I first posted this question on the UK Forum as it concerns a problem with a new UK Smart Meter, which may be over-reading. However, I guess some of you guys in the Sates will have a lot more information about how the Gateway 2 monitors power flow and the relative accuracies of the Gateway and Smart Meter data. I have had a Powerwall 2 installed since July. I have an existing Sunpower/Solar Edge solar setup, an Tesla Model S and, until a few days ago a mechanical drum type electricity meter. As well as the Tesla Powerwall app, I am logging various parameters via the PVOutput site. RF5PW 3.924kW | Live Output Don't ask me why there are gaps in the data - it seems to happen sometimes! The resolution of the Tesla Powerwall app is 0.1kW. The resolution (not accuracy!) of the PVOutput data is 1 watt (0.001kW). PVOutput is reading the Gateway data directly, but we don't know how accurate the Gateway monitors power flow. I have dual tariff electricity the Powerwall 2 is set to Advanced Cost Saving mode, so it only charges from solar during the peak period, but can share from the grid or solar during the night period. The Model S has been connected directly to the Gateway input side so that it never charges from the Powerwall, which would deplete it very quickly! Even without any solar input (it's rather cloudy here in the little ol' UK right now) the single Powerwall 2 has sufficient capacity to satisfy the whole normal house demand with some spare capacity during the peak rate period, provided it is near to fully charged to start with. Since installation in July, on most days the Powerwall has supplied all the peak demand. The old electricity meter, which had a resolution of 0.01kW, hardly ever moved. So measured consumption at Peak rate was maybe 0.1kW maximum. Both this electricity meter and the Powerwall/PVOutput data agreed with each other. Most times there was no peak demand from the grid, unless the Powerwall ran out of charge before the end of the Peak period. I am aware that the Gateway periodically draws a small current from , and also puts back a small current to the grid. This is presumably for calibration purposes and only amounts to bries 0.1kW flow or less. It doesn't measurably affect the overall power demand from the grid. The new Smart Meter has both a digital display of kWh consumed to the nearest kW, and a Chameleon remote display showing all sorts of useless info like the cost etc, but also the current power consumption with a resolution of 0.001kW, in other words it will display a change of 1 watt. The PVOutput 10 minute live data has been displaying to 0.01KW, but I have just realised that this is configurable and have changed it to display to 3 decimal places- 1 watt, like the Chameleon display. As soon as the new Smart Meter was installed I noticed that the Chameleon was showing a fairly constant power consumption of about 0.1kW, this while the Powerwall was supposed to be supplying all the house damand. This has varied up to 30% from day to day but shows no sign of reducing, and the meter is clocking up 1-2kW peak demand every day - that amounts to more than £150 per year - Not what I want! I have tried turning everything off, switching off the consumer unit main switches, the solar and the Model S charger, so that the house demand was ABSOLUTELY ZERO. This had little effect on the 0.1kW demand shown on the Chameleon display. I then turned off the Powerwall and the Chameleon display dropped to ZERO. Then I turned on the Powerwall again and the Chameleon showed 8-11W demand, possible I suppose, but certainly not as high as the 0.1kW normally shown, which reoccurred once I switched on the consumer units. I have made an initial call to my energy provider to flag up my concern. The lady didn't seem to be too clued up on Smart Meters, let alone home batteries! Anyway we agreed to monitor it for a couple of weeks so that they could get more data. My questions are: 1. How does the Gateway actually monitor power flow and to what accuracy? Presumably it is a direct measurement transducer, rather than the rather inaccurate remote clamp on devices you can buy for $20. 2. What accuracy, at very low power flow, should we expect from the Gateway monitoring and a Smart Meter? The Gateway Spec states an AC meter revenue accuracy of +/-0.02%. Quite what that represents I have no idea! Having been involved in calibration of LVDT's etc I am well aware that measurement of very small power flows, displacements etc tend to be rather less accurate than the full scale accuracy of any monitoring device. Of course, the old meter may have been significantly inaccurate at low power levels, however, because it agreed with the Gateway data I tend to believe that the new meter is over-reading unless I get accurately measured data verifiable to National Standards.