Engineering a Solar Lighting System: Solar Resource to Autonomy
A reliable solar lighting system is an energy-balance problem — the panel must harvest, and the battery must store, enough energy to run the light every night including the worst weeks of the year — so engineering it means working backward from the load through autonomy to the panel. Reliability isn't a property of the technology; it's the result of getting this balance right for the specific site.
This reference covers the energy balance, the backward-sizing method, and the real losses a credible design accounts for.
The energy balance
Every design balances three quantities: the nightly load (LED watts × run hours plus any auxiliaries), the storage needed for that load plus reserve days, and the harvest the panel must collect using the available sunlight. Undersize any one and the light goes dark. The three are interdependent, which is why solar can't be sold as a one-size product.
Working backward
| Step | Calculation |
|---|---|
| 1. Load | Watt-hours/night, adjusted for dimming/motion |
| 2. Battery | Load × autonomy at a safe depth-of-discharge, temperature-derated |
| 3. Panel | Replace the daily load (plus charge losses) using worst-month peak sun hours |
The sequence is always load → storage → harvest. Starting from a fixture wattage and guessing the rest is exactly how catalog systems get it wrong.
Real losses
Systems lose energy in the controller, wiring, battery round-trip efficiency, and soiling/temperature. A credible design applies these derates rather than assuming nameplate — which is precisely why catalog systems sized on ideal numbers fail in service. And autonomy is the reliability dial: set it to the site's climate and the application's criticality (more for security and northern sites, less for mild-climate amenity lighting). 360 Solar engineers each system to a site-specific energy balance.
Frequently asked questions
What makes a solar lighting system reliable?
An energy balance — the panel must harvest and the battery store enough to run the light every night including the worst weeks. Engineer it backward from load through autonomy to panel.
How do you size the system?
Calculate the nightly load, size the battery for load × autonomy at a safe depth-of-discharge with temperature derating, then size the panel for the daily load plus losses using worst-month sun.
Why do catalog systems fail?
They assume nameplate and ignore controller, wiring, battery, and soiling/temperature losses — a credible design applies these derates.
What is autonomy's role?
It's the reliability dial — the nights the system runs without sun — set to climate and criticality, and it sizes the battery.
Can solar be sold as a one-size product?
No — the load, storage, and harvest are interdependent and site-specific, so reliable solar must be engineered to the site.
Request an engineered solar layout. Get it at 360solarlighting.com/free-quote.