Electrical and Electronics Fundamentals Applied to Solar: Ohm's Law, Series/Parallel, Power, AC/DC and Diodes
This section covers electrical and electronics fundamentals applied to solar: Ohm's law, series and parallel circuits, power and energy calculations, AC/DC basics, semiconductors and diodes. The exam tests the arithmetic and circuit reasoning behind string, battery and cable decisions.
DC laws and circuits
Ohm's law: V = I × R. Power: P = V × I = I²R = V²/R. Energy: Wh = W × hours. In series, current is common and voltages add; resistances add. In parallel, voltage is common and currents add; 1/Rtotal = 1/R1 + 1/R2 + ...
AC basics
AC alternates at 50 Hz in India. RMS voltage is the equivalent heating value; peak = RMS × √2. Apparent power is VA, real power is W, and power factor = W ÷ VA. Single-phase and three-phase loads use different current formulas.
Semiconductors and diodes
A p-n junction conducts in forward bias above about 0.7 V for silicon and blocks in reverse. A bypass diode provides an alternate current path around a shaded substring; a blocking diode prevents reverse current from a battery. A PV cell is a photodiode operated in the fourth quadrant.
Worked example
Four 12 V, 100 Ah batteries each store 1200 Wh. All series: 48 V, 100 Ah = 4.8 kWh. All parallel: 12 V, 400 Ah = 4.8 kWh. Series-parallel: 24 V, 200 Ah = 4.8 kWh. A 500 W load on 24 V draws 500 ÷ 24 = 20.8 A; the same load on 12 V draws 41.7 A, so cables must be larger.
Traps
Adding both voltage and Ah in series; mixing Wh and Ah; using peak AC voltage in power calculations; forgetting power factor; forward-biasing a diode without a current-limiting resistor; assuming a bypass diode improves normal output.