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Low Usage Standing Charge with solar

  • 26-04-2022 9:17am
    Registered Users Posts: 16

    Hi folks,

    I have a 5kW solar with large battery and even with an EV and heat pump, it looks like I will be importing very little grid electricity from now until the end of summer, certainly less than the 2kwh per day (or 122 kwh per 61 days) to avoid the Low Usage Standing Charge of 5.25 as per

    Question: Does anyone know if I would be charged the full 5.25 if I used 121 kwh? i.e. is there an incentive for me to monitor usage and waste electricity (e.g. turn my PV system off for a day) towards the end of the billing period ?


    PS This is related, but the following would have been handy for me to know before I invested in solar ...

    • The maximum output of my inverter is 5kW and so if I run my 6kW heat-pump then it will always use 1kW from the grid even if the battery is full and the sun is shining. Therefore I wish I had bought a 7kwh inverter with the 18 panel array just for the satisfaction of being totally off grid.
    • PPS
    • My PV system knocks off for 2 min when the heat-pump turns on, probably due to low voltage due to the lack of a soft-starter
    • It's been sunny the last few days and have been exporting about 10kwh of the 33kWh per day to the grid ... so solar works well in Ireland outside the winter months


  • Registered Users Posts: 2,339 ✭✭✭bullit_dodger

    To partially make you feel better about your #1 point, there isn't such as thing as a 7Kw inverter. 6Kw generally is the max for 1 phase circuitry. Technically of course there's no reason why a manufacturer couldn't make one, but all the regulation from ESB and our brothers across the water in the UK have a 6Kw limit for export, so the manufacturers max out at that.

    Can you tackle the problem from the other side? i.e. can you lower the input requirements of your heat pump from 6Kw to 5Kw. Yes it will take a little longer for the water to heat, but it might be a solution?

  • Registered Users Posts: 519 ✭✭✭idc

    Looking at most of the new prices for EI starting 1st May it looks like low usage charge no longer applies as it is the same value as normal standing charge

  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    Well, as you have an EV just charge it at night some night (s)? Both day and night count to the low use minimum. I'm assuming you have a day night meter. With a heat pump and ev.

    Depends on how close you are to the minimum too. If your a couple of kwhs away from it sure. But if your running 100 kwhs away from it, and you use it on night rate, your spending 10 euro to save 5.

    Monitor your use for sure though, you can't control what you can't measure.

    (Also generally 6kw is the max inverter you can get, with 5kw from batteries)

  • Registered Users Posts: 11,997 ✭✭✭✭KCross

    the maximum output of my inverter is 5kW and so if I run my 6kW heat-pump then it will always use 1kW

    Are you sure it uses 6kW as opposed to outputting 6kW. A heat pump that uses 6kW to run it is not at all typical unless you have a massive house or just an oversized HP.

    My PV system knocks off for 2 min when the heat-pump turns on, probably due to low voltage due to the lack of a soft-starter

    You should get ESB to look at that. That should not be happening. They can put a monitor on you connection for a few days and determine if they need to fix it.

    Adding the soft starter would help too. If it knocks off the inverter it's probably affecting other sensitive electronic devices too and power cycling is what kills them usually. Do any other electronic devices fail or restart like that too?

  • Registered Users Posts: 2,121 ✭✭✭SD_DRACULA

    There is also the hidden "issue" that you might not be able to tell but you'll see it on your bill.

    The inverter is not 100% accurate at what you pull from the grid, basically whenever you put a high-ish load on, kettle/cooker/oven/washing machine etc, until the inverter/batteries pick this up you'll draw a little amount from the grid but the inverter will not register that.

    I know this because I have a separate CT on my mains and that can read that trickle amount (your meter will confirm this as well)

    I should have been "off-grid" for about 2 weeks now but I am seeing consumption of up to 1kwh per day so basically you might easily have 30kwh "wasted" like this per month anyway

    Also doesn't this mean there is no low usage charge in about 4 days from now?

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  • Registered Users Posts: 6,160 ✭✭✭Ubbquittious

  • Registered Users Posts: 6,160 ✭✭✭Ubbquittious

  • Registered Users Posts: 16 gidxl03

    Many thanks for all the replies, lots of great info there.

    - I hadn't noticed that confusing text at the top of the link about the Low Usage Standing Charge ending on May 1. The LUSC has been around for a long time, I wonder why they are ending it now, perhaps because the regular Standing Charge is going up.

    - I think the answer to the question about if there was an incentive to waste electricity to get from 121 to 123 kwh between billing periods is 'yes'. So just as well it is going on May 1.

    - The meter shows that I have used 7 units in the last 5 days ... most of that was when more than 5kW was being used at any one time (kettle, cooker + fridges), and part of it was due to the delay in the inverter kicking in as SD_DRACULA was pointing out. 

     From those numbers I was close to being on track to be in the crazy dilema where wasting electricity would save me money

    @nullit_dodger : I would love to reduce the 6kW input (18+kW output) heat pump to something like 4kW input but doesn't seem to be an option. I think it is oversized now that the insulation is improved (max 5 hours per night) so whenever it packs up, I'll replace it with a smaller one than runs all night.

    PS Would also love to send excess solar electricity into an air-to-water system for running during the day but didn't find any controller smart enough for that.

    @ graememk : good point that I wouldn't have to literally waste the electricity by turning on a heater I didn't need - I could have set a min SOC on the battery and that would cause consumption from the grid at night.

     Yes I have a Day/Night meter so at night rate 5.25/0.1113 is worth 47 units. This means that from 75(122-47) to 122 units , it would be cheaper to 'waste' units than pay the LUSC. (VAT and 18% discount not included in the above calculation)

    @ KCross : yes, the HP is 6kW input, visible on the HP itself and on the solar app. A few years ago the lights in the whole neighbourhood flickered at 11pm when my HP kicked in. This caused electicial problems for my next-door neighbour so we got the ESB out to measure and after a bit of persuasion they installed a second transformer and split 18 houses into two rows of 9. Am thinking that a soft starter is the proper solution, just have not been able to find anyone to do the job. The solar inverter doesn't show an error but counts down from 2 min after the HP starts and then brings the solar panels gradually back online again.

  • Moderators, Home & Garden Moderators Posts: 5,495 Mod ✭✭✭✭graememk

    A 6kw motor starting is a huge inductive load, (as a stationary motor is basically a short circuit)

    I know the 2 (2.5kw) motors on our crusher pulls about 100+ amps briefly when starting.

    Although the point seems moot anyway with it going away at the start of may!

  • Registered Users Posts: 16 gidxl03

    @graememk wow, am surprised 6kW HP doesn't blow a fuse.

    Internal fuse box says 63A.

    The external meter says

    1Ph 2 Wire

    E89ED-00D 230V 20-80A

    240rev/kWh CI 2 EN60521

    AC-21B Ie=80A

    so I guess it is an 80 Amp fuse which I guess can support more than 80A for a short time.

    From the solar app history view, I've seen peak consumption at 11kW sustained for a few minutes but with a HeatPump + EV + immersion, in winter I do try to avoid having more than 2 on at any time as I don't know the MIC (Max Input Current) and the HP is same age as house ~20 years old.

    Anyhow, have gone off topic so thanks for all the replies !

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