Solar panels, in the usual photovoltaic sense, work by converting sunlight into direct-current electricity through the photovoltaic effect. A panel contains multiple photovoltaic cells, and each cell contains semiconductor materials designed to absorb photons and generate mobile charge carriers. When sunlight strikes the semiconductor, photons with sufficient energy can excite electrons into higher-energy states, creating electron-hole pairs.
The electrical structure of the cell, commonly involving a semiconductor junction and an internal electric field, separates these charge carriers so that an electrical potential is produced. When an external circuit is connected, the separated charges flow through the circuit as electric current. The interaction of voltage and current determines the electrical power produced. Multiple cells are connected together inside a module, and multiple modules can be connected into an array to obtain the voltage and power required for a particular application.
Silicon is the most widely used material in commercial photovoltaic panels. A typical silicon solar cell is engineered so that regions with different electrical characteristics form a junction. The semiconductor's band structure determines which photon energies can contribute to electrical generation, while the junction's electric field assists charge separation. Metal contacts collect the generated current and conduct it towards the external circuit.
Anti-reflective coatings and surface structures can increase the proportion of incoming sunlight entering the semiconductor rather than being reflected. The cell must also minimise electrical losses caused by resistance, recombination and imperfect charge collection. Modern cell architectures have evolved substantially, with designs such as passivated emitter and rear contact cells, tunnel-oxide passivated contact cells and heterojunction cells improving efficiency by reducing specific loss mechanisms.
The amount of electricity a panel produces depends strongly on the sunlight reaching it. Irradiance changes with time of day, season, weather, atmospheric conditions and panel orientation. Under cloudy conditions, diffuse sunlight can still produce electricity, but output generally falls compared with direct full-sun conditions. Shading can be particularly important because cells and modules are electrically interconnected, so a shaded section can reduce output disproportionately depending on the configuration and bypass-diode arrangement. Panel temperature also affects output. For conventional silicon photovoltaic modules, higher operating temperatures generally reduce voltage and therefore power, even though the panel may receive strong sunlight. Manufacturers specify performance under standard test conditions, but real-world output varies continuously according to environmental conditions.
The electrical output of a photovoltaic panel is not simply a fixed voltage. A panel has an electrical current-voltage characteristic, and the product of current and voltage determines power. There is normally a point on this curve at which power is maximised, known as the maximum power point. Because irradiance and temperature change, the maximum power point also changes.
Solar inverters therefore commonly use maximum-power-point tracking, or MPPT, to adjust the operating point so that the connected array produces as much available power as practical. A string inverter can track one or more strings, while microinverters and module-level optimisers can perform tracking closer to individual panels. This power-electronic layer is essential because the raw electrical output from photovoltaic cells does not automatically match the voltage, frequency or waveform requirements of household equipment or the electricity grid.
Solar panels produce direct current, while most household electrical systems and public electricity grids use alternating current. A grid-connected photovoltaic system therefore normally includes an inverter that converts DC into AC and synchronises the output with the grid. The inverter can also monitor electrical conditions and provide protective functions. In a battery-equipped system, additional power electronics manage charging and discharging and coordinate energy flows among the panels, battery, building and grid.
Off-grid systems may use an inverter to establish an independent AC supply. The overall energy pathway is therefore sunlight to photovoltaic cells, photovoltaic DC electricity to electrical collection equipment, DC-to-AC conversion where required, and finally consumption, storage or export. Losses occur at each stage, so the energy delivered to a building is lower than the theoretical energy incident on the panel surface.
Solar panels do not store sunlight-derived electricity themselves. They generate electricity whenever sufficient light is available, while batteries or other storage systems are separate components. Likewise, panels do not need direct sunshine to function; diffuse daylight can generate power, although output can be substantially lower than under strong direct irradiation. Solar panels also do not produce unlimited power simply because their physical area is large. Output is constrained by available irradiance, cell efficiency, temperature, electrical configuration, shading and equipment ratings. Degradation over time can gradually reduce output, and manufacturing specifications normally provide expected performance characteristics rather than guaranteeing a constant power level under all conditions. Understanding these limitations prevents the common misconception that a panel's nominal wattage represents its continuous real-world electricity production.
Solar panels can be connected in series or parallel to achieve suitable voltage and current characteristics. Series connections increase voltage, while parallel connections increase current, subject to the electrical characteristics and limits of the equipment. Strings of panels are commonly designed around inverter voltage ranges, environmental temperature extremes and electrical safety requirements. Bypass diodes can provide alternative current paths around shaded or affected cell groups, reducing the effect of some partial-shading conditions.
Panels may be mounted on rooftops, ground structures, tracking systems, vehicles or other surfaces. Installation design must account for structural loads, wind, cable routing, electrical protection, fire safety, access for maintenance and local regulations. Thus the panel itself is only one component of a photovoltaic generation system.
The photovoltaic effect underlying solar panels was identified in the nineteenth century, while the development of practical semiconductor technology enabled useful solar cells in the twentieth century. Early photovoltaic applications included specialised power supplies for spacecraft, where solar generation offered an attractive alternative to carrying large quantities of fuel. Advances in silicon purification, cell design, manufacturing scale, power electronics and module engineering subsequently enabled widespread terrestrial deployment.
Modern panels can achieve substantially higher conversion efficiencies than early commercial devices, while bifacial modules can collect light from both sides under suitable installation conditions. Current research includes tandem architectures, perovskite materials, improved silicon structures and manufacturing processes designed to increase efficiency, durability and resource efficiency.
