Common technical terms used in solar panel datasheets and specifications.
- Voc (Open-Circuit Voltage)
- The maximum voltage a solar panel produces when no load is connected. Measured at Standard Test Conditions (STC). Higher Voc means better performance in low-light conditions. Used to calculate string sizing for inverters.
- Vmp (Voltage at Maximum Power)
- The voltage a panel operates at when producing maximum power (under STC). Combined with Imp to calculate Pmax. This is the working voltage under normal load.
- Isc (Short-Circuit Current)
- The current a solar panel produces when its terminals are shorted. The maximum possible current from the panel. Used for overcurrent protection sizing (multiply by 1.25).
- Imp (Current at Maximum Power)
- The current a panel produces at its maximum power point. Together with Vmp, determines the panel's power output (Pmax = Vmp × Imp).
- Pmax (Maximum Power)
- The rated power output of a solar panel under Standard Test Conditions (STC), measured in watts. Also referred to as the panel's "nameplate" rating.
- Module Efficiency
- The percentage of sunlight converted into electricity by the panel. Calculated as Pmax ÷ (Area × 1000 W/m²). Most modern panels range from 18% to 23%.
- STC (Standard Test Conditions)
- Industry-standard test conditions: 1000 W/m² irradiance, 25°C cell temperature, AM 1.5 spectrum. All panel ratings are measured at STC unless otherwise noted.
- NOCT (Nominal Operating Cell Temperature)
- The temperature reached by solar cells under 800 W/m² irradiance, 20°C ambient temperature, and 1 m/s wind. Typically 42–48°C. Used for more realistic energy yield estimates.
- Temperature Coefficient of Pmax
- The percentage change in power output per degree Celsius above 25°C. Typically –0.35%/°C to –0.45%/°C. Lower (less negative) values mean better high-temperature performance.
- Temperature Coefficient of Voc
- How much the open-circuit voltage decreases per °C above 25°C. Typically around –0.25%/°C. Critical for cold-weather voltage calculations.
- Tier 1
- A classification from BloombergNEF for solar manufacturers that are bankable, have been in business 5+ years, and have fully automated production lines. Tier 1 panels command premium prices.
- Bifacial
- A solar panel design where both front and back sides generate electricity. Rear-side can capture reflected light (albedo), increasing total energy yield by 5–30%.
- N-Type vs P-Type
- N-type cells use phosphorus-doped silicon with higher efficiency and lower LID (Light-Induced Degradation). P-type cells use boron-doped silicon; more common but slightly less efficient. N-type is increasingly preferred for modern high-end panels.
- Half-Cut Cells
- A technology where solar cells are cut in half, reducing current per cell and minimizing resistive losses. Half-cut panels often have higher efficiency and better tolerance to shading.
- LID (Light-Induced Degradation)
- Initial power loss of 1–3% in the first few hours of sunlight exposure, primarily in P-type PERC cells. N-type cells have negligible LID. This is why panels are tested after LID stabilization.
- PERC (Passivated Emitter and Rear Cell)
- A cell architecture that reflects unused light back through the cell for a second absorption pass. Adds 1–2% absolute efficiency gain over standard cells.
- HJT (Heterojunction with Intrinsic Thin layer)
- A hybrid cell design combining crystalline silicon with amorphous silicon layers. Offers higher efficiency (>24%) and better temperature coefficient than PERC, but is more expensive to manufacture.
- IBC (Interdigitated Back Contact)
- A cell design where all electrical contacts are on the rear side, eliminating shading from front busbars. Achieves the highest module efficiencies (up to 24%) but at a manufacturing complexity premium.