Solar street lighting fails for boring reasons. Not because the LEDs are dim or the panel is fake, but because somebody sized the system against an annual-average sun figure, specified two nights of autonomy for a site that needs five, and discovered it in the third week of a cloudy winter. The engineering is arithmetic. The discipline is in refusing to fudge the inputs.
Key takeaways
- Size against worst-month peak sun hours at the tilted plane, never the annual average. Good-sun sites run around 4.5 PSH; higher latitudes in winter drop to 2.5–3.0 PSH.
- Autonomy days is the specification that decides whether the light works in February: roughly 3 nights for residential and low-criticality roads, 4–5 for municipal collector and arterial, and 5–7 for critical corridors.
- LiFePO4 survives typically 2–4× more charge cycles than ternary lithium or gel lead-acid, and should be designed to a 60–80% depth of discharge rather than its 80–90% safe maximum.
- The sizing chain is short: nightly energy = LED watts × hours; battery = nightly energy × autonomy days ÷ design DoD; panel follows from battery and worst-month PSH.
- SINOCO builds all-in-one and split solar street lighting systems in China, with OEM and ODM programmes and configurations sized to the project’s actual location rather than a catalogue default.
Who Is Actually in This Market
The competitive field is unusually international for a lighting category, because solar street lighting grew out of off-grid development work as much as out of municipal lighting.
| Manufacturer | Base | Positioning |
|---|---|---|
| Fonroche Lighting | France | Autonomous solar street lighting at scale; more than 120,000 units installed worldwide, urban infrastructure and highways |
| Sunna Design | France | Battery resilience in high-temperature cycling, substantial patent portfolio; strong in Europe and African clean-energy projects |
| Greenshine New Energy | USA | Project-specific optical simulation and LED configuration by road geometry, dark-sky engineering, localisation support |
| SEPCO | USA | One of the longest-established US solar lighting firms; off-grid industrial, military and municipal work, long warranties |
| Leadsun | China | Modular all-in-one systems built for rapid installation; the Hyperion series integrates panel, battery, controller and fixture in one unit |
| SINOCO | China | All-in-one and split configurations, OEM and ODM, project-specific sizing and high-efficacy LED platforms |
Two things are worth reading out of that table. First, the European and American specialists compete largely on battery and controller engineering for hostile conditions — high-temperature cycling in particular, which is where cheap lithium packs die. Second, the fastest-moving segment is all-in-one integration, because installation labour, not hardware, is frequently the largest line item on a rural or retrofit project.
All-in-One Versus Split: A Real Trade-Off, Not a Marketing One
| Factor | All-in-one | Split (separate panel and battery) |
|---|---|---|
| Installation time | Lowest — one unit, one bracket | Higher — panel mounting, battery enclosure, cabling |
| Panel sizing headroom | Constrained by fixture footprint | Panel can be oversized freely for low-PSH sites |
| Battery thermal environment | Adjacent to LEDs and driver; hotter | Separate enclosure, or pole-base box; cooler |
| Battery replacement | Requires lowering or accessing the whole head | Ground-level or enclosure access on many designs |
| Theft exposure | Single unit at height, harder to strip | Battery box sometimes at ground level |
| Best fit | Urban and suburban retrofit, good sun, accessible sites | High latitude, low PSH, critical corridors, remote sites |
The thermal point deserves emphasis because it is where all-in-one systems most often disappoint. Lithium cycle life is strongly temperature-dependent, and a battery sitting in the same sealed housing as a driver and an LED board, on a pole in full sun, runs hot. That is precisely the problem Sunna Design built a patent portfolio around. If you are specifying all-in-one for a hot climate, ask for the battery compartment temperature under load in a 45 °C ambient — and treat a supplier who cannot answer as a supplier who has not measured it.
Sizing: The Arithmetic Nobody Should Skip
Step 1 — Nightly energy
Start from the load, not the panel. Nightly energy in watt-hours is the luminaire’s actual draw multiplied by the hours it runs at that draw. If the controller dims after midnight — and it should — calculate each segment separately.
