☀️ Solar PV How It Works: From Photons to Kilowatt-Hours

The Photovoltaic Effect

Solar panels generate electricity through the photovoltaic (PV) effect, discovered by Alexandre-Edmond Becquerel in 1839. When photons (light particles) from the sun strike a semiconductor material, they can knock electrons loose, creating a flow of electric charge. Silicon — the same element used in computer chips — is the dominant semiconductor material in solar cells.

A typical solar cell consists of two layers of silicon: an N-type layer (doped with phosphorus, extra electrons) and a P-type layer (doped with boron, "holes" where electrons are missing). At the junction between these layers, an electric field forms. When sunlight dislodges electrons in the silicon, the electric field pushes them in a consistent direction, creating a direct current (DC). Metal contacts on the cell collect this current and route it to the external circuit.

From Cell to Module to Array

A single silicon solar cell produces about 0.5–0.6 volts DC at maximum power — barely enough to charge a watch battery. Cells are connected in series (to increase voltage) and encapsulated in tempered glass and ethylene-vinyl acetate (EVA) to form a module (what most people call a "solar panel"). A typical residential/commercial module contains 60, 72, or 96 cells and produces 300–600+ watts at about 30–50 volts DC.

Modules are wired together in strings to form an array. A typical residential system might have 20–30 modules (8–15 kWp); a large commercial rooftop might have hundreds; a utility-scale solar farm might have millions.

Solar Cell Technologies

Monocrystalline silicon — cells cut from a single silicon crystal ingot. Highest efficiency (20–24% for commercial modules), most uniform appearance (uniform black), more expensive to manufacture. Best choice when roof area is limited.

Polycrystalline silicon — cells made from multiple silicon crystals; slightly lower efficiency (15–18%), lower cost. Recognizable by the "mosaic" or "flaky" appearance. Being phased out as monocrystalline prices have dropped.

Thin-film (CdTe, CIGS) — non-silicon cells deposited on glass or flexible substrates. Lower efficiency (10–13%) but very low manufacturing cost. First Solar's CdTe technology dominates utility-scale thin-film deployments. Best for large flat areas where efficiency matters less than cost per watt.

Inverters: DC to AC Conversion

PV modules produce DC power; buildings and the grid use AC power. Inverters convert DC to AC and maximize the power extracted from the array using Maximum Power Point Tracking (MPPT) algorithms.

String inverters — one inverter connects to a string of series-connected modules. Lowest cost, simplest design, but production of the entire string is limited by the worst-performing module (shading one module affects the whole string).

Microinverters — one small inverter per module. Each module operates independently at its own MPP. Optimal for roofs with shading, multiple orientations, or obstructions. More expensive but delivers higher production in shaded or complex conditions.

Power optimizers + string inverter — DC-DC optimizers at each module perform per-module MPPT and pass optimized DC to a central string inverter. A middle path between cost and performance.

System Efficiency and Performance Ratio

A 10 kWp array does not produce 10 kW continuously. Performance losses include: inverter efficiency (~97%), wiring losses (~1%), soiling (dust, pollen) (~1–3%), temperature derating (panels produce less power when hot — silicon efficiency drops ~0.35% per °C above 25°C STC), and shading. The Performance Ratio (PR) is the ratio of actual annual production to theoretical production at STC irradiance, typically 75–85% for well-installed systems.