Quick answer
Photovoltaic (PV) refers to any material or device that converts light directly into electricity, with no moving parts and no heat engine in between.
The word joins "photo" (light) and "volt" (the unit of electrical pressure). "Solar PV" is the everyday name for panels and systems that work this way, which covers every rooftop solar electric system sold to homeowners.
Quick facts
The key facts about photovoltaic, with sources:
- Converts
- Light → direct-current (DC) electricity 1
- Most common cell material
- Silicon: 96% of global solar shipments in 2022 were monocrystalline silicon 4
- Commercial panel efficiency
- Under 10% in the mid-1980s, about 15% by 2015, approaching 25% for state-of-the-art modules today 2
- First practical cell
- 1954, Bell Telephone Laboratories 2
- US electrical code
- NEC (NFPA 70) Article 690, as adopted by your state or city 6
- Not to be confused with
- Solar thermal, which makes heat
Key takeaways
- Photovoltaic means light in, electricity out, with nothing moving and nothing burning.
- Every solar electric panel sold for homes is PV. Solar water heaters are not.
- PV makes direct current (DC). An inverter turns it into the AC your home uses.
- Almost all panels today use silicon cells. Thin film is a small share.
- In the US, PV wiring follows the National Electrical Code, Article 690.
- PV output stops when the light stops. Night power comes from the grid or a battery.
What the word photovoltaic means
Photovoltaic describes a material that makes a voltage when light hits it. Voltage is electrical pressure, the push that moves current through a wire. The effect was put to practical use in 1954, when Bell Telephone researchers built the first useful silicon cell. Satellites used PV from the late 1950s.
Today the word mostly shows up as "PV" or "solar PV". It can mean a single cell, one panel, or a whole home system. The context tells you which. On a permit drawing, "PV system" means everything from the panels to the meter.
PV is different from solar thermal. Solar thermal catches the sun as heat. PV catches it as electricity. A roof can have both, but they are separate pieces of equipment.
How the photovoltaic effect works
The EIA describes what happens to light reaching a PV cell in four steps.
- Photons (particles of light) strike the cell. Some reflect, some pass through, and some are absorbed by the semiconductor.
- Absorbed photons knock electrons loose from their atoms.
- The cell’s built-in electric field pushes those freed electrons toward the front surface, building a voltage across the cell, like the two terminals of a battery.
- Connect a wire across the cell and the electrons flow as direct current.
Nothing moves and nothing burns, which is why PV panels have no fuel cost and very little maintenance. The power stops the moment the light does.
From sunlight to your outlets
- Sunlight → PV cells make DC
- DC → wired through the array to an inverter
- Inverter → AC power at the same frequency as the grid
- AC → your electrical panel and home circuits
- Extra AC → out through the meter to the grid, or into a battery
From cell to system: the PV ladder
| Level | What it is | Glossary |
|---|---|---|
| Cell | One semiconductor wafer producing 1–2 W, often thinner than four human hairs 1 | PV cell |
| Module (panel) | Dozens of cells wired together behind glass in a frame | Solar panel |
| String | Panels wired in series to raise the voltage | — |
| Array | All the panels in one installation, from two to hundreds 2 | Solar array |
| System | The array plus inverter, racking, wiring, disconnects, meter and any battery | Solar system |
Types of PV technology
| Technology | What it is | Where you see it |
|---|---|---|
| Crystalline silicon | Cells cut from silicon wafers. Monocrystalline was 96% of global shipments in 2022 4 | Nearly every rooftop panel. See monocrystalline panels |
| Cadmium telluride (CdTe) | A thin film on glass. Most of the remaining 4% of shipments 4 | Mainly large solar farms. See thin-film panels |
| CIGS | Copper indium gallium diselenide, another thin film 5 | Niche and flexible products |
| Perovskite | A newer crystal family, still in research 5 | Labs and pilot lines |
| Multijunction III-V | Stacked layers that each catch part of the light 5 | Satellites, where cells near 50% efficiency 2 |
| Organic PV | Carbon-based materials 5 | Research |
Silicon cell designs you will see on data sheets
Silicon cells have changed design over time. Older Al-BSF cells led until about 2018. Then PERC cells took over because they caught more light. Now n-type designs such as TOPCon and heterojunction (HJT) are replacing PERC.
