Solar Panel / Module
Power
Solar cells laminated in series behind glass: a '12 V' panel really peaks around 18 V so it can charge batteries through a controller. Watts are rated at full noon sun — plan on much less on average.
Schematic symbol
Photodiode
How solar panel / module appears in a circuit diagram.
Types & variants
Key specs
Pmax
WPower at standard test conditions (1000 W/m², 25 °C).
Vmp / Imp
V / AVoltage and current at the max-power point — what an MPPT tracks.
Voc / Isc
V / AOpen-circuit voltage (cold mornings push it higher!) and short-circuit current.
Temperature coefficient
%/°COutput drops as panels heat — roughly −0.4%/°C.
Markings
Rear label: all electrical specs + series fuse rating. Junction box with MC4 connectors.
Standard values
10–50 W hobby panels (36-cell, Vmp ≈ 18 V), 400–600 W residential modules.
How to choose
Size from daily energy need ÷ realistic sun-hours, match Vmp to your charge controller (MPPT tolerates ranges; PWM wants Vmp ≈ battery + 5 V), and mind Voc stays under the controller's max on cold days.
Pinout & package
MC4 + / − leads from the junction box. Series strings raise voltage; parallel raises current (fuse each string).
Example circuits
- 20 W panel + MPPT controller + 12 V battery for a gate opener
- Balcony micro grid-tie setup
- Solar water-pump direct drive
Common failures
Hot-spots and burnt cells under partial shading, cracked cells from hail/flexing (visible in IR), delamination and yellowing, corroded MC4s, bypass-diode failures.
How to test
In sun: Voc ≈ label (e.g. ~21 V for a '12 V' panel), then briefly Isc with the meter's 10 A range. Big shortfall in full sun = damaged string or dead bypass diode.
Substitutes
Any panel matching your controller's voltage window; two smaller series panels replace one large one if Voc total stays within limits.