How is system size measured for interconnection in California?

The published limits are stated in kilowatts without saying whether that is the inverter alternating current rating or the array direct current rating.

Is this address served by an investor owned utility? Rule 21 does not reach a publicly owned utility, and in that case none of the fees or screens here apply.

Only the utility holds this figure. Ask before you quote the job.

What is the published integration capacity analysis value at this point of interconnection? California uses it in place of the 15 percent screen when it is available.

Only the utility holds this figure. Ask before you quote the job.

California solar interconnection rules, tiers and fees

How the size is measured: not published

The published limits here are stated in kilowatts without saying whether that is the inverter rating in alternating current or the array rating in direct current. On a system near a threshold that decides which band it lands in, so the checker asks the question rather than choosing an answer.

Size bands and what each one obliges

Net billing eligible, 500 kW or less Size 0 to 500 kW	The interconnection request fee is $145 with no supplemental review fee and no detailed study deposit. California publishes no liability insurance requirement in Rule 21 at any size. $145 interconnection request fee No insurance requirement published in Rule 21
Above 500 kW, or not net billing Size 500.001 to 1000 kW	The interconnection request fee rises to $800, supplemental review is $2,500, and a detailed study deposit of $10,000 for a system impact study plus $15,000 for an interconnection facilities study applies at 5 MW and below. $800 interconnection request fee $2,500 supplemental review fee if required Study deposits if a detailed study is required

Net billing eligible, 500 kW or less Size 0 to 500 kW

The interconnection request fee is $145 with no supplemental review fee and no detailed study deposit. California publishes no liability insurance requirement in Rule 21 at any size.

$145 interconnection request fee
No insurance requirement published in Rule 21

Above 500 kW, or not net billing Size 500.001 to 1000 kW

The interconnection request fee rises to $800, supplemental review is $2,500, and a detailed study deposit of $10,000 for a system impact study plus $15,000 for an interconnection facilities study applies at 5 MW and below.

$800 interconnection request fee
$2,500 supplemental review fee if required
Study deposits if a detailed study is required

The screens that decide it

Exporting facility within the 1 MW Rule 21 ceiling Limit 1000 kW.
An exporting facility qualifies for Rule 21 only if its aggregate gross nameplate rating is 1 MW or less, or it uses a certified power control system to limit export to 1 MW or less. A non exporting facility has no size ceiling under Rule 21.
Below the 30 kVA point where protection and disconnect obligations change Limit 30 kW.
Rule 21 Screen J asks whether the gross rating is 30 kVA or less. Above it, additional protection and disconnect obligations apply.
Aggregate generation under 15 percent of line section peak load 15 percent of line section peak load, a figure only the utility holds.
California subordinates this to hosting capacity data. Where integration capacity analysis values are published for the point of interconnection, the test becomes 90 percent of the lowest value in the published profiles instead, and only falls back to 15 percent of line section peak load when those values are unavailable. Ask for the integration capacity analysis value at this address before relying on the 15 percent figure.

Ask the utility this, before you sell it

Is this address served by an investor owned utility? Rule 21 does not reach a publicly owned utility, and in that case none of the fees or screens here apply.
What is the published integration capacity analysis value at this point of interconnection? California uses it in place of the 15 percent screen when it is available.
Rule 21 does not state whether the gross nameplate rating is measured in AC or DC. Confirm which figure will be used to place this system.
Retail net energy metering is closed to new applicants. Confirm the current net billing compensation for this customer.

Worth knowing before you quote

Rule 21 publishes no liability insurance requirement at any size, which was confirmed by reading the whole tariff rather than inferred. It also publishes no days to permission to operate, only 15 business days for initial review and 20 business days for supplemental review. Retail net energy metering closed to new applicants on 15 April 2023 and new customers take the net billing tariff. California did not adopt the federal small generator interconnection procedures; Rule 21 is its own lineage with twelve enumerated export configuration options, the most granular storage treatment of any state read.

Utility programs we have read in California

Source

California Electric Rule 21, Generating Facility Interconnections, as filed by Pacific Gas and Electric under CPUC advice letters effective 2025

Read and recorded 2026-09-12. Rule 21 is a CPUC mandated uniform tariff filed by each investor owned utility. It governs only utilities over which the CPUC has jurisdiction, so publicly owned utilities including Los Angeles Department of Water and Power, Sacramento Municipal Utility District, Imperial Irrigation District and Roseville set their own terms and are outside it.

Solar and battery interconnection rules in California

Size bands and what each one obliges

The screens that decide it

Ask the utility this, before you sell it

Worth knowing before you quote

Utility programs we have read in California

What to do with this