PV plan and in-frame mounting options - am I going crazy?

[SuperPav]

So looking to get some PV onto the roof as we hopefully complete the never-ending project this year.

 

I have a sloped roof (35 deg, south-ish) on the garage which is approx 4.2x3.6m of surface, and next to it a flat roof about 7.5m long, so I was planning on getting 10 panels up there, to give me around 4kw of peak theoretical generation, capped at whatever the G98 limit is.. I was planning on the following layout:

 

6 in landscape 3 rows x 2 columns on the pitched roof in in-roof frames (roof isn't slated yet)

4 in landscape along the flat roof in renusol ballast buckets (world's biggest rip-off from what I can tell given they cost as much as the panels!)

 

However, all the reasonably priced panels I can find (£80 or so for 405-410Wp) are like 1700x1130 size, and I cannot for hte life of me find any compatible landscape GSE in-frame options! Do I just need to get smaller/more expensive panels to fit with their tiny frames (1600x1000 ish). What am I doing wrong? If I can't get them in 3x2 landscape on that roof, I'll need to reduce the number of panels to 4 in line, as I can't quite get 2 in portrait to fit along the roof slope on top of one another.

 

I was also planning on going for micro-inverters as we might have some partial shading due to neighbours trees during some parts of the year, but the enphase IQ7+ ones I look at have a peak output of 295kVA - does that mean I'm losing up to 30% of the panels output by going for microinverters? if that's the case, am I not better off just getting a string inverter and taking the 30% hit on partial shading?

 

All will be DIY'd with the sparky hooking everything up, I will stick a junction box on the flat roof for everything to run into which will then run back to the garage CU.

 

 

 

 

[Dillsue]

Quick Google search says Enphase IQ8s will handle 560w panels.

 

Avoid the junction box if you can which should be doable with micro inverters.

[Alan Ambrose]

>>> run back to the garage CU.

 

I was pondering something similar on my shed. I have a similar set-up with a small garage CU which runs via ~20m of SWA back to the house CU. I see that it's on an MCB, itself on one of the two RCDs in the CU. I suspect it shouldn't be on that main CU RCD as it has its own RCDs anyway.

 

Question is (I think you may have the same question) - can you direct attach the inverter to the garage CU, or do I (you) need to run a separate SWA back to the main CU?

 

Re: having a lower inverter capacity than the peak output of the panels you have.

 

I don't think this is as much of a problem/waste as it might seem - losing a bit of the peak output isn't that big a deal as (a) by definition the peak doesn't occur very often and (b) when it does, it's almost certain to be electricity you can't use and/or have to sell off cheap to the DNO anyway.

 

[SuperPav]

My garage feed is on a 50A MCB at the moment which having just had a look is indeed on a RCD on the main CU, which is indeed unnecessary I suppose as it could be rewired just straight off the main switch. Garage is fed by 16mm cable as it was sized to be big enough to feed a heat pump, two EV chargers (+ usual garage circuits), and be big enough to reverse-feed the house if we ever upgrade the supply to 3phase - the easiest way would be to run 3 phase to the garage and then split one phase off back to the main house for the domestic loads, as all the big stuff is in the garage.

 

As I'll only ever be able to get an absolute max of approx 4kwp on the roof (to , I'd try and use as much as possible of it via immersion dumping or dumping into one of our two EV's if we ever have a surplus, just seems crazy to lose 30% of the capacity of the cells, maybe I'm overthinking it...

 

I'll be honest I also don't quite understand how they can be rated to 400W DC and only 300kVA AC - what's the point of the 400W DC rating in that case?

[Alan Ambrose]

>>> 400W DC and only 300kVA AC

 

Yeah, I see, I'm looking e.g. at this: https://enphase.com/en-gb/download/iq7-microinverter-qdcc

 

 

Maybe something to do with peak input vs. continuous output power? As @Dillsue said - maybe you just need to choose beefier microinverters?

 

[Dillsue]

If your existing inverter is a 3.6kw unit and you're thinking of adding micro inverters to the garage you'll need DNO permission. If you want to avoid DNO permission you'll need a single 3.6kw G98 inverter and wire each of the 3 arrays to its own mppt input, or use optimsers.

 

If you're going down the DNO route then it's likely cheaper to install a dual mppt inverter in the garage, where your big loads are,  and split the east and west panels over the 2 inputs. If the existing inverter has dual input then move that to the garage and get a basic 2 kw inverter for the house.

[SuperPav]

I have no existing inverter, it's a "ground up" install. Plan to stay within G98 regs using enphase microinverters via their Envoy controller to keep it at sub 3.68kW total.

Looks like I'll need to go for the IQ7A's or IQ8's to avoid clipping, the price difference vs the IQ7 doesn't seem massive to be fair.

[Dillsue]

11 hours ago, SuperPav said:

I have no existing inverter, it's a "ground up" install. Plan to stay within G98 regs using enphase microinverters via their Envoy controller to keep it at sub 3.68kW total.

Looks like I'll need to go for the IQ7A's or IQ8's to avoid clipping, the price difference vs the IQ7 doesn't seem massive to be fair.

Sorry I read another thread and replied on yours!!!! Ignore me

[Dillsue]

20 hours ago, Alan Ambrose said:

Question is (I think you may have the same question) - can you direct attach the inverter to the garage CU, or do I (you) need to run a separate SWA back to the main CU?

Connect wherever you like so long as you consider circuit protection, discrimination and voltage rise when the inverters at max production.

[Alan Ambrose]

>>> Connect wherever you like

 

 

I'm still investigating but I think it's a bit more complicated than that. I believe (a) the inverter needs a specific set-up in the CU re RCD/MCB, and (b) in a number of cases the inverter needs a current clamp on the meter tails, which implies the inverter needs to be close-ish to them.

 

So, I'm wondering whether a separate SWA for raw DC back from the outbuilding to an inverter which is positioned not a million miles from the house CU is the best option. 

 

[Dillsue]

11 hours ago, Alan Ambrose said:

>>> Connect wherever you like

 

 

I'm still investigating but I think it's a bit more complicated than that. I believe (a) the inverter needs a specific set-up in the CU re RCD/MCB, and (b) in a number of cases the inverter needs a current clamp on the meter tails, which implies the inverter needs to be close-ish to them.

 

So, I'm wondering whether a separate SWA for raw DC back from the outbuilding to an inverter which is positioned not a million miles from the house CU is the best option. 

 

You asked if you could use the existing SWA or needed to run another one and the answer is you can do either. Concerns over distance from the incoming supply for monitoring wasn't mentioned but why are you considering a dedicated SWA if you think the shed is too far away??