Why is the term "autonomy days" often misused?

Autonomy Days is one of the most frequently cited specifications in solar street lighting—and one of the most misunderstood.

Autonomy Days is not a battery specification

Autonomy Days describe how many consecutive days a system can operate without sufficient solar charging. It is a 

system-level outcome, not a direct battery property.

Two systems with identical batteries can have very different autonomy depending on energy consumption and control logic.

What Autonomy Days actually depend on

Autonomy Days are influenced by:

• Daily energy consumption

• Lighting schedule and dimming strategy

• Battery depth of discharge

• Temperature and aging

• Controller behavior during low-charge periods

Without stating these assumptions, an autonomy claim has limited meaning.

Why autonomy claims often fail in practice

Many specifications assume:

• New batteries

• Constant weather conditions

• No degradation over time

In real deployments, weather variability and battery aging quickly invalidate these assumptions.

How buyers should interpret autonomy claims

Instead of asking “How many autonomy days?”, buyers should ask:

• Under what conditions is this calculated?

• What happens when energy is insufficient?

• How does output change during extended bad weather?

Engineering takeaway

Autonomy Days are not a number to compare.
They are a behavior to understand.