Gateway 2 and Smart Meter accuracy

[mikemillar]

@milimura, I just opened up the consumer unit and checked, actually, the small capacity twin cable covered in black woven fabric goes to a CT clamp on the solar positive wire to the CB. That makes sense because it's the only way the Gateway could get any info on the solar output, since it's only connected to the consumer unit. The Gateway 2 surely measures grid and battery flow using internal sensors.

 

[mikemillar]

One thing I have established from downloading the api raw output directly from the gateway is that when the Powerwall is supplying all the house power, the 'phantom' drain from the grid comprises a very small total power (instant_power), usually 5-10W, but very large reactive and apparent power, typically 100-200VA. That means a very low power factor, I think. Reactive power is wasted power which mainly goes up in heat and does no useful work, so it means that whatever in the Powerwall is drawing that power is very inefficient - not good environmentally. It also means that, since my new Smart Meter appears to be metering reactive power, which the old mechanical meters can't do, I'm paying for this wasted power, but not being credited for anything it puts back as export, is not metered. Maybe an electrical expert out there can confirm or refute my assessment. here's part of an api download:

..."2019-12-19T21:05:26.99020871Z","instant_power":-5,"instant_reactive_power":113,"instant_apparent_power":113.11056537742175,.....

Why it can't draw the power from the battery instead of the grid is a mystery to me. I can force it to do that by pulling the main 100amp CB, which disconnects it from the grid and puts it into backup mode.

 

[mikemillar]

And here is Tesla's reply. It rather confirms my suspicions about reactive power metering - If you have Powerwall, don’t get a smart meter installed!
I like the beer glass analogy. The only problem is that during the day my glass is almost empty!

"Thank you for your reply.

From our investigation we have noticed that most of the times you only import energy from the grid overnight and since the solar is really poor the battery usually offsets your house loads during the peak hours.

I suspect that this discrepancy is due to the fact that your meter reads also the ‘reactive power’ while the App does not. The app shows only the ‘real power’.

To make this difference clear here it is a good and easy example:

The App only shows the Real power while I suspect your meter shows also the reactive power.

You can also check online the specific differences between the two types of “power”.

By the way, the system does not seems to record any import from the grid except the tolerated 0.4/0.5kW that basically is the amount of energy that the inside inverter uses to keep the modules DC to AC and AC to DC ready to be used.

I also suggest you to contact your energy supplier to check the meter and the installer of the battery to maybe do some checks on the CT clamp positioned on the site side.

I will anyway escalate the case to our Tech. Support to let the double check because I do not see this data discrepancy but maybe they can help me."

 

[mikemillar]

I now have a definitive reply from my energy supplier:
"Your current SMETS2 smart meter does in-fact measure both active and re-active power, and is designed to do so...". -
My main thresd oin this is at

Beware SMETS2 meters

The Powerwall 2 uses a significant amount of reactive power synchronising with grid frequency while supplying power to the home load, and I'm being metered on it. The older non-smart meters don't do that.