PV Systems Fundamentals and Applications
Domain 1 tests the physical and application basics: how a PV cell converts light to direct current, what standard test conditions mean, and which system architecture fits a given load. Expect vocabulary questions on irradiance versus irradiation, orientation and tilt, and the difference between grid-tied, stand-alone, and hybrid systems.
From sunlight to DC
A PV cell is a semiconductor diode. Photons with enough energy free electrons, and the built-in field pushes them across the junction, producing current when a circuit exists. Module nameplate ratings use Standard Test Conditions: 1000 W/m² irradiance, 25 °C cell temperature, and AM 1.5 spectrum. Real output changes with irradiance, cell temperature, soiling, and shading.
Reading the resource
Irradiance is instantaneous power per area (W/m²); irradiation is energy per area over time (kWh/m²/day). Peak sun hours equal daily irradiation divided by 1000 W/m², so 4.5 kWh/m²/day is 4.5 peak sun hours. Tilt and azimuth should favor the season and load; fixed arrays in the northern hemisphere usually face south, but a flatter tilt helps summer and a steeper tilt helps winter.
System types and applications
Grid-tied systems export surplus through a utility-interactive inverter and do not provide backup without storage. Stand-alone systems use batteries, a charge controller, and often a generator. Hybrid systems combine PV, storage, and another source. Applications include rooftop, ground-mount, carports, water pumping, telecommunications, and remote cabins; each changes the balance-of-system requirements.
Worked example
A 5 kW array sits where daily irradiation is 4.5 kWh/m²/day. With an 80% overall derate: 5 kW × 4.5 h × 0.80 = 18 kWh/day. The derate covers inverter, wiring, soiling, and temperature losses; it is not a guarantee.
Traps
Do not mix kW (power) with kWh (energy). Do not use nameplate watts as real output. Do not ignore shading, even partial shading, which can disproportionately cut a string's output. Do not say PV needs direct heat; heat usually lowers output.