Consistent with the other provisions of this chapter, the net energy measurement, billed charges for kilowatt-hour consumption, and credits for excess kilowatt-hour generation by a net metered system, must be calculated in the following manner:

(1) The electric utility shall measure the net electricity produced or consumed during the billing period, in accordance with normal metering practices.

(2) If the electricity supplied by the electric utility exceeds the electricity generated by the customer-generator's net metering system and fed back to the electric utility during the billing period, the customer-generator shall be billed for the net electricity supplied by the electric utility, in accordance with normal metering practices.

(3) If excess electricity generated by the net metering system during a billing period exceeds the electricity supplied by the electric utility during the same billing period, the customer-generator:

(a) Shall be billed for the appropriate customer charges for that billing period, in accordance with RCW 80.60.020; and

(b) Shall be credited for the excess kilowatt-hours generated during the billing period, with the credit for kilowatt-hours appearing on the bill for the following billing period.

(4) If a customer-generator requests, an electric utility shall provide such a customer-generator meter aggregation.

(a) For a customer-generator participating in meter aggregation, credits for kilowatt-hours earned by the customer-generator's net metering system during the billing period first shall be used to offset electricity supplied by the electric utility at the location of the customer-generator's designated meter.

(b) A customer-generator may aggregate a designated meter with one additional aggregated meter located on the same parcel as the designated meter or a parcel that is contiguous with the parcel where the designated meter is located.

(c) For the purposes of (b) of this subsection, a parcel is considered contiguous if they share a common property boundary, but may be separated only by a road or rail corridor.

(d) A retail electric customer who is a customer-generator and receives retail electric service from an electric utility at an aggregated meter must be the same retail electric customer who receives retail electric service from such an electric utility at the designated meter that is located on the premises where such a customer-generator's net metering system is located.

(e) Credits for excess kilowatt-hours earned by the net metering system at the site of a designated meter during a billing period shall be credited by the electric utility for kilowatt-hour charges due at the aggregated meter at the applicable rate of the aggregated meter.

(f) If credits generated in any billing period exceed total consumption for that billing period at both meters that are part of an aggregated arrangement, credits are retained pursuant to subsections (3) and (5) of this section.

(g) Credits carried over from one billing period to the next pursuant to (f) of this subsection must be applied in subsequent billing periods in the same manner described under (a) and (e) of this subsection.

(h) Meters so aggregated shall not change rate classes due to meter aggregation under this section.

(5) On March 31st of each calendar year, any remaining unused credits for kilowatt-hours accumulated during the previous year shall be granted to the electric utility, without any compensation to the customer-generator.

(6) Nothing in this section prohibits a utility from allowing aggregation under terms different than the requirements of subsection (4) of this section if a customer-generator has an existing arrangement for meter aggregation in effect or a customer submits a written request for aggregation on or before July 1, 2019.

(7) Nothing in this section prohibits the owner of multifamily residential facility from installing a net metering system as defined in RCW 80.60.010 assigned to a single designated meter located on the premises of the multifamily residential facility where the tenants are not individually metered customers of the utility and distributing any benefits of the net metering to tenants of the facility where the net metering system is located. The utility must measure the net energy produced and provide credit to the single designated meter to which the net metering system is assigned in accordance with subsections (1) through (3) of this section or under the terms of a standard rate or tariff schedule established under RCW 80.60.020(3). The distribution of benefits to tenants of such a system, if any, is the responsibility of the owner of the net metering system and not the responsibility of the utility.