Nightly energy (Wh) = LED power (W) × operating hours (h)
Worked example: 40 W × 12 h = 480 Wh per night
Step 2 — Battery capacity from autonomy days
Autonomy days is the number of consecutive nights the system must run with essentially no charging. This is a risk decision, not a technical one, and it should be made explicitly:
| Application | Autonomy nights | Rationale |
|---|---|---|
| Residential and low-criticality roads | 3 | Brief outage tolerable; lowest system cost |
| Municipal collector and arterial roads | 4–5 | Public safety exposure, higher traffic |
| Critical corridors, remote and industrial sites | 5–7 | No quick maintenance access; failure is expensive |
Then divide by the design depth of discharge. Lithium chemistries can safely discharge to 80–90%, but designing to that limit trades cycle life for capacity on paper. A design DoD of 60–80% is the sensible range for a system expected to last years.
Battery capacity (Wh) = nightly energy × autonomy days ÷ design DoD
Worked example: 480 Wh × 3 nights ÷ 0.9 = 1,600 Wh — and at a more conservative 0.7 DoD, 2,057 Wh
Step 3 — Panel sizing from worst-month PSH
Peak sun hours is the number of hours per day of equivalent full-sun irradiance at the panel’s tilted plane. The critical discipline: use the worst month, not the annual average. A site averaging 4.5 PSH across the year may deliver 2.5 PSH in December, and a system sized on the average will be 45% short exactly when nights are longest.
Panel wattage then follows from the nightly energy the array must replace, the worst-month PSH, and system losses — charge controller efficiency, temperature derate, soiling and wiring. A combined derate in the region of 0.7 to 0.8 is realistic for a pole-mounted system in service.
Step 4 — Controller and dimming profile
An MPPT charge controller extracts meaningfully more energy than PWM under partial shade and in cold conditions, and it is the default for any system worth specifying. Beyond charging, the controller’s dimming profile is a legitimate design variable: running at 100% until midnight and 50% after can cut nightly energy by a quarter, which shrinks both battery and panel. Specify the profile explicitly rather than accepting a factory default, and make sure it still satisfies the road’s lighting class through the night.
Battery Chemistry: Where the Ten-Year Cost Sits
| Chemistry | Cycle life | Safe DoD | High-temperature behaviour | Practical verdict |
|---|---|---|---|---|
| LiFePO4 | Typically 2–4× ternary lithium or gel lead-acid | 80–90% safe, design 60–80% | Best of the lithium options | Default choice for serious projects |
| Ternary lithium (NMC) | Lower | 80–90% | Degrades faster when hot | Lighter and cheaper, shorter service life |
| Gel lead-acid | Lowest | 50% maximum | Poor | Legacy; heavy, large, frequent replacement |
The economics are straightforward once expressed per cycle rather than per kilowatt-hour of nameplate. A battery is the component most likely to force a site visit, and a site visit on a remote installation frequently costs more than the battery. Where the international guidance is relevant, IEC TS 62257-9-8 covers requirements for off-grid lighting and standalone systems and is worth naming in a tender document rather than relying on supplier self-description.
Specification and Verification
What to put in the tender
- Site data — latitude, worst-month PSH at the tilt angle you will use, ambient temperature range, and shading conditions.
- Lighting requirement — road class, target average lux and uniformity ratios to EN 13201 or ANSI/IES RP-8, pole height and spacing.
- Autonomy days, stated explicitly, with the criticality rationale.
- Battery — chemistry, nameplate Wh, design DoD, cycle life at that DoD, cell manufacturer, BMS protections, and expected capacity retention at year five.
- Panel — wattage, cell technology, and the worst-month yield assumption used in the calculation.
- Controller — MPPT, dimming profile, and whether the profile is field-configurable.
- Luminaire — LM-79 efficacy, IES photometric file, BUG rating, IP and IK ratings.
- Structural — pole wind loading to the local code, including the panel’s added sail area.
- Documentation — test reports, warranty terms by component, and spare-part availability commitment.
The verification that catches most problems
Ask for the supplier’s own sizing calculation for your site, showing the worst-month PSH they used and the derate factors applied. A supplier who sizes from your coordinates and shows the working is doing engineering. A supplier who answers with a catalogue model number and a lumen figure is selling a box.
Wind loading deserves a specific mention because it is the failure mode that damages more than the light. A solar panel is a sail. On an all-in-one unit the combined panel and fixture area must be checked against the pole and foundation design for the site’s design wind speed — not the factory’s default assumption.
Where Solar Actually Wins
Solar street lighting is not universally cheaper than grid. It wins decisively in specific conditions, and buyers do better by identifying those than by treating it as a general substitute:
- No grid at the site, where trenching and utility connection costs dominate — remote car parks, perimeter roads, rural corridors, industrial yards.
