that respect.

It sounds like you're ahead of me in terms of your thinking. We have a chalet bungalow so a pretty low roof that I built myself and can access off my scaff tower. I'm pretty happy monkeying around on it. I think I'm aiming for around 2kw, south facing.

I'd not considered doing a grid tie non-mcs/fit install. That's interesting. I wonder if I could be organised enough to run the washing machine etc at the right time of the day. Having the setup linked to the whole house has obvious benefits.

 

[garyo]

Well, you can get new black 330W panels for as low as £110. Most new panels I saw quoted 0.6% linear loss per year. So

Could you share a link? I see these at around £200, versus the £50 ex farm

 

[ptd006]

Could you share a link? I see these at around £200, versus the £50 ex farm

Here are 325w black JA for £114: https://www.triplesolar.co.uk/ja-solar-325w-mono-percium-half-cell-all-black.html

Ulica for £108 incl. VAT: https://www.triplesolar.co.uk/ulica-325w-mono-120-cell-solar-panel-all-black.html


I have definitely seen better deals recently from midsummer wholesale etc.

Delivery is the killer on smaller orders so the best deal will depend on who is local to you (if you can collect, I mean!)

Edit: the JA panel is slightly cheaper on https://www.tradesparky.com/solarsp...els/ja-solar-jam60s17-325-mr-mono-panel-black

 

[ptd006]

Self built house is impressive!

I guess grid tie would minimise hassle. Not sure how much cheaper standalone inverters are really.

I wonder if I could be organised enough to run the washing machine etc at the right time of the day

I am sorted on this at least- I recently shelled out on a Samsung smart things washer