Battery, solar and DC power basics for builders

The few numbers that size most battery and solar builds.

Watts, volts and amps

Watts = volts × amps. A 1,200 W heater on 12 V draws 100 A; on 48 V it draws 25 A, which needs much thinner wire.

Energy is watt-hours

Battery kWh = volts × amp-hours ÷ 1,000. A 48 V, 100 Ah battery holds about 4.8 kWh.

Usable is less than total

Plan to use about 80% of a lithium battery and less of lead-acid, and lose another 5 to 15% to the inverter and wiring.

Solar depends on sun hours

Daily solar kWh ≈ panel kW × peak sun hours × 0.75. Look up peak sun hours for your area.

Wire for voltage drop and heat

Keep drop under about 3%, and every wire must also be rated for its current and protected by a fuse or breaker.

Who to involve

Anything connected to a building, the grid or used by the public needs a licensed electrician and usually a permit.

Concept drafts are for planning, budgeting and talking to professionals. They are not engineering or build plans. Have a qualified professional check any design before you build or use it.