Really understanding the difference between 5kw and 8kw system

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christoff83

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Hi all,

As with many previous threads around this topic on this forum, and other forums, I’m wondering whether to install 5kw or 8kw inverter. Having read quite a few threads and articles, I want to try summarize my view on it.



For me, the top key takeaways from these discussions are:

  • Understanding the difference between inverting capacity and passthrough capacity. When an inverter is advertised as 5kw, typically that refers to its continuous “inverting capability” meaning – to me – that while eskom power is off, you cannot carry more than 5kw load; or even while power (eskom) is on, you cannot contribute more than 5kw from your solar array or battery.
  • BUT, a 5kw inverter does not mean that you are overall limited to run your house at a maximum of 5 kw all the time. I see many manufacturers refer to a continuous AC pass-through power or current. Today I’ve seen a few as 50A which – again, to me – means 230v AC @ 50A means around 11.5kw load you can carry in your house WHERE a theoretical maximum of 5kw could come from your solar array or battery.
  • Most high-quality inverters are informally known as “true hybrid inverters” which means in the above scenario, your house can run up to a total of 11.5 kw where the first 5kw will come from your inverting capacity (solar or battery) and the shortfall from 5 to 11.5 will be “blended” from eskom. This of course assumes eskom is on and that you also have 5kw available from your solar array or battery.
  • Some people prefer to parallel two 5kw’s instead of going for a single 8kw because:
    • Lower entry cost (you can start with one 5kw and add another later)
    • Redundancy. If an inverter fails, chances are you’ll have another while repairing…
    • More MPPT’s with added capacity and flexibility (depending on the brand).


So two questions for the audience:

  • Would you agree / disagree with my key takeaways above?
  • In light of the above, assuming it’s more or less correct, is there anyone who implemented a 5kw inverter who wished they had gone for 8 kw or anyone who had gone for a 8kw and realized that a 5kw would have been sufficient?


Any other comments welcome.

Cheers
 

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