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How to Monitor Grid + PV etc. Electricity?

Discussion in 'The UK and Ireland' started by WannabeOwner, Sep 8, 2017.

  1. WannabeOwner

    WannabeOwner Active Member

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    I record my meter readings (both Grid and PV generation) weekly, but it doesn't tell me anything about how much is actually imported / exported during any particular day. Who knows? perhaps I am exporting (and could buy a PowerWall) or Importing (and could buy more PV panels ... or a Wind turbine?). We have single-phase supply.

    I could, perhaps?, also have something to trigger usage by some device if PV is being exported. (Not sure what that might be though - Immersion seems like an easy candidate, but we also have Solar Hot water here, so not a particularly good "dump". Probably way too complicated, but dropping the temperature of Fridge / Freezer (we also have a Cold room) by a degree or so seems like a reasonable "dump" to me, but maybe a daft idea?

    My PV Panels and inverter are a long way from the grid meter / supply / distribution panel (no idea, off hand, if there is a dedicated cable between the two - there might be, but there is also a sub-distribution board near the Solar PV / inverter (sorry, I'm not technical, no idea if those two things are likely to be related). Is that a problem?

    PV installation, on roof, was part of a new-build extension, and there were definitely heavy duty cables from main distribution board to sub-board at that time.

    I could do with some advice as to what sort of kit might help with monitoring. A quick Google has turned up

    OWL Intuition-pv Solar PV Monitoring | Intuition PV | The OWL
    Wattson Energeno design and manufacture products and services to assist people to maximise the efficiency of their energy usage and energy generation both online
    PV OptiSmart Current Cost - Reducing your energy bills so you can live a greener life!
    Eco-Eye Smart PV Eco Eye SmartPV - Eco-eye electricity monitors

    The OWL, at least, is a name I know, but feedback suggests very inaccurate (maybe only at low wattage generation). Maybe that is true of the others too (characteristic of Cable Clamp metering perhaps?)

    All of them look like £100 would cover it, and having the benefit of the data is definitely worth that to me to then make an informed decision on further purchases, or make better use of my own generated PV ... or maybe something else?

    Not sure this is the best place to ask, but trying to Google for UK forums where this is discussed didn't turn up anything that had a recent discussion.
     
  2. arg

    arg Supporting Member

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    I don't have experience of those products, but cable clamp metering (done properly) should give reasonably accurate measurement of the current; however, if you don't have separate sensing of the voltage then you can't accurately calculate the power - this can lead to significant discrepancies against the electric meter reading even if the measurement made by the device is accurate.

    If you are just wanting to trigger demand diversion, all you care about is the current at the point where the supply enters the house (ie. next to the supply meter), so a single current clamp there is sufficient, and for that purpose you don't care about voltage, nor that much about accuracy as you only care if the current is positive or negative.

    If you are wanting to know what is going on - house demand vs solar generation, then you also need a clamp on the output of your solar inverter, and it sounds like that may not be adjacent (it may well have been connected to your existing submain leading to that part of the house). If you want actual quantitative results (as opposed to a qualitative feel for what is going on), then you will also need voltage sensing: your generation is likely to be at a higher voltage than your draw from the grid when it is dark.

    The trouble with all these diversion schemes (including the regular topic of charging the car from solar) is that it's conceptually easy to do, but by the time you've spent a couple of hundred quid doing it the payback is very long since the actual value of what you can save isn't enormous. And if you say "I don't care if the payback is long, I'm doing the right thing for green reasons", that's not entirely clear either: it may actually be better to generate into the grid in the daytime when there's lots of demand and charge the car of E7 overnight when there might be surplus wind generation available.

    The car-charging option suffers from the fact that you can't charge below about 1.5kW, and it's already getting quite inefficient at that level (having to run the car's battery management systems for much longer and so using a greater percentage of the total power for that overhead). Controlling it by hand it's too easy to accidentally charge from expensive daytime power when a cloud rolls past and so wipe out all the cost savings vs charging overnight on E7. It's no problem to design a piece of EVSE to track the available power and only charge when there's enough solar excess to make it economical, but the number of hours in the year when you've actually got that much spare power are limited and so the payback time is long.

    Likewise your refrigeration idea is reasonable, but the total money you are spending on power for refrigeration probably isn't huge, so saving some percentage of it is going to take a long time to pay back.
     
  3. WannabeOwner

    WannabeOwner Active Member

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    Thanks @arg, very useful input as always.

    I've had a couple of additional suggestions, which I think may help.

