Solar PV - paid for 4kw and got 3kw

slammeddeluxe_2

Hi

We were luckily enough to get one of the first solar PV feed in tarrifs. However - we had our system checked last week and although we have 4kw of solar panels our invertor is on 3kw. I understand that there is some 'flex' with these invertors - but looking at it - its maxing out at around 3.1 - 3.2kw. The installer has come back to me saying that it doesn't matter. I have heard that there is an historic calculator that if I put my postcode etc in it gives me what our PV system should have generated ? Does anyone know this website ?

Thanks

Paul

ajbell

Normally you get a 3.6kw inverter with a 4kw system.
I have a solis 3.6kw inverter which maxes out at about 3.75kw.

slammeddeluxe_2

Mine is only 3KW not 3.6kw

ChopperST

If memory serves you can install a 3.68KW system without notifying the DNO. Most installers will cap systems at this.

Could there be a reason locally that you had to have your system capped at 3KW i.e. too many installs in your area?

Martyn1981

slammeddeluxe wrote: »

Hi
I have heard that there is an historic calculator that if I put my postcode etc in it gives me what our PV system should have generated ? Does anyone know this website ?

Thanks

Paul

Hiya Paul. The PVGIS site is absolutely excellent, but it's an average, not an historic record.

For performance against average, you'll need to find someone close to you, but orientation will be important too.

My performance against targets have been:
2011 97% (partial)
2012 99%
2013 104%
2014 108%
2015 106%
2016 101% (partial)

I'm using older PVGIS figures, and they've been increased about 5% since I did mine, so you could knock 5% off my results to get an annual against average result. But only for Cardiff, and even then, only for a system with similar orientation(s).


Regarding, your inverter. It was fairly common practice to undersize an inverter in the UK in order to boost low light efficiency, but at the expense of some capping. This might be 10% or even 20%, but yours is a bit extreme at 25%.

Losses however won't be anywhere near 25% (or even 20% allowing for the fact the inverter can handle 3.2kW) since capping will only affect generation when above the max, and even then, hot panels will very quickly lose 10% efficiency, rising to 20% on a hot summers day.

It would be very interesting to know how your system has performed against PVGIS each year, to give us all an idea on the actual affect of your relatively low cap.

Mart.

Martyn1981

Paul, me again. What make and model is your inverter and do you have any shading?

Just wondering, as a simple inverter, such as a Samil, with a 10 year warranty wouldn't be that expensive, and might be more efficient. Add that to any lost generation, and multiply by 20 more years, and it might be worth considering a swap.

Mart.

slammeddeluxe_2

Hi mate - its a Sunnyboy 3kw invertor - will check the figures now..

slammeddeluxe_2

Here are my results

So it looks like they are fine after all


My postcode is DL14 its a 4KW system - zero shade and 1 degree off south facing.

System was installed on the 1/7/2011

And has generated 18088KWH up until yesterday

Installer says that's 3617 Per annum against projected of 3136 kwh ?

jimjames

You're certainly not losing 25% of your generation. However I'd take the estimates with a pinch of salt as they do tend to be on the low side.

With my 3kW system we've had over 3000kWh every year, you can see the details below to check how it compares. Our estimate was 2400kWh.

http://solar-panels-review.321web.co.uk/index.php/yearly-comparison-of-solar-pv

Based on our install, I'd suggest you could have got over 4000kWh pa if your inverter had been slightly larger so that's about £200pa. Add that up over the remaining time and you'll see if it's worth increasing the inverter - but will that trigger a reduction in FIT as it's a system change?

If you also look at the graphs here http://uk-solarpanels.blogspot.co.uk/2012/05/solar-panels-low-peak-output.html you can see that the peak is only reached at midday so the actual amount that will be capped is small and you will also get a better generation the rest of the time compared to a 4kW inverter. So the difference may not be massive

Martyn1981

jimjames wrote: »

Based on our install, I'd suggest you could have got over 4000kWh pa if your inverter had been slightly larger so that's about £200pa.

Hiya Jim, I chatted with Paul on a PM. He is quite northerly, up by Middlesborough, so 1000kWh/kWp is unlikely.

PVGIS gave an annual estimate of 3,580, v's the 3,617 he's seeing. Allowing for July generation so far this year (150?) then it's 3,580 v's 3,588.

I know PVGIS used to be a bit pessimistic, but I thought the uplift a year or so back took care of that.

I'm going to contradict myself here, but I'd have expected a small amount of loss, perhaps 5%, but the numbers suggest to me that it's generating absolutely fine, which is a shock to me, but fits in with many discussions I've read on Navitron, claiming that capping in the UK is much less than we might expect.

I find this 'real life' example very interesting, and quite surprising.

jimjames wrote: »

Add that up over the remaining time and you'll see if it's worth increasing the inverter - but will that trigger a reduction in FIT as it's a system change?

Changing an inverter won't trigger any FiT rate change as it's based on the kWp of the system. But, moving to an uncapped 4kW inverter on a 4kWp system probably requires DNO permission, but in this example a 3.68kW model would obviously work fine.

Thinking about it, I'm not sure you can trigger a FiT reduction. If you added more panels, or replaced panels with more powerful ones (due to fault/failure) then I think FiT would remain the same rate, but be calculated on an apportioned amount of generation:

eg take a 4kWp system with 16 250Wp panels, then replace a panel with a 285Wp panel. FiT would then be paid on 4,000/4035ths of generation. The important thing is to let the FiT provider know, otherwise you could void the whole contract.

Mart.

Martyn1981

Martyn1981 wrote: »

I find this 'real life' example very interesting, and quite surprising.

Are others as shocked as me? Up till now most discussions on capping have been theoretical, and based on inverters more closely matched to system size. But this example has a big kW to kWp difference.

Mart.