Inverter downsizing - Looking for advice

flyinggoose

Hello,

I'm in the process of having a 5kwp solar pv system installed.

The installer had initially said they would install a 4.5kwp

 solar edge Inverter, but after looking at the Inverter model online they've installed a 3.68kw Inverter.

You can imagine my annoyance, the installation hasn't finished yet so I have only paid a £100 deposit so far and I'll be having a word with them tomorrow so I'm not that worried about getting this sorted.

However what I started to wonder was that is a 3.68kw Inverter better anyway as opposed to say a 4 or 4.5kw Inverter with a 5kwp solar pv system?

I'm aware that inverters are almost always downsized but is 3.68kwp not too low for the size of the system or would this be more efficient? I'm in the North West of England if that helps, the panels are being installed over three roods, roofs faxing south east, south west and north west.

Would appreciate any advice on this, thank you. 

Edit - I should also point out that I'm having a Tesla Powerwall installed later this year, not sure if the lower rated Inverter would make any difference there?

2nd_time_buyer

Going backwards. The powerwall would only make a difference if it was connected on the DC side i.e. you have a hybrid inverter installed. In which case it can store energy that otherwise would be clipped. However, I believe powerwalls are AC coupled. Solaredge's own battery is DC coupled and is compatible with the standard HD wave inverters with a few extra bits and bobs so could be an alternative to the Tesla.

I have a 6.7kw solaredge system with panels facing SE and SW and a 5kw inverter. I wasn't expecting it to clip much because of the split orientation. However, it has clipped quite a bit e.g. for around 6 hours over the last 2 days. If I was getting it installed again, I would have gone for a 6KW inverter. It also gives more options for adding more panels later. 

The usual reason to underside an inverter is to get better performance at low light levels as the inverter will work more efficiently. However, with a Solaredge system, the voltage is constantly high for all panels. They are also generally connected in a single string and the inverters have a high efficiency even down to low power outputs. So I am not sure the usual reason holds as true.

However, you are installing over three roofs. So perhaps it will be okay. It is within spec of Solaredge inverters which is 155%. It will also make DNO approval for the system much easier which will probably mean you are exporting quicker.

ispookie666

Welcome to Green & Ethical money saving forum
Are you sure the inverter has 3.68KW capacity or is it limited to G98 for not needing DNO approval pre install?  Looks like the latter to me.
If the batteries are on the DC side, it would not matter but if on the AC side, it is likely a bummer.  

Still does not make sense

Reed_Richards

I have an 4.8 kWp system with an inverter and a battery on the DC side.  Export is limited to 3.68 kW by a software setting on the inverter.  Inside my house I can use all the power that my panels provide but my battery charging rate appears to be constrained; it never gets as high as 3 kW.  

Martyn1981

I also think that sounds a bit too small. The inverter itself will be OK, the Solaredge HD Wave inverters can cope with massive overcapacity (5.7kW DC for the 3.68kW model), but I think you're going to get excessive capping. Has this been done to meet DNO requirements, which require 3.68kW (or less) if you don't seek prior approval.

4kW would be real borderline, and 4.5kW would sound ideal.

Edit - See later posts. For a split system with three different orientations, 3.68kW might be fine.

QrizB

I think there are two issues, here, technical and contractual.

Technical: I agree that the smaller inverter will prove limiting at peak generation periods, although the effective will be relatively small since you'll only be clipping the hump. It will be a lot less than the 20% lower nameplate capacity would suggest, maybe a quarter to half that (ie. a 5-10% loss in annual generation).

Contractual: Your contract with your installer is for them to install a 4.5kW inverter. If they are fitting a lower-output one it may have cost them less, and they will also not be incurring the costs of a G99 application to your DNO. Even if you're happy with losing a bit of generation, you might still want them to refund their savings.

2nd_time_buyer

"the panels are being installed over three roods, roofs faxing south east, south west and north west."

