Solar Appliances and Small-Scale Applications
Small-system design
Solar Appliances and Small-Scale Applications covers lanterns, home lighting systems, street lights, pumps and small refrigerators. Each system needs a daily energy calculation in watt-hours, a battery sized for autonomy and depth of discharge, a panel sized for local peak sun hours, a controller matched to the array and battery, and a load that matches the inverter or DC voltage.
Matching and protection
Low-voltage DC appliances must match the system voltage, 12 V or 24 V. Use fuses on battery circuits and a low-voltage disconnect (LVD) to protect the battery. Pumps need dry-run protection and a controller suited to motor starting. Street lights need a dusk-to-dawn controller and a weatherproof enclosure.
Worked example
Three 7 W LED lamps run for 5 hours: 3 × 7 × 5 = 105 Wh/day. A 12 V, 40 Ah battery at 50 % DoD gives 240 Wh nominal, enough for two days with losses if the load is limited. A 100 W panel with 4 peak sun hours gives about 400 Wh/day, comfortably above 105 Wh plus losses. A 10 A controller is adequate for a 100 W, 12 V array, about 8.3 A.
Traps
Do not size a panel only from its wattage label while ignoring poor sun and cable loss. Do not run a pump without dry-run protection. Do not connect a 12 V appliance to a 24 V battery bank through a simple switch.