How Solar Panels Produce Electricity

Solar electricity begins with light. A photovoltaic (PV) cell is a semiconductor device that converts light directly into electrical energy. This page follows that energy from the moment a photon strikes the cell to the point where it powers a household appliance. Understanding the mechanism helps in interpreting production graphs, diagnosing performance issues, and making design decisions.

The process is purely physical. No fuel is burned, no moving parts are involved in the conversion itself. The only input is light, and the output is direct current (DC) electricity. That DC electricity is then converted to alternating current (AC) for use in homes and businesses.

The Photovoltaic Effect

The core of solar electricity is the photovoltaic effect, discovered in 1839 by Edmond Becquerel. In a PV cell, two layers of semiconductor material (usually silicon) are treated with impurities to create an electric field. One layer is doped to have an excess of electrons (n-type), and the other is doped to have a deficit of electrons, creating holes (p-type). The junction between these layers creates an internal electric field.

When a photon of light strikes the cell, it can transfer its energy to an electron, knocking it loose from its atom. This creates an electron-hole pair. The internal electric field then pushes the electron toward the n-type layer and the hole toward the p-type layer. If the cell is connected to an external circuit, the electrons will flow through that circuit to recombine with holes, doing work along the way. That flow is electric current.

A single silicon cell produces about 0.5 to 0.6 volts under load, regardless of its size. To get useful voltage and current, cells are connected in series and parallel within a panel. A typical panel has 60 or 72 cells, producing a DC voltage of 30 to 40 volts.

From DC to AC

Most household appliances and the grid operate on alternating current (AC), which changes direction periodically. Solar panels produce direct current (DC), which flows in one direction. To make the electricity usable, an inverter converts DC to AC. The inverter also manages the system’s output to match the grid’s voltage and frequency.

There are two main inverter topologies:

• String inverters: A single inverter handles the DC from a series (string) of panels. This is simple and cost-effective, but the output of the entire string is limited by the lowest-performing panel.
• Microinverters: Each panel has its own small inverter, allowing each panel to operate independently. This can mitigate the effect of shading or soiling on one panel.

Modern inverters also include maximum power point tracking (MPPT), which adjusts the electrical load to keep the panels operating at their peak power output under varying conditions.

What Affects Output

The amount of electricity a solar panel produces depends on several factors:

• Irradiance: The intensity of sunlight. More light means more photons and more current. Irradiance varies with time of day, season, and weather.
• Temperature: Solar cells are less efficient at higher temperatures. The voltage decreases as temperature rises, which reduces power output. Most panels have a temperature coefficient of around -0.4% per degree Celsius above 25°C.
• Angle and orientation: Panels produce the most when they face the sun directly. Fixed panels are typically tilted at an angle equal to the latitude for optimal annual production.
• Shading: Even partial shading of a single cell can disproportionately reduce the output of a string, because cells in series are limited by the lowest current. Bypass diodes can mitigate this, but shading should be avoided where possible.
• Soiling: Dirt, dust, and bird droppings block light. Rain often cleans panels, but in dry climates, soiling can be significant.

Degradation Over Time

Solar panels degrade slowly. The typical annual degradation rate is about 0.5% per year, meaning after 25 years, a panel might produce about 87% of its original output. This is a property of the technology, not a market figure. Most manufacturers warrant that panels will produce at least 80% of their rated power after 25 years.

What People Get Wrong

A common misconception is that solar panels work better on hot days. In fact, the opposite is true. While the sun is intense on a hot day, the heat reduces the voltage output of the cells, and the net effect is a decrease in power. This is a natural mistake because people associate bright sunlight with heat, but the temperature coefficient is a well-defined property.

Another mistake is thinking that a panel’s rated capacity (e.g., 400 W) is what it will produce under normal conditions. The rating is determined under standard test conditions (STC): 1000 W/m² irradiance, 25°C cell temperature, and air mass 1.5 spectrum. Real-world conditions rarely match these, so actual output is often lower.

Net Metering and Interconnection

When a solar system produces more electricity than the home uses, the excess can be exported to the grid. The rules for this—net metering, export compensation, interconnection agreements—are set by state and utility and they change. What applies in one jurisdiction may not apply in another. Check with the local utility for the current rules.

Safety Note

A PV array produces dangerous DC voltage whenever there is light on it, and it cannot be switched off at the panel. Never open a combiner box, probe a live string, or disconnect an energised connector. Work on the DC side should be done by a qualified professional. Roof work and mains connection are also licensed trades.

Conclusion

Solar electricity is a straightforward physical process: light knocks electrons loose, an electric field moves them, and that movement is current. The inverter converts that DC to AC for use. Output is influenced by irradiance, temperature, angle, shading, and soiling. Understanding these factors helps in predicting performance and troubleshooting issues.

For further reading, see the pages on panel technology, inverters, and system design.