Solar Photovoltaic Fundamentals
Solar Photovoltaic Fundamentals
This domain tests how sunlight becomes DC electricity, the meaning of irradiance and insolation, standard test conditions and the factors that change module output.
Core rules
- PV effect: photons with sufficient energy release electron-hole pairs in a semiconductor, producing current.
- Irradiance is instantaneous power per area (W/m²); insolation or irradiation is energy per area per day (kWh/m²/day).
- STC: 1000 W/m², 25°C cell temperature, AM 1.5. Nameplate ratings use STC.
- Module efficiency = electrical output / (irradiance × module area).
- Power falls with rising cell temperature; typical crystalline silicon temperature coefficient is about −0.4%/°C.
- Tilt and azimuth determine incident irradiance; shading reduces output disproportionately.
Worked example
A 250 W module is exposed to 800 W/m² and a cell temperature of 45°C. Irradiance factor = 800/1000 = 0.80. Temperature rise = 20°C; loss = 20 × 0.4% = 8%, so factor = 0.92. Estimated power = 250 × 0.80 × 0.92 = 184 W. This is an estimate before mismatch, soiling and cable losses.
Traps that cost marks
Treating W/m² as kWh/m²/day; using ambient temperature instead of cell temperature; applying STC output at dawn or under cloud; ignoring temperature coefficient sign; assuming a shaded cell only loses its own share rather than affecting the string.