30 industry terms explained. A free reference for solar engineers, installers, and procurement professionals.
N-Type silicon solar cells use phosphorus-doped wafers that offer higher efficiency, lower degradation (typically ≤1%/year), and better performance in low-light conditions compared to traditional P-Type cells. N-Type is the dominant technology for premium modules in 2026.
P-Type silicon cells are the traditional solar cell technology using boron-doped wafers. While cheaper to produce, they suffer from Light Induced Degradation (LID) of 1-3% in the first year of operation.
Tunnel Oxide Passivated Contact (TOPCon) is an advanced N-Type cell architecture that adds an ultra-thin oxide layer and polysilicon contact on the rear side. TOPCon cells achieve efficiencies of 22-24% and are the most widely adopted next-generation solar technology.
Heterojunction (HJT) combines crystalline silicon with thin amorphous silicon layers, delivering efficiencies above 22% with superior temperature coefficients (-0.24%/°C to -0.26%/°C). HJT panels perform exceptionally well in hot climates.
Passivated Emitter and Rear Cell (PERC) is a P-Type cell design that adds a passivation layer on the rear, reflecting unabsorbed light back into the cell. PERC improved efficiency by 1-2% over traditional cells and became the industry standard from 2018-2023.
All Back Contact (ABC) solar cells place all electrical contacts on the rear side of the cell, eliminating front-side shading losses. ABC technology achieves the highest commercial efficiency (up to 23-24%) with a sleek all-black appearance.
Bifacial solar panels capture sunlight from both the front and rear sides, boosting total energy yield by 5-30% depending on ground reflectivity (albedo). Ideal for ground-mount and flat-roof installations with reflective surfaces.
Monocrystalline solar cells are made from single-crystal silicon ingots, offering the highest efficiency and the longest lifespan. They are identifiable by their uniform dark black appearance and rounded corners.
Polycrystalline solar cells are made from multi-crystal silicon ingots, are lower cost, and have a characteristic blue speckled appearance. They typically have 1-3% lower efficiency than monocrystalline cells.
Thin-film solar panels are made by depositing photovoltaic material (like cadmium telluride or CIGS) onto a substrate. First Solar is the leading manufacturer. They have lower efficiency (16-19%) but perform better in high heat and diffuse light.
The temperature coefficient of Pmax measures how much a solar panel's power output decreases as temperature rises (units: %/°C). A lower absolute value (e.g., -0.29%/°C) means better hot-weather performance than a higher one (e.g., -0.38%/°C).
Standard Test Conditions (STC) are the industry-standard laboratory conditions for rating solar panels: 1000 W/m² irradiance, 25°C cell temperature, and AM 1.5 spectrum. All SolarSpecs Global datasheets use STC values.
Nominal Operating Cell Temperature (NOCT) represents the cell temperature under 800 W/m² irradiance, 20°C ambient temperature, and 1 m/s wind. NOCT values are more representative of real-world conditions than STC.
Module efficiency measures the percentage of sunlight converted into electricity. Commercial panel efficiency ranges from 19-23%. Higher efficiency means more power per square meter — critical for space-constrained installations.
Power tolerance is the permissible deviation from a panel's rated power output. A tighter tolerance (e.g., 0 to +5W) indicates better quality control and more predictable energy yields.
Fill Factor (FF) is the ratio of a solar cell's actual maximum power output to its theoretical maximum (Voc × Isc). A higher FF (typically 75-82%) indicates better cell quality and less resistive loss.
Light Induced Degradation (LID) is the initial power loss (1-3%) experienced by P-Type PERC cells during their first hours of sunlight exposure. N-Type modules have minimal to zero LID.
Potential Induced Degradation (PID) is a voltage-induced power loss caused by potential differences between the solar cells and the frame. Modern panels are PID-resistant, tested per IEC 62804 standards.
Premium solar panels offer a linear performance warranty guaranteeing output degradation of ≤0.4-0.5% per year (e.g., 92% output after 25 years), versus stepped warranties that drop to 80% after 10-12 years.
The product warranty covers manufacturing defects, typically lasting 12-25 years for premium panels. Industry leaders like Jinko and LONGi offer 25-year product warranties on their N-Type modules.
IEC 61215 is the international standard for crystalline silicon terrestrial photovoltaic module qualification testing. Certification indicates the panel has passed rigorous thermal, mechanical, and environmental stress tests.
IEC 61730 covers safety qualification testing for photovoltaic modules, including electrical shock, fire, and mechanical stress safety requirements. Required for most utility and commercial installations.
The junction box is the enclosure on the rear of a solar panel that houses electrical connections. Look for IP68-rated junction boxes for best moisture and dust protection. It contains bypass diodes that prevent hot spots.
Bypass diodes allow current to bypass shaded or damaged cells, preventing hot spots and power loss. Most panels have 3 bypass diodes (one per cell string). Schottky diodes are preferred for their low voltage drop.
MC4 connectors are the industry-standard solar panel connectors, rated for high DC voltages (up to 1500V). Quality matters — look for connectors from Stäubli (original MC4 patent holder) or compatible certified brands.
Half-cut solar cells are standard cells cut in half, reducing current by 50% and resistive losses by 75%. Half-cut panels operate more efficiently under partial shading and run cooler than full-cell panels.
Multi-busbar (MBB) technology uses 9-16 thin copper wires instead of the traditional 3-5 wider busbars. MBB reduces shadowing losses, improves current collection, and provides better mechanical strength.
Solar panel front glass is typically 3.2mm tempered (safety) glass with anti-reflective coating. Premium panels may use 2.0mm semi-tempered glass for reduced weight, or heat-strengthened glass for bifacial modules.
The backsheet is the rear protective layer of a solar panel (for non-bifacial modules). White backsheets reflect heat, while black backsheets offer a uniform appearance at the cost of slightly higher cell temperatures.
Solar panel frames are made from anodized aluminum for corrosion resistance and structural integrity. Frame thickness (typically 30-35mm) and reinforcement design determine the panel's wind and snow load ratings.
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