What Is Offset?
Offset is the percentage of a homeowner's electric usage that a proposed solar system is sized to cover, based on their historical utility bills, and it is usually the single number that matters most to a homeowner comparing what a system will actually do for their bill, more than the system's raw kW rating.
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Offset is the percentage of a homeowner's electric usage that a proposed solar system is sized to cover, based on their historical utility bills, and it is usually the single number that matters most to a homeowner comparing what a system will actually do for their bill, more than the system's raw kW rating.
Offset explained
A system's offset percentage is calculated against a homeowner's actual historical usage, not against an average or a generic assumption, which is why two homes with identically sized systems can carry very different offset numbers. It is sometimes listed in glossaries as its own separate entry, "offset percentage," describing the same underlying concept.
Offset math has gotten materially more complicated in states with net-billing changes. In California specifically, NEM 3.0 cut solar export credits by roughly 75% starting in April 2023, which changes the real value of any exported, unused solar production relative to what the homeowner consumes directly on-site. That shift is a direct driver of why battery attach has climbed to 45% nationally in Q1 2026: storage is increasingly what makes a stated offset percentage actually deliver the bill savings a homeowner expects, rather than an optional add-on layered on top of it.
A quoted offset number that doesn't state whether it assumes battery storage, and doesn't account for the state's current net-metering rules, can overstate what a homeowner will actually see on their bill.
Why it matters when you're buying
Walk through the offset number and its assumptions explicitly on every proposal, especially in a net-billing state like California. State plainly whether the quoted offset assumes battery storage, since leaving that assumption unstated is how a homeowner ends up disappointed by their first bill.
Frequently Asked Questions
What does "offset" mean on a solar proposal?
Does offset mean the same thing in every state?
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