Usage monitoring with solar - Doh!

Hi all,

We got our solar system commissioned last Friday and we're slowly learning about its performance and how to shift our energy usage to the daytime etc. One thing made me laugh on Sunday... :o

I was using our simple clip-on usage monitor (one that goes on the mains feed and then connects wirelessly to a display unit) to try and gauge our grid usage. I figured it would be good to know what I was drawing from the grid so I could see when I was using more than I was producing.

I was horrified to find that even after the dishwasher cycle finished I was still taking more than 2kw from the grid! I tried to think what could possibly be using that much electric then it dawned on me...

My energy monitor can't tell the difference between electric being drawn from the grid and electric being sent to it. And what I was effectively monitoring therefore was the net of my solar production and my usage (i.e. the balance that I was sending to the grid)! :rotfl:

Am I right in thinking that there's nowhere I can clip my current monitor (like around the meter or something) to measure my grid-supplied usage in real-time? I don't yet have a smart meter btw.

What do you guys do? Is there a different/cleverer sort of monitor I would need to measure just my grid usage?

Thanks,
Temrael

Don't use a long word when a diminutive one will suffice.
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Comments

  • ajbell
    ajbell Posts: 1,151 Forumite
    I have a Geo monitor which just shows generation then I have a dumb monitor which is like yours and can't tell the difference between import and export and then I have an iboost buddy which is smart and gives you a net figure based on import and export.
    I am afraid to say that I know the wattage of everything I use and when I see a few hundred watts to spare I will try to match my usage with my generation.
    I don't like to export anything.
    4kWp, South facing, 16 x phono solar panels, Solis inverter, Lincolnshire.
  • Temrael
    Temrael Posts: 394 Forumite
    Part of the Furniture 100 Posts Combo Breaker Mortgage-free Glee!
    Ahh ok thanks for that, I can't have an iBoost, sadly as I've not got a hot water tank (just a combi boiler).

    I've done a bit of Googling and there do some to be some monitors specifically designed to measure one's grid usage vs production but they look to be quite a bit more money. I guess now I understand that it's not measuring direction I can just take that into account for now while I'm still learning.

    We'll obviously move dishwasher, washing machine and EV charging to daylight hours whenever possible but that will still leave us producing an excess most of the rest of the time I'd think (if the current early results are anything to go by). It's not ideal from pure economics, but I guess it's not the worst problem in the world. :)
    Temrael

    Don't use a long word when a diminutive one will suffice.
  • EricMears
    EricMears Posts: 3,300 Forumite
    Part of the Furniture 1,000 Posts Name Dropper
    I have a Wattson meter that tries to work out what is being generated, what used and the difference between them. Can't say I'm wildly impressed with its accuracy though.

    Depending on how your system is wired, it may be possible to measure the input to the consumer unit. Obviously that falls down a bit if the inverter is connected directly to the CU but sometimes they can have a separate 'mini-CU' of their own so that 'real' CU input can be measured.

    My CU is a split-load type. Very few circuits (but one of them includes the inverter) are connected to the non-RCD side but virtually all the heavy users are on the RCD-protected side. I can therefore measure (most) usage with a clamp around the wire connecting the two parts of the CU.


    HTH
    NE Derbyshire.4kWp S Facing 17.5deg slope (dormer roof).24kWh of Pylontech batteries with Lux controller BEV : Hyundai Ioniq5
  • Martyn1981
    Martyn1981 Posts: 15,264 Forumite
    Part of the Furniture 10,000 Posts Name Dropper Photogenic
    Temrael wrote: »
    Ahh ok thanks for that, I can't have an iBoost, sadly as I've not got a hot water tank (just a combi boiler).

    I've done a bit of Googling and there do some to be some monitors specifically designed to measure one's grid usage vs production but they look to be quite a bit more money. I guess now I understand that it's not measuring direction I can just take that into account for now while I'm still learning.