In practice this will mean the South East and North West panels will not be generating at maximum power at the same time. What is the panel split between the elevations?

Solaredge design software calculates the amount of clipping in terms of number of kw hours for each month. Do you know if the installer has done this? I doubt they have as it involves 3d modelling the site but it is pretty neat.

Martyn1981

2nd_time_buyer said:

"the panels are being installed over three roods, roofs faxing south east, south west and north west."

In practice this will mean the South East and North West panels will not be generating at maximum power at the same time. What is the panel split between the elevations?

Solaredge design software calculates the amount of clipping in terms of number of kw hours for each month. Do you know if the installer has done this? I doubt they have as it involves 3d modelling the site but it is pretty neat.

Many thanks, I'd missed that completely, and it's really important, especially the NW panels if they represent a fair share of the total system.

I take back my earlier comments, and 3.68kW may be absolutely fine, certainly not a disaster.

Solarchaser

I think as you will get sun on different rooves at different parts of the day, the inverter will be Bob on for size.

You will be able to make electricity for longer than most of us due to your varied orientations

flyinggoose

ispookie666 said:

Welcome to Green & Ethical money saving forum
Are you sure the inverter has 3.68KW capacity or is it limited to G98 for not needing DNO approval pre install?  Looks like the latter to me.
If the batteries are on the DC side, it would not matter but if on the AC side, it is likely a bummer.  

Still does not make sense

It's definitely a 3.68kw inverter, model: SE3680H.

QrizB said:

I think there are two issues, here, technical and contractual.

Technical: I agree that the smaller inverter will prove limiting at peak generation periods, although the effective will be relatively small since you'll only be clipping the hump. It will be a lot less than the 20% lower nameplate capacity would suggest, maybe a quarter to half that (ie. a 5-10% loss in annual generation).

Contractual: Your contract with your installer is for them to install a 4.5kW inverter. If they are fitting a lower-output one it may have cost them less, and they will also not be incurring the costs of a G99 application to your DNO. Even if you're happy with losing a bit of generation, you might still want them to refund their savings.

They said they would be seeking G99 approval, maybe something went wrong there? Will have to wait until Tuesday for an answer and yes will also be querying about a potential refund.

2nd_time_buyer said:

"the panels are being installed over three roods, roofs faxing south east, south west and north west."

In practice this will mean the South East and North West panels will not be generating at maximum power at the same time. What is the panel split between the elevations?

Solaredge design software calculates the amount of clipping in terms of number of kw hours for each month. Do you know if the installer has done this? I doubt they have as it involves 3d modelling the site but it is pretty neat.

There will be 14 panels in total (JA Solar 360w x 14), plan is to install five panels on the south east roof (thats the maximum amount that roof can have), seven on the south west (although i think this is a bit optimistic on their part, six is more realistic) and the rest on the north west roof, so thats about three, although i will be asking them to install more panels on that roof if there is space remaining.

As for the 3d modelling they haven't done that.

Martyn1981 said:

2nd_time_buyer said:

"the panels are being installed over three roods, roofs faxing south east, south west and north west."

In practice this will mean the South East and North West panels will not be generating at maximum power at the same time. What is the panel split between the elevations?

Solaredge design software calculates the amount of clipping in terms of number of kw hours for each month. Do you know if the installer has done this? I doubt they have as it involves 3d modelling the site but it is pretty neat.

Many thanks, I'd missed that completely, and it's really important, especially the NW panels if they represent a fair share of the total system.

I take back my earlier comments, and 3.68kW may be absolutely fine, certainly not a disaster.

Yeah this is what i'm trying to figure out, really appreciate all the advice in this thread, alot of food for thought.

Spies

I clip with 4.29 over two orientations on a 3600w inverter when the sun comes out from behind the clouds but unsure how it will perform in summer as I'll lose some efficiency due to the panels heating up.

I do however think 3.68 is too small for your situation.