Automatic ToD turn on/shut off for high power appliances recommendation sought

[Burningislove]

I'm a few days away from my rooftop solar system installation (9kW, no batteries), and naturally trying to maximize power usage during the day when my system is generating and minimizing at night when I need to pull from the grid. There are certain appliances such as my electric hot water heater that I'd only want to run when the system can power it. I live alone and hence my hot water needs are not large, and my hot water heater is well insulated & efficient which keeps water hot for days without needing power.

Obviously, I could go into the basement and shut off the water heater's dedicated circuit breaker at night and only turn it on during the day, but that's rather cumbersome and was looking for something automated. It would also need to have a manual turn on so I could switch it on at night if needed, or after a storm when my panels are covered in snow and I'm reliant upon the grid.

I'm reasonably savvy with wiring, and could certainly wire an inline timer such as the one I use for my pool pump that is rated for that level of power. But I'm curious if there is a simpler solution without going the DIY route. There are a few other appliances like the deep freezer in my garage that don't require a 'persistent' power connection and would do just fine if they only drew power during the day.

[Mdm99]

Are you net metering ?

[Burningislove]

Are you net metering ?

Yes to net metering. If NGrid is only measuring over the entire (monthly) billing cycle, then no this wouldn't be needed. I guess I'm just expecting some fine print that's not apparent that will make this more complicated than I had thought.

[SunEagle]

There are a number of companies that make some type of Energy Load Management system for homes.

I do not know what they cost or how much it takes to install them but if you look on the internet you can find them.

[peakbagger]

The old X-10 system had the capability for remote outputs and AC carrier line switching, they also had a battery backup timer for addressing the switches. I used to use mine to switch my AC on before I got home. I also used it to send a signal to my floodlights at night just in case I left the darn things on (300 watt halogens). Its not a particularly secure setup, in that there were only 24 codes. Leviton made a spec grade version that was fairly robust. I still have 20 plus year old switched receptacles that I can remotely turn on and off from different switch plates in the house. I never saw a water heater contactor but they did have a switching device that could pull in an appropriately sized relay.

[SunEagle]

The old X-10 system had the capability for remote outputs and AC carrier line switching, they also had a battery backup timer for addressing the switches. I used to use mine to switch my AC on before I got home. I also used it to send a signal to my floodlights at night just in case I left the darn things on (300 watt halogens). Its not a particularly secure setup, in that there were only 24 codes. Leviton made a spec grade version that was fairly robust. I still have 20 plus year old switched receptacles that I can remotely turn on and off from different switch plates in the house. I never saw a water heater contactor but they did have a switching device that could pull in an appropriately sized relay.

Companies like Schneider electric make both the control system and "relays" that can turn a load on or off on command based on some type of parameter. They are a little more expensive but are probably on the top level concerning quality.

[J.P.M.]

Turning off the power when not needed will in theory and reality save energy.

However, when and for how long you interrupt power for a well insulated large thermal mass may need some consideration when reconsidering an operating schedule.

An 80 gal tank w/ say, R10 insulation will lose about 10 deg. F./24 hrs. when the water is about 60 deg. F above the surroundings.

If you turn the heating element off at nite, the tank will be about 3 deg. F. cooler in the A.M. than when you went to bed. That temp. diff. may not even be enough temp. drop to cause the thermostat to call for heat even if the heating element were powered.

One possible solution is indeed to keep it on a timer and adjust your use to the timer schedule, whatever that schedule may be as you choose - probably off peak if you can make the lifestyle adjustment.

[Mike90250]

I use a timer and contactor, to restrict my water pump (pumps from pond to 160' elevated 12,000 gallons storage) so that the pump only comes on during the sunny part of the day. So I'm shifting loads directly to the PV, and not running a large pump for hours off of the batteries.

[foo1bar]

I'm a few days away from my rooftop solar system installation (9kW, no batteries), and naturally trying to maximize power usage during the day when my system is generating and minimizing at night when I need to pull from the grid.

Most likely the POCO would prefer you run your appliances (like hot water heater) late at night.
They have usually have some baseline power generation that they have to keep running all the time, so any loads you run at 1AM instead of 5PM is better for them. Because they can use power you generate at 5PM to power the AC for you and your neighbors home - or the oven for you and your neighbors. And then they have less need for peak production to support those AC units and such.

You can (and should) check with your POCO on how they do the billing especially with net metering.
And some of them (ex. Los Angeles) have published how their power demands vary throughout a day.

off-grid systems are a completely different beast of course - so in those cases, shifting power so it's used during-the-day is a good idea/economic necessity.

[inetdog]

In the "old days" POCO would often have a rate plan for domestic hot water that included a separate meter with a built-in time clock.
The full time power went to the top heater element of the tank while the off-peak power went to the bottom element. That way if you ran out of water, only enough in the top part of the tank for your immediate needs would be heated, the bulk would take place overnight.

Electronic timers for the voltage and wattage of a water heater element may be hard to find, but the old clock motor mechanical timer switches are still around.

[foo1bar]

In the "old days" POCO would often have a rate plan for domestic hot water that included a separate meter with a built-in time clock.
The full time power went to the top heater element of the tank while the off-peak power went to the bottom element.

The one we had was just 1 element - since hot water rises and the cold water came in at the bottom (via a tube internal to the HWH) there was usually enough hot water for the day in the tank.
If you used it all up in the morning, you'd have to wait until the timer kicked in that night.

Electronic timers for the voltage and wattage of a water heater element may be hard to find

http://www.nsiindustries.com/catalog/nsiproducts/tork%C2%AE-digital-time-switches/digital-time-switches/dtwh40

I'm sure there are other manufacturers as well.

(NOTE - I still think you're better off NOT putting your larger loads during the day, assuming grid tie and net metering)