SO WHAT’S BEHIND IT? / EPISODE 001A patch of sunlight lands on a rooftop. Inside the house, a fan turns and a refrigerator keeps food cool. Between those events sits a remarkable device: a solar panel that converts light into electrical energy without burning fuel or spinning a generator.
But what actually happens inside a solar panel? It is not bottling sunshine for later, and it is not simply collecting heat. The explanation begins with light interacting with a semiconductor, then follows the electricity through a connected circuit.
This Episode 001 explainer takes that journey from a single absorbed photon to the electricity a home can use. The diagrams are teaching models, not installation instructions. You can follow the complete explanation without operating their optional controls.
What is a solar panel?
A solar cell, also called a photovoltaic or PV cell, is the device that converts light into electricity. Many interconnected cells, packaged into a protected unit, form a module—commonly called a solar panel. Several modules working together form an array.
Most conventional solar cells use silicon. It is a semiconductor: its electrical behaviour can be engineered through its structure and carefully introduced impurities. A useful cell needs more than a material that conducts electricity; it needs a structure that absorbs light and collects the resulting charge carriers.
A typical crystalline-silicon module has protective front glass, encapsulating material around the cells, a rear protective layer or rear glass, electrical connections, and usually a supporting frame. The packaging protects delicate cells while letting light reach them. Construction varies, so the exploded view is a simplified example rather than a manufacturer’s exact layer stack.
Further background: DOE solar photovoltaic cell basics.
An exploded teaching schematic: protective glass, encapsulant, silicon cells, and a backsheet or rear support. A frame supports the assembly. Real modules also have encapsulant behind the cells and may use rear glass.
Step 1 — Sunlight reaches the solar cell
Light carries energy in packets called photons. A photon’s energy depends on its wavelength. When an appropriate photon is absorbed in silicon, it can transfer enough energy to an electron to make that electron mobile within the semiconductor.
The electron’s former occupied state is left vacant. That vacancy is called a hole. It is not a tiny physical tunnel or a positively charged particle newly manufactured inside the panel. As neighbouring electrons move into vacancies, the vacancy can behave as a mobile positive charge carrier.
The mobile electron and hole together are an electron–hole pair. They are not created by every photon that arrives: some light is reflected, some passes through, and some absorbed energy becomes heat. Carriers can also recombine before they are collected.
Think of generation and collection as two separate questions: did the light create useful carriers, and can the device collect them before they recombine? Penn State’s photovoltaic-effect lesson explains the underlying semiconductor energy states.
A sufficiently energetic absorbed photon can create a mobile electron and a hole. Here a pair is drawn near the junction; generation can occur elsewhere too. The electron is a filled blue circle; the hole is a pink outline, representing a missing electron.
Step 2 — The p–n junction separates and collects charges
A conventional silicon cell includes regions with different doping. Doping means introducing controlled amounts of selected elements into the silicon.
In n-type silicon, electrons are the majority mobile carriers. In p-type silicon, holes are the majority mobile carriers. Both kinds of carrier can exist in both regions. The names do not mean that the entire n-type block is negatively charged and the entire p-type block positively charged.
At the p–n junction, diffusion and the fixed charges left near the boundary establish a built-in electric field. In our schematic, n-type silicon is above p-type silicon, so the junction field points downward, from n toward p.
An electron’s negative charge means its field-driven motion is opposite that field: toward the n side. A hole’s field-driven motion follows the field, toward the p side. This helps separate light-generated carriers near the junction.
Pairs can form elsewhere in the absorber too. Diffusion helps carriers reach the collecting region; recombination competes with collection. Real cells therefore involve more than particles simply sliding down a field arrow.
Conductive contacts allow carriers to enter an external circuit. The thin front contact pattern collects charge while leaving much of the surface exposed to light; the other contact completes the connection.
Read UNSW’s explanation of the p–n junction and PVEducation on junction formation.
The n-type region is above the p-type region in this schematic. The junction lies between them. Front and rear electrical contacts collect charge carriers; protective module glass is outside this cell cross-section.
Near the junction the built-in field points from n-type to p-type: downward in this diagram. Electron drift is upward toward n; hole drift is downward toward p. The external blue arrow represents electron flow from the n contact through a load to the p contact. Conventional current is opposite.
Step 3 — A connected circuit delivers electrical power
Light-generated carriers, together with the cell’s selective collection structure, allow a voltage to develop between its contacts. The built-in field is not an unlimited energy source: sustained generation depends on absorbed light.
