Start from the load
Every off-grid system begins with one number: how much energy the equipment uses in a day. Multiply the power of each device in watts by the hours it runs, and add the results to get watt-hours per day. A luminaire, a camera and a radio on the same pole each count.
The usage profile matters as much as the total. Lighting that dims after midnight or brightens only on motion uses far less energy than lighting at full output all night. Cameras, sensors and communications often run around the clock, so they set a floor the system must always cover.
- Wattage and operating hours of every device
- Dimming schedules, motion response and duty cycles
- Continuous loads such as cameras and sensors
- Room for loads you expect to add later
Design for the worst month
Solar resource is usually described in peak sun hours: the number of hours a day the site receives the equivalent of full sunlight. It changes through the year, so the panel array is sized for the month with the least sun and the longest nights, not for the annual average.
Shading from trees, buildings or other poles can cut output sharply, and panel tilt should suit the latitude and the winter sun. Where the site is windy, a turbine can add generation when the sun is weak, so the wind resource is assessed for the same difficult season.
Size storage for autonomy and recovery
Days of autonomy is how long the system can run on its batteries alone, with little or no sun and wind. Critical loads need more days than decorative ones. Recovery matters too: after a dull spell the array must be able to recharge the batteries while still powering the load.
Most systems today use lithium-ion batteries, often lithium iron phosphate (LiFePO4). Temperature affects every chemistry: cold reduces usable capacity and limits safe charging, while heat shortens battery life. Depth of discharge, the share of capacity used each night, trades against cycle life, so a battery sized with headroom lasts longer.
Manage every watt-hour
A maximum power point tracking (MPPT) charge controller draws the most energy the panels can deliver as light and temperature change. Load management then decides how that energy is spent: dimming in quiet hours, raising output on demand, and protecting the batteries when a long dull spell drains them.
Do not forget the structure
Panels, turbines and batteries add weight and wind area to a pole. The structure must be checked for wind loading at the site, the right pole height and mounting, the corrosion category of the environment and the full operating temperature range. A system that generates enough energy but cannot stand up to a storm has not been sized at all.
- Wind loading on panels, turbine and fixture
- Pole height, foundation and mounting
- Corrosion category, from inland to coastal sites
- Operating temperature range