Ideally you should try switching in manually  for at least a week to see if you have enough hot water.

I installed a 30A timer between the hot water cylinder and the switch inside the cupboard.   

The ripple control usually switches it on at 7-8pm but our free power doesnt start until 9pm.   

The daily power cut of a couple of hours in the evening through winter buggered the backup battery in the timer so it would keep loosing its clock time.    

So I swapped it out for a 30A wifi timer from aliexpress. 

Each time it powers on, it just reconnects to the wifi and seems to keep/redownload its config from the cloud and syncs its time with the internet/ntp server without issue.   

And the Tuya app shows its hourly power consumption, as well as the line voltage/amps.   

I have also turned up the temperature - no kids in the house (and tempering valves on the recently rennovated bathroom fixtures) so it can store more and stay above 60 degrees for longer because we use less hot water. 

It fully heats up every day and so never spends more than 16 hours per day below 60 degrees, and never spends more than 8 hours per week below 60 degrees (for legionnaires prevention). 

For 3 people in the flat, the 180L tank starts at 21:10 and is usually finished reheating by 22:20 (1hr10min) with a 3kw element. 

I originally had a 5-6am boost but found this wasnt needed. It was using about 1kw which would be the lost temperature between ~11pm and 5am - so losses are about 1kw per 6 hours or 5 degrees which explains why it would take 2-3 days to notice the luke warm shower when the original timer had failed and lost its clock on each occasion.    

I also went out and bought a second hand night storage heater. An electrician owed me a favor so i got a dedicated circuit for it installed back to the breaker board with a timer on the board. It charges up at 3kw and can store 24kwh of energy - but between 9pm and midnight it only gets about 9kwh which it then slowly releases at a constant 1.5kw during the night so in the morning the house is much warmer when we wake up. Hardly had to use the heat pump at all in the mornings this last winter. 
However i forgot to change the time when daylight savings started so it was costing me almost $1 per day for a month.     

Our power bills have never been lower. We were only $167 last month. Prior to good nights, it used to be about $220-$250. Through winter this year on good nights, with the night storage timer, and the hot water timer the maximum we had was $184 since we were using the heat pump much less than previous years. 

Our shifted loads now have us at about 40% of our daily kwh used being free 9-midnight.  

prob:

 

Thinking of getting a timer so that the hot water cylinder can be used during off peak / free power.

 

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Any other plans out there that will allow this to happen?

 

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Octopus Energy NZ, my power company, are trialling hot water heating control using the smart meter to shift heating to off peak rates.

https://octopusenergy.nz/blog/hacking-hot-water-to-save-money