IBC cells put all the metal contacts on the back, so the front has no lines. They are made in smaller numbers. The DOE says factory-made silicon modules reach 20%–22% real-world efficiency, with lab cells above 27%.
See PERC, TOPCon and HJT for how each one differs.
Sources: [4]
Example: how cells add up to a home system
This example uses only the cell output the EIA and DOE give, 1 to 2 watts per cell. It shows why panels hold many cells and homes hold many panels.
| Step | Math | Result |
|---|---|---|
| One cell | 1–2 W each 2 | Enough for a small calculator, not a home |
| One panel of 60 cells | 60 × 1–2 W | Roughly 60–120 W, the scale of older small panels |
| Modern panel | Bigger, better cells; read the data sheet rating | Today’s home panels are rated in the hundreds of watts |
| A home array of 20 panels | 20 × the panel rating | Several kilowatts, the size range most homes use |
The math is a rough guide. Always use the real wattage printed on the data sheet. Our panel wattage page explains the rating.
PV vs solar thermal
| Solar PV | Solar thermal | |
|---|---|---|
| Output | Electricity (DC, converted to AC by an inverter) | Heat, for hot water or, in power plants, steam for a turbine |
| Moving parts | None in the panel | Pumps, and in power plants, turbines and mirror trackers |
| On a house | Rooftop or ground-mounted panels | Solar water heating collectors |
| At utility scale | Large PV farms | Concentrating solar-thermal power (CSP), mirrors focusing sunlight 3 |
| Light it can use | Direct and scattered light | Plants with mirrors need direct sun |
Where "PV" shows up on your paperwork
Utility interconnection forms ask for the "PV system size" in kW DC (the sum of the panel ratings) and often kW AC (the inverter rating). Permit drawings label the "PV array", "PV disconnect" and "PV breaker". Your homeowner’s insurer may ask whether the home has "PV" so it can cover the equipment.
If a document says PV, it means the electric panels, not a solar water heater. When the two are combined on one roof, the paperwork lists them separately.
Across the US, PV is everywhere from calculators to solar farms. The EIA says most US PV systems have been tied to the grid since 2004. Small systems under 1,000 kW, mostly rooftops, made about 93 billion kWh in 2025. Utility-scale PV and solar-thermal plants made about 292 billion kWh.
Sources: [2]
Benefits and limits of PV
Benefits
- No moving parts in the panel, so little wears out.
- No fuel, no burning, no noise while it runs.
- Modular: add panels to build almost any size 1.
- Silicon modules lose less than 1% of output a year, the DOE says.
- Works with scattered light, not only direct sun.
Limits
- Makes nothing at night.
- Output drops with cloud, shade, dirt and heat.
- Makes DC, so a home system needs an inverter.
- Most home panels turn only about a fifth of the light into power.
- Needs real roof or ground space.
How efficient is PV, and why it matters less than you think
Efficiency is the share of sunlight hitting a panel that leaves as electricity. The EIA puts commercially available panels at under 10% in the mid-1980s, about 15% by 2015, and close to 25% for state-of-the-art modules now.
A higher figure means more watts from the same roof area. It does not by itself mean cheaper electricity. If you have plenty of roof, a slightly less efficient panel can do the same job. Our solar panel efficiency guide compares current panels.
Heat also cuts PV output. Panels make less power on a hot day than a cool, bright one. The temperature coefficient on the data sheet tells you how much.
Sources: [2]
What drives the cost of a PV system
We do not print one price, because quotes vary by home. The main drivers are system size in kW, panel and inverter type, roof type and condition, permits, labor and any battery. Our cost per watt guide shows how to compare quotes fairly.
Lifespan matters as much as price. The DOE cites a Berkeley Lab survey: the average working life of a panel rose from about 20 years in 2007 to 25–35 years in 2025. Inverters often need replacing sooner. Warranty terms come from each maker, so read the data sheet.