    It turns out that my inverter has an add-on piggy-back board which will monitor and output to network. I have CAT5 sockets in the vicinity, so should be possible to log that output somehow. (Just checked the manual and it looks like its only WiFi, which is annoying as that is likely to be far less reliable for me, needing to rely on a repeater nearby powered and running 24/7 ... looks like there is also an RS485 module, dunno if I would be able to more easily use that for logging)

    The second thought was to change my supply meter to a Smart Meter, and then use the data the power-company logs/provides to give me data for the supply side. Am I right to assume that will be at least as good/useful as the cable-clamp type?

    I might get some benefit from the Smart Meter supplier wanting to then, in near future, persuade me to have some devices that turn-off during peak load. I'm OK with that, as that would appeal to my Eco Side - contributing to the prevention of a short-use power station being brought on-line
     
  4. arg

    arg Supporting Member

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    The quality of the raw data will be better. Whether or not you can actually access it is another matter.

    The smartmeter programme is in a mess. Nearly all smartmeters installed so far are 'SMETS1' which are individual to each supply company (rather than using a common clearinghouse arrangement as is the plan), so if you change suppliers your meter becomes 'dumb' again. There's supposed to be a second generation 'SMETS2' which have both common technical standards for the meters themselves, and crucially a common security architecture to allow the same meter to be 'taken over' by your new supplier when you switch, but the roll-out of SMETS2 has been repeatedly delayed.

    Currently, the standard smartmeter offering just provides remote meter reading (ie, occasional reading by the supplier of the totals accumulated by the meter), and display of real-time consumption information on a wireless display device in the house. The remote reading isn't frequent enough for suppliers to provide a 'cloud based' real-time display or fine-grained historical data ('half hourly' is the maximum rate envisaged). In theory you should be able to connect other devices to the 'home area network' that feeds the in-home display, but there seems to be no imminent prospect of equipment to let you do so (I believe some suppliers have offered a gateway with their SMETS1 products, but in a proprietary fashion). The security arrangements prevent third-parties from offering such devices to 'listen in' on the transmissions - they are encrypted.

    That indeed would make smart meters actually useful. It's currently looking a long way away on UK smart metering.
     
  5. WannabeOwner

    WannabeOwner Active Member

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    That makes very disappointing reading, I hadn't realised the bar had been set so low :(

    Looks like I'll have to install my own choice of logging kit then.
     
  6. DrBobM

    DrBobM Member

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    I had solar pv installed recently and was looking for a monitoring solution. I ended up with emoncms - an open source raspberry pi project that does everything I want. My situation is complicated by the solar installation being on my detached garage 10 metres from the house. I've got 2 solar arrays, one facing east the other west, each has its own inverter connected into the garage consumer unit. The house consumer unit and meter box is just over 20 metres from the garage.

    I have the main emonPi unit in the house with 2 CT sensors, one on the main grid supply to the consumer unit and another on the feed from the consumer unit to a secondary consumer unit for my Tesla wall charger. In the garage is an emonTx unit that connects to the emonPi in the house via 433MHz RF and that has CT sensors on the output for each inverter and a pulse sensor on the solar export meter. The emonPi connects in to the domestic wifi.

    You can either connect to it locally or upload the feed to a website, either to an emoncms.org account or to a dedicated server and display whatever you want. I do the latter, here's my output to show you an example. The reason the proportion of solar exported is so low is because I have a swimming pool with a circulation pump and air source heat pump that's been running all summer. I had the pv installed in June so during the day that's been sucking up most of the power although the pool heater's now switched off so I'll be exporting more. Time for a Powerwall perhaps ...

    It's also possible to connect in control nodes for things like your immersion heater etc.
     
    • Informative x 1
  7. oktane

    oktane Active Member

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  8. WannabeOwner

    WannabeOwner Active Member

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    Thanks, very helpful

    Sounds like that would do for me too.

    We heat our pool with Solar Thermal (alongside the PV on the roof), no idea if Heat Pump would be more cost effective than Thermal ... I'd be interested in a comparison (academic interest only, but we also have Solar Thermal for Domestic Hot Water and we've had leak / loss pressure at some point, so wasn't "zero maintenance" in practice :rolleyes: so maybe Heat Pump and PV is better).

    Our circulation pump is on a timer for 1 hour a day only (mid day, on the basis that's the mostly like time that the sun will be out anyway) and then also triggered whenever the Solar Thermal circulation pump comes on - so on a sunny day the filter pump is on all day, but in practice I will have PV then too. I doubt there are many days in Summer when the Solar doesn't trigger the filter pump for at least the recommended number of hours, but we've never had a problem with water quality and Sun, Water Temperature and thus Filtration Amount are very closely linked with the "want" to swim :) The pool is 90F+ throughout the Summer and uses the house central heating Biomass boiler to get it heated in Spring and if the kids decide they "must" bring all their mates home for a weekend in the middle of November!
     

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