Solar Photovoltaic Fundamentals and System Types
What this domain tests
This section covers Solar Photovoltaic Fundamentals and System Types. It checks whether you can explain how a PV cell converts light into DC electricity, read standard ratings, and identify the main system architectures used in small installations.
Core rules
- Irradiance is measured in W/m². Standard Test Conditions (STC) are 1000 W/m², AM 1.5G spectrum and 25 °C cell temperature. Module labels normally quote STC values.
- A cell's current rises almost linearly with irradiance, while voltage rises logarithmically. Key points on the I–V curve are Voc, Isc, Vmp and Imp. Fill factor FF = Pmax / (Voc × Isc); efficiency = Pmax / (module area × 1000 W/m²).
- Cells in series share the same current and add voltages; parallel strings share the same voltage and add currents. Bypass diodes limit hot-spot heating; blocking diodes prevent reverse current in some battery systems.
- Off-grid systems use a battery and charge controller. Grid-tied systems export to the grid and need anti-islanding protection. Hybrid systems combine PV, battery and often a generator or grid.
Worked example
Two 100 W modules are wired as two series strings, then paralleled. Each module has Vmp 18 V and Imp 5.5 A. One string gives 36 V at 5.5 A; two parallel strings give 36 V at 11 A. Array power = 36 × 11 = 396 W, not 400 W, because the calculation uses the actual Vmp and Imp, not the rounded label.
Traps
Do not mix STC with real roof conditions; a cold, bright day can push Voc above the label value. Do not parallel strings of different voltages. Do not assume every inverter can work without a battery.