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Solar Diverter with Series of Priorities, Is This Possible?

  • 13-11-2022 5:46pm
    Registered Users Posts: 1,489 ✭✭✭


    As per other threads we're in the middle of a build that's going to have a really large (up to 50kw) solar install and large battery (up to 50kwh of storage).

    I'm familiar with some of the MyEnegi products such as their Eddie which will divert to heating or Zappi for car charging.

    But what I'm ideally looking to have is kind of simple, programmable system that will follow a series of priorities such as:

    (1) Use electricity being currently generated for any current household usage, such as lights/appliances/ventilation etc.

    (2) If there is a surplus above this provide heating (if it's heating season). We're going to have underfloor electric heating in the floor so ideally this would switch on/off when there was sufficient electricity to power it, ie if it suddenly becomes very cloudy this flicks off, when there is sufficient power it comes back on and stays on till it reaches 20 degrees in house or whatever it is. I think this heating is fine to flick on/off vs running a heat pump which would need to be on constantly so the idea is we just heat when there is sufficient power to do so. House is very well insulated so it should retain heat fine even if it's just being heated during daytime hours. The concrete should also help store the heat/release it slowly.

    (3) If the house is sufficiently heated (or if there is power to run both) heat hot water (just a basic electrical immersion in a 500l tank)

    (4) If there is still available electricity charge the 2 electric cars if plugged in

    (5) If there is still available electricity divert it to the batteries to be used later when the sun goes down.

    (6) Export all surplus electricity and get paid tariff

    This is not the exact order and it might need some adjustment but is it possible to do this relatively simply?

    Basically I'm trying to take advantage of using all the solar energy possible when it's available and in the case of heating/hot water/car charging pretty much limit this to only be used when there's PV electricity available

    Any advice on how this could be achieved would be much appreciated!



  • Moderators, Sports Moderators Posts: 18,483 Mod ✭✭✭✭slave1

    MyEnergi will let you go as far as 3 with EDDI, Zappi and then AC coupled but I can’t see why a number of EDDIs or Zappis can’t be added. For your heating I’m not sure as EDDI needs a resistive element to function…

  • Moderators, Home & Garden Moderators Posts: 5,524 Mod ✭✭✭✭graememk

    It's doable. But nothing really off the shelf,

    Possibly heavy into the home assistant/home automation/getting everything talking to each other

    Need good power monitoring, so when any diverts are active, the system knows how much power is being used.

    So, totally bespoke unfortunately .

  • Registered Users Posts: 21,058 ✭✭✭✭ELM327

    Other then step 2, it's pretty much available if you have Eddi and 2 Zappi chargers. Eddi have two outputs, perhaps see if you can connect the ufh to this and then bingo you've it set up.

    If not, you'll need to create something as this doesnt come off the shelf

  • Registered Users Posts: 2,126 ✭✭✭SD_DRACULA

    Some inverters also have an AUX (or two) port which is basically just like a second output on an eddi and you send power to whatever is connected to it based on priority

    But like @graememk said you would want smart monitoring on all your circuits (something like the shelly EMs) for maximum flexibility and then manage it all using something like Home Assistant.

  • Moderators, Home & Garden Moderators Posts: 5,524 Mod ✭✭✭✭graememk

    Ive built some diverts and having the actual power draw is very useful in the automation,

    Usually because if you turn something on, the excess goes away, so power used has to be accounted for in the code.

    But some z-wave or ZigBee temperature sensors in each room. And base the automations around that.

    Another option is let the battery get first choice and let the rooms heat by themselves and draw from the battery and not try and divert to rooms.

    Is the electric heating just stuck on top of the screed or deep in the screed like normal underfloor heating?

    Also with hybrid inverters, the myenergi only sees any power not captured by the battery

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  • Registered Users Posts: 1,489 ✭✭✭blobert

    Thanks for that. I asked MyEnergi but unfortunately the EDDI can only divert up to 3.8kw so while it would be fine for water heating, our underfloor heating is going to be about 9-11kw

    Also they said that Eddi is single phase only so you'd have to have 3 of them which would not be great. They are working on 3 phase products but not available now.

  • Registered Users Posts: 2,126 ✭✭✭SD_DRACULA

    For that kind of load I think you will need a massive inverter and possible one (or two) of something like these for the batteries if you want to draw 10kw or more.

  • Registered Users Posts: 1,489 ✭✭✭blobert

    Thanks, bespoke always worries me as it's likely to = $$$

    Any idea who would be in a position to advise on this/build somthing that would work?