The federal 25D homeowner credit is gone. The IRS says it "is not available for any property placed in service after December 31, 2025." Treat any quote that still promises it as a red flag.
How a PV system gets installed
A licensed installer and electrician do every step that touches wiring.
- Site check: roof condition, shade, direction and your last year of power use.
- Design: the installer picks panels, inverter and layout and estimates yearly kWh.
- Permits: plans go to your city or county for a building and electrical permit.
- Utility application: the installer asks your utility for interconnection.
- Install: racking, panels, inverter, disconnects and wiring go in.
- Inspection: a local inspector checks the work against the adopted electrical code.
- Permission to operate: the utility approves and you switch on.
Our permission to operate guide covers the last step.
Looking after PV equipment
PV panels have no moving parts, so most care is watching. Check your monitoring app each month. Compare kWh with the same month last year, not with last month, because seasons change output.
Rain cleans most panels. Heavy pollen, dust or bird droppings can cut output. Stay off the roof. Hire a pro for panel cleaning if needed.
When panels finally retire, the DOE notes that recycling programs and rules are still growing. Our solar panel recycling guide explains the options.
Warning signs and when to call a pro
Call your installer or a licensed electrician if you notice any of these. Do not touch PV wiring yourself.
- Zero or very low output on a clear day.
- An error code or red light on the inverter.
- Burn marks, melted plastic or a hot smell near any part.
- Cracked glass, brown spots or bubbles on a panel.
- Loose or hanging wires under the array.
- Output falling year after year faster than the warranty allows.
Safety rule
A PV panel makes voltage whenever light hits it, even when the system is switched off. Only a licensed electrician or installer should work on it.
Codes and rules that govern PV
Electrical code. In the US, PV wiring is covered by Article 690 of the National Electrical Code (NEC), published by the NFPA as NFPA 70.
The 2023 edition revised Article 690, including rapid shutdown in section 690.12, and rewrote parts of Article 705 on connecting to the grid.
Each state or city adopts an edition, so ask your installer which one your permit uses.
Building code. Roof loads and fire paths come from the building code your area adopted. South Carolina, for example, enforces the 2021 state codes based on the 2021 IRC and IBC.
Shutdown at the roof. Rapid shutdown rules exist so firefighters can de-energize roof wiring quickly.
Tax. The federal 25D credit ended for property placed in service after 31 December 2025, per the IRS.
Misconceptions about PV
- Myth PV panels need direct sun to work.
- Reality They use any light, including scattered light on cloudy days. Output is lower, not zero.
- Myth PV panels store power.
- Reality They make power only while lit. Storage takes a separate battery.
- Myth Hot, sunny days give the most power.
- Reality Bright light helps, but heat lowers PV output. Cool, clear days can beat hot ones.
- Myth PV and solar thermal are the same thing.
- Reality PV makes electricity. Solar thermal makes heat.
- Myth Turning off the inverter makes the panels safe.
- Reality Panels still make DC voltage in daylight. Only trained pros should handle them.
PV in SC, GA and VA
The physics is the same everywhere, but the rules for your PV system change by state.
South Carolina enforces the 2021 state building codes 9 and pays exported PV power under Act 62 Solar Choice tariffs for newer customers 10. Georgia Power caps residential renewable systems at 10 kW 11.
Virginia law allows residential net metering up to 25 kW on investor-owned utilities 12.
When the word PV matters to you
You need to understand PV when you:
- Read a quote: check the kW DC size and the yearly kWh estimate.
- Compare panels: look at cell type, wattage and degradation, not only the brand.
- Sign a permit or utility form: confirm the "PV system size" matches the quote.
- Buy a home with PV: ask for the data sheets, warranty and monitoring login.
Next steps
- How a home solar system worksThe full path from sunlight to outlet
- Solar system size calculatorTurn your yearly kWh into a kW size
- Inverter types: string, micro and hybridThe box that turns PV DC into AC
Questions about photovoltaic
What does PV stand for in solar?
