Solar diverter options...

Forums › Home Workshop DIY › Solar diverter options...

Bewildered

106 posts

Master Geek

#315092 12-Jun-2024 17:46

Octopus have cut their Solar buy-back rates (to 15c) and they have simultaneously raised their prices for all their rates so it was time to look around for alternatives....and Meridian had the best deal going. While the new Meridian flat rate was more than the Octopus night rate it was the same or less than the Octopus off-peak and peak rates...so on the whole cheaper...and their solar buy-back is still 17c. And it is fixed for five years....so as the solar buy-back rate keeps falling and the costs keep climbing I'll be able to sit pretty on 17c, and the rates I've locked in...while still be able to quit and go anywhere without penalty. Oh...and there was a $300 welcome credit (which you lose if you leave within two years). So on the whole a good deal!

In the past however I would export as much solar power as I could and load shift into the night for the cheap night rate...on a flat rate this isn't needed (whether or not flat rates are good for NZ Inc is another discussion...spoiler alert....it's not) but equally because of this flat rate the cheapest power I now have is my own solar.....so maximising self-consumption becomes the new game I must play!

To that end I'm looking at the economics of managing the hot water cylinder....I could use home automation to switch the HWC on/off based on the solar production but this comes with several downsides - firstly cycling the HWC on and off is going to wear out my relay pretty quick, and secondly the element will draw way more power than I'm able to produce, particularly in the colder months or on overcast/patchy days. So this method at best gives me a "discount" on the hot water heating as I'll only ever use a random % of my own power on any given day...and I should expect to pay for relay replacements.

On the other hand something like a solar diverter can more efficiently match the power fed into the HWC with the power coming from the inverter so it will heat the water slower and over a longer time but not import much power to get the job done...then I can just boost it at the end of the day to get the temperature to max so we go into each evening with a full hot tank.....and then let it get cold overnight before the process starts again the next day when the sun comes up. On really sunny days the end of day boost will do nothing, while on rainy days the boost will do almost all the heating....but it is what it is...

The question is how much do diverters cost, how long do they last, and then what's the payback period? There's no point getting something that has a payback period of 8 years with an expected life of 5 years.

Ideally it would be something I can integrate with HA....particularly to programme the end of day boost and to automatically bypass the HWC when we are away for a week....

I'd be keen to hear from some people with experience, especially if they have recommendations!

Cheers!

eonsim

398 posts

Ultimate Geek

Trusted

#3248172 12-Jun-2024 20:05

You've got a few options, last time I checked a lot of them seemed to be around the $1000 mark.

Catch power Green - Small, automatic, minimal options doesn't need internet or wifi, tracks solar production well https://www.catchpower.com.au/product-page/green-catch-power

Eddi - Connects up to the internet provides you mobile app and probably smart home access, whole ecosystem of car chargers, power diverters, power monitoring and home batteries that will work together with your solar: https://www.myenergi.com/product/eddi/

Paladin - NZ system apparently works well but don't know much more than that https://www.paladin.nz/

Ge0rge

2052 posts

Uber Geek

Trusted

Lifetime subscriber

#3248205 12-Jun-2024 21:05

I have a Paladin, around $1000 + installation. It's brilliant, I wish I had installed it at the same time as I put my solar in, as the hot water bill has pretty much vanished.

Solid-state relay that diverts any export to the cylinder until the cylinder reaches 70°C, then it exports. While there is excess, it holds the cylinder at 70. If you use a heap of water over night, it has a user selectable lower temp limit of 40° or 50°, which it will keep the cylinder at using mains power until the sun is shining again, then it will use export to heat. If you have a prolonged period of bad weather, it will automatically top the cylinder up to 60° every 72 (from memory) hours to kill any bugs.

There's no need to turn it off when you go away. If you aren't using any hot water, then it's only the natural heat loss of the cylinder each night, and your solar tops it back up again during the day - you will come home to hot water that hasn't cost anything.

Ken, the developer and manufacturer of Paladin, is on GZ as @Terciops and is a fantastic person to deal with.

neb

11294 posts

Uber Geek

Trusted

Lifetime subscriber

#3248737 14-Jun-2024 12:07

You don't use the relay to cycle it on and off, you have a relay with NO contacts that you close when you have excess power. You'll be closing them maybe once or twice a day, and it's a purely resistive load so shouldn't cause any stress on the relay. That's the setup I've got here.

