Who is PowerOptimal? Solar water heating discussion

They appear to have a connection to Kwikot…

Looks like just another PV-solar water heating thing… :slight_smile:

The Elon®uses advanced proprietary switching technology to allow for direct provision of DC (Direct Current) power from solar PV (photovoltaic) modules to electric geyser and optimised solar power use in a single compact unit. The system can be connected to the grid (AC mains) as well, and intelligently switches between AC and solar power supply. The system requires no inverter and no battery, and can be connected to standard AC geyser heating elements and AC thermostats, which translates into the most cost-effective solar water heating option today.

It uses a DC/DC converter in other words, and a changeover relay when it needs to switch to the grid. So sure, just half-an-inverter needed then :slight_smile:

I now wonder about the claim that it is the most cost-effective solution on the market. It is really really hard to beat a good old solar water heater, simlpy because those things are 60% efficient at putting solar energy into the water, while a PV module can hardly hit 20% for the same area.

But… that might not matter, you just have to cover three times the roof space in PV modules, assuming you have the space, and (critically) it is cheaper.

Just thinking out loud, you need around 8kWh to heat 150 liters of water a day. That’s around 1.5 - 2kWp of PV, which is not going to be any less than 20k… plus the cost of the DC/DC converter.

For 20k I’d still take the heat pump option :slight_smile:


And where does PowerOptimal fit in??

Name of the company. Could be that they have more products coming… :slight_smile:

When you install an EV tube/heat pump the first time, you get a clear-cut ROI i.e. instant reduction in ones Eskom bill. If you “train” the family, you maximize it.

After 5-10 years when the system needs replacement, it costs a lot again, but this time you don’t save more, you spend to keep the Eskom cost pegged at the previous level before the replacement.

After immense savings over 9.5 years on our EV tube system, I installed 2kw elements, added 4 more panels and a Geyserwise timer, and let the grid-tied inverter handle the heating of the geysers on schedules, the family already “trained”.

Found this the most economical option, by using what is in place already.

Some may point out that the inverter also needs replacement, rather replace having used it, than adding more costs to the entire system, having to replace two parts, thinks I.

Some may point out one will use more Eskom to heat water, true, the question one needs to ponder on, the follow-up replacements, how long before you get an ROI on them … if any?

My 2 cents.

Oh I disagree. If you don’t replace it, the cost goes back up. By replacing it you avoid (and therefore save) that cost. This starts a new ROI cycle.

It may well be that a bunch of other stuff you installed already now allow you to get back there with less money. Which is your use case.

I’m trying to wrap my mind around that … we agree. If I don’t spend it, the cost goes back up

My point. The first time you go solar water heating there is an ROI like R30k spent, made back over ±24 months in savings followed by ±7 years of near-free hot water.

The 2nd time you are spending the heating costs upfront, a huge difference compared to the 1st round.

What am I missing?

What interests me is the estimated life of your system. I understand EV tubes don’t last decades and inverters will die too.
But PV panels have a much longer life so if you build your system on products that have a long lifespan you can reduce your overall running costs (which includes replacement).

1 Like

You’re missing nothing. Just the usual things in life where you have to spend money you didn’t plan on to get back to where you were. Eg when losing a vehicle. Insurance puts you back in the same place you were in terms of a valuation… but inevitably the vehicles you can buy at that price is not in the same state as the one you just lost… because you take care of your own stuff.

Or spending money to paint a wall that was fine two years ago but is now peeling… you’re spending money to get back where you were.

Perhaps another way to look at it… the previous solar water heater had finished paying for itself, and then started returning on the investment (ie, it made your life better). When it breaks, this immediately stops. Now it takes another 24 months (or even more) before you are even again. But you cannot NOT do it… that is worse.

Despite the high cost of living, it remains popular though.


I would argue that the EV tubes themselves have the same or even longer life expectancy than PV panels. They have the same failure modes, but PV have some additional ones. (In the case of a pumped system)

I haven’t had to replace the tubes on my system as yet. Going about 18 months now. When I got my system, the tubes were relatively cheap, as in 200-300 rands a piece. Not sure what the lifespan is but I would imagine the major thing I need to factor in is breakage due to hail. There isn’t any moving parts in there otherwise.

