Mostly DiY Installation - options?

[Carrerahill]

On 31/12/2022 at 17:10, JamesPa said:

I am intending to install 4 panels in 2 arrays, one array of two panels on a flat roof, and one array of two panels at the apex of the pitched roof (of my 2 storey house).  This will add to my existing capacity, but as a totally separate system to preserve the FIT payments on the existing.  The DNO is happy with the proposed total 5.5kW peak (based on microinverters  - probably the best bet anyway as the array on the flat roof is subject to differential shading, so effectively there are 3 'strings' from a shading standpoint).  

 

With only 4 panels to install, the economics of a fully 'professional' job aren't great, and I'm anyway happy to do most of the work myself.   Im also installing an ASHP, so it makes sense to get an electrician to make the final connections into the CU for both and certify (actually, I cant see a reason why they cant share a connection - but that's a question for later).  It would be easy enough to find someone to do this alone at a sane price.

 

However I don't have the head for heights to climb on the pitched roof, and also export payment terms intervene.  I'm on octopus outgoing agile, and its a condition that the installation is MCS certified, which of course my existing installation is.  So in the ideal world I would find someone to do the work on the pitched roof (is this a task for a roofer or electrician?), make the connection to the CU for the new panels/ASHP, and MCS certify the new installation after I have done all the 'grunt work' other than high up on the pitched roof.  

 

Does anyone have any experience of a division of labour of this kind.  General electricians are used to 'first fix/second fix' and many are happy just to do second fix (its the high value and interesting bit after all).  However I get the impression that most of the (fairly few) MCS contractors locally are pretty much wedded to the idea of doing the whole job and charging an exorbitant amount for the privilege.  

 

Any suggestions here of how to avoid being totally ripped off?

Why don't you just add them, the meter will register more generation you get higher payments. 4 panels won't raise in eyebrows.

 

I had the roofer fit the rails and panels, he connected them up as per my instruction and left me two DC tails which I dealt with from there. 

 

I also have an array on the garage and shed. I fully DIYed them. 

 

My advice: Just get on with it.

Edited January 5, 2023 by Carrerahill

[billt]

On 01/01/2023 at 20:45, JamesPa said:

There are some periods where the peak input exceeds 4.2kW but neither the voltage nor the current will be outside the limits, so I wonder if the inverter will care?   Im guessing perhaps not, it may just operate slightly sub optimum.  I wonder how to find out - perhaps ask SMA..

 

SMA have a design tool which you can use for 'what if' scenarios. It will also tell you if the panels exceed the capacity of the inverter.

 

https://www.sunnydesignweb.com/sdweb/#/

 

You have to create an account to use it.

[Ronski]

I've managed to find the info with regards to not requiring MCS certification to get paid for exports - see this post here

[JamesPa]

1 hour ago, Ronski said:

I've managed to find the info with regards to not requiring MCS certification to get paid for exports - see this post here

Thank you, I will definitely investigate

[Dillsue]

20 hours ago, Ronski said:

PS I don't think it's a good idea mixing different panels with different ratings on the same string, even with optimisers.

But that's exactly what optimisers are designed to deal with. There's no difference in varying panel outputs from a mix of shaded and unshaded panels compared to a mix of panel sizes/outputs. We have 310 and 320w panels on one string and 335 and 405w panels on a second string.

 

Being able to use differing size panels is an often overlooked feature of optimisers that allow a system to be very easily expanded over time without having to source panels to match originals that may have been obsolete for years. Like the OP our original FIT system uses 250w panels and I doubt Id be able to easily find 250w panels if I wanted to expand that system. Fortunately that system uses optimisers so I can add pretty much whatever panels I want up to the inverters DC input limit😁

[Dillsue]

20 hours ago, Carrerahill said:

Why don't you just add them, the meter will register more generation you get higher payments. 4 panels won't raise in eyebrows.

Adding 1.5kw to a 4 kw system is around a 40% hike in generation. Factor in the new panels will almost certainly be more efficient that the old 250w panels and that's a blatantly obvious hike in generation. I'm not sure if FIT payers monitor that sort of thing but it would be very easy to do. Youd almost certainly get your FIT payments suspended and possibly loose them entirely for not notifying the system extension.

 

I'm not sure how the FIT scheme is funded but likely we all contribute through eleccy bills/tax, so taking payments youre not entitled to is money out of everyone else's pockets!!

[Carrerahill]

37 minutes ago, Dillsue said:

Adding 1.5kw to a 4 kw system is around a 40% hike in generation. Factor in the new panels will almost certainly be more efficient that the old 250w panels and that's a blatantly obvious hike in generation. I'm not sure if FIT payers monitor that sort of thing but it would be very easy to do. You'd almost certainly get your FIT payments suspended and possibly loose them entirely for not notifying the system extension.