Connect a suitable external load and charge can move around a complete circuit. In the diagram, blue arrows show electron flow from the n contact, through the load, toward the p contact. Conventional current is defined in the opposite direction. Mixing those two arrow conventions is an easy way to make an explanation misleading.
Three quantities describe different parts of the process:
- Voltage, measured in volts, is electrical potential difference: energy available per unit charge.
- Current, measured in amperes, is the rate of charge flow.
- Power, measured in watts, is the rate of energy transfer. For this DC example, power equals voltage multiplied by current.
A disconnected illuminated cell can have voltage without delivering power to an external load. Voltage alone is not evidence that an appliance is being powered.
This light-to-electricity conversion is the photovoltaic effect. DOE’s performance explanation connects cell voltage, current and power.
Step 4 — From solar cells to panels and arrays
A single cell is a starting point, not a complete rooftop system. Manufacturers connect cells to produce practical combinations of voltage and current.
For suitably matched cells in series, voltages add while the same current passes through the string. For suitably matched strings connected in parallel, currents add at a common voltage. The arrangement must suit the components; it is not a recipe for connecting arbitrary panels together.
Packaging those cells forms a module. Combining modules forms an array. More active cell area can collect more sunlight, but output also depends on light intensity, conversion efficiency, cell temperature, shading and electrical losses.
Shading deserves particular attention because a shaded cell can constrain a series-connected group. Real modules use design features to manage such effects.
Read Penn State’s module and array explanation.
Step 5 — An inverter converts DC to AC
The output of a solar cell is direct current, or DC. Its polarity is consistent during normal generation, although its voltage and current can change as sunlight and operating conditions change.
Household wiring and the electricity grid generally use alternating current, or AC. With AC, voltage polarity reverses periodically, and current can alternate direction. The waveform illustration shows voltage against time; it is not a slowed recording of actual household electricity.
A solar inverter uses power electronics to convert DC into AC with the required electrical characteristics. A grid-connected inverter also synchronises with the grid and provides relevant control and safety functions. An inverter converts electricity; it does not create additional energy.
The overall journey is:
Sunlight → Solar Cells → DC Electricity → Inverter → AC Electricity → Home
DOE’s inverter guide explains this conversion in more detail.
- Sunlight
- Solar cells
- DC electricity
- Inverter
- AC electricity
- Home
Sunlight → solar cells → DC electricity → inverter → AC electricity → home. These are energy-conversion stages, not installation wiring instructions. Grid and optional battery equipment are not shown.
The DC voltage stays on one side of zero. The AC voltage crosses zero and reverses polarity periodically. These are illustrative voltage-versus-time sketches, not measurements, operating frequencies or current traces.
What happens to excess solar electricity?
The home can use solar electricity as it is generated: this is self-consumption. If generation exceeds the home’s demand, what happens next depends on the installation.
Where regulations, metering and equipment permit, surplus electricity may be exported to the grid. If a compatible battery and control system are installed, some energy may be stored for later. Other systems may limit generation when there is nowhere suitable for the electricity to go.
A panel is a converter, not a storage device. A battery stores energy through a different process and can release it later. Adding storage also introduces capacity limits, conversion losses and control requirements.
Do not assume that every rooftop installation includes a battery, permits export, or provides backup. The system’s design determines those capabilities.
Do solar panels work at night?
Ordinary rooftop PV panels need sufficient illumination to generate useful electrical power. In normal nighttime conditions, they do not produce meaningful power for the home. Describing moonlight as a practical substitute for daytime generation would be misleading.
The home can instead draw from the grid, or from a charged battery system if one is installed and configured for that use. The electricity is then coming from another supply or previously stored energy.
A power cut is a separate issue. Standard grid-tied solar equipment generally stops supplying electricity when the grid fails, helping prevent unsafe energisation of lines. Having panels does not automatically provide backup.
Supplying an isolated home during an outage requires suitable equipment, controls and system design. DOE’s solar resilience guide explains why solar panels alone are not a backup system.
Do solar panels work on cloudy days?
Yes. Panels can respond to both direct sunlight and diffuse light that has been scattered in the atmosphere. Clouds can block much of the direct beam without removing all daylight, so generation can continue.
Output is generally lower under heavy cloud than in strong sunshine, but there is no universal “cloudy-day percentage.” Cloud thickness, the changing sky and the installation all matter. The comparison below deliberately avoids a numerical output prediction. DOE’s solar radiation guide explains direct and diffuse light.
