A solar system isn't one piece of equipment aging uniformly — it's three different components with three different clocks.
Panels: the longest-lived component by far
Most tier-1 panels are warrantied for 25 years at 85-88% of original output, and many continue producing meaningfully beyond that point — panels are typically the last component to need replacement in a system's lifetime. See the degradation calculator for what output looks like at any specific year.
Inverters: the component most likely to need mid-life replacement
String inverters typically carry 10-15 year warranties and commonly need replacement once during a 25-year panel lifespan — a cost worth budgeting for at the outset rather than treating as a surprise. Microinverters, distributed across each panel, often carry longer warranties (sometimes matching the panels) since a single unit failing affects only one panel rather than the whole array.
Batteries: the shortest-lived, most variable component
Battery lifespan is measured in cycles as much as years — a battery cycled deeply every day wears faster than one cycled occasionally, which is why depth of discharge matters so much for longevity. See the depth of discharge calculator for how DoD choices affect expected cycle life. Most quality lithium batteries are warrantied for 10 years or a specific cycle count, whichever comes first.
Planning around staggered replacement
Because these three components age on different timelines, a realistic long-term cost picture includes a probable inverter replacement around year 10-15 and possible battery replacement or capacity fade requiring augmentation somewhat earlier than the panels' own 25-year horizon. Factor this into any long-term ROI calculation rather than assuming zero maintenance cost across the full system life.
Frequently asked questions
Do I need to budget for an inverter replacement?
It's a reasonable planning assumption for a system owned 20+ years, since most string inverters carry 10-15 year warranties and commonly need replacement once within a panel's 25-year lifespan — factor this into long-term cost expectations.
Why do batteries have such variable lifespan compared to panels?
Batteries degrade through charge/discharge cycling, not just time, so usage pattern (how deeply and how often they're cycled) has a much bigger effect on lifespan than it does for panels, which degrade primarily from environmental exposure over time.