  • Registered Users Posts: 2,126 ✭✭✭SD_DRACULA

    To be honest you could probably work out all the local control via Home Assisstant yourself, a wealth of knowledge here and online on the subject.

    The very most important thing is to get the gear that can talk to it or that provides some sort of local API access/control, the Victron stuff is good at that but one of the more expensive ones but at the same time, new build, so you're throwing money around anyway, might as well get something good 🤣

  • Moderators, Home & Garden Moderators Posts: 5,524 Mod ✭✭✭✭graememk

    Yep paying someone to build from scratch isn't gonna be cheap.

    How is the ufh currently planned to be controlled? Thermostat in each room?

    Ones that could communicate (and controlled) with home assistant would be useful.

    But I'd be leaning to just having the extra battery power/capacity. Let them do their thing and let the battery be the buffer.

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  • Registered Users Posts: 1,489 ✭✭✭blobert

    Thanks UFH probably going to be controlled by thermostat in each zone. It's cable buried in the screed/concrete as opposed to a mat above.

    With the battery are you suggesting we just charge the batteries where possible and run the house from that? That way, where possible we're running on either battery power (which was from solar), solar power itself or grid if neither of the first 2 are not available.

    I guess that could work but unless I had loads of battery power I wonder if we would not run into issues. Let's say during winter it's the morning and our batteries are depleted from the evening before. There is minimal electricity being generated now but later in the morning it's going to be better.

    If I had a system that only put the heating on when there was generation happening it would not put the heating on yet. However if I was just running off the battery it would put the heating on, there's no battery so we're running from grid electricity. Which ideally I'd like to avoid.

    Other thing is I'd imagine always running from batteries would wear the batteries out quicker?

  • Registered Users Posts: 1,489 ✭✭✭blobert

    Thanks, I think I've seen some of these in DIY battery videos!

  • Registered Users Posts: 2,344 ✭✭✭bullit_dodger

    I think your over complicating the issue. I see what your logic is trying to do, but it's overkill IMHO. Ultimately, you either want heat or you don't. If you don't want heat then your solar goes to the battery as normal and everything is good.

    If you do want heat, some of the energy requirements will be taken from the solar array, some from the battery and the remainder from the grid. The battery is unlikely to be able to supply 9-10Kw (even if you have 50kwhr of storage without going 3 phase). With 50kwhr of storage, I'd probably just charge that up to 65% or so every night, leaving a bit of space for some solar energy to be stored should it be a good day and be done with the lot.

    Getting into 3 phase inverters, custom off the shelf bit.....yeah, i think you could get it to work, but the cost wouldn't be worth it. Occam's razor there for me on that one I think.

  • Moderators, Home & Garden Moderators Posts: 5,524 Mod ✭✭✭✭graememk

    Or KISS. Keep it simple..

    Batteries are there to be used though.

  • Registered Users Posts: 1,489 ✭✭✭blobert

    Thanks for that.

    I'd agree with keeping it simple where possible

    We are going with 3 phase power for the house as it needs it so that will be there.

    The other thing is because we have up to 50kw of panels that should be generating a lot of electricity over the course of the year I'd like to be able to use that as much as possible and as little grid power as possible.

    But I am also wary on spending a fortune on a fancy system that may not work

  • Registered Users Posts: 1,341 ✭✭✭Nelbert

    I'd suggest a number of shelly ems and smart switches (like shelly plus 1pm which can monitor the usage on the circuit it turns on) rated for the load (the UFH in particular, I would assume would be a significant load).

    Grid shelly em detects export.... Logic kicks in to start turning things on in sequence. You'd probably need a collection of inter-related automations (I'd suggest home assistant) to get it all working.

    The reason I suggest the shelly plus 1pm for the switches is that if you can see what's pulling what power wise you can then have an automation kick in if sun goes away and you start importing from grid by 1kw that you turn off lowest and second lowest priority as they are 1kw together and then they go back on if sun comes back out.

    The priority list you have is good on paper, getting it all to work as intended with automations will be a bit of trial and error (which I'd enjoy if doing myself to be fair).

    Also your priority list will likely develop ifs ands & buts.... Like don't turn on ufh if it's already 21 or if the hot tank is below a certain temp heat that not the UFH first type of thing.

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,039 Mod ✭✭✭✭Jonathan

    Why are you going with resistive heating rather than a heat pump?