Also distinguish brightness from temperature. Typical silicon cells can lose efficiency as their temperature rises. Solar photovoltaic panels convert light, not heat, into electricity; heating a panel is not a way to make it generate more.
Solar thermal systems use heat differently. This article concerns photovoltaics, not every technology that uses energy from the Sun.
Strong direct sunlight generally supports higher output. Clouds scatter and reduce daylight, but diffuse light can still generate electricity. This qualitative comparison does not predict an output percentage. Heat is not the photovoltaic energy source.
How much electricity can solar panels generate?
Keep power and energy separate. A system rated at 5 kilowatts has a specified power capacity under reference conditions. It does not promise a constant 5 kW output from sunrise to sunset.
Suppose, purely for illustration, its day’s output is equivalent to four hours at the full rated power:
5 kW × 4 hours = 20 kWh
The four hours are an equivalent full-output duration, not necessarily four consecutive hours on a clock. In this example, assume that figure already represents the day’s real-world production after relevant effects and losses; do not silently subtract another loss factor from the same assumed output.
The result is energy: 20 kilowatt-hours. That is often described as 20 electricity “units.” Actual energy depends on location, season, orientation, cloud, temperature, shading and equipment losses. It is not a guaranteed daily yield.
See the Australian Government’s panel rating guide and EIA’s explanation of electricity measurements.
Common solar panel myths
“Solar panels need hot weather.” They need light. High cell temperature can reduce the performance of typical silicon cells.
“Solar panels store electricity.” Ordinary panels convert energy while illuminated. Storage needs additional equipment.
“Solar panels always work during power cuts.” Standard grid-tied systems generally shut down. Backup depends on suitable system design.
“Solar panels stop working whenever it is cloudy.” Diffuse daylight can still support generation, usually at reduced power.
“A panel always delivers its rated power.” The rating describes reference test conditions. Actual operating conditions vary.
These distinctions matter when reading product claims: generating, converting, storing and backing up electricity are different functions.
Frequently asked questions
How do solar panels generate electricity?
Absorbed light creates mobile carriers in semiconductor cells. The cell structure helps separate and collect them, and a connected external circuit allows electrical energy to reach a load.
What is the photovoltaic effect?
It is the conversion of light energy into electrical energy in a device such as a solar cell. In a silicon cell, absorption, carrier generation and collection work together.
Why is silicon used in solar panels?
Its semiconductor properties can be engineered into effective solar cells, and it is widely used in established photovoltaic manufacturing. Silicon is not the only possible PV material.
Do panels work without direct sunlight?
They can generate from diffuse daylight. Available light, rather than the simple presence or absence of a visible Sun, determines what generation is possible.
Can panels power a home at night?
The panels themselves do not normally generate meaningful nighttime power. A home may use stored energy from a battery or electricity from the grid.
What does a solar inverter do?
It converts a panel system’s DC output into AC suitable for the connected electrical system. Grid-connected models also coordinate with the grid.
What is the difference between kW and kWh?
Kilowatts measure power at a moment; kilowatt-hours measure energy over time. One kilowatt maintained for one hour delivers one kilowatt-hour.
From sunlight to understanding
A solar panel’s story starts with photons, continues through mobile electrons and holes, and becomes useful power when collected charge moves through a connected circuit. Modules combine cells, and an inverter makes their DC output usable by an AC household system.
The Episode 001 video section below is ready for the detailed YouTube explanation once it is available. Meanwhile, explore how a circuit works or how coloured light combines to follow the next question.
Curiosity starts here.
Sources and further reading
The science was checked against these educational references. Diagrams reuse original Episode 001 studio artwork, with web-specific annotations; none are copied from the sources below.
- U.S. Department of Energy — Solar photovoltaic cell basics.
- Penn State — Photovoltaics: effect, junctions and system scale.
- UNSW — Understanding the p–n junction (PDF).
- PVEducation — Formation of a p–n junction.
- Penn State — PV modules and arrays.
- U.S. Department of Energy — Inverters and grid services.
- U.S. Department of Energy — Solar and resilience.
- U.S. Department of Energy — Solar radiation.
- U.S. Department of Energy — PV performance and efficiency.
- Australian Government — Solar panels and power ratings.
- U.S. Energy Information Administration — Measuring electricity.
EPISODE VIDEO
A closer look, coming soon.
The detailed YouTube explanation will appear here once the video is available. No video has been embedded yet.