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.
• While living with higher self-consumption, 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).
  • Lower noise levels on the 5kw potentially.
• Have wheels, will travel.   When estimating usage, one can probably add 20-30% on your current usage as one would be inclined to use electricity more freely when it becomes free off sun power.

 

So two questions for the audience:

1. Would you agree / disagree with my key takeaways above?
2. 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

Edited January 18, 20233 yr by Christoff83
Updated with feedback from the thread.

8 minutes ago, Christoff83 said:

Any other comments welcome.

The negatives with 2 X 5kW vs 1 X 8kW is that I'm pretty certain the self consumption of the 2 are higher than for the one, so energy wasted, which, if you are sailing close the power limits of the battery bank used, could be a real big issue...

I was looking at the 8kW Sunsynk in 2020, but could not stretch the finances and ended up with the 5kW Sunken Synk, well, we haven't had any issues, we're mostly off the grid, but have an extension lead to the neighbour rated at 10A/2k2W, so in case of cases, assuming Eksdom hasn't left the building, like they did yesterday, just 20minutes after our 4hour rolling blackout, only to come back at around 1600 today, we can draw some from the neighbours extension lead, but never had to, for actual load, this end, so 5kW is probably close to our peak consumption...  (actually had a few spikes around the 7kW mark, with Eksdom awol and me cutting the lawn with my trusty '80s vintage Wolf 2000, 1k8W rated, but startup current on inductive load... 'nuff said.)

Either way, you'd need to look at your usage graphed out minute by minute over a week or two, to see what you need in terms of inverter size. Here we may need to consider adding in the future, certainly solar panels, since an air conditioner/cooler or two are probably on the horizon for us, these will be used during the day to keep the house cooler and those electrons will have to come from somewhere, the extension lead will no be around in the future either...

37 minutes ago, Christoff83 said:

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.

This is correct. How much passthrough depends on the inverter and not all of them can do it. Assuming you are talking about the sunsynk and deye derivatives, then yes.

37 minutes ago, Christoff83 said:

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).

 

This is quite a nice reason to go for the 2x5kw but do remember that the 8kw sunsynk does have higher current ratings on the MPPTs so you can use larger panels without clipping.

In the end I went for the 8kw as it works out cheaper upfront and is a single install rather than having to pay for two installs at different times. 8kw is more than enough for most households and the batteries tend to be more of an issue at the end of the day anyway. For me, the only benefit of the 2x5kw setup is redundancy and that might be a major driving factor for some - even if more expensive overall.

One thing to note is that the 8kw sunsynk/deye has quite loud fans which come on every so often. This is not an issue if you install inside a garage but if installed in earshot, it is irritating. AFAIK the 5kw (and therefore 2x5kw) synsunk/deye inverters do not have this "issue".

Edit: I must add, if you have a few aircons and a pool pump - we have an old school aircon that draws 3kw when running - then the 5kw one is likely not enough. With that said, I have a friend who put his whole house on a 5kw system and has had no issues.

Edited January 18, 20233 yr by SteveP

1 hour ago, Christoff83 said:

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.

Small difference, using the example of Sunsynk/Deye: Your essential loads are limited to the passthrough current of say 35A for the 5kW, and 50A for the 8kW, but the whole household including the non-essential loads can draw up to 80A or whatever your main circuit breaker is rated at, and the inverter capacity can also feed surplus to the non-essentials.

I have a 5kW for cost containment. A greater passthrough would have been useful on occasion but you learn to adjust.

If I have for example this 8kw Deye inverter and the grid is on. No loadshedding. And I have all my non-essential running together. Which will be more than 8kw. Will the inverter trip or does it run normally from grid to appliances? I don't want to limit my whole house to just 8kw output in normal grid times. Obviously with loadshedding load needs to be reduced.

41 minutes ago, Bennyyao said:

If I have for example this 8kw Deye inverter and the grid is on. No loadshedding. And I have all my non-essential running together. Which will be more than 8kw. Will the inverter trip or does it run normally from grid to appliances? I don't want to limit my whole house to just 8kw output in normal grid times. Obviously with loadshedding load needs to be reduced.

The inverter will not trip. Non-essentials run from grid, but the inverter can blend in surplus solar or battery power to reduce the grid energy you buy if you choose the relevant settings. More info on the forum history if you search for info on the CT coil.

1 hour ago, Bennyyao said:

If I have for example this 8kw Deye inverter and the grid is on. No loadshedding. And I have all my non-essential running together. Which will be more than 8kw. Will the inverter trip or does it run normally from grid to appliances? I don't want to limit my whole house to just 8kw output in normal grid times. Obviously with loadshedding load needs to be reduced.

Adding on to what Greenfields said.  If you are running a load over the inverter rating, it will take from pv first, then battery if necessary to get to the 5kW/8kW and thereafter the grid and blend all together without you even noticing.

Here is a graph that show how it worked on mine:

On 2023/02/23 at 7:13 AM, PearlJam said:

Adding on to what Greenfields said.  If you are running a load over the inverter rating, it will take from pv first, then battery if necessary to get to the 5kW/8kW and thereafter the grid and blend all together without you even noticing.

Is this regardless of essential / non-essential? ie. Will it blend all 3 if it's on inverter AC output (essential) or back-fed via AC input (non-essential)?

9 hours ago, Kappa said:

Is this regardless of essential / non-essential? ie. Will it blend all 3 if it's on inverter AC output (essential) or back-fed via AC input (non-essential)?

Yes, it can blend all sources of power in basically any combination to supply any type of load, whether only essential, or non-essential also. That depends firstly on how much of that energy source is available in the first place at any given time, but you can also pre-set the limits to be taken from each source, even in some case at different times, so it's not entirely random, but it all happens in the background without you thinking about it anymore.

Edited December 19, 20232 yr by GreenFields

Hi All,

@Christoff83 , did you go with the 2x5 kW or the 8 kW?

Is the noise on the 8 kW a big issue? It seems like it can be irritating.

Lastly, (an actual operational question). Will the 2x5 kW have an ac pass thorough of 2 x 35 A = 70 A?