I had an X-Stream tank at my previous place. It is made of Fibreglass. I was told that these units do crack and fail after some time. When I left there it was 9 years old and working like the day it was installed. There was a similar 200-liter unit around the corner (in Belmondo estate, for those who know the area) that’s been there as long as I can remember too, and must be equally old. Now even though I (and said house around the corner) was lucky, I can still see that tank fail in a few years. When it does… you replace the tank only, which costs less than a whole new solar water heater, and involves less labour too (piping is already there).

So again, I think maintenance or even repairs on a solar water heater isn’t a whole new investment, it does cost somewhat less.

I’m sitting with the same issue out back with the heat pump. In all likelihood (based on my neighbour’s experience with his), it’s going to need a service sometimes this decade… :slight_smile:

Actually, my story is not quite over. My parents have a Siemens indirect system on the farm. I was barely in high school when we installed that, and it still works perfectly. It must be going on 30 years old now… though in today’s money probably nobody would install one :slight_smile:

Moral of the story: We all like to be Optimal (in power and other spending), but you can’t always get there.
Just try to do the best you can at that time and be content that it was the best option at that time.

1 Like

9.5 years later:
10-year warranty Duratherm geyser started leaking, no warranty, they changed it.
Replacement tubes were nowhere to be found, as a few had no more vacuums.
Pump needed replacement.
Eskom damaged the Geyserwise system, which triggered the in-depth investigation.
±R25k to replace it all.

Bugger no!

4 more panels
2 x 2kw elements
2 x Geyser Wise timers, the cheap ones.
1 x B+ Rated geyser.

… and use the existing grid-tied inverter to warm the geysers, on schedules, as the 2kw elements fit nicely into the exiting house loads during the day otherwise I will have had too much paneling, even before the 4 more, if not for the geysers.

1 Like

It sounds like you just got unlucky and everything went at the same time. The clincher was the tank itself I assume. Otherwise you’d throw on another retrofit (manifold and tubes) for under 10k and be done with it.

But I am with you on that decision. I did the same by going for a heat pump instead of a solar water heater. Over a whole year it is NOT the most efficient method, but it gives a much more levelised electricity bill. At my previous house the bill would simply triple in winter as the water use, the ambient water temp, and the amount of available PV all went the wrong way simultaneously :slight_smile:

This decision became clear with the previous history of the system and it makes sense.
Initially I looked at heating my geyser by 220V generated from a grid tie setup. However I couldn’t envisage how to manage this load intelligently (using available PV power) since my inverter doesn’t have a non essential output. Scheduling this load on a time of day basis or reducing the geyser element such that the system could cope with that load seemed like a messy option.
So that’s why a stand alone hot water system made sense for me…

Note: Hot water is a NEED, not a WANT, never a HOBBY … with “langhaarhuisdiere”.

My point - for general thought:
EV tubes/Heat pumps systems have a lifespan.
Inverters have a lifespan.

One has to replace an inverter as it is saving on Eskom AND deals with load-shedding, maybe even generating an income.

The water heating using EV tubes/Heat pumps is an additional cost on top of the inverter, after the 1st ROI.

So I don’t see how the continued replacements of EV Tubes/Heat pumps can be seen as having any ROI as it is done to contain cost, or differently put, pay upfront to enjoy the lower continued costs.

If managed best one can with one’s annual PV production, coupled with lifestyle changes, it can take decades to spend on bad PV days what a new EV Tube/Heatpump replacement costs, with the maintenance done for warranty purposes. So add more panels they said …

The scheduling using off-the-shelf timers is not messy.
Replacing the element is not messy, it is quick or do it with at installation of a new geyser.
Timing the geyser heating with excess panel power can be an interesting thing to solve if that is one’s interest/hobbies/challenge. Not everyone’s cup of tea, as it becomes more “complex” than a simple timer.

The simplicity of a timer works best, as it allows me over weekends to switch off the geyser and use the spare power for the aircon.

And for the life of me, I cannot fathom having dedicated PV panels to heat a geyser. A low-pressure flat plate system is a more cost-effective solution methinks, but that can be “messy”.

Having spent my time as a control engineer I like to see elegant control systems. For me allocating time slots for different loads to ensure there’s power available for those loads isn’t elegant at all.
It would be way better if the system can determine what power is available and power that load if all is well.
This topic of managing loads on a RE system seems to be the elephant in the room since I don’t come across much on this subject…