Glossary · Rules and the grid

What Is Interconnection? Connecting Solar to the Grid, Explained

InterconnectionAnd the interconnection agreement

The utility's rules and approval process for connecting a generator, like rooftop solar, to the grid; the interconnection agreement is the contract.

  1. The CPUC adopts the first version of Rule 21, its interconnection tariff
  2. SB 868 is signed: qualifying plug-in devices need no interconnection agreement
  3. The exemption takes effect, for certified systems up to 1,200 W AC per home
  4. The exemption ends unless the Legislature extends it
Interconnection in California, from the first version of Rule 21 to the plug-in solar exemption.

At a glance

Who sets the rules
State utility commissions; they vary by state
Common basis
IEEE 1547 and UL 1741
Small systems
Often eligible for a simplified, fast-tracked process
California
Rule 21, first adopted in 1982
Plug-in solar
California exempts qualifying devices from 2027 (SB 868)

Before rooftop solar or a home battery can send power onto the grid, the utility has to approve the connection. State utility commissions set those interconnection standards, and they vary by state, explains the DOE’s National Laboratory of the Rockies. Many states base the engineering and safety requirements on IEEE 1547 and UL 1741, and small inverter-based systems can often use a simplified, fast-tracked process. The interconnection agreement is the business contract between the utility and the customer for the project.

How does it work in California?

California’s investor-owned utilities connect generators under Rule 21, a tariff covering interconnection, operating and metering requirements. The CPUC adopted its first version in 1982, and each utility keeps its own version of the rule.

Does plug-in solar need interconnection?

Where a state has a plug-in solar law, qualifying systems are exempt. California’s SB 868 says utilities can’t require interconnection, an interconnection agreement, approval or fees for a certified device up to 1,200 W AC per home, from January 1, 2027; a utility may ask for a simple online registration. Where there’s no such law, plug-in systems fall under the utility’s usual rules. Details in our guide to the California plug-in solar law.

Published by the Plugged Sun editorial team

Sources

  1. Energy System Interconnection Standards (Official document, National Laboratory of the Rockies (US Department of Energy), 2026)
  2. Electric Rule 21: Generating Facility Interconnections (Official document, California Public Utilities Commission, 2026)
  3. Best Practices for Interconnection Agreements (Source, US Department of Energy, 2019)
  4. SB 868: Electricity: portable solar generation devices (status, chaptered text and digest) (Source, CalMatters Digital Democracy, 2026)

Where Interconnection comes up