Newbie

[Steve_rutland]

Hi, I'm new on here and am looking for advice about fitting pv on both aspects of my roof ( east / west ).
Cheers
Steve

 

[FB.]

Split systems are fine, as long as the price is right.

A split system will produce a useful amount of power for a longer period of time, since it will catch the sun both in the mornings and the evenings.

However, the side effect of splits is that the sun only rarely be on all the panels at the same time, so the peak output will be lower (and the trough output higher) than a system which faces all in one direction.

To put it into perspective, if I had a 4kW East-facing system, a 4kW West-facing system, and a 2kW East + 2kW West system, each would probably generate 20-odd kWh of power over a whole day on a good day in late spring/early summer, but the power production would vary as follows:

4kW East-facing:

6am: 1.5kW output/hr = 4.5kWh
9am: 3kW output/hr = 9kWh (13.5 so far)
12noon: 1.5kW output/hr = 4.5kWh (18 so far)
3pm: 0.75kW output/hr = 2.25kWh (20.25 so far)
6pm: 0.25kW output/hr = 0.75kWh (21 by dusk)

------------------

4kW East-facing:

6am: 0.25kW output/hr = 0.75kWh
9am: 0.75kW output/hr = 2.25kWh (3 so far)
12noon: 1.5kW output/hr = 4.5kWh (7.5 so far)
3pm: 3kW output/hr = 9kWh (16.5 so far)
6pm: 1.5kW output/hr = 4.5kWh (21 by dusk)

------------------

A split system would be a hybrid of the two above, so roughly:

6am: 0.875kW output/hr = 2.625kWh
9am: 1.875kW output/hr = 5.625kWh (8.25 so far)
12noon: 1.5kW output/hr = 4.5kWh (12.75 so far)
3pm: 1.875kW output/hr = 5.625kWh (18.375 so far)
6pm: 0.875kW output/hr = 2.625kWh (21 by dusk)

-----------------

So the East or West one-directional arrays, on a good day in late spring/early summer, will have something like:

Three hours at 3kW output.
Six hours at 1.5kW output.
Three hours at 0.75kW output.
Three hours at 0.25kW output.

Whereas a split system would have something like:

Six hours at 1.875kW output.
Three hours at 1.5kW output.
Six hours at 0.875kW output.

.

Of course, if you have an East-only system and the sun comes out in the afternoon, the panels will not be well-placed to catch it.
Similarly a West-facing system will "miss out" if there's a sunny morning which turns to a dull wet afternoon.

Whereas a split system will catch some sun whenever it may appear in the day.

 

[Steve_rutland]

I am looking at 2 separate systems ie, 2 x 3.2kw systems, one on each side of the roof. I'd be using 2 separate inverters but I don't know if this means I'd need to have the G59 connection? Seems to be a lot of info out there but some is contradictory.

 

[FB.]

Above 4kW (sometimes above 3.6kW), the only definite answers will come from the DNO as it's their power network which may be affected and they will have the final say.
So speak to your DNO.

Also the FiT rate will be different in the 4-10kW band compared to the sub-4kW band.

 

[Gavin A]

I am looking at 2 separate systems ie, 2 x 3.2kw systems, one on each side of the roof. I'd be using 2 separate inverters but I don't know if this means I'd need to have the G59 connection? Seems to be a lot of info out there but some is contradictory.

Why 2 separate inverters?

A dual MPPT inverter will track both arrays entirely separately but then combine the AC output into 1 feed. Depending on the angle of the roofs you may even be able to install 6.4kWp via a dual MPPT inverter such as the power one, or sma 3600TL so that it still complies with the 3.68kW AC output limit for G83. IIRC the biggest east west split system we've done this for was a 5.5kWp system comprising 2.5kWp on a relatively steep east facing roof, and 3kWp on a relatively shallow west facing roof. We've been monitoring this system remotely, and it's never topped out above 3.5kW AC output, and usually hovers around 2-3kW through from mid morning to mid afternoon in summer. I'd think 5.5-6kWp split equally across the east and west roofs would work well on a dual MPPT 16 amp limited inverter as long as the roof was above something like 30deg pitch, and the higher the pitch, the greater the size of array that would work ok with only very minimal limiting.

If such a system does limit occasionally, it's likely to be below 1% of total annual generation that's affected, whereas you'll gain somewhere in the region of 0.5% efficiency on the inverter, with the SMA 3600 / 4000TL anyway, as they're most efficient when operating towards the top of their capacity and voltage range.

Bear in mind when considering this that the panels in full sunlight will be producing around 10-14% below their rated output due to the higher operating temperatures (0.45% efficiency reduction per degree above 25 degC, X around 20-30 degC), the inverter will lose around 5-6% in conversion, so you've already reduced the nominal peak output by 15-20% before you even start working out the impact of the orientation and angle of the split arrays.

You're a bit off our patch though, but there are installers on here in your area who I'm sure would be able to assist, and if they were unsure I'd be happy to give them access to the data from the 5.5kWp east west system we've been monitoring.

