Choosing a solar panel for street light installations is not the same problem as choosing panels for a roof. A street light module is small, works at low voltage, sits in a fixed orientation for a decade, and must keep a battery charged through the worst week of winter. Get the solar panel for street light sizing wrong and the lamp dims by February. This guide covers the sizing arithmetic, panel types, mounting practice and the specifications worth insisting on.

What the panel actually has to deliver

The module must replace every watt-hour the lamp consumes, plus losses, on the shortest day of the year. That last clause is the whole design. A panel sized against annual average irradiance will fail in winter, when both output and daylight hours are lowest and the lamp runs longest. Design for December, not for the average, and the system works all year.

Sizing: from lamp wattage to panel wattage

The sizing formula

The working formula is straightforward. Daily energy equals lamp wattage multiplied by operating hours. That figure, divided by peak sun hours for the worst month multiplied by a system efficiency factor of roughly 0.7 for controller, battery and wiring losses, gives the required array wattage.

A worked example

A 60W lamp running twelve hours needs 720 Wh per day; at 3.5 winter peak sun hours and 0.7 efficiency the array must be about 295W. Rounded up for degradation, a 300W array is the honest answer — which is why most "100W panel, 60W lamp" kits underperform after the first season.

Panel types for street lighting

Monocrystalline half-cell modules dominate because they pack high wattage into a small frame and handle partial shading better than full-cell designs. For pole-mounted luminaires, compact framed modules in the 50-80W range suit short poles, footpaths and garden lighting, while 100W and above serve main-road poles with taller masts and larger batteries. Three sizes cover most designs: the DLXN-M10 50W module for path and compound lighting, the DLXN-M10 60W module for residential streets, and the DLXN-M10 80W module for higher-output heads. The full small application module range extends to 230W for larger arrays.

Tilt, orientation and shading

Fixed panels should face the equator at a tilt close to the site latitude, adjusted a few degrees flatter in dusty regions so rain and cleaning water run off. Avoid mounting flat: even a five-degree tilt sheds dust and improves winter output noticeably. Check the shading path from trees and buildings across the whole year, not just at installation, and keep the panel clear of the luminaire's own arm and the pole cap.

Battery and controller pairing

Panel sizing is only half the system. A LiFePO4 battery sized for three to five days of autonomy carries a street light through cloudy spells, and an MPPT controller recovers 10-20% more energy than a PWM unit in low light. Specify the controller for the panel's open-circuit voltage with margin for cold mornings, when voltage rises, and confirm it protects the battery against over-discharge and low-temperature charging.

Cabling, voltage drop and pole integration

Low-voltage DC runs on a tall pole are lossy, and the loss is silent: the lamp simply dims earlier each evening. Keep the module-to-controller cable short and size it so voltage drop stays under 3% at peak current, and mount the controller at the battery rather than at the panel head so the long run carries the higher battery voltage. On retrofit poles, check that the existing mast and foundation can carry the added panel area and its wind load, because a larger module raises the overturning moment more than its extra weight suggests. Cable glands and connectors should be UV-rated and mechanically supported; a degraded connector at head height turns a ten-dollar part into a maintenance visit with a bucket truck.

Specification checklist

• Power tolerance and flash-test values, not just nameplate rating.
• Low-light performance and temperature coefficient of power for hot climates.
• Frame and junction box rated for outdoor exposure, with IP65 or better ingress protection.
• Wind load rating appropriate to pole height and local conditions.
• Certification for the destination market and a warranty that covers power output, not only materials.

Procurement mistakes worth avoiding

The recurring errors are undersized arrays justified by summer testing, PWM controllers paired with panels that need MPPT, and batteries sized for one night of autonomy in a climate with week-long overcast periods. Ask suppliers for the winter-case calculation in writing; a vendor who cannot show that arithmetic is selling a kit, not a design.

Frequently asked questions

What size solar panel for street light with a 60W LED?

Budget around 300W for twelve hours of nightly operation in a mid-latitude winter. Shorter operating hours, dimming schedules or higher winter irradiance reduce the requirement proportionally.

How many days of autonomy should a solar street light have?

Three to five days is the practical range. Two days works only in reliably sunny climates; five days is the safer choice for monsoon or overcast regions.

Monocrystalline or polycrystalline for street lights?

Monocrystalline. It delivers more wattage per square metre, which matters when the panel must fit a small pole frame, and it performs better in low light and high temperature.