I've just installed a modified Geyserwise PV system. I thought I would post some of my findings, as it took a while for me to compile the information I needed. 

The objective was a solar PV retrofit to a standard Kwikot 150 L geyser, aiming for a payback period of 3-4 years. We use relatively little electricity (~270 kWh/month in summer, 420 in winter) so I wanted to keep overheads down to maximise ROI. 

A full Geyserwise install was going to come to about R 25k, but I went the DIY route and got it down to about R 12.5k in parts plus or minus some tools I'm sure I'll get to use again. 🤣

 

COMPONENTS

• 2x JA Solar 565 W panels on a north-facing IBR roof.
• Schletter ClampFit mounting hardware, end clamps and don't forget screws.
• Geyserwise 2 kW / 1100 W AC/DC PTC element (spec sheet), flange and "pocket". 
• Geyserwise 72 V MPPT
• Custom controller based on ESP8266 (i.e. no Geyserwise TSE). 
• Pre-existing CBI Astute in DB remains for AC switching. Existing thermostat for AC safety cut-out. 

 

MOUNTING

I'm very happy with the Schletter ClampFit system. I went for it almost entirely on the basis that there is a short YouTube animation demonstrating the extremely simple installation procedure. Not having been up on my roof prior to this job, this was what I needed to have confidence I could do it myself. I think it's also a good fit for this kind of installation. With only two panels, and needing to have them separated by about a metre, any solution involving rails made no sense at all. 

Another thing I wasn't sure about was how manageable the panels would be. But one wife was sufficient. They are light enough that one person can raise a panel up while the other grabs and hauls over the edge.  

 

GEYSERWISE ELEMENT

First impression: you could do some damage with this! It's bigger and heavier than expected. I was annoyed at having to replace an almost-new standard 3 kW element with this much more expensive PTC element but it's the key component in this system. It physically blends AC and DC power while keeping them electrically isolated.

The wires look thin in the photos and even thinner in real life. The DC wires (blue/white) are only 14 AWG or ~2.5mm². Weirdly, the AC wires are slightly thicker at 13 AWG. The spec does not list rated DC current. I assumed it would be 1100/72 = 15.3 A but it draws closer to 20 A, possibly only limited by the MPPT. So I remain a little concerned...

I did not buy the Geyserwise AC "thermal cutout" because as far as I can tell this is just a thermostat with a fixed setpoint. I used my old geyser thermostat. One thing to note is that it was a tight fit in the tube/pocket and you're supposed to jam both the digital temperature sensor for the controller plus the 75-degree DC cut-out switch in there as well. I ended up clamping the latter to the back of the element instead. 

There is an integrated gasket/seal at the back of the element. I'm not sure it's designed for repeat use so I hope not to have to ever remove it from the flange. 

Since PTC is by definition non-linear I was expecting a significant drop-off in power output as the temperature rose, but in this range it seems to be fairly close to a straight line. I was pleased to find the AC output starts well above 2, closer to 2.5 kW in ~35 degree water. 

  

 

GEYSERWISE MPPT

The MPPT was a bit of an unknown quantity. It has this spec on its label:

• Voc: 150 Vdc 
• Max DC load voltage: 72 Vdc
• Max DC load current: 20 A
• MPPT efficiency: 99%

It also looks suspiciously similar to this device sold in New Zealand, which has a bit more info. 

The potential-free / dry-contact input (labelled "remote") means it can be controlled with a simple switch or a relay. It comes with a cable to connect it to the controller, with a BH-A1D self-resetting normally-closed 75 C thermal switch, inline in series. In the event of loss of external control, this switch should open and force the MPPT off before the water starts boiling. 

It comes with a mounting bracket to maintain a gap behind the heatsink, and with some ferrules, which is a nice touch. 

I had a look inside and found no interesting clues as to manufacturer etc. Just a couple of large 105-degree-rated caps and a huge inductor. Unfortunately it does not seem to have (an obvious) serial port or aux power output, but I plan to investigate a bit more at a later stage. I would like to be able to draw 5 V parasitically for the controller. 

In full sun with the 1130 Wp of panels (and cold water) the MPPT reports something like:

• PV input: 67 V
• Output: 19.8 A at 56 V (1108 W) 

That kind of current makes the DC element wires warm to the touch. The heatsink also gets quite hot. I measured 25 degC above ambient. I did see a thermistor when I looked inside so I'm sure it is safely thermally limited. It might not be quite 99% efficient but it's not far off. The absence of a fan is a good thing from a dust perspective. 

  

 

CONTROLLER

I already have a CBI Astute in the DB to control the geyser's AC input, with some custom home automation scripts handling the timing. So I suspected the TSE1 was going to be mostly redundant. But I did need a way to monitor water temperature and of course to switch the MPPT. I put together a simple controller based around the ESP8266 (in a WeMos D1 Mini) that listens for an enable signal and setpoint over WiFi, and then acts as a digital thermostat, switching a relay connected via the supplied cable to the MPPT. The sensor itself is just a thermistor. 

    

 

IMPRESSIONS

If the model and the MPPT hold up I'm fairly confident the 3-4 year payback is possible. Of course much depends on performance in more marginal conditions, so we'll see. I'm also pretty sure quicker payback is possible with a different design. In particular I'm still not convinced the monolithic element nor the PTC technology are required; two separate resistive elements would surely suffice. There's also no reason the MPPT couldn't be 3 times cheaper. 

 

 

Edited December 27, 20241 yr by TTT
Pics

Pics?

Added some photos. 

Also, 1-month update: it's been great. We've had more hot water than we've needed, and no grid power required, despite a few cloudy days. I am looking forward to it getting more interesting in winter, to be honest.

However, I just ran into my first issue yesterday. With roof temperatures reaching above 40 C, the MPPT locked up. LCD just froze, showing 1000 W output, but there was no heating. Fortunately it came back on after toggling the DC isolator off and back on. But I am reconsidering placement. The MPPT is only rated to 45 C, so the attic is just not a suitable location, unless perhaps there's a fan and ducting for ventilation. Which is a schlep. 

In any case, a lockup requiring a power cycle is not the ideal response to overtemperature either, so it's good to know I guess. I have added ambient-overtemperature cut-out in software to pre-empt this more gracefully in the mean time. 

 

 

Edited December 27, 20241 yr by TTT

Nice happy it works .

I also installed on a friend geyser one of these cylinder shaped  1.5 kw element . That runs from an 3.3 kw inverter . 

As he is living alone it's no issue to manage the system when the geyser is running.

He is loving his setup as it's saving him now on high electric bills .