Free engineering tool
Solar street light calculator
Size the battery and solar panel for a solar street light from your lighting schedule and your site's sun. Every formula is shown below the result, so you can check our numbers or anyone else's.
How the sizing works
A solar street light must store enough energy on a sunny day to run through the night, and enough in the battery to get through runs of cloudy days. The calculator follows three steps: the energy the LED uses per night, the battery that stores that energy for the chosen number of nights, and the panel that refills it in the worst month of the year.
Check the result against the rainy season at your site with the battery autonomy calculator, and compare the total cost with a grid-powered option in the solar vs grid cost calculator.
Questions about this calculation
How do I calculate the battery capacity for a solar street light?
Multiply the LED power by the equivalent full-power hours per night to get the daily energy in Wh, divide by the driver efficiency, multiply by the number of nights of autonomy, then divide by the usable depth of discharge of the battery. Divide the result by the battery voltage to get Ah. Example: a 60 W light running 5 h at 100% and 6 h at 30% uses 60 × (5 + 1.8) = 408 Wh. With a 0.9 efficient driver that is 453 Wh per night. Three nights of autonomy with LiFePO4 at 90% depth of discharge needs 453 × 3 / 0.9 ≈ 1,511 Wh, which is about 118 Ah at 12.8 V.
How do I size the solar panel?
Divide the daily energy by the peak sun hours of the worst month and by the overall charging efficiency (typically 0.65–0.75, which includes temperature and dust losses, controller efficiency and battery charge efficiency). Using the worst month instead of the annual average is what keeps the light on in the rainy season.
Where do I find peak sun hours for my location?
Use a free solar resource database such as Global Solar Atlas (globalsolaratlas.info) or PVGIS from the European Commission. Look up the daily global horizontal irradiation for the worst month in kWh/m²/day; that number equals the peak sun hours. Many tropical sites are between 3.5 and 5.5, and desert sites can exceed 6.
Why does dimming after midnight matter so much?
Running at 30% after midnight cuts the energy of those hours by 70%. On a typical 12-hour night, a dusk-to-midnight 100% / 30% after midnight profile needs only about 65% of the energy of running at full power all night, so the battery and panel can be about a third smaller.
More free tools
- Street light pole height & spacing calculatorRecommended pole arrangement and maximum spacing from road width, pole height and LED lumens.
- Solar battery autonomy & rainy-day calculatorHow many rainy days your solar street light battery lasts, and whether it survives your rainy season.
- Solar vs grid street lighting cost calculatorTotal cost of ownership over 5–25 years: trenching, cabling and electricity vs. solar street lights.
- High bay lighting calculatorHow many LED high bays a warehouse, factory or sports hall needs, with layout and W/m².
- LED retrofit energy savings & payback calculatorEnergy, money and CO2 saved by replacing sodium, metal halide or fluorescent lights with LED.
Next step
Ask our engineers to check your design
Calculators give planning figures. Send us the site location, drawings and quantity, and we return a photometric or solar sizing check and a quotation for the complete set.
Email us
[email protected]Tell us the product, quantity, site location and any drawings or specifications. An engineer reads every email and we reply within one working day (China time, GMT+8).