Bewildered

106 posts

Master Geek

#3249094 14-Jun-2024 16:16

@neb - Yes...the relay I have now is NO and I activate that for heating HWC on night rate so it only cycles once a day. However a small inverter that is only 5kW and it is mostly below 2.5kW during winter months a diverter is probably better in terms of matching the profile. In summer the inverter flat lines on 5kW as there connected solar panels are oversized, but not on the short/cloudy days. Even with a 60s (or even 300s) average generation value I could be cycling the relay 100 times a day to when there is good power generation and then off again when the output drops.... :-(

@Ge0rge - I've seen those and I've emailed them...I have since seen here that they've got a LoRa-based remote sensor (which is good because there's no way to get a tidy CAT6 connection between the HWC and the Paladin) and I think there must be a way to replace/augment their manual three-way rotary switch with some relays to automate the mode switching....that way it can be all HA-integrated. I've got one reply and then nothing....so not sure what the deal is....I might try to DM the guy you mentioned....

Failing that I might need to branch out and look at something else....can 't buy something that isn't offered. :-)

The Eddi (at least in NZ) looks like it is out of stock...and the Catch Power looks very 'dumb' and I definitely do not want an automatic 11pm hot water 'boost' - I want that to happen when I want it....and that is at the end of the day (4pm ish) so we go into the evening with a full tank....the fact the showers etc come off it and it gets cool overnight is good - I want to recharge on solar, not at 11pm so I start the day with a tank already full of hot water. I don't know how it figures out the time...but this is what their manual says....

So Paladin still looks good...and the fact that people can get them repaired is another bonus....I always prefer repair over replace.

I also saw a DIY kit in the UK...but I'm not keen enough to try that!

And I need two...because if I get one my brother will want one too!

eonsim

398 posts

Ultimate Geek

Trusted

#3249110 14-Jun-2024 17:32

Bewildered:

The Eddi (at least in NZ) looks like it is out of stock...and the Catch Power looks very 'dumb' and I definitely do not want an automatic 11pm hot water 'boost' - I want that to happen when I want it....and that is at the end of the day (4pm ish) so we go into the evening with a full tank....the fact the showers etc come off it and it gets cool overnight is good - I want to recharge on solar, not at 11pm so I start the day with a tank already full of hot water. I don't know how it figures out the time...but this is what their manual says...

There is a solar only mode on the Green Catch power which will only use solar to heat the hotwater, unless it's been long enough with out sufficient solar that the temperature may have dropped into a dangerous range. We have one installed and it works fine, it's just set and forget.

There are 4 modes for the catch, heat now, allow upto 5hrs of mains power a day, allow upto 2.5hrs of mains power a day, solar only. If the tank reaches it's correct temperature only on solar then the system automatically reduces the amount of time it's allowed to use mains on the 2.5/5hrs option until it reaches a steady state (only really useful if your solar system is very small).

Bewildered

106 posts

Master Geek

#3249117 14-Jun-2024 18:06

I'm not sure how the Green Catch 'knows' the water could be cold if it doesn't have a temperature probe, doesn't know the volume of the cylinder so can't tell how much power is 'enough', and doesn't know how much water has been taken from the tank. But "solar only" sounds like it might work if it is possible to wire in a regular old relay in parallel that can feed grid power to the cylinder on a schedule....especially if it can do this without taking the Catch offline first....

eonsim

398 posts

Ultimate Geek

Trusted

#3249121 14-Jun-2024 18:34

Bewildered:

I'm not sure how the Green Catch 'knows' the water could be cold if it doesn't have a temperature probe, doesn't know the volume of the cylinder so can't tell how much power is 'enough', and doesn't know how much water has been taken from the tank.

The hotwater cylinder knows when it's at temperature (otherwise they would draw 48-72kWh per day and boil constantly), and the catch will know if the hotwater cylinder is trying to pull power to heat up. It would also know if solar is being generated and if any is being exported. Then it can adjust the power sent to the hot water cylinder if there is spare solar and the cylinder wants/will use power.

Equinox IT

Cloud spending continues to surge globally, but most organisations haven’t made the changes necessary to maximise the value and cost-efficiency benefits of their cloud investments. Download the whitepaper From Overspend to Advantage now.

