Solar PV cheaper than roof tiles?

[Nickfromwales]

4 hours ago, Dillsue said:

So it's not a case of "you're not allowed" to install optimisers in the roof space, it's only an MCS requirement/guideline not to.

Yes, IF you want it to be MCS etc (as far as I know). 

 

I'm not 'in the industry' enough to know if these little blighters ever go 🔥, but I assume MCS had stipulated this for 1 or more 'good reasons'.

 

This advice was of 2019, but it had actually changed at the time or I asked and it was found out afterwards /whatever, so worth noting at the very least I guess? My 2 cents is to fit them where they can be accessed btw, but MCS (apparently) says otherwise.

[Tony L]

On 28/01/2025 at 07:24, Alan Ambrose said:

I have seen one supplier that does a 100% panel roof - no tiles at all. Looks great. But … does this not generally fall foul of the general installer guidelines? That is, are you expecting to have ‘tiles around the edges’?

 

On 28/01/2025 at 08:32, G and J said:

I saw an ad for them.  Looked fab, PV one side, almost matching standing seem roof the other.  However, I looked at the gloss of the marketing, thought fondly of our budget and the fact that we want slates, and I didn’t save the details.  I categorised it as something for someone else’s grand design.

 

Here's one that fits this description.  There are probably others.  When I have time, I'll investigate further.  I think the same company sells the matching edge panels too, & gutters, fascias, soffits, ridge pieces, flashings for roof lights & dormers.  So you can get your whole roof done, with integrated PV, by one installer.

 

[G and J]

6 hours ago, Nick Laslett said:

I bought my solar panels, GSE in roof trays and associated components from https://midsummerwholesale.co.uk

 

They have a web based tool called EasyPV that will tell you exactly all the components you need. Although I fitted my panels myself, I had already discussed with my electrician getting the MCS paperwork from him. 
 

I went with Enphase micro inverters. They may be a little more expensive, but they have many benefits, and are considerably safer, because each panel is electrically separate, whereas a string inverter all the panels are live, so there is a lot more volts. Remember a solar panel is essentially live as soon as it is receiving sunlight. 

Brilliant, thank you Nick.  I think you may have mentioned that when I visited but I failed to retain - sorry!

[sgt_woulds]

The reason that MCS guidelines do not advise Micro inverters in the loft is that they run hot, very hot.  Surface temperature over 60 degrees...

 

After a couple of years of experience installing various micros, we advised people with hard-to-access roofs to bring the inverters into the roof space.  This was a PITTA and reduced the efficiency somewhat, (low voltage DC running through longer cables creates losses) but gave a significant practical advantage.  

 

Hopefully things have changed now, but in those days Enphase Micros had a failure rate of 2 per 16 installed (average number of panels per install) within 3 years.  Remember that the manufacturer will only provide replacement inverters if they fail, they won't pay for scaffold and labour to replace.  If you have a bungalow, then by all means fit them on the roof.  Otherwise consider access for replacement.  

 

We mounted them on Unistrut in free air and a cage was built around them to prevent accidental touch with large warning signs.  We also paid attention to the ventilation in the loft or eaves and added additional vents if required.  Cable management becomes is onerous, and you need to consider the larger roof penetration and protection of the cables, (so many installers just slip the DC cables under a tile with no mechanical protection). 

 

Remember, MCS like building regs are guidelines, not absolutes.  If you can demonstrate that an alternative approach is just as safe, and especially where it has additional benefits, (ease of access, possible cooler running due to more free space around the inverter) then an MCS installer can certify it.  

 

With full roof arrays you'd need to justify other things anyway;  the panels will be closer to the roof edges which requires uplift calculations and additional fixings/amelioration.

 

One advantage of using PV panels instead of tiles is that the finished roof tends to be lighter, which allows more panels on a truss frame roof, especially if re-roofing one built between 1995 & 2005.  I've seen so many roofs with more panels than they should have - how many Solar installers run structural assessments of the roofs before install?

 

For a long while, (after MCS funding suddenly disappeared overnight due to ministerial idiocy) fixing other installer's mistakes kept our company afloat when all of the goldrush boys were going out of business...  Happy days 

[Dillsue]

3 hours ago, sgt_woulds said:

The reason that MCS guidelines do not advise Micro inverters in the loft is that they run hot, very hot.  Surface temperature over 60 degrees...

 

 

 

 

Not sure that applies to optimisers?? Certainly our Solaredge units run cool.

 

Is the MCS guidance in respect of micro inverters and optimisers or just inverters??

 

[LnP]

On 28/01/2025 at 20:07, Nickfromwales said:

When I contested it on another downstream project, because I like the idea of possible points of failure going where I can get at, I got a firm FO. Apparently MCS guidelines said (then?) that they now need to be with the panel with the factory leads from the optimiser attached directly, un-bastardized, vs connected via the 'extension leads' I had the fitters make up to set these in the attic plant space.

 

If I ask someone to MCS a solar PV install for me, I have to bow to their terms, so the next one had the optimisers under the panels. The fail sate with them is negligible anyhoo, so it's not like these things are dropping out 1 a year etc. 

 

 

The guidance I previously linked to says this (emphasis added):

 

5.7.4 Mixing of PV DC connectors from different manufacturers should be avoided, and all panel connections should use the connector(s) recommended by the panel manufacturer. System operators should hold spare PV DC connectors compatible with the PV installation for future maintenance, to avoid the potential use of incorrect PV DC connectors. Internationally documented PV fire loss data identifies faults with DC connectors and DC isolators as primary causes of fire. Therefore, it is essential to use the correct PV DC connector, assembled according to the manufacturer’s guidelines, with the correct length and thickness of exposed DC cable, the correct crimping tool for the connector pins, and the correct torquing of the connector cable glands. IEC 62548:2016 and IEC 60364-7-712:2017 explicitly do not allow the connection of DC connectors from different manufacturers.

 

So the concern could be demonstrating that you connectors and extension leads are up to the job.

Edited 1 hour ago by LnP

[Nickfromwales]

Thanks for that, great bit of supporting info and clarifies things for sure  

 

I guess that was the hoo-ha over that back then, more about the multiples of (unnecessary) additional MC4 connectors then being inside the dwelling vs the optimisers themselves. 👍

 

Good point about the rotary isolators too, but most of these we put in the attic spaces immediately off the roof (usually some type of plant or equipment ends up in there also) and the plant rooms. I ALWAYS fit a (multi-sensor) smoke detector in any space that's got any type of equipment / plant etc in it, so that's as good / safe as it can be I guess.