  • Registered Users Posts: 2,344 ✭✭✭bullit_dodger

    If you've the 3 phase in for sure anyway, then you have half the risk already taken. However, to be fair, I probably wouldn't do squat until I'd at least 1 winter in under the belt. As you say (and I'd be of the same mindset) spending money to properly solve a problem is ok, but spending money to come up with a solution which may or may not be fit for purpose probably isn't a good use of resources.

    I'd monitor it for 1 winter and then from the telemetry you can size your system appropriately. You may find that the situation isn't what you expected and a system 1/2 the size is what's needed, or vice versa you need something even bigger than your planning. You are however very much on the cusp of industrial electrical engineering.

    I do think 20-30Kwp of panels if you are planning that is a good investment anyway. Even if you don't use the power yourself, you'll get paid a FIT for it, so really there's little/no risk in getting them in. Even as you say 50Kwp you could well be earning a tidy sum off that (ESBN permitting - they might not be able to take that kind of a uplink)

  • Registered Users Posts: 1,341 ✭✭✭Nelbert

    I'd ask this question myself.... The electric underfloor Vs laying pipe.... The principle of heating the concrete pad is the same.... but the A2W heat pump is likely to be more energy efficient at doing it.... So may use less electricity for the same "warmth".....

    If your plan is to generate enough in winter to power an electric floor then you'd be generating more than enough to run a heat pump (I'd have thought) and have the benefit of a simplified hot water setup too (i.e. one piece of equipment to do both).

    If I'd a larger household hot water need I'd supplement my heat pump tank (200L) with a buffer tank but the heat pump is so efficient as a heat source I'd use that over an Eddi solar type solution for the immersion whenever possible on it. I.e. I'd set the heat pump to act like an Eddi and heat while the sun shines on solar panels I've yet to make the jump on personally but hope to soon.

    Only caveat no matter the heating source is being careful with south facing rooms with lots of windows.... Pad warmed on night rate, followed by a sunny day leads to a sweat box by lunch time!

  • Registered Users Posts: 6,438 ✭✭✭zg3409

    I would recommend placing all controls nearby in a plant room type set up so everything could be linked and automated later.

    Ducts or pipes to allow cables to be ran later may help

    The limits of zappi and Eddi are well understood. You may want

    1) hot water

    2) when water hot then charge car

    3) when car full then get Eddi to trigger underfloor heating to come on.

    You can have manual/app over rides to use non solar energy when required.

    Battery control mainly depends on what options battery has. For value you may want cheaper battery models which may limit options. In summer excess should fill battery but you want to trigger charging cars or hot water overnight when battery full. Make sure you have a controller you can at least set charging discharging hours and ideally house load based. Ideally you vary this summer to winter to maximise use. Many batteries warranty is X years or X charge discharge cycles, so yes using battery constantly will reduce battery wear.

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  • Registered Users Posts: 1,489 ✭✭✭blobert

    There was just a massive difference in cost. I think the Heat Pump/Underfloor heating everywhere etc was about €40k vs the €7k for the resistive heating.

    The house despite being a very big bungalow has a very low heat load. So I'd never make up the €30k+ difference in my lifetime. Basically as we'd spent a lot on a very well insulated house it didn't make sense to spend way more on a very efficient heating system. We also knew we'd have a massive solar array which again would make efficiency less important if we have a lot of "free" electricity available.

  • Registered Users Posts: 1,489 ✭✭✭blobert

    Thanks for that, Shelly seem to think it's possible with their equipment:

    Thanks for getting in touch. We have the Shelly 3EM which can be used to measure your solar output, your grid import/export or your consumption. To get the full picture, you will need to use at least 2, one for your solar output and one for your grid import/export, and from these 2 you can deduce your total consumption. You can then use our power monitoring relays (or a Shelly EM with a contactor for high loads) to control your heating, electric car chargers and hot water tanks. 

    However, to achieve all the above requirements, you are going to have to code some complex automation. I would recommend looking into using a dedicated home automation server, e.g. Home Assistant, to run all of your scenes and automations, and then use Shelly devices to measure and control your devices.

    It looks like most of their controllers are not that expensive but I don't know it would be that hard to code/automate.

    In my mind it seems like it should not be that complex to have the generated electricity divert to one of a couple of options but maybe it is.

    I wonder could I find a guy on Fiverr or similar to do the automation coding, I suspect that side of it would not be that hard if you knew what you were doing.

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,039 Mod ✭✭✭✭Jonathan

    I'm a bit surprised by that €40k figure, but maybe the floor area will be very big. Given your heating load is very low, have you considered an air to air system? You'd have the advantage then of cooling during the summer as well.