 

I'm not sure how the FIT scheme is funded but likely we all contribute through electricity bills/tax, so taking payments you're not entitled to is money out of everyone else's pockets!!

You get very excited about PV matters!

 

Maybe on paper - in real life? Lets be realistic.

 

Even if there was a noticeable 20% (750W) hike in generation, it could quite easily be attributed to the removal of a immersion heater or other electricity hungry appliance - if you think someone is going to notice a theoretical 40% increase where the overall numbers are less than 10kW then you are giving the system far far more credit than it is due. 

 

3 ways he can do it: Firstly - adds it to his system and everyone stops getting so very excited, or second, he just adds the system to his house for self consumption and any that gets exported is his loss, thirdly he calls them up and asks them what will happen if he renews his panels with more efficient ones, if they accept, he declares his new peak generation capacity (I would go this route rather than trying to tell them I am adding a new system as it's more clear-cut).

 

The OP's annual export figures would be worth reviewing first. 

 

 

 

  

 

 

[eandg]

I've been priced £5,050 for supply and install of a 4.92kW array system (with spark having to do a wee bit of work to enable it). Looking on Midsummer Wholesale I can get the panels alone for about £2.4k. I don't have the expertise to find a supplier for all the other bits - invertors and the like - but does anyone with it know roughly how much extra the ancillary bits are likely to be and I could work out the cost differences in splitting supply and labour? Thanks. 

[Carrerahill]

22 minutes ago, eandg said:

I've been priced £5,050 for supply and install of a 4.92kW array system (with spark having to do a wee bit of work to enable it). Looking on Midsummer Wholesale I can get the panels alone for about £2.4k. I don't have the expertise to find a supplier for all the other bits - invertors and the like - but does anyone with it know roughly how much extra the ancillary bits are likely to be and I could work out the cost differences in splitting supply and labour? Thanks. 

Use the sunshine solar system builder.

 

I would allow about £500-1000 for the inverter (depending on functions you want), £50 for cabling, £50 for the 2 isolators. Not sure how many panels you are talking but say £300 for rails and mounting - that is about you. 

 

Break the system into easy components.

 

Roof rails, PV panels, DC cables, DC isolator, invertor, AC isolator, generation meter if you want then consumer unit connection.

 

Plenty of companies sell the rails, rails, splice kit, mounting brackets and roof mounting brackets. To work out the rail requirement you just need to know the panel size (usually width) for mounting requirements.

 

For the inverter its fairly simple, size it to your array, a few technical details to consider but its pretty easy.

 

If you are going for a 4.92kW system then I would size the inverter about 4.5kW - you may struggle to get one bang on so I would see if I could go up in power density to a panels that gave me about 5.5kW then use a 5kW inverter.

 

If you can get the roof bit done, get a friendly, imaginative spark in to do the rest - they do exist, I know of about 5.

 

 

Edited January 6, 2023 by Carrerahill

[eandg]

35 minutes ago, Carrerahill said:

Use the sunshine solar system builder.

 

I would allow about £500-1000 for the inverter (depending on functions you want), £50 for cabling, £50 for the 2 isolators. Not sure how many panels you are talking but say £300 for rails and mounting - that is about you. 

 

Break the system into easy components.

 

Roof rails, PV panels, DC cables, DC isolator, invertor, AC isolator, generation meter if you want then consumer unit connection.

 

Plenty of companies sell the rails, rails, splice kit, mounting brackets and roof mounting brackets. To work out the rail requirement you just need to know the panel size (usually width) for mounting requirements.

 

For the inverter its fairly simple, size it to your array, a few technical details to consider but its pretty easy.

 

If you are going for a 4.92kW system then I would size the inverter about 4.5kW - you may struggle to get one bang on so I would see if I could go up in power density to a panels that gave me about 5.5kW then use a 5kW inverter.

 

If you can get the roof bit done, get a friendly, imaginative spark in to do the rest - they do exist, I know of about 5.

 

 

Thanks - I'll look into it. 

[Dillsue]

1 hour ago, Carrerahill said:

You get very excited about PV matters!

 

Maybe on paper - in real life? Lets be realistic.

 

Even if there was a noticeable 20% (750W) hike in generation, it could quite easily be attributed to the removal of a immersion heater or other electricity hungry appliance - if you think someone is going to notice a theoretical 40% increase where the overall numbers are less than 10kW then you are giving the system far far more credit than it is due. 

Why would adding 40% more generation capacity, in the same location, only give a theoretical 40% increase in generation? OP is putting 2 panels on a pitched roof and 2 on a flat roof which may or may not be angled but I dont think that gonna cost him a loss of half his additional generation which youre suggesting at quoting 20%.