    We'll obviously move dishwasher, washing machine and EV charging to daylight hours whenever possible but that will still leave us producing an excess most of the rest of the time I'd think (if the current early results are anything to go by). It's not ideal from pure economics, but I guess it's not the worst problem in the world. :)

    My Solaredge kit now shows export, and has a clamp on device. I don't know exactly how it does it, but it's definitely monitoring export as it's often greater than generation (the ESE clever SE inverter, doesn't know there is a separate WNW system).
    Mart. Cardiff. 8.72 kWp PV systems (2.12 SSW 4.6 ESE & 2.0 WNW). 20kWh battery storage. Two A2A units for cleaner heating. Two BEV's for cleaner driving.

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • ajbell
    ajbell Posts: 1,151 Forumite
    Am I the only one that takes offence at the idea of exporting my precious kwhs? .
    4kWp, South facing, 16 x phono solar panels, Solis inverter, Lincolnshire.
  • Dave_Fowler
    Dave_Fowler Posts: 622 Forumite
    Part of the Furniture 500 Posts Name Dropper
    I've built a circuit which can differentiate between imported and exported power. It uses a single clip on current clamp as used by the simple Owl power monitor. The circuit is built on a piece of Vero board.

    The circuit checks the phase of the mains supply and compares it with the current measured by the current clamp. If it is in-phase then it is import, if its out of phase it is export. The output from the current clamp is switched between two outputs, one for import and the other for export.

    I've used one current clamp and two Owl monitor receivers - one displays import and the other one export.

    If you're handy with a soldering iron and understand a bit of electronics, it is not too difficult to build. Drop me a PM if you're interested.

    Dave F
    Solar PV System 1: 2.96kWp South+8 degrees. Roof 38 degrees. 'Normal' system
    Solar PV System 2: 3.00kWp South-4 degrees. Roof 28 degrees. SolarEdge system
    EV car, PodPoint charger
    Lux LXP 3600 ACS + 6 x 2.4kWh Aoboet LFP 2400 battery storage. Installed Feb 2021
    Location: Bedfordshire
  • mre15
    mre15 Posts: 85 Forumite
    Part of the Furniture 10 Posts
    Does your electric meter have a red led that flashes. If so then a geo minim led version can be used.
    4.6kWp PV Comprising 16 x Jinko Solar Maxim Optimised 290W panels SSE Facing, Solis Hybrid Inverter and 7.2 kWh Pylontech batteries. Gloucestershire.
  • Zarch
    Zarch Posts: 393 Forumite
    Part of the Furniture 100 Posts Name Dropper
    emonPi and https://openenergymonitor.org/ is what you're after.

    I had exactly the same issues with older/useless monitoring not knowing the difference between ins and outs once solar was added to the mix.

    emonPi and their other offerings use an onboard circuit board to determine the differences and is really spot on and accurate.

    It works independent of your inverter etc (which aren't always wholly accurate either)

    Granted, a full two clamp emonPi set up is close to £200, but it just works!! I love mine!! :D
    17 x 300W panels (5.1kW) on a 3.68kW SolarEdge system in Sunny Sheffield.
    12kW Pylontech battery storage system with Lux AC controller
    Creator of the Energy Stats UK website and @energystatsuk Twitter Feed
  • Temrael
    Temrael Posts: 394 Forumite
    Part of the Furniture 100 Posts Combo Breaker Mortgage-free Glee!
    Thanks all, lots of options there! What a knowledgeable bunch you are. :)

    The Geo Minim LED monitor that MRE mentioned looks like good value (my grid supply meter has a flashing LED).

    I've not really got any soldering experience sadly, that sounds very clever though, Dave.

    I take the point that exporting is admitting defeat to a certain extent, but I guess if I've moved what usage I can to daylight hours, and am using all I need but still producing a surplus then (short of battery storage) there's no alternative but to export it?
    Temrael

    Don't use a long word when a diminutive one will suffice.
  • 1961Nick
    1961Nick Posts: 2,106 Forumite
    Tenth Anniversary 1,000 Posts Name Dropper
    mre15 wrote: »
    Does your electric meter have a red led that flashes. If so then a geo minim led version can be used.
    I'd just like to add that the Geo range of pulse counting monitors are virtually 100% accurate.
    4kWp (black/black) - Sofar Inverter - SSE(141°) - 30° pitch - North Lincs
    Installed June 2013 - PVGIS = 3400
    Sofar ME3000SP Inverter & 5 x Pylontech US2000B Plus & 3 x US2000C Batteries - 19.2kWh
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