The brochure on the kitchen counter
There’s a homeowner in suburban Ohio reading a solar installation brochure at 9:30 PM and the brochure contains the word “photovoltaic” twelve times across four pages. He stops at the line “Our PERC monocrystalline modules leverage advanced photovoltaic conversion to deliver superior energy yield.” He reads it three times. He still has no idea what’s actually happening when sunlight hits a panel. Neither, statistically, does the salesperson who handed him the brochure. The industry has built a wall of jargon between consumers and a piece of physics that’s genuinely simple at its core.
Let’s tear down that wall. Here’s what’s actually happening when a photon hits a solar panel, explained the way it should have been explained to you the first time.
The one-sentence version
Sunlight knocks electrons loose from silicon atoms. The panel forces those loose electrons to flow in one direction. Flowing electrons are electricity. That’s it. The rest is engineering.
The slightly longer version
Silicon atoms have four electrons in their outer shell. When silicon atoms bond into a crystal, those outer electrons are tightly held in place. They don’t flow. Pure silicon is not a good conductor.
Manufacturers do two things to fix this:
- They “dope” some of the silicon with phosphorus, which has five outer electrons. The extra electron has nowhere to go in the crystal structure, so it sits loose. This is called n-type silicon (n for negative, because of the loose electron).
- They dope other silicon with boron, which has three outer electrons. The missing electron leaves a “hole” in the crystal where an electron should be. This is called p-type silicon (p for positive, because the hole acts like a positive charge).
Now: place a layer of n-type silicon on top of a layer of p-type silicon. At the boundary (the “junction”), the loose electrons from the n-type wander into the p-type to fill holes, and the holes from the p-type wander into the n-type. This creates a permanent electric field at the junction that wants to push electrons back into the n-type side.
This setup is just sitting there, doing nothing useful, until light arrives.
What light does
A photon (a particle of light) hits a silicon atom in the p-type layer. If the photon has enough energy, it knocks an electron loose from the silicon’s outer shell. That electron is now free to move.
The electric field at the junction grabs the loose electron and pushes it across into the n-type layer. The electron can’t easily come back — the electric field keeps it on the n-type side.
Now you have an excess of electrons piled up on the n-type side and a deficit (more holes) on the p-type side. Voltage exists between the two sides. If you connect a wire between them with a load (a light bulb, a phone charger, a battery), electrons will flow through the wire from n-type back to p-type, lighting the bulb on the way. That flow is current. Current x voltage = power.
Every photon that gets absorbed (in the right energy range) creates one electron-hole pair. Trillions of photons hit each cell per second. Trillions of electrons flow. That’s how you get a panel rated at 400 watts.
From cell to panel to system
One silicon cell, roughly 15×15 cm, produces about 0.5 volts at maybe 9 amps in full sun — about 4.5 watts. Useful for a calculator. Useless for a house.
To get useful voltage and power, manufacturers wire many cells together in a panel. A typical 400W residential panel has 60 or 72 cells wired in series (their voltages add up to ~40V) and parallel groups (their currents add up). The cells are sandwiched between glass on top, an encapsulant (EVA polymer) around them, and a backsheet (polymer or another sheet of glass) on the bottom. A metal frame holds everything together.
Multiple panels wired in series form a string. Multiple strings feed an inverter, which converts the DC electricity from the panels into AC electricity for your house or the grid. That’s a complete solar system in five sentences.
What makes panels more or less efficient
The Shockley-Queisser limit (covered in our efficiency article) caps single-junction silicon at about 33% in theory. Real panels are 20–23%. The gap exists because of:
- Photons with too little energy: pass through the silicon without doing anything
- Photons with too much energy: get absorbed but lose excess energy as heat
- Reflection: some light bounces off the glass and back into the sky
- Recombination: some loose electrons find holes before reaching the junction, releasing energy as heat
- Resistance losses: the wires and contacts have small resistance that costs power
Different cell architectures (PERC, TOPCon, HJT, IBC) reduce specific losses. PERC adds a rear surface passivation layer to reduce recombination. TOPCon uses a thin oxide layer for better passivation. HJT uses amorphous silicon layers to passivate both surfaces. The acronyms hide what’s mostly the same idea: fewer electrons getting lost on their way to the junction.
FAQs
Why are solar panels usually dark blue or black?
To absorb more light. Anti-reflective coatings (usually silicon nitride) reduce light bouncing off and give panels their characteristic color. Untreated silicon would be a reflective gray.
Do panels work in cloudy weather?
Yes — at reduced output. Diffuse light (clouds scattering sunlight) still contains photons. A panel typically produces 20–30% of rated output on a cloudy day. Heavy overcast can drop that to 10%.
What happens to a panel in the snow?
Light snow lets some sunlight through and panels still produce. Heavy snow blocks production until it melts or slides off. Most residential panels at typical tilt angles shed snow within a few sunny hours.
Do panels work at night?
No. No photons, no electricity. Some experimental “anti-solar” panels using radiative cooling to space can produce tiny amounts of power at night, but they’re research-only.
Why do panels lose efficiency in heat?
Heat increases the rate of recombination (electrons finding holes before reaching the junction) and reduces the voltage of each cell. Every panel has a temperature coefficient telling you how much efficiency it loses per degree above 25°C.
Are there panels that use different materials than silicon?
Yes — cadmium telluride (CdTe), CIGS, perovskite, gallium arsenide (used in space applications). Silicon dominates residential because of cost and maturity. Other materials win in specific niches.
The landing
Photons hit silicon. Electrons get loose. Electrons flow. Electricity. The brochure on the kitchen counter could have said exactly that in three sentences and saved everyone time. The reason it didn’t is the same reason most technical brochures don’t: jargon makes the salesperson sound smart and keeps the customer dependent. You don’t need to be a physicist to understand solar — you need someone willing to skip the photovoltaic-conversion line and just explain what’s happening. Now you have one.