[Hannah LS (OP)]

Nikki asks:

Can you please tell me if the AC Watthour Meter will record as accurately backwards as it does forward? We know the meter turns the wheel forward recording the kWs coming in, but if this was reversed and the wheel went backwards would it accurately record this electricity?

In short, if the meter reading was zero and 10kW came in, and then 10kW went out, would the meter still read zero.

What do you think?

[RD]

If you're thinking of trying to wire the meter backwards to cancel-out your bill,
(apart form it being dangerous & illegal), it probably won't work today ...

In the 1970/80’s a number of illegal activities were identified which attempted reduce the energy recorded on the meter by reversing the meter, or forcing reversed energy flow through the meter. As a result of these attempts of energy theft, electromechanical meters procured after c.1985 were fitted with a ‘backstop’... Electronic meters also offered the ability to ‘flag’ the data if there was any ‘reverse energy flow’ was detected.

https://meteroperators.org.uk/images/FAQ_and_Stakeholder_Info/Reverse_running_meters_20130820.pdf

[alancalverd]

A laboratory energy meter can measure watt-hours or joules in either direction with identical accuracy. In principle, a domestic spinning-disc device could, although after a few years' wear, the forward and reverse calibrations would differ as the gear frictional losses would be asymmetric.

You can of course get a "reversible" meter if you have a feed-in contract from your windmill or solar panels, but the forward and reverse tariffs will be different and time-variable so it will have separate in and out displays.

[evan_au]

There are intentional losses built into domestic kWh meters to prevent "meter creep" when there is no current being drawn, but AC voltage is still being applied.

So if you drew 10kWh (energy) from the grid by drawing 1kW (power) for 10 hours, that would register quite accurately (within 1% or so).
However, if you fed back 10kWh into the grid by delivering 2W for 6 months, that would hardly register on the meter at all - it would be treated as "no load".

[Bored chemist]

A meter that measures energy output accurately is necessarily a meter that measures energy input accurately.
If the meter measures how much energy a battery gives to a lamp, then it measures the energy taken by the lamp from the battery- because they are the same.