PV systems with modules on south facing & South west facing aspects of roof

[bigsparks]

Hi

I am drawing up a quote for a PV system. The property is a double bay semi detached property with a small dormer rafter pitch at the front, which is the south facing aspect of the roof. Due to the dormer pitch, we can only fit 5 x 195w panels, in a staggered formation, onto this south facing aspect. I would like to use 250w panels but the width dimension of the panel would be too big and would protrude over the ridge tiles, a big no no. So we have to have 5 x 195w panels to the front (south facing). There is a larger roof space to the side of the property that is south west facing that we can fit 8 x 250w panels onto.
When calculating kwp, I will add both strings together, and use one sma inverter to generate.
Can you advise best way to calculate SAP performance. Will it be just a case of calculating produced kwh of south & south west strings separately and then adding together. Or as im using one SMA inverter with 2 strings connected will I have to take anything else into consideration as the roof aspects face different positions??
Any help appreciated.

Cheers

 

[optician]

Where in the Country is the Roof?

 

[bigsparks]

It is in Suffolk, East Anglia.

 

[optician]

Sorry, also should have asked pitch of each roof?
Also consideration needs giving to how far away from each other the roofs are?

 

[optician]

Assuming 30 degree pitch for each roof, Smallest South facing array may produce 790 kwh and the Largest SW facing array may produce 1680 kwh per year.
Are you connecting in series or parrallel? what is the spec of your inverter?

 

[Worcester]

@Optician

The two arrays cannot be connected in series and certainly not in paralletl as they have different characteristics, they need to go either to seperate inverters, or an inverter with twin MPP Trackers

 

[Worcester]

@bigsparks, -

a)Which PV training course did you go on?
and
b)Which SMA Inverter were you thinking of using?

 

[bigsparks]

@ Worcester

I did 2372 training at MGS in Surrey, the training I recevied was not the best, hence, the question on the forum. Why do you ask?
I am aware there are twin MPPT inverters on market but wanted to see how other installers had overcome the same problem and then maybe decide best course from there on.
I have used SMA inverters various sizes on our existing installs. These installs have been straight forward systems Ie single roof space all facing same orientation and we used SMA inverters with single MPPT's.
I may be an easier solution to use 195w panels throughout to negate the need for a twin MPPT inverter and leave the SMA to invert to its optimum MPPT.

 

[MikeXl426]

This won't work even on a single MPPT inverter. They are different aspects with different string lengths. As Worcester says, dual MMPT or 2 inverters.

Mike

 

[bigsparks]

@ Worcester
Looking into it, the smallest SMA inverter they have with twin MPP is the 4000TL-20 which will be too big for the systems. Will probably look to fit a SMA SB1200 & SB1700 on each orientation.
One last question, when doing this, my assumption is that there will still only need to be one dedicated circuit at the CCU, looping between the AC isolators and one feed in meter???
Thanks for guidance

 

[edexlab]

separate dedicated circuit /Ac isolators/Mcb for each inverter

 

[bigsparks]

Thanks for info. I assume that applies to the generation meter as well? Separate one for each array/circuit?

 

[Worcester]

Nope, 1 x Ac Isolator, 1 x Gen Meter, One CU with 2 x MCB's, 2 x AC isolators etc

Other bits as nescessary depending upon location, how it's wired (buried cables etc), type of inverter(s) (TL or not), and wether your going into the main cu or henley block before it etc etc .

 

[BathKate]

Hi,

On a similar note I have just received a quote for a 4 kWp PV system in Bath with 9 units on a SE facing roof and 7 units on a SW facing roof. There seems to be just one inverter specified, it is an "SMA Sunnyboy 4000HF Inverter with MPP Tracker & remote Bluetooth Monitor"

I'm concerned that with just one inverter this will be very inefficient or am I missing something?

We're also having Solar Thermal - they have chosen to put this on the other bit of SE roof - does this make sense?

Thanks
Kate

 

[SolarCity]

Hi Kate,

I've not heard of a 4000HF model so I wonder if the installer is getting mixed up with a 4000TL inverter? The SB 4000TL has two MPP trackers and sounds ideal for your scenario.

 

[Graeme Harrold]

It will work a treat, think of the 4000TL as 2 inverters in 1 box. Its got a good DC range with low start voltage.....

Download the SMA software and check out your setup and it will show the suitability of the panels on each string. Also get the Sunnyexplorer software as I always pass this on with a USB bluetooth dongle (dont forget to change the installer password)

 

[BathKate]

Hi guys,

Thanks for your help! I'm getting wildly different stories from the 3 suppliers I've had quotes from which is making it rather difficult!

In total we have 3 usable sections of roof for Solar thermal and pv. The largest is SE facing (9 units) then there is a SE and a SW available at about 7 units each. On the SE facing roofs, the smaller one is set slightly forward of the bigger one - say 2m? Which 2 roofs would you say are best for PV?

One supplier has also stated that we MUST have Enecsys micro-inverters, are they more expensive? is it worth it?

Thanks again

 

[Worcester]

Are the two SE roofs at the same angle / pitch and same orientation, if so (and shading doesn't affect either group) then the panels on the SE roof can be combined onto the one tracker, if not then you'll effectively need three trackers, and with the latest enecsys 360's that should work out cheaper than multiple string inverters (a dual MPP and a single MPP).

Enecsys Micro-inverters work out to be the correct solution, where you need 3 trackers, or the shading issues are a big problem.

Yes they will cost more, however you'll get a system that works.

You have to be Authorised by Enecsys to design specify, purchase and install their micro-inverters, as they are installed and configured differently from a normal string inverter.

 

[BathKate]

Hi,

Thanks again for your help - it's much appreciated.

Yes, the 2 SE roofs are at the same pitch and orientation, the only potential shade issue is the small SE roof onto the larger SE roof - but I think it should be ok.

How much extra does it cost to have an inverter like the 4000TL rather than a bog standard single one?

The 3 quotes I have for the same building range from a capacity of 1.92kWp to 3.36 kWP, all using the same plans to quote........ and bizarrely the quote in the middle uses all 3 roofs rather than just 2. The price range is £10k to £13600 with the largest system at £10k (!) but only using a single inverter. All the quotes use Sanyo panels due to the restricted space, using 240, 245 and 250 W panels.

Cheers

 

[Ramjam]

Don't forget that Western Power have demanded the immediate disconnection of Enecsys micro inverters. The inverters were type tested G83 in isolation and not connected together as a system, their characteristics change with multiple units and collectively would fail G83, WP are demanding a re-test and have ordered that all existing systems be switched off....as I understand it....correct me if you know better!

I got enecsys authorised but when you look into them in detail it's shabby and they're not very good...opinion!