Expanding a 4kW PV Only System

Screwdriva

Given the advent of Flux, I've decided to take advantage of the Barclays Green Home Reward and expand upon our 4kW LG Bifacial PV system (roof pictured below). Leaving 100cm for Velux windows at the very North of the roof, it would appear that we may have space for 4-6 additional panels on East & West aspects, making this a theoretical 5.6-6.4 kW system. I expect to retain the SolarEdge 3.68 inverter and remain on G98 for now. I face the following questions:

1) Given LG no longer supply panels, I need to match a similar looking panel for one aspect and move the 2 panels over to the opposite aspect. 
2) I need to research if the MCS Certificate needs to be updated/ or reissued and/ or DNO notified to highlight that increased generation capability

Any thoughts from the experienced are most welcome! 

ABrass

If you're increasing the inverter size you'll need to go through a variant of G99 and the MCS would need to be updated. Given its a split aspect you could just stay with the same inverter size assuming it can manage the potential peak power levels.

I'd be pleasantly surprised if the Barclays scheme would accommodate an atypical improvement like that.

Screwdriva

ABrass said:

Given its a split aspect you could just stay with the same inverter size assuming it can manage the potential peak power levels.

Should be fine as the South facing string has 6 panels on it (2 on the East/ West strings).

Waywardmike

@Screwdriva

You're in the same boat as me....  I can definitely squeeze more panels on, the question is should I?  Old FIT system so I'd like to leave it alone, but when we had them fitted we had them placed off center as we were planning a loft conversion and wasn't sure where the velux would be exactly.  Turns out nowhere near the panels leaving me with some considerable real estate for more panels. 

They're on the front of the house so I want them to match, but the likely hood of that is close to 0.  Of course the other option is to replace them with 10x 400W and then fill the rest of the roof on another inverter.  The problem with that is, they're performing spectacularly, far better than even the installer predicted so I really don't want to touch them. difficult decisions...

 

Martyn1981

Hiya. As you sticking with the same inverter/cap, then the DNO won't have a problem, but they may still need to be informed, so perhaps give them a call and just ask, to cover your back.

Good luck matching panel look, and also size, as they do seem to a vary a lot now, v's the old 1m x 1.6m that most were in the past.

Are you on FITs? If so, remember to inform your provider of the change in system size, so they can apportion payments in the future. For instance, if you go from 4kWp to 6kWp, they will pay out based on 4kWp/6kWp (2/3rds) of generation. But, I'd strongly recommend confirming this in advance, and getting it in writing (so use e-mail), to double/triple check this is how the increase will be treated.

Also worth checking the limit for the 3.68kW Solaredge inverter. Data sheet says 5,700W DC. But I don't know if that's the power it's processing (yours will be less than the panel total with multiple aspects), or the amount of kWp in panels connected?

ABrass

While you're doing it you could get a battery installed. 

Screwdriva

ABrass said:

While you're doing it you could get a battery installed. 

Good one! I will likely get one installed when we get a heat pump but that's a decade away atleast. Right now I'm trying to maximize solar export to make hay while the sun shines (literally!)

Martyn1981 said:

Are you on FITs? If so, remember to inform your provider of the change in system size, so they can apportion payments in the future. For instance, if you go from 4kWp to 6kWp, they will pay out based on 4kWp/6kWp (2/3rds) of generation. But, I'd strongly recommend confirming this in advance, and getting it in writing (so use e-mail), to double/triple check this is how the increase will be treated.

Also worth checking the limit for the 3.68kW Solaredge inverter. Data sheet says 5,700W DC. But I don't know if that's the power it's processing (yours will be less than the panel total with multiple aspects), or the amount of kWp in panels connected?

Wise words of advice. I am on Octopus Flux so a bit more straightforward in terms of SEG payment. Even with 4 additional panels, the likelihood of hitting 5.7 kW DC is very unlikely across the 3 aspects (to date it has rarely ever hit the 3.7 kW peak), especially when the shading from that chimney is factored in. That said, I will likely use this as the rationale for limiting system size to 5.6kW total.

Waywardmike said:

They're on the front of the house so I want them to match, but the likely hood of that is close to 0.  Of course the other option is to replace them with 10x 400W and then fill the rest of the roof on another inverter.  The problem with that is, they're performing spectacularly, far better than even the installer predicted so I really don't want to touch them. difficult decisions... 