  • Registered Users Posts: 1,341 ✭✭✭Nelbert

    Do yourself a favour and have a look at home assistant....

    I control all lights, loads of smart plugs, energy monitoring (via smart plugs and shelly em), smart switches (shelly 1pms behind regular wall switches) and have my heat pump controllable there too.

    Building an automation is GUI driven and the flow is simple triggers (what kicks off an action), conditions (restrictors to only run the automation at the right times) and actions (what you want it to do, but these can be conditional based on what triggered it etc).

    A simple example -

    Trigger - it's 7am

    Condition - hot water tank is below 45⁰

    Action - force hot water on heat pump

    This tops up my hot water tank for the day in the last hour of night rate in case the morning showers haven't used enough water to trigger it by temp drop.

    There's a lot of users of HA on here for energy monitoring functions with their solar installs. Getting someone else to set it up for you might sound great... But what happens when you want to tweak it to add conditions or kick off more as actions?

    I'm shocked at the 40k cost for the heat pump driven UFH..... Ours for HP, approx 100m2 of UFH downstairs, rads upstairs and full plumbing redone was less than half that. If install hasn't happened yet, happy to pass on my installers details.

  • Moderators, Home & Garden Moderators Posts: 5,524 Mod ✭✭✭✭graememk

  • Registered Users Posts: 64,359 ✭✭✭✭unkel

    Good to see your independent thinking. Efficiency isn't a god we should worship. Pragmatism is where it's at. With a huge PV array and a huge battery and a very well insulated house, you're likely to only need minimal importing from the grid for space heating. You'd never make make the extra investment in a more efficient heating system (heat pump) pay back. Over €30k extra, yikes!

  • Registered Users Posts: 1,341 ✭✭✭Nelbert

    Even at 400m² there is something very off with that heat pump quote..... It's 'just' more pipe....

    You'll never make that cost difference up in efficiency based on that quote.

    In practical terms using about a third of the electrical energy for the same heat output means your PV array and battery can be used for other things like FIT, that would help payback some of the difference.

    Definitely need other, more competitive, quotes though.

  • Registered Users Posts: 1,489 ✭✭✭blobert

    Thanks, I got a couple of quotes, all about €30-40k just for a A2W heat pump and underfloor everywhere.

    The house is a 450m2 bungalow so it's pretty big/there's a bit of work in installing all the pipes. I think there was also an element of jacking up the price as the house is pretty nice/looks like it costs a lot and so they were assuming I'd be ok with big $$$ prices. This has happened a lot throughout the build.

    The electric underfloor we're going with is about 7-8k and we are using an air to air heat pump/air conditioning unit also (about 8k installed) mainly as we want to have the option of air con if the house is roasting (we have a lot of south facing glass) but also as mentioned previously if we dont have a heat pump we'll have a terrible BER.

    We can use the air con/heat pump to heat/partially the place, in theory it has a really high COP. But I'm not a big fan of heating through the air, we have this in a holiday place abroad (all heating through same air con units that do cooling in summer) and I don't like it for heating, I find it quite drying. So if air heating works and it doesn't annoy us great, we'll use that for the majority of heating and it will be cheaper to run. If not we'll use the electric underfloor and as I say I think that would work well with the solar power in being able to put heat into the screed/concrete when the sun is up and "store" it for slow release.

  • Registered Users Posts: 1,341 ✭✭✭Nelbert

    We'd similar, prices via our architect or via anyone that saw the floor plans were always higher Vs giving someone a spec for a quote. Assumptions made about budget were always that it was way higher than it was!

    Just a shame to potentially lose some of the precious winter kWh you'll generate to 100% efficiency rather than 300%.

    Your prioritisation for solar excess is very doable but I'd encourage you to consider doing it yourself as the temptation to tinker will take hold eventually and best to be able to do it yourself.

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  • Registered Users Posts: 1,489 ✭✭✭blobert

    Hello again, just coming back on this as we have to decide what we're doing ASAP.

    I'm leaning towards going with a simplified system that would (1) house uses any PV energy being used as needed (2) surplus goes into batteries/EVs via a Zappi/equivalent (3) any further surplus is exported (4) when house load is higher than being generated house runs on batteries until they run out (5) house uses mains electricity if needed.

    This way to some extent I don't really need to worry about sequencing things/having priority etc and everything is running from solar power (live or stored) where possible.

    Just wanted to check this sounds feasible/fairly straightforward? House is going to have 3 phase power and (as planned currently) about 40kw of solar panels with max export of about 30kw.

    Thanks again!