Is my solar installation incorrect

djglover

Hi Everyone

I am a solar newbie.  I have just had panels fitted in anticipation of getting an Electric Vehicle

I got 5.2kw from 14 X 370w pannels

The inverter that was fitted is a solax x1 with a maximum recommended DC power of 4000w.  and a nominal power of 3680w

This means my solar is being clipped I think at 3680w, meaning I cant take advantage of any production over that threshold.

The company have told me that this is standard practice but I am not sure if I have been mis-sold an oversized system, or an undersized inverter.  I appreciate I can achieve better outputs when its cloudy but by 10am this morning my production was clipped

The company said that any larger inverter, even with export throttling, would need to be DNO approved.

Does everthing seem above board with this?

Thanks!

Martyn1981

What they are saying is true, but that doesn't mean it's right.

You should have been told about this beforehand so you had the option to install / pay for less panels, so I don't think the company has acted appropriately, since this wasn't explained in advance.
Also, they could, and perhaps should have asked the DNO for permission for a higher export figure, to allow for a more powerful inverter to be used. They still can, and if permission is given, then replace the inverter with a 'bigger' one.

Regarding their claim that it's standard practice, I think that's misleading. Yes it's OK to cap the system to 3.68kW to meet DNO rules/regs, and since your system in strong sun and warm temps will probably only be around 80% efficient, then that's 4.16kW, so not as bad as 5.2kW. However, that's 0.48kW, possibly for hours per day, and also higher 'losses' (but shorter periods) in good sun and cold temps in Apr/Oct for example, which we are currently enjoying.

Obviously, whenever the system is generating 3.68kW or less then you aren't losing out, and depending on location, it's common to install an inverter that's 10-20% undersized in the UK, as that maximises efficiency in poor generation periods, which of course, the UK gets a lot of, but 30% undersized is a bit much, especially if your system is south facing, where -10% may be more appropriate.

There's also an historic element as there was a subsidy reduction (wayback) for systems that were larger than 4kWp, so 3.68kW inverters were, and are very common.

Sorry for all the waffle and circular explanations, but in short, capping like that should have been the last resort, after first asking the DNO for permission for an inverter of around 4.5kW(ish) (just my opinion), and if they said no, then explaining the situation to you, and then agreeing on the system size you are happy with.

Personally I'd rather have the 5.2kWp with the 3.68kW inverter, than a smaller PV array, but again, that's the last resort, not the first, and you should have been fully informed, or at least better informed.

Solution - Suggest they apply to the DNO and ask for permission, then swap out the inverter for a larger one (4.5kW(ish)) if the DNO says yes, or alternatively, offer you some reimbursement for misleading you by omission*.

*I'd suggest 0.5kWh x 8 hours on a summers day, so 4kWhs, and 0kWh's loss in the winter, so an average of 2kWh's per day x 365 x 10p x 25yrs = £1,825.    But I doubt they'd agree with me!

Ectophile

The 3.68kW figure is near enough 16A, which is the limit to how much you can install without asking the local DNO (district network operator) for permission first.  So it's common to cap export to that.

It's also common to over-size the panels a bit, as they only generate full power on a cool sunny day, when the sun's at just the right point in the sky.  So you only lose out on a small amount of power over a year.

But 5.2kW of panels capped at 3.68kW does seem a bit odd.

djglover

Thanks both, doesn’t seem overly odd, I do remember them saying not to get any more powerful panels than 370, so perhaps there is some logic behind the maths

Solarchaser

I'd agree with Martyn entirely here.
At best you have been misled,  at worst mis-sold.
And I can tell you from the 5 calls a week I get, you can legally pursue mis-sold solar panels.

You have paid extra for premium panels, if they installed 300w instead you would have paid less for them but still been at 4.2kw.

You are not alone in this, its quite commonplace. 
I recall looking at my inverter and wondering why it said 3.6kw when I was supposed to have a 4kw system.
Sales people omit these things deliberately if you ask me.

djglover

Today as an example, the array hasn't hit the limit, so presumably I have been benefiting from a 20% better generation outcome than with a 4.2kw system and on the average day, I guess that will be the case.  They did advise me not to go any bigger than the 5.2 when I asked about 385w panels they said that would be too big for the inverter.  If the system will give me almost 20% more benefit than a 4.2 array over time then it seems OK, just a pity to miss out on those nice peaks like yesterday

Martyn1981

djglover said:

Today as an example, the array hasn't hit the limit, so presumably I have been benefiting from a 20% better generation outcome than with a 4.2kw system and on the average day, I guess that will be the case.  They did advise me not to go any bigger than the 5.2 when I asked about 385w panels they said that would be too big for the inverter.  If the system will give me almost 20% more benefit than a 4.2 array over time then it seems OK, just a pity to miss out on those nice peaks like yesterday

Hiya. First, glad you are not getting too upset and appreciate that you have a good system, if not 'perfect'. But, the issue here, I feel, is that what you have is the best system/solution for a property that can't exceed 3.68kW, and crucially, having agreed to it in full knowledge. They've sold you a system that should only really have been installed after they've asked the DNO and received a no, and then asked you if you are happy to still go big (for a 3.68kW cap).

I'm trying to word things carefully to say that it's OK, and also that I can understand how you could (crucially could, not should) be in this position, but as Solarchaser states, I do feel you have been missold, and I think that comes before you accept that it's Ok.

Whilst a suitably qualified sparkie/company has to submit an application, you can ring up the DNO yourself and at least ask if you think a request for more than 3.68kW would be considered. They can't say much, but if you ask nicely and explain that you aren't going to hold them to anything, you may be able to weddle out of them whether it would be a 'no', or a 'might be no'. They won't give you a yes, as you can understand, but just knowing if it would be a no, or not, would at least guide you on whether to pursue the issue.

Just for guidance, I have permission for 5.9kW, and many others on here have asked for more, and got it.

PS. Another solution would be a DC based battery, that's to say on the DC side of the inverter, rather than the AC side. This would direct some of the generation from the panels via the inverter, but not changing it to AC, and into the batts. This would then reduce the amount of gen available for AC when the panels are producing more than enough to hit 3.68kW AC. Again, this is an option that could have been offered to you, though of course you may not have wanted all the extra expense of a hybrid inverter and battery pack?

djglover

Thanks for your invaluable advice Martyn. I am partly minded to kick up a fuss and see if they will refund 50% of the difference in cost of the 4.2 and 5.2 system and leave it at that. 

Reed_Richards

My inverter caps my export at 3680 W but I'm not aware of any cap on my actual generation; it got up to the nominal maximum of 4800 W earlier today.  Is that what we are talking about here or is it really as bad as the OP indicates?    

Solarchaser

Reed_Richards said:

My inverter caps my export at 3680 W but I'm not aware of any cap on my actual generation; it got up to the nominal maximum of 4800 W earlier today.  Is that what we are talking about here or is it really as bad as the OP indicates?    

You have a DC battery system?

Export limitation is a good way to control it if that is enabled

Reed_Richards

Solarchaser said:

Reed_Richards said:

My inverter caps my export at 3680 W but I'm not aware of any cap on my actual generation; it got up to the nominal maximum of 4800 W earlier today.  Is that what we are talking about here or is it really as bad as the OP indicates?    

You have a DC battery system?

Export limitation is a good way to control it if that is enabled

Yes, my battery is on the DC side of the inverter.  The export control limit is a software setting but I don't know if I could actually change it if I tried; since my export is deemed for payment purposes there isn't really any point in trying.