BlargHonk:

 

You are putting something from AliExpress in your switchboard?

 

No! After switchboard ofc. Electrician reviewed.

dukezoid:

 

Pardon, yeah not suggesting these for diverter-style (constant switching) operation. Just timed operation e.g. across peak solar hours and/or off peak import hours.

 

63A rated and tear down comments suggest relay is of decent quality. We’ve not had any issues.

 

While 63A sounds like a lot of headroom for the 13A load of a 3kW HWC, this isn't any guarantee of safety. The headline rating on devices like this usually refers to the internal breaker or relay contact’s theoretical carry capacity, not the assembled product's practical continuous switching capability. 

What that means is the breaker mechanism may be sized to pass-through a 63A current okay, but it doesn't tell you anything about the unit's endurance when handling such loads. An hour's load from a HWC element at 13A is going to cause the PCB to heat up significantly - especially when it's installed in an enclosed switchboard with no air flow.

Even if you're only switching the contacts infrequently on a timer, if it's under load when switched it will create substantial arc energy relative to the size of the relay. Over time this will cause pitting and carbon buildup on the relay contacts. Eventually this can result in welding and open-circuit failure.

If the device isn't designed by the manufacturer to support HWC loads, I would not use it. Although it may work fine for a few years, the risk of failure grows over time, and the result will be a fire.

A timer switch is a relatively simple and inexpensive approach, and there should be no reason to go to AliExpress rather than your local electrical supply retailer for a suitably rated timer switch.

For a switch solution there are at least two important considerations:

 

1. how you control the switch.  The approach the Catch Relay uses is to monitor excess solar, and switch the HWC system on when that exceeds a threshold, e.g. the nominal power rating of your cylinder.  It also does a 'top-up' overnight if the switch hasn't been on for long enough during the day.
2. requies your solar system to be large enough so that you do have sufficient excess solar to exceed the threshold, i.e. the power rating of your HWC

e.g. if your cyclinder is 3kW, and you've set the threshold at 3kW, then your cylinder will switch on whenever you have excess solar exceeding 3kW.  Binary- it is either on or off.

A diverter is a lot more complex - it will vary the voltage across the HWC element to shape the power into the cylinder to the available excess power.  e.g. if you have 1.8kW excess solar, then it will put 1.8kW into the cylinder ...

In both cases, the thermostat in the cylinder operates per normal to turn the heating off when the water is sufficiently hot.

So - how are you controlling this AliExpress "smart" relay?  Where are the smarts?  It says on the AliExpress website that it is not compatible with HomeAssistant, but can their provided app monitor excess solar and provide the appropriate logic to turn the switch on and off?

My installer chucked in a Theben SYN 160 a (Analogue Timer) for free, typical cost 75$, I just set it to Summer: 10am–7pm / Winter: 9am–5pm. On a 300L "Thermal Battery" (17.4 kWh @ 65°C) water cylinder. 

Upcoming to 1 year install in march, will show results then.

cruxis:

 

My installer chucked in a Theben SYN 160 a (Analogue Timer) for free, typical cost 75$, I just set it to Summer: 10am–7pm / Winter: 9am–5pm. On a 300L "Thermal Battery" (17.4 kWh @ 65°C) water cylinder. 

 

Upcoming to 1 year install in march, will show results then.

 

EgorNZ:

 

HarmLessSolutions:

 

HWC consumption is typically >30% of a home's electricity demands. They are also a storage device so essentially can be regarded as a battery storing your generation as heat until such time as it is needed. The most effective way to do this is by including a HWC diverter as part of your solar set-up, which unlike a simple timer won't draw from the grid when a cloud moves over your panels.

 

Having had solar on two properties over the past 14 years I know that most homes will struggle to self consume >50% of their solar generation even when charging an EV under manual control. It is important to realise that your exported generation typically loses half or more of its value when exported. Solar diversion of EV charging and HWC heating is the key to maximising self consumption which is the optimum way to maximise ROI, without the added expense of batteries. Manual control is a hassle most people can't be bothered with and is ultimately nowhere near as effective in getting the best return on your solar investment.

 

 

HWC diverters can be expensive for what they are, but I agree they're worthwhile for solar installs without batteries.

 

In theory 180L of water heated to 65C has an energy capacity of over 10kWh, which is comparable to a home battery. But as energy storage it is obviously much less versatile; there are only so many showers you can take or other uses for hot water in a day. If you don't cycle through 180L of hot water daily then the usable capacity is going to be much less than this figure. And it's a storage device that's constantly leaking energy through heat loss.

 

When you do have a battery, the added value from HWC diversion is reduced.

 

With a battery and without HWC diversion, I average 70-80% self consumption:

 

Congrat's on your high self consumption levels.

In regard to the analogy of a HWC as a battery our 250L cylinder is good for stashing away about 9 kWh/day with most of that hot water used within a 24 hour period with minimal heat loss as it's a modern well insulated cylinder. a 3 kW element will raise 250L of water by about 10 degrees C per hour so a useful way to increase our morning generation's self consumption which typically entails raising our HWC from its grid demand set-point of 40 degrees to the ~70 degree maximum I have set the cylinder to.