 

[Eco Deal]

A single inverter with a dual MPPT would be fine here or solar edge power optimizers just for the extra warranty and online monitoring
even if its unshaded roof.

see www.solaredge.com

for more details

 

[FB.]

I'd be happy to give them access to the data from the 5.5kWp east west system we've been monitoring.

The 2kW North + 2kW South array which I have the pleasure and fascination to observe (fairly shallow around 30 degree roof slope, maybe a few degrees shallower) is attached to an Aurora PVI 3600.
Despite 4kW of panels and a 3.6kW inverter, the inverter seems to top-out around 3.25kW. So they could have had 4.5kWp and be topping-out around 3.6kW for maybe an hour a day, on occasions, in ideal conditions.
Most of the time the sun is not at the perfect angle, or there is some cloud or haziness preventing full solar radiation getting to the panels, or it's hot outside and panel performance drops considerably as a side effect, so overloading isn't much of an issue.

On an East-West split, I'd definitely be comfortable with 5kWp on a 3.6kW-capped-G83 inverter. I'd not go as high as 6kWp on a 3.6-capped-G83 inverter unless the roof angle was steep.

 

[Steve_rutland]

I already have a 3.2kw grid tie inverter so was looking at getting another simply to keep costs down. My current ( off grid ) system feeds into 24 fork truck batteries then into an inverter and it does all our house lighting. My plan was to get rid if that and go grid tied and earn some dosh from it hence I'm on a tight budget lol.

 

[Steve_rutland]

My plan is......was.....is to try and find an installer who would be happy to do as little work as possible. I can easily fit the roof rails, mount the inverter and do as much as I can to limit the labour charges. Ideally I'd like to do the lot but realise not many people would certify something they haven't done. Just trying to find out if it's actually going to be viable for me to do this. ?

 

[whinmoor]

My plan is......was.....is to try and find an installer who would be happy to do as little work as possible. I can easily fit the roof rails, mount the inverter and do as much as I can to limit the labour charges. Ideally I'd like to do the lot but realise not many people would certify something they haven't done. Just trying to find out if it's actually going to be viable for me to do this. ?

We wouldn't be able to work with you under such terms. It risks running into difficulties if/when something goes wrong. ( e.g. Who carries the responsibility for a leaky roof a few weeks later after the scaffolding has been removed?) A decent installation team should be able to complete the job in two days at this time of year. Labour is only a small proportion of the total cost of the installation.

The most we've allowed a customer to do was a bit of spadework when we were digging the foundations for a ground-mount. Apart from that, they can observe the action from the ground, but not participate. If they wish, they can briefly climb up to the roof at their own risk (and wearing PPE) but most don't want and steer well clear. (They are, however, actively encouraged to provide hot drinks!)

Saying that, the proposal above sounds very sensible so get yourself some quotes and advice from local installers.

 

[Steve_rutland]

I know what you mean regarding this which is why I need to find a local installer I can talk to. I have and still do work on many roofs and with mine being a modern roof have no problem in taking responsibility for it. I'm not sure if what I want is possible with most installers, ie, me doing some of the work. I know a lot of the cost must be labour as I know the cost of the components to me and this is the reason I'm willing to do the work.

 

[Eco Deal]

All installers labour cost are rock bottom right now , I can not see anyone wanting to remove more of the labour from the price as it would not be worth doing an installation.

good luck with the project anyway

 

[Steve_rutland]

I guess my point was, if you charge £1000 for 2 days work, if say the roof work was done ( rails fitted ) and the inverter screwed to the wall. If this bought it down to £500 for a days work, you're still earning the same but my outlay would be less ;-). Just need to find someone local who thinks like me now lol!

 

[Eco Deal]

Ok I see your point but still we do most jobs within a day roof and AC.

so I dunno depends on the installer I guess but margins are tight already so it be hard to find an installer willing to put his name to a system for little monies it just not worth the hassle. your forgeting the paper work side to the installtion this can be 4-5 hours maybe longer after all is done on site.

The problem will be when somthing goes wrong whos to blame blar blar ......

what if the inverter goes faulty etc who will swap it ? you or the MCS installer ?

if it was as simple the problem with this game is if its a dull morning for example and the inverter does not kick in your phone starts ringing because people do not understand how a system works. i have had some bizarre phone call from previous customers asking this and that and it always turns out that its nothing but the time and effort to explain to them on the phone takes much time up.

I had one today asking me about Ice droplets on panels
but the most common is dull day start ups

ring ring ''my system not working''

Me ''is it dull''
Customer ''yes''
Me ''what time is it''
customer ''8.30 am''

then I have to explain about start up voltages etc.

installers spend more time on after service & paper than on a roof

 

[Steve_rutland]

Yes, I think I am going to struggle too on this one. Have had off grid for 4 years I know how the system works and I guess what I'm sort of after would be just the paper work side of things. I'll be quite happy to sign a waiver on the install as I'd like to buy and fit as much of the kit as possible. Will have to see what the New Year brings. Can't even get in touch with my DNO yet at my emails are getting bounced back....not a good start.
Happy New Year all!!