Making the most of night rate power

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SumnerBoy

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#1019800 7-Apr-2014 10:20

I am on the Genesis Day/Night rate and have a fairly smart home able to take advantage of this. For example, I run a hydronic underfloor heating system, with an air-to-water heatpump as the source. I only run the heatpump from 9pm till 7am - the 'night' hours on Genesis. The cost per kilowatt is about 1/3 of the day rates, so even though the heatpump probably has to work a little harder due to the colder ambient air temp at night, I am pretty confident I am saving plenty. The beauty of this heating system is the concrete slab is 'charged' up with heat each night and then radiates that heat during the day. I work from home and even in the depths of winter the internal temp doesn't drop below 20. And my monthly power bills never go above $200, usually around $180.

I also have a solar hot water system, which means in summer I hardly ever have to heat my cylinder using electricity. In winter it needs a top up most nights unless we have a couple of sunny days in a row. But again, this electricity top-up is scheduled to happen at 4am during the cheaper rates.

I have a delay timer on my dishwasher so I try to ensure that only ever runs after 9pm. I don't have this on my washing machine unfortunately, but the next one I buy will definitely have it.

I am very interested to hear how others use/monitor their electricity usage. The old man has just built a new house (earthquake rebuild) and he has opted to install solar PV cells on the roof. In his situation I think he is probably better off running his underfloor heatpump during the day, to make sure of the solar gain when it is available. But ideally he needs a smart home automation system to monitor the PV panel output and only turn on the underfloor heating when it is generating enough to make it worthwhile.

This is the sort of thing you can get very clever with. I.e. schedule a dishwashing/washing machine load when you leave home in the morning and have your 'smart home' monitor the PV output and turn on the appliances when there is enough juice being generated. This is a far more efficient use of electricity than pumping it back into the grid, getting reduced rates, and then using full price electricity in the mornings/evenings when you have no solar (as already mentioned).

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gzt

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#1019853 7-Apr-2014 11:59

You have night rate available? Buy an electric car ; )

SumnerBoy

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#1019855 7-Apr-2014 12:00

Don't worry - I am keeping an eye on them!! That new Mitsubishi Outlander looks pretty tempting...if I had 60K lying around...

SaltyNZ

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#1019886 7-Apr-2014 12:53

kiwitrc:
Aredwood:
SaltyNZ: We don't have it here either, so I'm thinking of switching to solar at night.

How do you use solar power at night? Am I missing something - Night time means no sunlight so how could you possibly use solar power at night?

You need to use "internet enabled solar", when its dark here you get your solar from enabled ones in parts of the world where the sun is still shining.

Exactly. I feel this is a very underserved market, and I'm sure there's a killing to be made!

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Aredwood

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#1020166 7-Apr-2014 19:12

SaltyNZ:
kiwitrc:
Aredwood:
SaltyNZ: We don't have it here either, so I'm thinking of switching to solar at night.

How do you use solar power at night? Am I missing something - Night time means no sunlight so how could you possibly use solar power at night?

You need to use "internet enabled solar", when its dark here you get your solar from enabled ones in parts of the world where the sun is still shining.

Exactly. I feel this is a very underserved market, and I'm sure there's a killing to be made!

Sign up to UFB and connect a solar panel into that. There must be alot of light going down those fibres since they always say "Don't stare into the end of a fibre optic cable". Otherwise UFB should definitely help internet enabled solar to work faster.

Shoes2468

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#1020188 7-Apr-2014 19:39

Thanks for all the fantastic feedback,

Aredwood: To the OP

How is your hot water cylinder controlled? Does it only heat at night or is power available to it all the time? And does it have 2 elements or just the 1? If all the time switch it to night rate only. You can also get a "one shot" circuit connected to the cylinder as well. if you run out of hot water and can't wait till night time press the button to have it do just 1 heating cycle. If you have a chest freezer, stick it on a timer so it will only run during the night rate period. Swimming pool or spa, only run pump during night rate period.

I currently have a hot water cylinder with one element which runs night rate only with a switch in the fusebox to boost if required. I am with genesis energy in christchurch.

maslink: Yes, if there is a significant drop in temperature overnight, then doing the initial heating on night rate will potentially save you some money. If, for example, you needed to run a 6kW Heatpump for 1hr/day to return the room to the desired temperature, then this would be a saving of ~2kWh @ 10c/kWh (rate differential), or $6/month. There are probably bigger savings from Hot water load and other timeshiftimg however.

Thanks for this calculation, our lounge heat pump is around 9kw and puts things into perspective

SumnerBoy: Don't worry - I am keeping an eye on them!! That new Mitsubishi Outlander looks pretty tempting...if I had 60K lying around...

I too have been keeping an eye on them with the outlander looking like the best yet, but as you say to have a spare 60k lying around, and then there is the additional maintenance cost.

raytaylor

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#1020234 7-Apr-2014 20:28

1) Fill your garden shed with a concrete block, and insulate.
You want to run a heatpump based hot water heater. Pump hot water through pipes laid out within the concrete block to heat it at night.
During the day, cycle water through alternate pipes in the concrete block and direct it through a radiator in your hallway. It works like a storage heater, except on a much bigger scale. Basically you want to store heat created during the night, for daytime release.

2) Become nocternal
Get a job where you work mostly in the offpeak period, so all your daytime power consuming activities take place at night.

