Quick answer
Size the system from nightly watt-hours and the site’s solar resource, rather than prescribing one panel and battery pair for every 50W light. Calculate the operating profile, add losses and auxiliary loads, choose the autonomy requirement, then check battery limits, worst-month solar yield and recovery charging. The following numbers are illustrative assumptions, not a standard MCL Solar configuration.
1. Calculate the nightly load
| Operating segment | LED power | Duration | LED energy |
|---|---|---|---|
| Full output | 50 W | 5 h | 250 Wh |
| Dimmed output | 15 W | 7 h | 105 Wh |
| Total | — | 12 h | 355 Wh |
The table assumes the dimmed setting actually draws 15W; verify this by measurement or the driver specification. If the light runs continuously at 50W for 12 hours, the correct LED energy is 600Wh. Add controller, communications and other auxiliary demand separately.
2. Convert load energy to nominal battery capacity
Assume 90% efficiency from battery to LED and no additional loads for this example. Battery draw is 355 ÷ 0.90 ≈ 394Wh per night. For two nights without solar input and 80% allowable depth of discharge, nominal energy is 355 × 2 ÷ (0.90 × 0.80) ≈ 986Wh. At 12.8V this is about 77Ah, before temperature, ageing and reserve allowances. An Ah value is incomplete without voltage.
3. Calculate PV power and recovery
If the overall PV-to-LED energy factor is assumed to be 0.75 and the design month provides 3.5 peak sun hours, daily-balance PV power is 355 ÷ (3.5 × 0.75) ≈ 135Wp. This is a daily-balance estimate only. More PV may be needed to recharge a depleted battery while operating the light, and lower winter sun hours change the result. Do not apply losses twice when changing the measurement boundary.
4. Check the model and installation
- Battery charge/discharge temperature ranges, BMS limits and permitted charge current.
- Controller PV voltage/current limits and compatibility with the battery bank.
- IES photometry for road width, pole height, spacing and the required lighting class.
- Panel orientation, shading, wind loading and foundation design.
- Access for maintenance and the scope of the written warranty.
5. What to include in the quotation
| Input | What the supplier should document |
|---|---|
| Load | Measured or specified power at each dimming level |
| Battery | Voltage, Wh, usable depth of discharge and temperature assumptions |
| PV | Worst-month sun hours, losses and recharge margin |
| Autonomy | Number of nights, initial charge and operating programme |
| Lighting | IES file and project-specific calculation |
6. FAQ
Is a 100W panel enough?
It may be sufficient for some profiles and sites, but compare its expected design-month energy with demand and recovery requirements.
Does LiFePO4 guarantee several rainy days?
No. Autonomy follows usable stored energy and the defined load.
Can these examples be copied into a tender?
Use the calculation method, then replace every assumption with the project’s actual requirements and model data.
7. Project support
Send the site, required photometric targets, mounting layout, dimming programme and autonomy target to sales@mclsolar.com or WhatsApp for a model-specific proposal.