If your 3k MP II is big enough for when you are on batteries (at night), then you might consider adding PV inverter to it’s output. Then you keep your current batteries (or expand if you want) but you get direct use PV for a bit cheaper.
If you need more inverter power when running from batteries, then I would suggest that a 5k MP II is less complex. Trying to match your current model with a new might be harder than you think as the cpu models and chips have to match.
Technically the two 3 kVA’s in parallel will give you a bit more power, 4800W vs the 4000W of the one 5 kVA, so it all depends how much you need.
Trying to find a matching 3 kVA to parallel might be a mission depending what age the one you already have is.
Buying a new 5 kVA gives you a new fresh warranty.
Cost wise for just the inverter quick Google on current pricing tells me either move will cost you more or less the same if you can sell your 3 kVA for around R12k.
However there will be extra costs if going the parallel route with a second set of cables, breakers etc. so keep that in mind.
Then also don’t discount the suggestion by @Louisvdw
of course depends on the night time vs day time capacity you need, but a AC PV inverter will bump up your systems efficiency during daytime quite a bit.
Just means I need to first outright fund the new 5kVA unit, and then sell / recover some $$$.
My current inverter gets overloaded at times… when I’m drawing base current, washer is on, and water/booster pump kicks in, or my air compressor kicks in, thus leading to me wanting to upsize it a bit.
I also recommend the 5kVA. Parallel is not an issue if you buy units from the same batch. The moment they are a few months apart, and especially in this day and age of component shortages, the picture changes. Sometimes there is a change in supplier and something as simple as a different relay can make the balancing of the units interesting. Doable… but you need to KNOW your stuff. As someone on the receiving end of the support-load… I would much rather tell people not to do that
Talk to @JacoDeJongh I recall him snapping up second hand MPII 3 kVA’s pretty quickly in the past here on the forum. Don’t know if that was for a specific project or whether he keeps them in stock as a less expensive option for potential clients.
If it overloads during islanded operation, and there is NOT a temperature warning and alarm preceding it… then it’s not because it is derating.
The derating only happens while connected to the grid. When running islanded, the loads determine how hard it works, and it will simply do its best as long as 1) you remain under 200%, 2) the battery voltage doesn’t sag, 3) the AC voltage can be maintained, and 4) it doesn’t overheat.
That means that it can do 200% for about a second, and it can do 120% for several minutes. Even at 100% it will eventually overheat. But you will always see a temperature alarm at the same time if that happens.
Guess i need to look closer at my alarms and the loads at the times.
with you having access to my system you would have seen I overload alarm allotttt… might also be that some of my thresholds are set bad, you will recall i modified my voltage alarm a bit, as it seems the incoming voltage is not that stable down here for me.
I have 2 conditions that i’;m aware off… 1: overload alarms while on grid, curious… 2: overload/trip when off grid, well to be expected if i’m cursing a high load and water pump that’s suppose to be 750W kicks in and for a second/2 draws 2KW, but then interesting that you saying it should be able to do 200%, which makes me think it should be able to handle the pump startups without crying fowl.