Washington Solar Energy Systems: Key Terms and Definitions

Solar energy systems installed in Washington State operate within a specific framework of electrical codes, utility interconnection rules, state incentive programs, and local permitting requirements. This page defines the core terminology used across that framework — from photovoltaic components and system classifications to net metering, interconnection agreements, and performance metrics. Readers engaging with installation proposals, utility agreements, or public incentive programs will encounter these terms repeatedly, and precision in their use matters for compliance and financial planning. For a broader orientation to how these systems function in Washington's regulatory environment, see the Washington Solar Energy Systems home page.

Definition and scope

Solar energy system refers to any assembly of components that converts sunlight into usable electrical or thermal energy. In Washington State, the term encompasses grid-tied photovoltaic (PV) arrays, off-grid PV systems, solar thermal collectors, and hybrid configurations that integrate battery storage. The Washington State Department of Commerce uses this broad definition when administering incentive programs and energy planning policy.

Photovoltaic (PV) system — the most common installation type in the state — converts solar irradiance directly into direct current (DC) electricity using semiconductor cells, typically silicon-based. An inverter then converts DC output to alternating current (AC) for household or grid use. System capacity is measured in kilowatts (kW) for instantaneous output and kilowatt-hours (kWh) for energy production over time.

Grid-tied system connects to a utility's distribution network, enabling export of surplus electricity. These systems require an interconnection agreement with the serving utility and compliance with IEEE Standard 1547-2018, which governs distributed energy resource interconnection to electric power systems. Grid-tied systems cannot operate as backup power during outages unless paired with battery storage and a transfer switch — a distinction with direct safety implications.

Off-grid system operates independently of the utility grid and relies on battery banks, charge controllers, and backup generation. Requirements for off-grid configurations differ substantially from grid-tied systems; for a structured comparison, see Washington Grid-Tied vs. Off-Grid Solar.

Solar thermal system captures heat rather than generating electricity, typically for domestic hot water or space heating. These systems are classified separately from PV under both the International Energy Conservation Code (IECC) and Washington's adoption of that code through the Washington State Building Code Council.

How it works

A grid-tied PV system follows a defined energy conversion pathway:

1. Irradiance capture — Photovoltaic cells within panels absorb photons from sunlight and release electrons, producing DC electricity. Panel output depends on irradiance (measured in W/m²), cell temperature, and shading conditions.
2. DC-to-AC conversion — A string inverter, microinverter, or power optimizer converts DC output to grid-compatible AC at 120/240V for residential systems.
3. On-site consumption — AC electricity powers on-site loads first; surplus flows to the utility grid.
4. Net metering accounting — Utilities track exported and imported electricity under Washington's net metering framework (RCW 80.60), crediting exported kWh against consumption charges. The /washington-net-metering-explained page covers credit mechanics and utility-specific rules.
5. Monitoring and reporting — Production meters or integrated monitoring platforms record system output for performance verification and incentive documentation.

A conceptual overview of how Washington solar energy systems work provides additional detail on each phase of this process.

Common scenarios

Residential rooftop PV — The most prevalent configuration, typically sized between 5 kW and 15 kW for single-family homes. Roof orientation, pitch, and structural load capacity are evaluated during permitting; Washington Solar Panel Roof Suitability addresses those criteria.

Commercial and industrial PV — Larger arrays (often 50 kW to 1 MW+) installed on commercial buildings or ground-mounted on adjacent parcels. Additional interconnection study requirements apply at this scale. Washington Solar Energy for Commercial Properties covers the relevant distinctions.

Community solar — Subscribers purchase or lease a share of a centrally located array and receive bill credits proportional to that share's output. Washington's community solar program is administered under SB 5939 (2019). See Washington Community Solar Programs for subscriber eligibility rules.

Agricultural solar — Arrays co-located with crop production ("agrivoltaic" systems) or used to power irrigation and processing loads. Washington Solar Energy for Agricultural Operations addresses land-use and utility classification considerations unique to this scenario.

Battery-paired systems — DC-coupled or AC-coupled storage added to PV systems for backup, self-consumption optimization, or demand charge management. Safety classification follows NFPA 855 (Standard for the Installation of Stationary Energy Storage Systems), with additional Washington local amendments possible. Washington Solar Battery Storage Options addresses sizing and code considerations.

Decision boundaries

Not all configurations are interchangeable, and classification determines which codes, permits, and incentive pathways apply:

The regulatory context for Washington solar energy systems page maps specific statutes and agency authorities to each system type.

Scope and coverage limitations: This page covers terminology applicable to solar energy systems installed, permitted, or operated within the State of Washington. Federal tax credit rules originate with the Internal Revenue Service and are not Washington-specific; Washington Federal Solar Tax Credit Applicability addresses how federal provisions interact with state programs. Rules applicable to tribal lands, federal installations, or systems in neighboring states (Oregon, Idaho) are not covered here. Local jurisdictions — counties and municipalities — may adopt amendments to the state building code; those local variations fall outside this page's scope and must be verified with the applicable building department.

References

• Washington State Department of Commerce — Energy Planning and Policy
• RCW 80.60 — Net Metering, Washington State Legislature
• Washington State Building Code Council
• IEEE Standard 1547-2018 — Interconnection of Distributed Energy Resources
• International Energy Conservation Code (IECC), ICC
• NFPA 855 — Standard for the Installation of Stationary Energy Storage Systems
• SB 5939 (2019) — Washington Community Solar, Washington State Legislature
• National Electrical Code (NEC) Article 690 — Solar Photovoltaic Systems, NFPA 70 (2023 edition)