- Expensive or slow utility connection, where the interconnection process itself is a project risk.
- Grid instability, where an autonomous light is more reliable than a connected one.
- Phased or temporary infrastructure, where fixtures may be relocated.
- Sustainability mandates with a defined carbon or renewable target attached to the project.
Conversely, a dense urban street with existing feeders and good maintenance access usually favours grid-connected fixtures with a controls layer — which is why most serious suppliers, SINOCO included, sell both.
Where SINOCO Fits
SINOCO manufactures solar LED street lights alongside its grid-connected LED street light and roadway ranges, in both all-in-one and split configurations, with OEM and ODM programmes for distributors, contractors and municipal buyers.
Because the same engineering team covers both solar and grid platforms, a project that mixes the two — solar on the unserved sections, grid on the rest — can standardise on one optical distribution and one visual appearance across the whole scheme. Our complete solar LED street light buyer’s guide goes further into supplier evaluation, and the commercial solar street lighting guide covers campus and commercial deployments specifically.
Sizing a solar lighting project? Send SINOCO your site coordinates, road class and autonomy requirement and we will return a sizing calculation with the worst-month PSH and derate factors shown — or browse the solar LED street light range.
Frequently Asked Questions
How many autonomy days should a solar street light have?
Roughly 3 nights for residential and low-criticality roads, 4 to 5 for municipal collector and arterial roads, and 5 to 7 for critical corridors, remote sites and industrial installations. Autonomy days is a risk decision about how long the light must keep working with no charging, so it should be stated explicitly in the specification rather than left to the supplier’s default.
How do you calculate solar street light battery capacity?
Multiply the LED power by its operating hours to get nightly energy, multiply that by your autonomy days, then divide by the design depth of discharge. For example, a 40 W fixture running 12 hours uses 480 Wh per night; over 3 autonomy nights at 90 percent DoD that is 1,600 Wh, and at a more conservative 70 percent DoD it is about 2,057 Wh.
What are peak sun hours and why does the worst month matter?
Peak sun hours is the daily equivalent of full-sun irradiance at the panel’s tilted plane. Sizing must use the worst-month figure, not the annual average, because that is when the system is under the most stress and the nights are longest. A site averaging 4.5 PSH annually may deliver only 2.5 PSH in midwinter, so average-based sizing can leave the system roughly 45 percent short in the month it matters most.
Is LiFePO4 better than lithium-ion for solar street lights?
For this application, generally yes. LiFePO4 typically survives two to four times more charge cycles than ternary lithium or gel lead-acid and handles heat better, which matters because solar street light batteries are frequently mounted in hot locations. Ternary lithium is lighter and cheaper up front but degrades faster, and lead-acid is limited to about 50 percent depth of discharge.
All-in-one or split solar street light — which should I choose?
All-in-one is faster to install and suits urban and suburban retrofit on accessible sites with good sun. Split configurations allow the panel to be oversized independently for low peak-sun-hour locations and keep the battery out of the hot fixture housing, which suits high-latitude, remote and critical installations. The deciding factors are usually installation access and the site’s worst-month sun.
Why do solar street lights fail in winter?
Almost always because they were sized against annual-average peak sun hours instead of the worst month, or because autonomy days were set too low for the site’s cloud patterns. Both produce a system that performs well in summer and runs the battery flat in winter, when nights are longest and charging is weakest.
Do solar street lights need MPPT charge controllers?
MPPT is the appropriate choice for any system worth specifying. It extracts meaningfully more energy than PWM under partial shade and in cold conditions, which directly reduces the panel and battery size needed for a given autonomy requirement. Also specify the dimming profile explicitly, since reducing output after midnight can cut nightly energy by around a quarter.
What wind loading should a solar street light pole be designed for?
The site’s design wind speed under the governing local code, calculated with the solar panel’s added sail area included. This is frequently overlooked because the pole is specified for the luminaire alone, and an all-in-one unit adds substantial projected area. Failures here damage far more than the lighting.
Conclusion
Nothing about solar street lighting is technically mysterious. The systems that disappoint were sized optimistically, usually by taking the annual-average sun figure, the lowest defensible autonomy number and the battery’s maximum depth of discharge all at once — each individually arguable, collectively a system that fails in the worst month.
Specify the worst month, state the autonomy days and the reason for them, design the battery below its safe limit, and require the supplier to show their sizing calculation for your coordinates. The projects that do this are, almost without exception, the ones still lit five winters later.