Jase2985

13457 posts

Uber Geek

ID Verified

Lifetime subscriber

#3249201 14-Jun-2024 20:04

The thermostat/element circuit is just that its either open circuit or its closed with some resistance. the unit can measure that and apply power when there is excess solar, it's not rocket science.

neb

11294 posts

Uber Geek

Trusted

Lifetime subscriber

#3249229 14-Jun-2024 21:27

Bewildered: Even with a 60s (or even 300s) average generation value I could be cycling the relay 100 times a day to when there is good power generation and then off again when the output drops.... :-(

Ah, OK, so it's a solar-only setup. Mine cycles once from 9pm - midnight for free power and then whenever there's excess solar being exported, but it's just on and then off again once a day, I'm not trying to optimise every watt out of it since the batteries smooth over any gaps.

catdog

107 posts

Master Geek

#3251967 22-Jun-2024 16:52

I have an eddi, so some comments from my experience with it

It does a really good job of tracking the excess solar power and diverting it to the HWC
The newer version includes WiFi built in (the previous version required a separate hub), which is great to allow it to be controlled from their app or with HA. There's a (cloud) integration for it in HA which makes it simple, although I have only used HA to monitor it. I'd expect that you could control boost etc. easily too.
It doesn't actually measure the temperature of the HWC - the eddi simply tries to send power to the HWC and the standard thermostat in the HWC will turn off when it's hot. This makes installation easier since you don't need to connect a probe wire between the HWC and the eddi. The eddi should be installed close to the switch board since you need to connect a current clamp to the main house feed, but my cylinder is on the opposite side of the house.
- However, for my 2 element cylinder this results in annoying behavior where the eddi switches a relay back and forth every 15mins (configurable) to check if the top element is hot before switching back to the bottom element to continue heating.
- Eventually the relay in my unit got "sticky" and wouldn't switch the bottom element on (I could get it to work by tapping the relay!), so then the eddi thought that it was fully up to temperature. Support is based in the UK, so they took a while to decide what to do with poor communication during this period, but eventually they couriered out a brand-new replacement unit.
- To avoid this problem again, I have now connected it so the element selection is performed by the HWC itself (heats the top element and then automatically switches to the bottom element). The eddi only sees a single element and does not need to switch the relay. It works fine in this configuration, but there's less info available to know if you are about to run out of hot water as the eddi no longer knows if the top element is being used (therefore there is not much hot water remaining)
- Just to be clear, the relay only controls the selection of which element to use. The actual power control uses transistors (or IGBTs from memory)
I have a boost timer setup to use 3 hours of free power in the evenings. This is easy to configure on the unit itself or in the app, although I got caught out once when it messed up its clock timezone setting (via WiFi) and thought it was in the UK? and turned on early.

Bewildered:

Ideally it would be something I can integrate with HA....particularly to programme the end of day boost and to automatically bypass the HWC when we are away for a week....

While the boost is configurable, I don't think you can disable the solar diverter. It's always enabled, unless you power off the eddi with the physical switch.
I have not seen any smarts built into it for Legionnaires' disease prevention. So, you have to manually make sure that the boost timers etc. are sufficient to guarantee it reaches maximum temperature periodically. I actually use HA to monitor this - it sends me a notification if it hasn't reached max temp during the last 36 hours so that 1) I know we might be running low on hot water (since it doesn't measure the actual temperature) and 2) I can manually boost it if tomorrow's weather forecast looks bad and I'm not expecting much solar.
The LCD display is quite simple, but I've found that my wife will look at it to see if there's enough excess solar to turn on the clothes dryer etc. during the day since it shows how many kW are being sent to the HWC and how many kW are being sent/consumed from the grid. It's just easier than opening an app 😉

Bewildered:

The question is how much do diverters cost, how long do they last, and then what's the payback period? There's no point getting something that has a payback period of 8 years with an expected life of 5 years.

Cost is about $1000 + installation. By avoiding my relay issue I'd expect it to last a long time (transistor switching for power control, no fans to wear out etc.). Payback period is going to depend on many individual factors (difference between buy-back rate vs buy-in rate, how much solar you export, how much hot water you use etc.)

Bewildered

106 posts

Master Geek

#3252002 22-Jun-2024 20:15

That's super helpful thanks! For now I need to wait for the price difference between the solar buyback rate and the cost of power to diverge as the difference of 5c makes it really hard to get an economic return on the investment.

Ideally, I'd use something like a Schneider ITL+ (good for 5,000,000 cycles) to control the cylinder so I can cycle it in and out in 5 minute intervals....but I don't think a Shelly relay is good for that many operations. So I'd need something super reliable to cycle it in an out.....or I have to go to something else with a solid state relay....there's no load per se...it would only be energising the HW relay...but whatever it is it would need to be HA-integrated and DIN rail mounted. :-)