Competency 1 asks you to relate volts, amps, watts and ohms in a working system. Practise the sizing chain: daily load (Wh) ÷ battery voltage = amp-hours needed; multiply by 2 for 50% depth-of-discharge on lead-acid. Panel watts = daily load ÷ sun-hours ÷ 0.7 system losses. A home using 1,200 Wh/day on a 12 V battery needs ~200 Ah of battery and ~350–400 Wp of panel. These three lines of arithmetic are the difference between a happy customer and a dead battery bank.