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Wattwatchers solution – Auditor 6M+One – installed in Solar PPAs

by Murray Hogarth
posted on Sunday, June 14th, 2020

There are two main kinds of solar PPA: Gross, which requires billing class monitoring on the solar inverter output only; and net, which requires billing class monitoring on the solar inverter output as well as the grid feed in.

PMC Installation

The PMC billing class meter should be installed on the output of the solar inverter.

Whole Current (direct connect) PMC meters installed on the inverter should have the input side of the meter connected to the inverter.

CT PMC meters should have the CTs installed pointing away from the inverter.

Because the energy registers of the PMC are named on the assumption that the PMC is installed as a grid meter, the PPA configuration means that the energy registers need to be interpreted as follows:
kWh_Imp == solar generation
kWh_Exp == dark inverter load

A note on units

The Modbus channel reports data unchanged from the PMC, using the units provided by the PMC. In the case of the kWh_Imp, kWh_Exp and similar values, the units are 0.01 kWh. See also the Modbus documentation for the REST API.

A note on PMC meters

PMC220 single-phase meters are direct connect only, and handle currents to 63A

PMC340 three-phase meters are either:
– PMC-340-BA (Direct Connect)
– PMC-340-BB (Transformer Coupled)

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