PV stands for photovoltaic: making electricity directly from light. "Solar PV" and "PV system" both mean solar electric panels and the equipment that goes with them. You will see PV on quotes, permit drawings and utility forms. It never means a solar water heater, which makes heat instead of electricity.
Are all solar panels photovoltaic?
Every solar panel that makes electricity is photovoltaic. Solar water-heating collectors look similar on a roof but make heat, not electricity. If a product is sold to lower your electric bill by making power, it is PV. If it heats a water tank, it is solar thermal.
Is a PV system the same as a solar panel?
No. A panel is one module. A PV system is the whole installation: the panels plus the inverter, racking, wiring, disconnects and any battery. When a utility asks for "PV system size", it wants the total of all panel ratings, not the size of one panel.
Do photovoltaic panels need direct sunlight?
No. They respond to all light reaching them, including diffuse light on cloudy days, but output falls as the light weakens. Shade from trees or chimneys hurts more than haze. A good production estimate already uses years of local weather, so cloudy days are built in.
How does a photovoltaic cell make electricity?
Light knocks electrons loose inside a semiconductor, usually silicon. An electric field built into the cell pushes those electrons one way, which creates a voltage. When a wire connects the two sides, the electrons flow as direct current. Nothing moves and nothing burns.
What material are most PV panels made of?
Silicon. The DOE says monocrystalline silicon made up 96% of global solar shipments in 2022. Most of the rest was cadmium telluride thin film, used mainly on large solar farms. Perovskite and organic cells are still in research.
How efficient are photovoltaic panels?
Most home panels turn about a fifth of the light into electricity. The DOE puts real-world factory silicon modules at 20%–22%, and the EIA says the best commercial modules are near 25%. Special cells for satellites reach close to 50%, but they are far too costly for homes.
Do PV panels work in the winter?
Yes. Cold does not hurt PV; it actually helps, because panels work better when cool. Winter output is lower because days are shorter and the sun is lower. Snow blocks light until it slides off or melts.
What code covers photovoltaic systems?
In the US, Article 690 of the National Electrical Code (NFPA 70) covers PV wiring. Article 705 covers connecting to the grid, and Article 706 covers batteries. Your state or city chooses which NEC edition to enforce. Your installer and inspector work from that edition.
Is PV the same as solar power?
Mostly, yes. On homes, "solar power" almost always means PV panels. Strictly, solar power also includes solar-thermal plants that use mirrors to make steam. If someone is quoting panels for your roof, they mean PV.
Sources
- US DOE Solar Energy Technologies Office, Solar Photovoltaic Technology Basics, retrieved .
- US EIA, Solar explained: Photovoltaics and electricity, retrieved .
- US DOE Solar Energy Technologies Office, How Does Solar Work?, retrieved .
- US DOE Solar Energy Technologies Office, Crystalline Silicon Photovoltaics Research, retrieved .
- US DOE Solar Energy Technologies Office, Photovoltaics, retrieved .
- IAEI Magazine, John Wiles, 2023 National Electrical Code and Photovoltaic Power Systems (23 Mar 2023), retrieved .
- US DOE Solar Energy Technologies Office, End-of-Life Management for Solar Photovoltaics, retrieved .
- IRS, Residential Clean Energy Credit (§25D), retrieved .
- SC Building Codes Council, code adoption, retrieved .
- South Carolina Code Title 58 Ch. 40 (Act 62 of 2019, customer-generators), retrieved .
- Georgia Power, Behind-the-Meter Interconnection Summary for Residential Customers (rev. 15 Aug 2025), retrieved .
- Code of Virginia §56-594 (net energy metering), retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: The mechanism, cell output, efficiency history, cell technologies and market share are paraphrased from the EIA and DOE pages cited.
NEC changes are from the IAEI summary of the 2023 edition. State facts come from sc-local/facts.js and verified GA/VA rows. Paperwork labels describe common permit and interconnection forms, not one utility’s form.
Suggest a correction. We fix errors and say what changed.