 

In terms of 'getting excited" I like people to see the bigger picture, which includes the risks in doing certain things, like breaching the FIT rules, as you suggested. We had our FIT payments suspended a few years ago due wholly to an admin error by our FIT payer, Scottish Power. Despite extensive dialogue with them the payments only got reinstated after 6 months following a formal complaint to OFGEM. If youd breached the rules and had payments suspended I could see that taking a very long time to sort out, based on my experience.

[Ronski]

4 hours ago, Carrerahill said:

Even if there was a noticeable 20% (750W) hike in generation, it could quite easily be attributed to the removal of a immersion heater or other electricity hungry appliance

No it couldn't, as the loads are after the generation meter, so make absolutely no difference to what the generation meter records.

 

 

 

[Ronski]

6 hours ago, Dillsue said:

But that's exactly what optimisers are designed to deal with. There's no difference in varying panel outputs from a mix of shaded and unshaded panels compared to a mix of panel sizes/outputs. We have 310 and 320w panels on one string and 335 and 405w panels on a second string.

 

Being able to use differing size panels is an often overlooked feature of optimisers that allow a system to be very easily expanded over time without having to source panels to match originals that may have been obsolete for years. Like the OP our original FIT system uses 250w panels and I doubt Id be able to easily find 250w panels if I wanted to expand that system. Fortunately that system uses optimisers so I can add pretty much whatever panels I want up to the inverters DC input limit😁

 

Whilst it does appear you can do it, there is a 25% rule, so you do need to choose panels carefully.

 

https://support.tigoenergy.com/hc/en-us/articles/203419277-Mix-and-Match-Different-PV-Module-Types#:~:text=Tigo optimizers enable system designers,(polycrystalline vs mono-crystalline)

 

 

[Dillsue]

26 minutes ago, Ronski said:

 

Whilst it does appear you can do it, there is a 25% rule, so you do need to choose panels carefully.

 

https://support.tigoenergy.com/hc/en-us/articles/203419277-Mix-and-Match-Different-PV-Module-Types#:~:text=Tigo optimizers enable system designers,(polycrystalline vs mono-crystalline)

 

 

Interesting stuff. I'd have thought that there would be more than 25% difference between identical shaded and unshaded panels so not sure how Tigo deal with that??

 

Solaredge dont seem to have the same restriction as you can have 250w and 500w optimisers in the same string. Probably not relevant to the OP unless he's gonna migrate the lot to SE

[JamesPa]

55 minutes ago, Ronski said:

 

Whilst it does appear you can do it, there is a 25% rule, so you do need to choose panels carefully.

 

https://support.tigoenergy.com/hc/en-us/articles/203419277-Mix-and-Match-Different-PV-Module-Types#:~:text=Tigo optimizers enable system designers,(polycrystalline vs mono-crystalline)

 

 

That messes things up.  My current panels, Sanyo HIT 250, have a current rating of 7.2A.  Modern 400W panels appear to be typically 11-12A, the increased power comes from increased current rather than increased voltage.

 

I haven't yet had a response from SMA solar as to whether my existing inverter can tolerate a situation where the available input power exceeds the spec, but neither the voltage nor current does.  if this comes out in the negative, Id be looking at fitting separate (micro) inverters anyway.  I had hoped that it would come out in the positive and I could just tack the new panels onto the existing inverter as suggested by Dillsue, using optimisers to match them.  But it seems Tigos might not do the job.

Edited January 6, 2023 by JamesPa

[Carrerahill]

On 06/01/2023 at 15:49, Ronski said:

No it couldn't, as the loads are after the generation meter, so make absolutely no difference to what the generation meter records.

 

 

 

Agreed - my mistake, I do forget I have an unorthodox setup (I am not using it for payments of any sort, just global export monitoring).

[Carrerahill]

On 06/01/2023 at 13:04, Dillsue said:

Why would adding 40% more generation capacity, in the same location, only give a theoretical 40% increase in generation?

He mentions flats roofs, different pitches, on separate inverters. 

 

I accept that of the existing overall it’s still a 40% increase, however, in practise this is only a 750W increase in generation. 

[Dillsue]

1 hour ago, Carrerahill said:

He mentions flats roofs, different pitches, on separate inverters. 

 

I accept that of the existing overall it’s still a 40% increase, however, in practise this is only a 750W increase in generation. 

I genuinely don't understand why you think theres going to be a 50% loss in generation for the new 1.5kwp of panels.

 

Inverter losses are a few % so having a second inverter is going to have negligible impact.

 

Putting half of the new panels on a flat roof will have an impact but not much. Running 1.5kwp of panels through PVGIS gives annual generation of 1376kwh at 35 degrees and 1251kwh at 10 degrees inclination, so a loss of under 10%. OP only has 2 out of 4 panels on a flat roof so under 5% loss.

 

How much shading there is on the OPs 2 flat roof panels we dont know, but we have 3 out of 16 of our panels shaded til lunchtime and our array still generates significantly more than the MCS forecast year on year so the shading cant be too detrimental.