Background of Metering and Monitoring Requirements

In D.06-08-028, the Commission issued general metering guidelines and directed the metering subcommittee to adopt specific metering requirements for solar installations. As reflected in the CSI Program Handbook, very small systems, 10 kilowatt (kW) or less, may use meters with accuracy ratings of + 5% (including inverter integrated meters that meet this accuracy standard) but all other systems must install meters with accuracy ratings of + 2%, the standard of accuracy generally used by utility billing meters.

The Commission also required that solar installations include communication systems that allow for remote monitoring and reporting of system performance (PMRS). Under the decision, the cost of such systems plus meter costs is subject to a cost cap of 1% of the total installed cost for systems up to 30 kW or less, and 0.5% for larger systems.1

The following table summarizes the metering and performance monitoring requirements pursuant to D.06-08-028.

Table 1

Current CSI Metering and Monitoring Rules Pursuant to D.06-08-028

System Size

Minimum Meter Accuracy

Performance Communication and Reporting Requirement

Metering & Monitoring Cost Cap

< 10 kW

+/- 5%



10 kW to 30 kW

+/- 2%



30 kW and greater

+/- 2%



1 D.06-08-028, p. 77.

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