Sourcing Solar Street Lights From China: Capacity Claims, MPPT and the Rainy-Season Test Nobody Runs

The first time I bought solar street lights, the quote said 60Ah lithium battery and the units died by night three of a cloudy spell. When I opened one up, the "60Ah" pack was a 12.8V 30Ah pack with a sticker on it, and the charge controller was a cheap PWM board that threw away a third of the panel's output on anything but a perfect sunny afternoon. That is the whole game with this category: the numbers on the quote sheet and the numbers in the box are two different things.

Battery Capacity Is the First Lie

Ask for the pack's nominal voltage, cell format and measured capacity, not just an Ah figure. Ah alone means nothing without the voltage — a "60Ah" claim sometimes means 60Ah at 3.2V cell level folded into 12.8V, which is a quarter of the energy a straightforward reading implies. A real 12.8V 60Ah LiFePO4 pack holds roughly 768Wh, and that is the number a reputable factory will confirm with a discharge test report.

Also ask what chemistry. LiFePO4 is the default for outdoor street lights because it tolerates heat and deep cycling far better than the NMC packs used in cheaper units. A LiFePO4 pack rated 2000+ cycles at 80% depth of discharge is a different product from a 500-cycle pack, even when both say "lithium".

The Controller Decides Whether the Panel Counts

A PWM controller clamps the panel to battery voltage and wastes whatever the panel could have delivered above that. An MPPT controller tracks the panel's maximum power point and typically recovers 15 to 30 percent more energy, which on an off-grid light is the difference between "runs all night in winter" and "goes dark at 2am in November". If a supplier cannot tell you which controller type they use, or says "smart MPPT" without a model number, assume PWM.

Panel Wattage and Derating by Latitude

A 100W panel in a lab is 100W at 1000W/m² irradiance and 25°C cell temperature. In the field at 40°C ambient, cell temperature pushes past 60°C and the panel loses 12 to 18 percent to heat alone, before you account for dust, haze and a less-than-ideal tilt angle. Then winter daylight hours halve. A system sized for "100W panel, 30W LED, runs all night" on a sunny equator estimate will not survive a European winter or a Southeast Asian monsoon without oversizing.

The honest way to size this is to give the supplier your latitude, the worst-case sun-hours for your location and the number of consecutive cloudy days the light must ride through. A serious factory will size to that and tell you the autonomy days. A trading company will just quote the standard 100W/60Ah/30W configuration and hope.

Light Output and Optical Quality

Lumen claims on solar street lights are the most inflated of any lighting category. A "30W, 3000 lumen" fixture usually delivers 1800 to 2400 lumen because the chips are driven below their rated current to preserve life, and because the lens loses 10 to 15 percent. Ask for an integrating-sphere report or an IES file. Also look at beam distribution — a street light wants a type II or type III distribution to spread light along the road, not a tight spotlight that makes one bright pool and leaves everything else black.

IP Rating Is Not Just IP65 on the Box

Every spec sheet says IP65. What matters is the gasket design, whether the LED module compartment is sealed separately from the battery and controller compartment, and whether the cable entry uses a proper sealed gland or just a hole with silicone. The failure mode I see repeatedly is water tracking down the pole cable into the controller box. Ask for a photo of the internal layout and the cable entry design.

What to Put in the PI

• Battery: chemistry, nominal voltage, measured Wh, cycle life, and a discharge test report
• Controller: type (MPPT preferred), model number, and rated charge current
• Panel: mono or poly, cell efficiency, and expected output after temperature derating
• Autonomy: number of consecutive no-sun days the system must sustain, stated by the supplier
• Certification: battery transport documentation (UN38.3), and any lighting safety marks relevant to your market
• Warranty split by component — panel, battery and controller often carry different terms

None of this is exotic. It is just the difference between buying a lighting product and buying a set of optimistic numbers. Get the tested figures in writing before you commit to a container, because once the lights are on a pole in a remote area, nobody is sending them back.