3) Compute the mysky time delay
In my head, it may possibly work out cheaper to run your mysky during the evening onpeak to record programmes as they air, but watch them after 1am as the power to run the tv while playing back the programmes may be slightly cheaper than watching them live.

4) Electric car
Recharge it during the night

5) Get a silent dishwasher, or move it and the washing machine/dryer out to the back shed.
Hey actually if you leave a little space in the garden shed, and add a clothes line inside, it could become a clothes dryer with the hot concrete block providing a heat source.

6) Battery storage
There was an idea a few years ago that suggested that one could use his electric car at night to recharge the batteries, then sell power back to the grid at higher rates during the day. Why not just use the power in your home, and not bother with selling back - just buy a bunch of SLA deep cycle batteries to run appliances and recharge them at night.

In the UK, they use a similar system called Rapid delivery power systems or something like that. During the morning at offpeak times, they pump water up a hill to a lake.
At the 7.10 coronation street ad break that evening, everyone turns on their kettles so to deliver the power, they release the water back down the hill through a hydro system, selling it at onpeak prices to the grid. Then when the power is cheap again, they use it to pump the water back up the hill.

So you can do the same thing using SLA batteries. If power is really only half price during the offpeak hours, then it could become possible to do this where you store your electricity during the offpeak hours, and then use it from your batteries during the onpeak. You would have to test some batteries to see what the total cost of ownership/replacment etc is to find out if it is worth it.

7) Fridge, Freezer timer and water bottles
Fill the empty space in your fridge or freezer with water bottles. When you open the door, the cold air would fall out, and the warm air that replaces it needs to be cooled back down - wasted power.
If you fill empty space in there with water bottles, the air(water) wont fall out because its held there in the bottles, and therefore wont need recooling when you close the door.

If it is a chest freezer, move it outside where the surrounding air is cooler, still fill the empty space with water bottles, and put it on a timer.

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Geektastic

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#1020307 7-Apr-2014 23:22

SumnerBoy: I am on the Genesis Day/Night rate and have a fairly smart home able to take advantage of this. For example, I run a hydronic underfloor heating system, with an air-to-water heatpump as the source. I only run the heatpump from 9pm till 7am - the 'night' hours on Genesis. The cost per kilowatt is about 1/3 of the day rates, so even though the heatpump probably has to work a little harder due to the colder ambient air temp at night, I am pretty confident I am saving plenty. The beauty of this heating system is the concrete slab is 'charged' up with heat each night and then radiates that heat during the day. I work from home and even in the depths of winter the internal temp doesn't drop below 20. And my monthly power bills never go above $200, usually around $180.

I also have a solar hot water system, which means in summer I hardly ever have to heat my cylinder using electricity. In winter it needs a top up most nights unless we have a couple of sunny days in a row. But again, this electricity top-up is scheduled to happen at 4am during the cheaper rates.

I have a delay timer on my dishwasher so I try to ensure that only ever runs after 9pm. I don't have this on my washing machine unfortunately, but the next one I buy will definitely have it.

I am very interested to hear how others use/monitor their electricity usage. The old man has just built a new house (earthquake rebuild) and he has opted to install solar PV cells on the roof. In his situation I think he is probably better off running his underfloor heatpump during the day, to make sure of the solar gain when it is available. But ideally he needs a smart home automation system to monitor the PV panel output and only turn on the underfloor heating when it is generating enough to make it worthwhile.

This is the sort of thing you can get very clever with. I.e. schedule a dishwashing/washing machine load when you leave home in the morning and have your 'smart home' monitor the PV output and turn on the appliances when there is enough juice being generated. This is a far more efficient use of electricity than pumping it back into the grid, getting reduced rates, and then using full price electricity in the mornings/evenings when you have no solar (as already mentioned).

The problem is, electricity is not yet expensive enough to make many of the more technological tricks worthwhile. Even solar/wind to provide 70% of our needs would take us 5 years to recover, not including things such as the cost of replacing fridges, freezers etc with more expensive ultra-high efficiency models and so on. If I was building a new house, then certainly I would incorporate many of these things but retro-fitting them is usually not worth the aggro.

In many countries there are useful government grants or local authority grants, reduced GST/VAT on power etc but I don't see much evidence of that here.

Coil

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#1020308 7-Apr-2014 23:37

1) Fill your garden shed with a concrete block, and insulate.
You want to run a heatpump based hot water heater. Pump hot water through pipes laid out within the concrete block to heat it at night.
During the day, cycle water through alternate pipes in the concrete block and direct it through a radiator in your hallway. It works like a storage heater, except on a much bigger scale. Basically you want to store heat created during the night, for daytime release.

Expensive routine.

In my house we use about 800-1000L of water a day, And during winter have 2 gas heaters on 24/7, gas hot water cylinder x2, gas stove.

SumnerBoy

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#1020344 8-Apr-2014 07:49

Geektastic:The problem is, electricity is not yet expensive enough to make many of the more technological tricks worthwhile. Even solar/wind to provide 70% of our needs would take us 5 years to recover, not including things such as the cost of replacing fridges, freezers etc with more expensive ultra-high efficiency models and so on. If I was building a new house, then certainly I would incorporate many of these things but retro-fitting them is usually not worth the aggro.

Very true - it is more of a hobby of mine (the whole home automation/technology thing), with some beneficial side effects. I built my house 2.5 years ago, and there are already a raft of things I wish I had done differently!

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