Control AC Depending on Level of Solar Battery

I am planning out what I would envisage for my next home and apart from having lots of home automation, one other feature I would like to include is someway to control the AC depending on the solar battery. I am not sure it is the best idea but what I am thinking so far is to have solar panels that charge a battery that would hold enough charge for about a day. Charge during the day in the sun, then expend the battery overnight until the sun comes out again.

At night I would like to have the AC going until the battery reaches say 10% or at worst case runs out of juice. I am guessing this might be on it's own circuit to the battery (if it is just to power off on 0 battery), that way I would need a switch to change from battery power over to mains.

Any thoughts or ideas? Am I stupid for thinking about this (don't answer this JV)?

Comments

  • +4 votes

    Sounds like would need something like Home Assistant and something to control it all.

    There would need to be some interface between your battery/invertor and your AC.

    Might be some examples out there to look at, but probably need to work out what kind of input/output your AC and solar system accept.

    •  

      If it was with home assistant then I would need an AC that integrates with it, so it knows if it is on or off (so it doesn't turn on when battery is gone) and also have a battery that integrates its charge level with home assistant.

      When you say look at the in/output they accept, you are talking more controls rather than direct power yeah?

      •  

        If your AC uses an IR remote then you can get an IR blaster.

        It doesn't confirm the AC actually turns off but I find the broadlink IR blasters very reliable with my aircon.

        I have solar as well and would love to work out the code to get the AC to be controlled according to the solar output but Im not smart enough with home assistant to get that working yet.

        •  

          Yeah my only concern with that is it might turn the AC on if it is already off haha. To get around that I would need to 'run' the routine every time I put the AC on at night. I would like if possible to set it once and forget it, then it auto turns off when low power on battery.

          PS. I already used a broadlink IR blaster :P

          • +1 vote

            @knobbs: The codes for my Fujitsu to turn on and off are different.

            So the only concern is the IR blaster code somehow doesn't make it to the aircon and it doesn't turn off. You can get around this but sending a 2nd turn off code a few seconds after the first to be sure.

            •  

              @No: Oh that is nice then, mine is the same signal :(

              • +1 vote

                @knobbs: Some people chuck a door sensor on the blades or a temp sensor so you can verify its on or off.

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                  @No: A door sensor is a great idea. Never thought of that.

  •  

    How much power do you envisage your AC will use? Mine uses very little power once it starts.

    •  

      No idea, as little or much as it will need. The only time I might take that into account is picking a battery size I think

    •  

      Depends on the weather in your location, the size of the AC system/ rooms heated. AC and water hearing are the biggest energy consumers in a house. We have a 14kw Ducted Fujitsu inverter RCAC. Also have 2 x 6.5kwh solar batteries. The AC will flatten the battery completely in 2hrs, using 5kw to heat 2 bedrooms, lounge, kitchen. That being said, we run it for 20 mins and the house is warm enough for the night.

      If I had my time again I'd probably go with a couple of spilts, but still around 1kw per room in this weather.

    •  

      a small 2.5kw system probably pull around 6-700w when it's up and run but my 8kw will easily chew through 3kwh each hour in the early winter morning.

  •  

    I'd look at the numbers around running the air con off batteries vs exporting/using when the solar panels are on and importing from the grid at night. When i was crunching the numbers a decent sized battery 8-10kwh would require around 8-10 years to pay back from memory (assuming no battery degradation). At this stage i believe you'd be better off waiting until batteries come down in price and hedge your bets with a hybrid inverter.

  •  

    Do you envisage having Single Rate or Time of Use (TOU)?

    Not sure why you want to separate AC from other power use. Is your goal lowest cost billing or something else?

    The round trip cost of the battery may cost more than Off-peak power on TOU

    •  

      Not sure yet on single or TOU, depends on how big the battery is I guess.
      Not separate it, everything will run from the battery if possible but want AC to turn off if battery is low/off.
      I am not putting the solar and battery in for just AC, this is just a small part of running off a battery I would like to incorporate. I would love to be able to work everything out so that I am basically not using any mains and self sufficient.

  •  

    Surely if you need AC, you will keep it running irrespective of the battery level?

    •  

      If needed then yes I would swap over to mains before going to sleep. Although I have never 'needed' AC before to sleep.

      • +1 vote

        Although I have never 'needed' AC before to sleep.

        Then what's the obsession with running it now?

