Hi,

We are installing the following system in our new build home:

20x 600w panels, 1x 16kw inverter and 2x 16kwh batteries.

Our avg daily use is about 20-25 units (kwh) per day.

This system will serve us well in summer, but my concern is winter. We dont have much more useable roof space for more panels either.

The battery bank is basically enough to carry our house for 24hours, if going to 80% discharge, then it needs recharging whilst house runs off panels or generator for a while.

I want to connect a generator that can charge the batteries whilst the house runs off the panels in the day or charge batteries and the house loads when panels are not enough - is it possible to connect an auto stop-start gennie this way? So it will prioritise battery charging then the house load thats needed after house uses all available solar?

Eskom is falling apart in the overstrand area and we have gone 14 days with no power this last month.

What size generator would I need to achieve almost off grid capabilities with the solar system mentioned above for those weeks when eskom is broken???

I was thinking 10kva but likely too small?

many thanks in advance!!

Your system is slightly larger than ours and we are very close to off grid while averaging 30-40kwh per day, so I think you've got good head room in terms of system size.

Most inverters will have a dry contact switch for starting/stopping an auto-start generator. From my experience this is normally set based on SOC. So when battery SOC drops below a set point, the gennie starts and when it goes above another set point it stops the gennie. Your house loads would be carried by the combo of the battery and gennie. Most inverters have an option to set the maximum power you can draw from the generator, so choosing the generator's size comes down to how long you want it to run to recharge to your ideal set point.

An example:
Charge from 30%-80% (16kwh)
House loads of 1000W
10kw Gennie
It would take roughly 2 hours of generator on time, assuming no solar helping.

Personally I think a 10kw generator is plenty if your average consumption is around 25kwh. And the beauty of a hybrid inverter is if you do suddenly need to use 16kw from the inverter while running off the generator, the excess will be pulled from the battery. And it's highly unlikely that you'd see sustained 16kw loads at home. We have 10kw of inverter capacity with a household of 4 and a flatlet and I can count on my hand the number of times we've been above 10kw. We have no gas appliances and two geysers (admittedly with smaller 2kw elements fitted).