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The off grid season has started

  • 13-04-2023 2:26pm
    Registered Users Posts: 65,249 ✭✭✭✭
    Chauffe, Marcel, chauffe!

    Now we shook off the last wintery days of the year, it looks like the off grid season has started. Maybe I am a bit optimistic, but I hope / expect to not buy and significant electricity from the grid until late August. That includes all my hot water, all home heating, all general electricity use and fully charging my car

    Fingers crossed!


  • Moderators, Home & Garden Moderators Posts: 5,995 Mod ✭✭✭✭graememk

    In April so far I've imported 15 kwh of night rate.

    Had to have the stove on the last few days though, it has been bitter outside

  • Registered Users Posts: 65,249 ✭✭✭✭unkel
    Chauffe, Marcel, chauffe!

    I had the central gas heating back on the last few days. But that will hopefully stay off now until autumn.

  • Registered Users Posts: 4,430 ✭✭✭Gerry

    Haven't had the heating back on. Could have done with fire in sittting room Wednesday night, as much to dry off. Looking forward to export season now, propping up the grid and paying for winter.

  • Registered Users Posts: 824 ✭✭✭HotSwap

    I’m still charging my battery between 2-4 am. So it’s always at 100% at 4am; then looses 10-15% until sun comes up and starts generating enough to sustain the house and charge the battery.

    I have a few fancy automations running in home assistant;

    1. only charge the battery to a lower % based on the solar gen forecast for the following day and allow the sun to charge it. But with the 21 cent export; and the 12 cent between 2-4 it feels like a better option to just top it off and start exporting sooner the following day.
    2. when the battery gets to 100% and I’m exporting when the sun is up; dump to the grid until the battery gets to 80% and then start charging again. This allows me to “clip” less; as I can get the full 7.5 from the panels; 5to the battery and 1.5 to the home / grid; but this cycle I feared was doing damage to my battery so it’s off now.
    3. dump whatever charge I have in the battery at 1am; selling for 21 cent; and then buying it back between 2-4 for 12 cent. Again I feared this was going to kill the battery before it’s time.

    what I have now; 7.5kwp / 10kWh bat / 6kwh inverter I can see will basically leave me with no bills when I export enough in the summer to pay for what I need to import in Nov - Feb.

    my concern now is that we are still using oil for heating and water (no point in using the eddi as the .21 is too good) and I’ve no EV. If I move to a heat pump and get an EV; I’m back in the situation where I’ll be buying power; which I’m not into.

    we use about 6L - 7L of oil a day on heating; which is about 60kw of energy after losses in the boiler. So with a heat pump at a COP of 3.5 I’d need 20kw per day. So I think maybe a DIY battery is the way forward on this point.

    this is based on the house as it is now; I’m getting tripple glazed and external insulation and new front and back door so I would hope that the 6-7 L would go down significantly; but time will tell.. it better :)

    to make a heat pump work the way I would want to; I feel I would need a dedicated 15-20kwh battery just for that to guarantee I’m not going to get robbed.


  • Moderators, Home & Garden Moderators Posts: 5,995 Mod ✭✭✭✭graememk

    Battery is there to be used. Make it pay it's way.

    No reason that discharging to the grid would be any different that a normal load.

    It's LFP batteries, a real work horse.

    Re heat pump, possibly off load some of the dwh to an immersion? On a wifi switch, run it at midday for an hour or so.

    External insulation etc should drop the heating demand alot, and allow rads to run at a lower temperature, meaning a cop of 3.5 is entirely possible.

    DIY battery and inverter shouldn't be too much outside of your wheelhouse, possibly an me3000 running in passive mode, where you run the inverter "manually" to avoid possible fighting with the hybrid inverter.

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  • Registered Users Posts: 824 ✭✭✭HotSwap

    on the discharging to the grid; yeah it’s the same; just putting more cycles on the thing than needed.

    I have an eddi but no immersion. I’m gonna get one and try a few experiments; but with the current price of oil (about 1 euro a L) it’s Cheeper to use the oil. If it goes back up I’ll reconsider.

    I love the idea of a DIY budget battery setup for the heat pump; but being honest it’s prob 5 years out as I only have the oil 2 years. I’ll get the retrofit insulation stuff all done and see where I stand.

    I was talking to several air to air solution guys at the RDS few weeks ago. I’m interested in this; could put a unit in the kitchen and living room as a start.