        •  

          Not sure how you got obsession from this, I am just looking at being efficient and trying to be self sufficient staying off mains. If I have excess power I would prefer to use it on something like a nice to have AC running than getting rebated from a power company.

          •  

            @knobbs: Get an inverter with a smart meter, that can also control a load. Have it turn the AC off if battery drops too far. You don't want to take batteries to 0% or 100% by the way.

            Also, getting some money from feed in, rather than using an AC you don't necessarily want to use, may be better.

            •  

              @brendanm: Good point about the battery life and not going too far either way. I guess highlights my point even further to be able to control something based on charge level.

              So with certain smart meters, you can have it control loads/circuits that come from it. So you could have say a gang of 'nice to have things' and then also an essential always powered kind of setup? I would just need to get a sparky to wire up the 'nice to have things' on another circuit to the inverter, but also add a switch into the 'nice to have things' to swap them over to mains/essential?

              • +1 vote

                @knobbs: You set up the inverter (assuming you have an all in one "hybrid" inverter), to only charge the battery to 90%, and discharge to 10% as an overall limit, no matter the device in use.

                Yes basically you should be able to set up things to only turn on when the inverter is supplying power, either from solar or battery, should also be able to have it prioritise charging the battery over running things during the day, but I'm not 100% sure on that.

                Features change all the time on this sort of stuff, you'd be best off having a chat with your installer about what equipment they can supply, and its capabilities.

                •  

                  @brendanm: Sounds great, I think this fits what I am looking for.

      •  

        If needed then yes I would swap over to mains before going to sleep.

        It will be a primitive system if there's a need to "swap over".

        Good luck getting a choice between TOU & Single Rate. They'll force you onto TOU.

        •  

          When I say swap over, I am referring to swapping the appliance from 'only working if battery above %' to mains. Not swapping TOU and single rate power plan in the case that I need it.

          •  

            @knobbs: I know you mean swap from battery to mains. It doesn't work that way. You don't physically swap, it just happens seamlessly.

            For what you want to do you need to engage a Solar PV & battery supplier that has experience in off-grid technology and automation.

            Step 1 of your personal research should be to understand how much power (watts) a modern inverter Ac pulls. My 3.5kw unit runs off a standard 10amp circuit.

            Reading what you want to do, it's like you are willing to spend $1000 to save an extra $100/year.

            Are you the guy that was asking about 3 phase?

  • +1 vote

    Most if not all batteries will have this done automatically. You don't need to switch back to mains manually once the battery is depleted or at whatever level you choose

    •  

      Are you referring to the battery just swapping everything over to mains, rather than deplete to 0%? I am trying to achieve something a little more complicated. Where certain things only work if battery has power, rather than swap everything over once it is low.

      • +1 vote

        Must have misread, apologies

  •  

    It sounds like you are interested in making your ACs more energy efficient. I have all of mine controlled with Ambi Climate . It improves their efficiency, makes the rooms more comfortable and is easy to automate through IFTTT. Once they're connected to an automation platform like IFTTT, the sky's the limit.

  • +2 votes

    I have Growatt batteries. Everything runs of the batteries until they are depleted (I've set that at 15%). Then switches over to the grid. But you can customise the output however you want.

    You can buy current sensing switches you could install on the Battery output side. Once no current is running from the batteries, it will switch off whatever is connected to it. https://www.ebay.com.au/itm/174484789614

    Note though that the hole on this is likely too small for the wiring to fit through with a Low Voltage solar battery (50v battery). HV battery might be ok, or find similar with a bigger hole.

    Alternatively an ATR (auto transfer relay will work), but cutting an AC off directly might be a bad idea. They normally ramp down/ keep the fan spinning outside to cool off when you turn them off.

  • +2 votes

    It seems to me that what you are after is a comfortable temperature in your next home with minimal cost. The simple way to achieve that is through passive solar design. Get your building to grab or exclude heat directly without the ‘middle men’ ie panels, battery, air con, control systems.

    The key elements of passive design are: building location and orientation on the site; building layout; window design; insulation (including window insulation); thermal mass; shading; and ventilation. Each of these elements works with others to achieve comfortable temperatures and good indoor air quality.

    We have an existing house that we did a minor renovation on using some passive design elements at minimal cost and even that made a major difference. We heat and cool with a RC air con and only use it about once a week even in the middle of the Adelaide winter. Currently seriously looking at retrofitting a simple, smart ventilation system.

