This is now cheap to do, including the related calibration of the sensors. If non-metering products are not achieving results like this, they really need to get their act together.
Again, as a meter designer don't be fooled by the BOM cost of the meter. It's not like an inverter manufacturer could just add those components on the inverter's main PCB. Due to physical requirements the grid point net meter has to be separate. Even if inverter manufacturer started to manufacture their own meters (some do, e.g. Kostal offers both inverters and meters) it is unlikely they could significantly cut prices compared to existing MID compliant meter manufacturers.
The cost of the chips or current sensors in the meter is irrelevant, customer pays for the market price of the meter which is much more than BOM, plus extra install work, which is always at customer's site. These inverters
already offer two options for the grid point net metering: using a MID certified (with any accuracy you want) meter using RS485 wiring, or clamp-on CTs. The former option is approx. 150-300EUR more expensive (install cost included), not some cents.
Probably the sweet spot in cost would be to algorithmically improve low-load offset errors, at least if the inverter manufacturer thinks they will be selling in large numbers to compensate for the NRE cost.
Thanks for explaining the accuracy details, the information is not too easy to find without diving deep into the actual standards. % of value indications are most misused metrics, they always require extra attributes like some minimum threshold, otherwise they always imply infinite accuracy and as such are impossible.
One thing to remember is that offset issue is not only at low loads. Say we have two meters which are provably +/-1% accurate
in value, so MID compliant (was it class B for 1%, I don't remember). Now let's say one meter is used for billing, other for inverter control, and your consumption is 2000W for 12 hours a day (whatever clothes washing, air conditioner use, cooking). One meter shows 1980W, another 2020W. 12 * 40Wh = 0.5kWh of unwanted import or export is thus billed
even if offset error at low loads was completely absent and
even when metering is utility-level accurate and compliant to billing requirements. And this 0.5kWh would be enough for some people to complain. So for true no-import-when-production-exceed-consumption, data integration to the meter which does the billing is a must. Even if you designed a perfectly accurate to 0.0001% meter, it won't help because the existing billing meter is not that accurate.