Why rainy season sizing fails in real projects

Common failure pattern:

• Supplier claims “X nights autonomy”
• Real-world solar input is lower than assumed for multiple weeks
• Battery never fully recovers → daily SOC keeps dropping → early shutoffs

The fix is not “bigger wattage”. The fix is disclosed assumptions + worst-month check + auditable energy budget.

Step 1) Start with the energy budget (you must have this)

You cannot size for rainy season without a clear daily load.

Required inputs (must be declared)

• Dimming profile (time steps or PIR logic)
• Average power under dimming (Wavg)
• Night runtime hours (h)

Daily load energy:
Wh/night = Wavg × runtime hours

If you don’t already have this structure, use:
Autonomy Days Calculation (Backup Nights)

Step 2) Set the autonomy target (backup nights)

Autonomy nights is how long the system can run without effective charging.

Usable battery energy:
Whusable = Whnominal × usable factor

Autonomy nights:
Autonomy = Whusable ÷ Wh/night

Rainy season projects should use conservative assumptions and require the supplier to disclose the usable factor and what it includes.

Related:
LiFePO4 Battery Lifespan (What actually changes over time)

Step 3) Worst-month PV yield sanity check (the key rainy season step)

Autonomy alone is not enough. The system must also recover.

Ask the supplier to disclose:

• PV module rating (Wp)
• Worst-month solar assumption (or conservative equivalent)
• Charging efficiency assumption (declared)

Simple check (supplier must fill values):
PV daily energy (Wh/day) = PV_Wp × Worst-month PSH × charging efficiency

Then:
Net daily balance = PV daily energy − daily load energy

Interpretation:
If net daily balance is negative in the worst-month model, the system will “walk down” in SOC over time and fail earlier during extended cloudy weeks.

Step 4) Choose the right architecture for rainy season risk

When Split Type is usually safer

• You need scalable PV and battery sizing for worst-month
• You want easier component service and clearer warranty execution
• You expect long rainy seasons or frequent multi-day storms

Guide:
Highway All-in-One vs Split Type (Engineering Comparison)

When All-in-One can still work

• Lower-risk roads and shorter requirements
• Supplier provides auditable energy budget + disclosed worst-month assumptions
• Model-specific IES files are available if roadway spacing is claimed

Step 5) Controller strategy matters (especially in rainy season)

In rainy season, “smart energy” often saves projects:

• Time-based dimming keeps a predictable energy budget
• PIR boost + low base brightness can cut Wh/night significantly

Related guides:

• PIR vs Time Dimming
• MPPT vs PWM Controller

Step 6) Procurement PASS/FAIL rules (rainy season)

Mark a bid FAIL (Not Comparable) if it lacks:

• Energy budget sheet (dimming profile, Wavg, hours, Wh/night)
• Battery nominal Wh + declared usable factor assumption
• Worst-month PV yield disclosure (PSH or conservative equivalent) and charging efficiency assumption

For roadway projects where spacing is claimed, also require:

• IES files + DIALux-ready inputs — see: IES & DIALux Resource Center

Copy/Paste RFQ Clauses (Rainy Season Ready)

Clause 1 — Energy budget sheet (mandatory)

Supplier shall submit an energy budget sheet including:

• dimming profile used
• average power under dimming (Wavg)
• nightly runtime (hours)
• Wh/night calculation

Clause 2 — Rainy season / worst-month disclosure (mandatory)

Supplier shall declare:

• PV module Wp
• worst-month solar assumption (or conservative equivalent)
• charging efficiency assumption

and submit a PV yield sanity check showing net daily balance.

Clause 3 — Autonomy basis (mandatory)

Supplier shall declare:

• battery nominal Wh
• usable factor assumption

and calculate autonomy nights using Whusable ÷ Wh/night.

Clause 4 — Bid comparability rule

Bids missing the rainy season worst-month PV yield disclosure and energy budget sheet shall be labeled “Not Comparable / High Risk” before price comparison.

Request Rainy Season Sizing Worksheet

Get the editable worksheet used to standardize worst-month sizing:

• Energy budget sheet (Wavg, hours, Wh/night)
• Autonomy calculator (Whusable and backup nights)
• Worst-month PV yield sanity check block
• PASS/FAIL screening checklist for rainy season bids

FAQ

What is “worst-month sizing” in simple terms?

It means the system is checked against the month with the lowest solar input (or a conservative equivalent), so it can survive extended cloudy periods without drifting into low battery SOC.

Why isn’t autonomy nights enough for rainy season projects?

Because a system can run for several nights but still fail long-term if it cannot recover daily charge during the worst-month conditions.

What documents make a rainy season quote comparable?

An energy budget sheet, declared usable battery assumptions (Wh), and a worst-month PV yield sanity check with disclosed assumptions.