What Are Solar Panels?

Solar panels are assemblies of photovoltaic (PV) cells mounted in a common frame that convert incident sunlight directly into direct-current (DC) electricity through the photovoltaic effect. Also called PV modules, they are the fundamental building block of solar power systems, from small portable chargers to utility-scale installations covering hundreds of hectares. A single solar panel typically contains 60 to 120 cells wired in series and parallel to produce voltages in the range of 30 to 50 volts and peak power outputs of 200 to 600 watts under standard test conditions (1000 W/m² irradiance, 25 °C cell temperature). The discipline encompassing their design and manufacture draws from semiconductor physics, materials science, and power electronics.

Solar panels are distinct from solar thermal collectors, which capture sunlight as heat rather than electricity. Their appeal in modern energy systems rests on the absence of moving parts, silent operation, modularity, and the dramatic cost reductions achieved over the past two decades through improvements in cell efficiency, manufacturing scale, and supply chain optimization.

Cell Technologies and Materials

The vast majority of commercially deployed solar panels use crystalline silicon cells, either monocrystalline (single-crystal) or polycrystalline (multicrystalline) silicon. Monocrystalline cells, grown from a single silicon ingot using the Czochralski process, achieve higher efficiencies, with production panels routinely exceeding 22 percent and laboratory cells reaching 26 percent under standard AM1.5G illumination. NREL's research on high-efficiency crystalline photovoltaics targets n-type wafer architectures, including heterojunction (HJT) and interdigitated back-contact (IBC) designs, to push single-junction silicon cells toward 25 percent efficiency. Thin-film technologies occupy a smaller but significant market share: cadmium telluride (CdTe) panels, manufactured at scale by First Solar, achieve module efficiencies above 19 percent; copper indium gallium selenide (CIGS) films offer flexibility for building integration. Perovskite solar cells have emerged as a research-intensive class, with perovskite-silicon tandem devices demonstrating efficiencies above 30 percent in laboratory conditions, though long-term stability and manufacturing scale-up remain active areas of development.

Module Construction and Efficiency

A solar panel consists of a front glass sheet (typically 3-4 mm tempered glass), an encapsulant layer (most commonly ethylene-vinyl acetate, EVA), the cell array, a rear encapsulant, and a backsheet or rear glass for bifacial modules. Cells are electrically interconnected by soldered ribbons or, in back-contact designs, by conductive adhesives. The assembly is framed in aluminum and fitted with a junction box containing bypass diodes that protect shaded cells from reverse-bias heating. Module efficiency is lower than cell efficiency due to inactive interconnects, frame, and edge areas. NREL's champion photovoltaic module efficiency chart tracks record efficiencies for each module technology class over time, providing a reference for commercial and research performance targets. Panel degradation rates average about 0.5 percent per year for modern silicon modules, supporting warranty periods of 25-30 years.

Mounting, Installation, and Grid Integration

Solar panels are deployed in fixed-tilt ground mounts, single-axis or dual-axis trackers, and rooftop racking systems. Single-axis trackers increase annual energy yield by 15-25 percent compared to fixed-tilt installations by following the Sun's daily east-west arc. DC output from panels is converted to AC by string or central inverters, or by module-level power electronics (microinverters and DC optimizers) that mitigate shading losses and enable module-level monitoring. Grid-connected systems are subject to interconnection standards that govern anti-islanding protection, voltage regulation, and power factor. NREL's solar cell efficiency tables document the state of confirmed efficiencies across cell and module technologies, providing the benchmark against which new installations are evaluated.

Applications

Solar panels have applications across a wide range of sectors, including:

• Residential and commercial rooftop electricity generation
• Utility-scale ground-mounted solar farms
• Building-integrated photovoltaics (BIPV) in facades, windows, and roofing
• Off-grid power for remote telecommunications, water pumping, and rural electrification
• Space power systems for satellites and spacecraft
• Portable and mobile charging for consumer electronics and military equipment