Any way you could have two parallel arrangements? One via SEG and the other via FIT? Also, at initial glance, the REC all black 365W panels are a very close match.

Martyn1981

Screwdriva said:

ABrass said:

While you're doing it you could get a battery installed. 

Good one! I will likely get one installed when we get a heat pump but that's a decade away atleast. Right now I'm trying to maximize solar export to make hay while the sun shines (literally!)

Martyn1981 said:

Are you on FITs? If so, remember to inform your provider of the change in system size, so they can apportion payments in the future. For instance, if you go from 4kWp to 6kWp, they will pay out based on 4kWp/6kWp (2/3rds) of generation. But, I'd strongly recommend confirming this in advance, and getting it in writing (so use e-mail), to double/triple check this is how the increase will be treated.

Also worth checking the limit for the 3.68kW Solaredge inverter. Data sheet says 5,700W DC. But I don't know if that's the power it's processing (yours will be less than the panel total with multiple aspects), or the amount of kWp in panels connected?

Wise words of advice. I am on Octopus Flux so a bit more straightforward in terms of SEG payment. Even with 4 additional panels, the likelihood of hitting 5.7 kW DC is very unlikely across the 3 aspects (to date it has rarely ever hit the 3.7 kW peak). That said, I will likely use this as the rationale for limiting system size to 5.6kW total.

Waywardmike said:

They're on the front of the house so I want them to match, but the likely hood of that is close to 0.  Of course the other option is to replace them with 10x 400W and then fill the rest of the roof on another inverter.  The problem with that is, they're performing spectacularly, far better than even the installer predicted so I really don't want to touch them. difficult decisions... 

Any way you could have two parallel arrangements? One via SEG and the other via FIT? Also, at initial glance, the REC all black 365W panels are a very close match.

My bold - yes you can .... but (big BUT) I think they'd need to be separate systems. For instance my E and W systems are both on FiT's, but one is early and sub 4kWp, and the second is a later FiT and 4-10kWp (as the 2kWp system took the household total over 4kWp). But they are completely separate systems, they don't share an inverter nor TGM.

Whilst I'm on deemed export, I'd also assume that the FiT part (not the generation subsidy, just the export) would have to move from deemed export to SEG, otherwise, you'd be getting double paid on metered export, as some of that would be 'deemed'. Hope that makes sense, but I'm guessing here, so assume the simpler option of all SEG would be the best choice?



Edit - Silly thought, but thinking about that capacity limit for the inverter, you could swap in a larger model with a higher capacity, but still have it capped at 3.68kW for DNO reasons (or ask if you can go higher). The 4kW model will take 6,200W for example.

Obviously that involves greater costs though.

Waywardmike

Screwdriva said:

Any way you could have two parallel arrangements? One via SEG and the other via FIT? Also, at initial glance, the REC all black 365W panels are a very close match.

I just checked the spec sheet...  they are 1.5cm wider (probably not noticeable), but 4.6cm longer which almost certainly would be noticeable.  might be worth scouring the net for a panel that most closely matches (and is all black).

As for them being on separate systems, that would be the plan, and further to @Martyn1981, I currently have a spreadsheet running to see if I would be better off moving to metered export rather than deemed.  As I now have a battery, consumption of our own generation is currently running at ~88% for this year, the answer was always going to be no I believed, but with the current export prices that may be different.  For all our sakes though I hope energy prices plummet back to what they used to be.

Screwdriva

Martyn1981 said:

Edit - Silly thought, but thinking about that capacity limit for the inverter, you could swap in a larger model with a higher capacity, but still have it capped at 3.68kW for DNO reasons (or ask if you can go higher). The 4kW model will take 6,200W for example.

Obviously that involves greater costs though.

Not silly at all. The inverter has 22 years of remaining warranty attached to it. The pragmatic goal was to stay as close to the £1K that Barclays is expected to reimburse us (4 panels X 4 SolarEdge Optimizers = £1200 + installation). 

EricMears

Waywardmike said:

Screwdriva said:

 at initial glance, the REC all black 365W panels are a very close match.

I just checked the spec sheet...  they are 1.5cm wider (probably not noticeable), but 4.6cm longer which almost certainly would be noticeable.  might be worth scouring the net for a panel that most closely matches (and is all black).

Can you actually see your panels from your own property ?  I can only see ours from a point well outside our boundaries (or by standing on a stepladder).

Do you really care if other people lie awake all night worrying about their view of your roof ?