  • Registered Users Posts: 1,081 ✭✭✭silver_sky

    I'm charging based on a low forecast or if the battery is not high enough to see through to morning it charges to a min amount. Personally I wouldn't be dumping to the grid at the current rate. If we had the likes of Octopus agile here where you could get a higher export at peak times I'd consider it.

    I think everyone has a different goal with this. Mine is minimum grid use (and cost).

  • Registered Users Posts: 4,430 ✭✭✭Gerry

    Is it feasible to charge battery slower, based on forecast during the day, export a little and end up with a fully charged battery for night but less cycles on it.. obviously you need good forecasting

  • Registered Users Posts: 189 ✭✭connesha

    Sounds like you're trying to maximise export, while not buying anything except EV-rate (2am-4am) from the grid?

    You could possibly achieve this a bit easier, without actually cycling the battery.

    Here's what my automatons are doing from now through summer, with a Solis Hybrid, large array, large battery, and export (back flow) capped to stay under the 6kw. Where EV-rate import is 7 cents, and export is 25 cents.

    I expect the below alone could be worth a couple of euro a day on top of the normal export, come the good days in May/June/July. And it's pretty simple automations so no daily effort. Agreed, the summer can cover the winter usage and standing charge for big setups, and leave you up over the course of a year.

    • During the EV window, charge the battery if necessary, to bring to an SOC proportional to your forecast. I vary from 60% to 100% depending on forecast: 60% for a super day, 95% for a bad summers day (i.e. 25kwh or so).
    • Set the backflow limit on the inverter, so you dont exceed the grid limits (do this once ever)
    • Set the inverter to Feed In Priority (FIP) mode each morning right after the EV window (i.e. before sunrise)
    • So now, all generation from the start of the day will be consumed by the house or exported (battery wont charge). Also, any time you consume more than generation it'll be taken from the battery
    • The battery SOC may drop a little during the first couple of hours of generation, thats fine.
    • When you get towards peak (midday) generation (more than you are are allowed export), the inverter will dump the remainder into the battery automatically. e.g. it'll send 6kw out to the grid, 100w to house base load, and the rest will go into the battery.
    • So, your battery is now charging with the truly free electricity (i.e. you are exporting the max allowed, running the house, and also charging the battery with what would not even be generated otherwise)
    • Over time as you see how your own system behaves, you can make better guesses as to what to charge the battery to in step one, based on your daily forecast. I would aim that you map it so that the battery will probably hit 95% during the day, so that there is some space left if you have better production than expected.
    • Depending on your forecasts/night usage/battery capacity, you may have enough left in the battery to not even need an EV-rate charge (or can dump from the battery in the evening and recharge at EV-rate - I don't do this. But its only one discharge for the day, so wont be an issue)

    And as for the Eddi:

    When on Smart Tariffs with good FIT/low EV rates, the standard way of using an Eddi doesn't really add up: its better to boost it at EV-rate than waste potential FIT during the day.

    It does have good use though if you have more generation that can be exported: instead of setting the standard export margin at 0W (or 150W or whatever), set it to near your grid export limit. So, then the eddi wont kick in until you're almost maxing out the grid export limit. Again, it'll take the the power you wouldn't have been generating otherwise, same as was done for the battery.

    Note: This is the basic idea. You'd need a bunch of safeguards to disable the above during a day where production/usage didn't go as expected, so you'll always last until EV-Rate. For instance, I have hourly/by minute forecasts: so forecast what generation is remaining at each point during the day to make sure there is enough to get to 2 AM.

  • Registered Users Posts: 824 ✭✭✭HotSwap

    I can achieve what you describing using the “excess PV energy use in TOU” set to “fed to grid”.

    I have a 6kwh inverter and a 7.5kwp array so the only time that the battery would charge (other than from grid 2-4am) is when I’m “clipping”; which is good; I’m just concerned that I wouldn’t get the battery high enough to get me from sunset to 2am on a given day.

    I only have 10kWh battery so everything is very marginal; sounds like you have a much bigger battery? I could add another 5kW to my battery for 2400; but I’m not sure if that is money well spent at the moment as it’s working quite well with 10kWh bat.

    it’s worth a try to see what happened though.

    Your point on the eddie is a good one; but not applicable to me as my one and only inverter is 6kwh. I’m thinking about getting a second inverter to hook up another 8-10 panels; in which case I could be inverting more than my export limit. So your essentially using the eddi as an export limiting device rather than setting that in the inverter. Or set the eddi to kick in at 5900W and also have a hard limit of 6000w in the inverters config.

