Solar Streetlight Sizing Calculator

Project and Design Basis

Project name

Location

Installation type

Calculation mode

Critical design month

Solar resource method

Minimum ambient temperature (°C)

Maximum ambient temperature (°C)

Design notes

Streetlight Load and Smart Dimming

Number of streetlights

LED module power per light (W)

Driver efficiency (%)

Auxiliary load per light (W)

Operating hours per night

Standby load per light (W)

Extra backup hours

Operation control

Emergency mode

Dimming schedule

Period	Start	End	Brightness (%)	Motion boost likelihood (%)
1
2
3
4
5

Solar Resource, Array, and Orientation

Peak sun hours

Daily irradiation (kWh/m²/day)

Panel rated power (W)

Panel Vmp (V)

Panel Voc (V)

Panel Isc (A)

Panel efficiency (%)

Panel tilt angle (°)

Panel azimuth (°)

Hemisphere

Mounting type

Engineering safety margin (%)

Shading loss (%)

Cloud loss (%)

Soiling loss (%)

Temperature loss (%)

Wiring loss (%)

Mismatch loss (%)

Manufacturing tolerance (%)

Panel degradation allowance (%)

Orientation loss (%)

Battery Storage and Autonomy

Battery chemistry

System voltage (V)

Required autonomy (days)

Maximum depth of discharge (%)

Charge efficiency (%)

Discharge efficiency (%)

Temperature capacity factor (%)

Aging capacity factor (%)

End-of-life capacity factor (%)

Battery reserve margin (%)

Battery unit voltage (V)

Battery unit capacity (Ah)

Cloudy-day simulation length

Starting state of charge (%)

Cloudy-day solar production (%)

Charge Controller and Protection

Controller type

Controller efficiency (%)

Controller safety margin (%)

Maximum PV input voltage (V)

Cold-weather Voc correction (%)

Low-voltage disconnect (V)

Reconnect voltage (V)

Overcharge voltage (V)

Surge protection rating

Lighting Performance and Pole Layout

Target average illuminance (lux)

Target minimum illuminance (lux)

Road width (m)

Pole spacing (m)

Pole mounting height (m)

Boom-arm length (m)

Luminaire tilt angle (°)

Luminous efficacy (lm/W)

Fixture lumens (optional)

Zero uses lamp watts multiplied by efficacy.

Utilization factor (%)

Maintenance factor (%)

Light-loss factor (%)

Uniformity ratio

Road layout

Beam distribution

Color temperature

Ingress protection

Impact rating

Cable Sizing and Voltage Drop

Conductor material

Allowable voltage drop (%)

Installation method

Segment	One-way length (m)	Selected cable area (mm²)
Panel to controller
Controller to battery
Battery to distribution
Pole base to luminaire

Pole, Structural, and Installation Checks

Design wind speed (km/h)

Maximum panel area (m²)

Equipment enclosure location

Foundation condition

Luminaire arrangement

Structural review status

Financial and Environmental Estimate

Panel cost per watt ($)

Battery cost per kWh ($)

Controller cost ($)

Luminaire cost each ($)

Pole cost each ($)

Cables and protection ($)

Installation cost ($)

Annual maintenance ($)

Lifecycle period (years)

Battery replacement interval (years)

Grid electricity price ($/kWh)

Grid emissions factor (kg CO₂e/kWh)

Avoided grid-extension cost ($)

View formulas

Formula Used

Daily lighting load
E_load = Σ[(P ÷ η_driver) × h × brightness] + auxiliary + standby

Adjusted source energy
E_adjusted = E_load ÷ (η_controller × η_charge × η_discharge)

Solar array size
P_solar = E_adjusted ÷ (PSH × combined solar derate) × safety factor

Battery capacity
C_Ah = required stored energy ÷ (V × DoD × efficiency × temperature × aging)

Controller current
I_controller = array watts ÷ battery voltage × controller safety factor

Average illuminance
Lux = lumens × utilization × maintenance × light-loss × layout factor ÷ area

DC voltage drop
ΔV = I × (2 × resistivity × length ÷ conductor area)

Cloudy-day state of charge
Stored energy = previous energy + reduced solar charge − nightly lighting load

How to Use This Calculator

Enter the fixture count, lamp power, and nightly schedule.
Use the lowest reliable peak sun hours available.
Enter realistic losses for heat, dust, shade, and wiring.
Select battery chemistry, voltage, autonomy, and capacity limits.
Check controller voltage, current, cable drop, and protection.
Enter road dimensions and verify the estimated illuminance.
Run the cloudy-day simulation and review every warning.
Export results before completing engineering and photometric reviews.

Example Design Data

Input	Example value	Purpose
Streetlights	10 fixtures	Defines the total connected load.
LED rating	40 W each	Sets the lighting energy demand.
Operating schedule	12 hours with dimming	Reduces overnight battery consumption.
Peak sun hours	5 hours	Sets the worst-month solar resource.
Battery autonomy	3 days	Provides resilience during poor weather.
System voltage	24 V	Controls current and cable requirements.
Road geometry	7 m × 30 m	Supports an approximate illuminance check.
Voltage-drop limit	3%	Controls conductor sizing and losses.

Frequently Asked Questions

What peak sun hours should I use?

Use the lowest dependable monthly value for the site. Avoid annual averages when winter conditions control the design.

Does dimming reduce battery size?

Yes. Lower overnight power directly reduces nightly energy demand and required storage.

Which battery chemistry is best?

LiFePO₄ often offers high cycle life and usable capacity. Final selection depends on temperature, cost, maintenance, and availability.

Why is the recommended panel larger?

The calculator includes system losses, battery charging losses, degradation, and safety margin.

Can this replace a photometric study?

No. The illuminance estimate is preliminary and cannot replace an IES-file roadway analysis.

How many autonomy days are typical?

Two or three days are common starting points. Cloudy climates may require more storage.

Why check cold panel voltage?

Solar-panel open-circuit voltage rises in cold weather. Excess voltage can damage the controller.

How is cable size selected?

The tool calculates resistance, voltage drop, and power loss. It then selects the next standard area.

Does the tool design the pole foundation?

No. Pole, wind, arm, panel, and foundation loads require qualified structural verification.

Can the calculator size integrated lights?

Yes. Use the integrated mounting option and enter the actual internal component ratings.

Why does cloudy simulation show low reserve?

Reduced solar charging may not replace each night’s load. Increase storage, array size, or dimming.

Technical disclaimer: This calculator provides preliminary sizing estimates. Final designs require local solar data, certified equipment curves, electrical protection coordination, photometric verification, structural review, and applicable code compliance.