Also agree with a diverter's reduced usefulness when a battery is present, as would be expected as the HWC is being regarded as a second battery in essence.

HarmLessSolutions:

 

cruxis:

 

My installer chucked in a Theben SYN 160 a (Analogue Timer) for free, typical cost 75$, I just set it to Summer: 10am–7pm / Winter: 9am–5pm. On a 300L "Thermal Battery" (17.4 kWh @ 65°C) water cylinder. 

 

Upcoming to 1 year install in march, will show results then.

 

Just a thought regarding your scheduling in that if you are with a supplier with peak export rates maybe look at delaying that start time in summer until 11am. In our case we're generating at a pretty high rate between 10 - 11am on a clear day, and exporting most of it as our diverter is disabled until 11am.

 

Thanks — I’ll set that now and see how it goes. I’ve had too many mornings with an annoying 300‑plus‑watt grid top‑up kicking in for a while.

I have a pdl bluetooth timer on hot water that runs from 9 am to 3pm over summer that gives heaps of hotwater. I have thought about controlling it so it only turns on when sun is out but that gets messy if the whole day is overcast.

prob:

 

I have a pdl bluetooth timer on hot water that runs from 9 am to 3pm over summer that gives heaps of hotwater. I have thought about controlling it so it only turns on when sun is out but that gets messy if the whole day is overcast.

 

So essentially you are planning on modifying the functionality of your timer to that of a diverter. A timer will definitely schedule to whatever duration required to fully heat a HWC but it will supplement from the grid every time a cloud shades your panels. The difference is how effectively your solar generation is utilised.

HarmLessSolutions:

 

prob:

 

I have a pdl bluetooth timer on hot water that runs from 9 am to 3pm over summer that gives heaps of hotwater. I have thought about controlling it so it only turns on when sun is out but that gets messy if the whole day is overcast.

 

 

So essentially you are planning on modifying the functionality of your timer to that of a diverter. A timer will definitely schedule to whatever duration required to fully heat a HWC but it will supplement from the grid every time a cloud shades your panels. The difference is how effectively your solar generation is utilised.

 

Not quite a diverter, as that would also be able to shape the power into the HWC to match the excess solar (i.e. by adjusting voltage using a device such as a  triac).  It more closely matches the function of a smart relay such as https://www.catchpower.com.au/.  We have one fitted and it works well in summer, as excess solar regularly exceeds the capacity of the HWC.  Of course, in winter you can choose to set the threshold lower to use a mix of grid and solar, e.g. 2.4kW threshold to use a mix of 2.4kW solar + (nominally) 0.6kW (peak) grid.  To complicate things a little, my HWC is nominally 3kW, but actually consumes around 3.25kW due to the high voltage at our location - so with the Catch threshold set to 2.4kW, it will supplemement with 0.85kW off the grid @ 33c/kWh.  That is still better than selling the 2.4kW @ 17c/kWh during the day and buying back 3.25kW at 23c/kWh on off-peak overnight (Meridian/Orion network).

Looks like Orion will allow up to 10kW - applications open in April:

https://www.oriongroup.co.nz/our-story/the-latest/export-limits

ashtonaut:

 

Looks like Orion will allow up to 10kW - applications open in April:

 

https://www.oriongroup.co.nz/our-story/the-latest/export-limits

 

But note

These will change over time which dictates the need for us to move from static limits to dynamic limits in the future.

Wouldn't it be great if the government provided support for domestic solar uptake to the degree they are for these farmers.

https://www.thepost.co.nz/business/360950502/energy-minister-backs-rural-solar-power-costs-bite-rural-businesses

fastbike:

 

ashtonaut:

 

Looks like Orion will allow up to 10kW - applications open in April:

 

https://www.oriongroup.co.nz/our-story/the-latest/export-limits

 

 

But note

 

These will change over time which dictates the need for us to move from static limits to dynamic limits in the future.

 

Exactly the same as what vector are proposing

But there needs to be a minimum they can reduce the export down to, say 5kw as it currently is.

And there also should be a condition on it that they need to be reinvesting into their network to provide more resilience for solar.

HarmLessSolutions:

 

Wouldn't it be great if the government provided support for domestic solar uptake to the degree they are for these farmers.

 

https://www.thepost.co.nz/business/360950502/energy-minister-backs-rural-solar-power-costs-bite-rural-businesses

 

Unfortunately, that's behind a paywall, and I've been unable to find the details elsewhere - can someone with access please post the pertinent details?  How does it compare to the 30% solar and battery rebate for residential solare in Australia?

I've always thought just making it GST free would be logical.  Social benefit by contributing to the grid would justify a tax-free status.  15% should be enough to incentivise and help build the market.  30%, per Australia, seems to have overdone it, causing cash-up people to over-build (and taking up the funds that arguably would be better being spread around those less able to pay big upfront capex to reduce power costs ...)