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  • Registered Users Posts: 824 ✭✭✭HotSwap

    4 of the last 7 days I think this approach would be very beneficial indeed. I’m going to try it. But I fear my 10kWh battery is too small to give me this freedom; but I’ll let ya know how it goes.

  • Registered Users Posts: 824 ✭✭✭HotSwap

    @connesha From Today:

    I switched from "Fed to Grid" to "Charge" priority just after 2pm so that I would get the battery to 100%. I think to keep things simple, I will just schedule HA to toggle this setting after the peek has passed each day. But I did 100% get some power out of the system today that would have been left on the table before, so its a great suggestion.

  • Registered Users Posts: 547 ✭✭✭PCDub

    Good sun today, managed to fully top up my 8kwh of off grid batteries. That should cover the cooking, washing machine and tv for the week.

  • Registered Users Posts: 6,165 ✭✭✭con747

    8kwh for a week? Do I need glasses or do you use next to nothing per day? My base load is 150w and I use about 8-10kwh per day after cooking, showers and so on. 2 people household and cut back as much as possible in usage without reverting to cave living!

    Don't expect anything from life, just be grateful to be alive.

  • Registered Users Posts: 189 ✭✭connesha

    Great. And it's only going to get better for the next few weeks. I got few kwh extra out of today too using this system. Some into the Immersion and some into the battery.

    As for disabling it, yea, a little after the peak is pretty good. Or, here's what I'm doing:

    • Have a good solar forecast by hour/minute, where you always know how much generation is left for the day. Represent this as a (template) sensor that updates (every minute) with how many wh of generation is left for the day, per your forecast.
    • Have another template sensor that updates with roughly how many wh you need from now until the EV window tomorrow morning. Look back on previous days to know how much you use at various times of the day to formulate this sensor (my sensor updates each minute)
    • With both of these (and battery SOC) you now can track excess capacity you have left for the day, at every minute during the day (template sensor). i.e. (RemainingForecastWh + BatteryUsableWh) - NeededUntilEvWindowWh = ExcessWh
    • When ExcessWh goes negative (or low), then its time to disable

    Getting a pretty accurate ExcessWh sensor takes a little work to set up, but you may find a lot other uses for it, where it can really simplify other tricky automations. For example, during winter time you can use it to automatically dump some power into electric rads without risking running out before Ev Window. e.g. If ExcessWh > 3000 Then turn on heater until ExcessWh < 2000.

    RE your comment on Eddi "So your essentially using the eddi as an export limiting device rather than setting that in the inverter."

    Not quite: the inverter has the export limit set, so it doesn't abuse the grid. The Eddi has its margin set a little below the inverter export limit. So, when you approach the inverter export limit, the eddi will kick in.

  • Registered Users Posts: 547 ✭✭✭PCDub

    :D..think cave living is what ERyan wants us all to revert too...

    The batteries are just for specific loads, e.g. TV, induction hob, air fryer and washing machine all other stuff still on grid such as fridge, shower etc. Suppose its kinda like load shifting to off grid. I've got a 3kwh bluetti, 2kwh oukitel and my own 3kwh system with a 1kw inverter for tv/home audio.

  • Registered Users Posts: 824 ✭✭✭HotSwap

    I’ve taken a slightly different approach today.

    I have left the excess power on charge; and will let the system charge to 90% at which point I’ll change the mode to feed the excess to grid. It’s likely this will happen before we reach the peak time so I shouldn’t loose any excess. Edit: now that I’ve thought about it I won’t loose any; I would only loose some of the battery got to 100%.

    Then if there is enough excess above my 6kw inverter to charge the battery to 100% at some point in the day; I change the mode of the battery to dump it to the grid down to 90% again and repeat.

    I prefer to know I’ll have the battery at 90% at least; your solution works too; but I didn’t have time to get into it in that much detail yesterday evening.

    will let ya know how it goes.

    Post edited by HotSwap on

  • Registered Users Posts: 369 ✭✭munsterfan2

    I was monitoring my usage last few days as I changed my inverter to only import between 2 - 5 and export 0a between 5 - 8 (Leaf usually charging still) and had enough power to run house through to 2:00am today. However my bord gais meter readings disagree ( and appear to be completely wrong). First up is the myenergi import graph for yesterday - no real usage from 08:00 to 00:00

    and here is the bord gais one

    Has anyone see this before, I'll keep an eye on it, and compare against the esb networks data when it comes out ( usually a day behind )