    If it was a new build we would go completely solar passive.

    •  

      Yes 100% this as well, passive/solar climate control is a major component of what I want in a house as well. My current townhouse is terrible, all the sun in summer and 0 in winter, leaves us with chilly winters and hot summers. I need to look a bit further into some others I haven't really considered like window insulation and thermal mass though.

  • +1 vote

    You need to figure out a way to control the AC first. If using Tesla Battery then you can use the API to automate switching the AC on and off.

    Just keep in mind that according to your description the AC is on the same circuit as the rest of the house, so your battery will supply the house AND the AC through the night. With something like Homeassistant (or a smart climate controllers) you can automate the AC shutdown.

    As an alternative, you could size your batteries to carry you through the night. I'd personally hate to wake up to a very cold bedroom because my batteries died in the middle of the night turning the heating off.

    Most avg. sized houses would probably be fine with 2x Powerwall (so 2x 13.5kWh capacity with 2x 5kW max output). You will get much better mileage if you invest a bit in efficiency - sealing air gaps, double- or triple-glazed windows, wall insulation, etc. Many of those can be had cheaper than a Powerwall with installation and potentially can yield more savings.

    •  

      Yeah it is looking like the easier thing to do is control AC with IR blaster and getting a smart inverter I can pull the info from to do things with. Will have to do some further research on wall insulation, not sure if my current place has that.

  • +1 vote

    Hello there fellow automation enthusiast. I actually have effectively set almost exactly your use case up with Home Assistant.

    As others have mentioned, you don't specifically need an AC that can integrate directly, as there's the excellent Broadlink integration paired with a bunch of Broadlink RM3 Minis near each of the split systems in my house.

    Combined with this, I use a few custom integrations that make life a lot easier for achieving my goals. For controlling the ACs, I use SmartIR which turns your IR blasters into 'fake' climate devices. This means you can control them as you would any fully integrated climate device. One of the other benefits of them is that you can use another device/entity to accurately determine whether the AC is truly on/off (as IR blasters are just a one-way communication). In my instance, I'm using contact sensors on the vanes of the AC, so that when the vanes open, SmartIR knows that the device is on. This way, it's on state is still reflected if you manually control the AC.

    The next major component is a good smart meter. I specifically got a Fronius inverter as their API/meter was quite well supported in Home Assistant. This combination allows me to see the draw of the house, the generation of the panels, and the excess left over. From there, it's pretty simple to write an automation to turn on/off ACs based on whatever requirements you have. However, as others have mentioned - automating the LEVEL of the AC based on the excess/battery is kinda overkill as there's very little difference in draw. A simple on/off automation at 24c is all you really need.

    I have taken these automations further and done stuff like set up a "comfort" automation where if the bedroom gets to 26c for 30 minutes or more during summer, it puts the AC on for 2 hours. We're in Brisbane where humidity gets pretty bad, so this has saved us many times from waking up sweaty. I also automate all the ACs to turn off automatically if we leave the house and accidentally left them on, as well as automatically turn them on when we leave from work if it's above a certain temperature.

    Here's a little snap of my AC and Solar control/monitoring tabs in the Home Assistant interface.

    •  

      Dam that is the kind of level of automation I would love to get to! Great work, have you done up a post anywhere before detailing it all? I would be interested to read it.

      •  

        Unfortunately not. My knowledge is pieced together over a few years in the hobby and a lot of help from the Home Assistant Discord server. Happy to help out with any specific problems if you come across them though.

    •  

      this is pretty much spot on with Home assisant and SmartIR integration. Just note that for most modern AC the remote IR signal always got sent in a bunch of preconfigured options, such as ON with heat mode, temperature 25 and fan at auto, when never you press the next button it sends the whole set of config to the AC so you don't need to know the existing state (so if you're on heat mode at 25 and press down to reduce temperature, the remote actually send the whole set "heat mode, 24.5, fan auto". The only state you need is whether it's on or not which can be easily detected using current sensing or vane status as above.

  •  

    Yes, this can be done.

    You need a battery system that outputs it's status, a way to read that status and decide on a control method for the the aircon.

    This could be as cheap as buying a battery with a low power contact used to turn off power to the aircon or as expensive as a PLC + programming. You don't need an over the top, over engineered home assistant set up to do this. But if you like tinkering, with a bit of research, a home assistant system will allow you to get PLC like control for a fraction of the cost and learning curve.