New build: Choosing an inverter and Water heating


I’m building a new home and initially planned to add a 150l indirect evacuated tube geyser as well as a gas geyser. I always planned to add PV and now I’m beginning to think that just having 2 geysers (150 an 100l) on PV might be the better route. The bathrooms are at opposite ends of the house, hence 2 geysers. I’m not sure how the SANS 10400-XA regulations apply in that case because it stipulates that 50% of water heating must come from other than resistive heating? If anyone has knowledge of how these regulations apply, I’d be interested to hear about it. It looks I’d save around 20k on the solar and gas geyser setups, which I could use towards an inverter.

In any case, if there is an exception for SSEG installs I’m looking for a grid tied inverter. I have space for 8 455W JA solar north-facing panels. I’d like to add backup at a later stage. I’ve had a look at the Sunsynk 5kW but it looks like it will clip the DC current at 9.9A which will lose me some power production. I then came across the Solis RHI 6k 5G which seems like a great inverter at a great price. Is there reason not to go for this inverter?

I’m in Stellenbosch municipality but power is provided by Eskom, if that has any relevance.

Solar water heating is at least 4 times more efficient and much cheaper. A solar water heater (SWH) can absorb at least 60% of the energy into the water, while a PV module is lucky to hit 18% (before conversion losses). PV modules also work on a very small range of the electromagnetic spectrum (basically only the part that can knock an electron out of a silicon atom’s orbit), which means that an SWH works significantly better on partly overcast days.

Unless you have a problem with roof space, I would not swap the SWH for PV modules.

If you prefer to go with PV modules instead, then at the very least look at using a heat pump to heat the water. Heat pumps have a COP of at least 3, usually 3.5 or better. That means it makes 3 times as much heat for the same amount of electricity. Combined with a ~20% efficient PV module, if you ignore conversion losses, that at least gets you close to the efficiency of a SWH. But generally a heat pump is more expensive than a SWH.

If you are looking at a grid-tied inverter, this is the pecking order: 1) Fronius, 2) ABB, 3) Solis. If you want to integrate this with a Victron backup system, I suggest sticking with the first two, since they actually support Sunspec. The Solis does not support Sunspec.

Thanks Plonkster. I’m aware of the efficiency gains with SWH, but my reasons for going the PV route are the following:

  1. I want to install PV anyways due to the fragility of the grid infrastructure and rising electricity costs.
  2. Once the water is heated, PV can do other things. SWH sits idle.
  3. PV modules have a much longer lifespan than solar collectors or heat pumps and need next to no maintenance.
  4. I can always retrofit a SWH if I need my PV for other things (eg installing a pool later)

As for the Solis mentioned, it’s not a pure grid tied inverter, but a proper hybrid (Solis Energy Storage 6kW Hybrid 5G Inverter with DC switch — The Power Store). I won’t need a Victron or something later.

No idea if they are any good. @JacoDeJongh has had good experiences with the grid-tied version. They are made by Ginlong in China, and Ginlong is one of the better inverter makers, but some of their earlier attempts (some of which was actually rebadged as a Victron PV-inverter, if my facts are not completely wrong) didn’t really work out all that well.

They have a 5 year warranty and for not much extra you can extend it to 10 years.

Stellenbosch, keep an eye out for inverters on this list:

We’re direct Eskom customers though.

Is Stellenbosch actually part of CoCT? Isn’t it Drakenstein or Stellenbosch Municipality?

Last I read Eskom does not yet allow grid tying.

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With the correct application they do accept it.


I’m in a similar situation as you using PV to heat my geysers. I have a 100l and a 200l geyser (if I recall correctly, keep on forgetting). The 100l has a 2kW element while the 200l has a 3kW element. I run the 100l one for about 2 hours every day (one hour of which is at 5am, so not on PV) and the 200l geyser for about 45mins to an hour. This isn’t all that much kWhs or time so most of the time my PV is used for other stuff.

For a 5kW inverter, I’ll just make sure not to use a 3kW element. It takes up too much capacity and I often find myself with enough PV to run the 2kW but not the 3kW.

If you are so inclined, you might be able to benefit from putting two elements in each geyser. A 1kW element and a 2kW element that you can individually control. On bad days, you only turn on the 1kW element, on great days you turn on both. You could maybe even backup the 1kW elements for those loadshedding days with good sun.

Probably not too difficult to do something like that with Home Assistant.

I have been looking at adding a heat pump, but before I do that, I’d first want to consolidate all my hot water into one geyser. Really don’t want to buy two heat pumps as well as find a place outside for the heat exchanger.

It’s Stellenbosch Mun but they follow CoCT’s inverter list. But, as I said, we’re on Eskom still for the time being so it’s not applicable.

Another option is the Sofar HYD 6000. Also looks like really good value.

No, separate municipality. Generally much more accepting of PV than CoCT, quite similar to Paarl really.

@jykenmynie I’m not too concerned about the larger elements as it will not overload the inverter - it can always pull from the grid what it can’t supply from PV. Probably best to ensure they don’t try heating at the same time though.

Yeah, agreed. I just thought that if you are doing it from scratch (building the house) you might as well optimise now.

It might also be nice to be able to backup a small element you can confidently run during the day time even when there’s loadshedding.

I’m finding loadshedding very disruptive to my carefully planned geyser timers… Because then both geysers would come on at the same time when loadshedding ends, and for some reason my area typically gets shed from 1200 to 1430 so then I end up wasting the best part of the PV yields for that day…

Welcome Kari, I have to advice you to rather stay with reputable and proven brands. You will not be to happy if your investment stops doing what is should do when you need it most.

Victron works fine fith a few inverters on its output, even with a solis. one problem though, you would need to install a Carlo Gavazzi to monitor its production, its not like using a Fronius thats got proper communication with Victron.

What I did on 2 x 150l geysers was to first replace the elements with 2kw elements and then I bought a bottom end Geyserwise timer for each.

Using the timers I scheduled times, during peak production hours, when each one can start heating.

Like 1st one starts at 11am and the 2nd one at 1pm. A 150l geyser does not take long to heat, 2 hours I found was max.

Once a geyser is heated it stays on till about 5pm as it is seldom that both will “top up” at the same time, and If it happens … so what, Eskom is there.

Did the above after our EV tune system failed after 9.5 years. Had to replace the entire system cause some tubes had no more vacuum, pump made a noise, Eskom failures damaged the controller and the 10 year warranty geyser started leaking.

EDIT: And IF there are clouds, Eskom is primarily used during the times for trust me, with females in a home, warm water is more important than saving a few cents on the rand. :wink:

Yes, TTT, this is basically exactly what I want to do. Do you have the geysers switched on at night or do they last until morning (or do you make sure everyone showers in the evening only?)

Geysers are off at night, as the house runs primarily off batteries.

After a lot of looking around I bought B+ rated geysers. And I mounted them outside the house as I’m sick and tired of geysers bursting and water in the house.

If managed properly the 150l can handle with ease 3+ showers, T&C’s apply, either all in the mornings or evenings or 1 shower morning and 1 evening. But that is a “risk” if the first person showered too long.

But because there are always extenuating circumstances, worst case, press the Red Button and heat the geyser anytime using Eskom.

The geyser for our bathroom I only heat from 13:00 to about 14:15 to 60 degrees. Can still shower at 23:00 and the water is fine. Wife sometimes complains that it is hot enough at 23:00, but she enjoys being burned alive. If you keep a schedule of showering at say 20:00, then it will be no problem to heat it during the day and keep until the evening.