Solar charging while parked: plan energy for the whole day

A power figure in watts describes the rate of energy use or production at a particular point. Multiplying watts by hours gives watt-hours. This lets you compare energy across a day rather than comparing only labels. A panel's watt rating is not a promise of that output throughout daylight. REDARC's planning guidance notes that sunlight, weather and other conditions affect actual production.

For a simple example, a 12-watt light used for four hours consumes 48 watt-hours. An 8-watt device used for five hours consumes 40 watt-hours. Together that is 88 watt-hours for those two loads. This example assumes both devices draw the stated power for their full operating time. Use realistic average consumption and operating time for your own appliances; equipment that cycles or changes output needs more than its peak label.

• Power in watts × operating hours = energy in watt-hours.
• List each load separately, then add the daily amounts.
• Include all intended equipment and explain uncertain estimates.
• Keep a margin in the plan for different use and less favourable conditions.

The solar controller must accept the panel arrangement and suit the battery system. Victron's installation manual gives model-specific PV voltage requirements and limits, showing why total panel wattage alone is not enough. Provide the panel and controller models and the battery details before expanding a setup. A connector fitting physically does not establish suitable voltage or polarity. Leave wiring, configuration and connection changes to someone competent with the exact equipment.

Compare daily energy needs with realistic charging opportunities. Will the vehicle remain parked, move between sites, or have another charging source? Where will the portable panel actually be used? Record the conditions behind an estimate rather than assuming a fixed number of productive hours every day. REDARC starts its planning with the loads and available battery energy. The permitted usable capacity must come from your exact battery and system instructions, not a universal discharge percentage.

Learn the system's normal status display and retain any history it provides. Record appliance use and charging conditions together so an unexpected result has context. Ask which indication needs attention, what loads should be reduced under the agreed operating plan and what the fallback charging arrangement is. Avoid changing battery settings to chase an output figure. A useful handover explains the assumptions, operating limits and what must be reviewed before more equipment is added.

Related guidance from motoring organisations and equipment manufacturers. Use the instructions for your exact vehicle and equipment when making a decision.

• REDARC: Choosing a solar blanket from daily loads
• Victron: SmartSolar MPPT installation limits