Peak generation of a north facing array

[SimonSays]

With arrays facing the sun, we can usually work out what the peak generation is likely to be. I don't think it's possible to calculate this (at least, I can't see a way) for north facing arrays that never receive direct sun.

Is there a way to do this without waiting for mid-summer?

The back story is that I need a new dual MPPT inverter. My 3.6kW Growatt is clipping most days from about 10.15 to 2.45 with both arrays connected. To me, it seems to be a question of sizing a new inverter with a tradeoff between a little better efficiency in lower light and a little potential clipping vs an oversized inverter with potentially a little less efficiency in lower light.



Am I overthinking this?

(the back, back story is that I purchased a lightly used Growatt 5k hybrid from a business on ebay which turned out to have the strangest issue. The seller told me to dispose of it, so I gave it away to a member here. The seller then sent a 6k hybrid which had only one MPPT working. Now waiting for a refund)

[Stinsy]

With arrays facing the sun, we can usually work out what the peak generation is likely to be. I don't think it's possible to calculate this (at least, I can't see a way) for north facing arrays that never receive direct sun.

Is there a way to do this without waiting for mid-summer?

The back story is that I need a new dual MPPT inverter. My 3.6kW Growatt is clipping most days from about 10.15 to 2.45 with both arrays connected. To me, it seems to be a question of sizing a new inverter with a tradeoff between a little better efficiency in lower light and a little potential clipping vs an oversized inverter with potentially a little less efficiency in lower light.



Am I overthinking this?

(the back, back story is that I purchased a lightly used Growatt 5k hybrid from a business on ebay which turned out to have the strangest issue. The seller told me to dispose of it, so I gave it away to a member here. The seller then sent a 6k hybrid which had only one MPPT working. Now waiting for a refund)

IMO a well-designed system does involve clipping and it isn't a sign of some kind of fault that needs rectifying. Solar panels are so cheap that it is economically viable to size the array for bright-overcast conditions and just accept that you're leaving some energy on the table in (rare?) bright sunshine.

If you do want to make more use of the power then you could maybe buy a 2nd solar inverter and have one of your arrays AC coupled. This would result in you taking a bit more of Octopus' 15p on the sunniest days. This could possibly be worthwhile if you're comfortable buying used and DIY-ing the job. However the recent sunny weather is unprecedented, in other years you wouldn't have been clipping this time of year...

[SimonSays]

Thanks Stinsy. I’m happy to DIY house electrics.
I bought this this which I think will be well sized to the array’s maximum generation and I’ll get it logging into Home Assistant.
Despite it’s 2000 moniker it can apparently output up to 2.2kW.

[nowty]

That sounds like an optimal solution, both technical and financial.

[AGT]

Doesn’t PVGIS let you pick orientation?

Been a long time since I’ve used it though

[nowty]

Doesn’t PVGIS let you pick orientation?

Been a long time since I’ve used it though

It does in terms of yield but what SimonSays wants is the peak power output which is a bit more complicated. I think the old version used to have more options to give more detailed info on the theoretical watts / m2 verses time of year and day.

As he is already clipping, he needs a bit extra inverter power, probably about 50% more of the north facing panel STC panel ratings which he is now going to get with the extra inverter.

[Stinsy]

Thanks Stinsy. I’m happy to DIY house electrics.
I bought this this which I think will be well sized to the array’s maximum generation and I’ll get it logging into Home Assistant.
Despite it’s 2000 moniker it can apparently output up to 2.2kW.

That'll do the job nicely and is priced low enough that you'll see the money back, particularly if you see the labour cost as being a "hobby" that you get satisfaction from.

What are your plans for installation? What size breaker is your existing inverter on? What is the cable size?