Panel to inverter ratio to maximise G98 generation?

[cloudy]

I'm looking at running a simple on grid system, preferably within the G98 requirements for ease of DNO registration. The panels will be minimally slanted, and can only face slightly E/W or flat (large garden - will go on top of existing large (9x3m) pergolas).

 

It would seem to make sense, given the less than optimal PV panel situation, that I should significantly over provision the output, to ensure cloudy/winter days maximise the 16A for as long as possible. I understand the inverter will clip any excess generation - but am unsure on how far that can be pushed. ie: if generating 6kw on midsummers day, the inverter is having to clip 2kw, becoming a large heater! (or perhaps it just takes the MPPT into a less efficient zone to help dissipate power?) I guess this depends a lot on the inverter chosen - but interested to hear whether this line of thinking makes sense...

 

Edited December 10, 2020 by cloudy

[ProDave]

The inverter won't clip or dump 2kW of power, it will just take it to a less eficcient MPPT

 

The issue will be input DC voltage per string, so you will need to check carefully what the inverter can support. My gut feeling is 6kW of panels into a 3.68kW inverter will be too much.

[SteamyTea]

There seems to be some disagreement about what constitutes 16A per phase  for export purposes.

I think it is limited by module capacity, not inverter capacity.

[SteamyTea]

1 minute ago, ProDave said:

My gut feeling is 6kW of panels into a 3.68kW inverter will be too much

Generally no more than 30% undersizing. I fitted 3.5 kW to a 3 kW inverter. It got very noisy and the fan chucked out loads of hot air. This caused the room it was in to become unusable.

[cloudy]

Thanks ProDave - that makes sense.

To put some numbers to it - the inverter I was looking at can do MPPT up to 580v at 14A with 2 strings. In theory with 36 OCV panels that could be 16x2strings - giving approx 7.5kW...

 

SteamyTea - really based on DC output? I had thought it seemed to be the inverter certification/maximal AC output that the DNOs want to check - but that's just from my limited research to date...

 

 

 

 

[SteamyTea]

2 minutes ago, cloudy said:

SteamyTea - really based on DC output

There was some debate, and i think someone posted up the rules.

Too many people like to think they know best, but don't understand our electrical standards are very robust and need to be kept to.

If your inverter was overproducing, it would hit the voltage limit, this can cause problems down the line.