Quick answer
Solar Panel A solar panel, called a solar module in the industry, is a weatherproof assembly of photovoltaic cells wired together behind glass in a frame, which turns sunlight into direct-current electricity.
Residential panels are rated in watts at standard test conditions, and a home system strings a dozen or more of them together into an array. "Panel" and "module" mean the same thing; data sheets and permits use "module".
Quick facts
The key facts about solar panel, with sources:
- Also called
- Solar module, PV module
- Made of
- PV cells, glass, encapsulant, frame, junction box and cables
- Rated at
- Standard test conditions: 1,000 W/m², 25 °C cell temperature, AM 1.5 spectrum 2
- Example rating
- 435–450 W for one current residential module line 2
- Output
- Direct current (DC); an inverter converts it to AC 3
- Typical aging
- Often less than 1% output loss a year 6
- Average working life
- 25–35 years in 2025, per a Berkeley Lab survey the DOE cites 7
- Safety and design tests on data sheets
- IEC 61215 and IEC 61730; US fire rating to UL 61730 2
Key takeaways
- A solar panel is a sealed frame of PV cells. Panel and module mean the same thing.
- It makes DC power. An inverter turns it into the AC your home uses.
- Compare panels on wattage, efficiency, temperature coefficient and warranty.
- Heat trims output. A hot roof can cost several percent of rated power.
- Panels usually age slowly, often losing less than 1% a year.
- Never walk on or open a panel. Repairs are for your installer.
What a solar panel is, in plain terms
A solar panel is a flat, sealed box of solar cells. Each cell makes a small amount of power. The panel wires dozens of them together so the voltage and power are useful. Glass on the front and a sealed layer on the back keep out rain and dirt for decades.
The DOE notes the panel is only one part of a solar system. You also need racking to hold it, an inverter to change the power, wiring and safety switches. On its own, a panel cannot run your home.
Parts of a solar panel, read off a real data sheet
| Part | What it does | Data-sheet entry |
|---|---|---|
| Cells | Turn light into DC electricity | 6 × 16 monocrystalline half cells |
| Front cover | Lets light in, protects against hail and weather | 1.6 mm thermally pre-stressed glass |
| Back cover | Seals the rear; glass on bifacial panels, a polymer backsheet on many others | 1.6 mm semi-tempered glass |
| Frame | Stiffens the panel and gives the racking something to clamp | Black anodised aluminium |
| Junction box | Holds bypass diodes and the cable connections | 53–67 × 28 × 17 mm, IP68, with bypass diodes |
| Connectors | Snap panels together into a string | Stäubli MC4-Evo2A, IP68 |
| Size and weight | Sets how many fit and the load on the roof | 1,762 × 1,134 × 30 mm; 20.9 kg |
The junction box
The junction box is the small sealed box on the back of the panel where the cell circuits end and the output cables begin. Inside are bypass diodes.
When part of the panel is shaded or a cell fails, the diode lets current skip that section. This limits both the power loss and the heat build-up that can damage cells.
Look for an ingress-protection rating on the data sheet; IP68 means sealed against dust and immersion. A cracked or scorched junction box is a repair for your installer, not a homeowner. See the solar repair page for the signs.
Sources: [2]
How a panel’s power gets used
- Sunlight → cells inside the panel make DC
- Junction box → cables and connectors carry it out
- Panels in a string → voltages add up across the array
- DC → an inverter or a microinverter makes AC
- AC → your home first, then the grid or a battery
Types of solar panels
| Type | How to spot it | Glossary |
|---|---|---|
| Monocrystalline | Even, dark cells. The usual home choice. | Monocrystalline panel |
| Polycrystalline | Blue, speckled cells. Rare in new home systems. | Polycrystalline panel |
| Thin film | Smooth, uniform surface; mostly on solar farms. | Thin-film panel |
| Bifacial | Glass on both sides; catches light from the back too. The example panel has a bifaciality of 80% ± 10% 2. | Bifacial panel |
| Solar shingles | Panels built into the roofing itself. | Solar shingles |
The numbers that matter when comparing panels
| Rating | Example (Qcells 435 W class) | Why it matters |
|---|---|---|
| Power at STC (Pmax) | 435 W, tolerance +5 / −0 W 2 | Sets system size: panels × watts = kW DC |
| Efficiency | ≥ 21.8% 2 | More watts from the same roof area |
| Temperature coefficient of Pmax | −0.28% per °C 2 | How much output falls as the panel heats above 25 °C; smaller is better in hot climates |
| Nominal operating temperature (NMOT) | 45 ± 2 °C 2 | A more realistic rooftop temperature than the 25 °C test |
| Design load, push / pull | 3,600 / 1,600 Pa 2 | How much snow and wind the panel is built to handle |
| Performance warranty | At least 98.5% of nominal power in year 1, then at most 0.33% loss a year 2 | Your guarantee against faster-than-promised degradation |
| Product warranty | 25 years 2 | Covers defects in materials and workmanship of the panel itself |
Example: how hot weather trims a panel’s output
Illustrative arithmetic using the data-sheet temperature coefficient. Panels on a summer roof run well above the 25 °C test temperature.
| Step | Math | Result |
|---|---|---|
| Rated power at 25 °C | From the data sheet 2 | 435 W |
| Cell temperature 45 °C (the NMOT) | 45 − 25 = 20 °C above test | 20 °C |
| Loss from heat | 20 × 0.28% | 5.6% |
| Power at that temperature, same sunlight | 435 W × (1 − 0.056) | ≈ 411 W |
This isolates temperature only. Real output also depends on how much sunlight reaches the panel, which is why proposals model annual kWh rather than multiplying the wattage.
Where panels go, and how one becomes a system
A single panel rarely stands alone on a house; the EIA notes an array can run from two panels to hundreds. Panels are wired into strings, the strings form an array, and the array plus inverter, racking and wiring make up the solar system.
Most go on racks on a sloped roof. The DOE says arrays are usually tilted near the local latitude and face south in the US for the best yearly output. Panels can also go on a ground mount or a carport.
Use the panel count calculator to see how many panels a target size needs.
Benefits and limits of solar panels
Benefits
- No moving parts and no fuel.
- Slow aging: often less than 1% a year 6.
- Long product and performance warranties from most makers.
- Can be added in steps if the inverter has room.
Limits
- Output drops in heat, shade and dirt.
- Adds weight to the roof: about 20.9 kg each for the example panel 2.
- Roof work later may mean removing and refitting the panels.
- Cannot be fixed in place; a failed panel is swapped.
Limits to plan around
Roof space and shade set the ceiling on how many panels you can use. A north-facing roof makes less. Trees can cut output more than most people expect. See our guide to shade.
Roof age matters. If your roof needs replacing soon, do it first. Taking panels off and back on later costs money; see removal and reinstall.
Weight matters on older roofs. An installer checks the structure before adding panels. Our roof loading guide explains how.
What drives panel cost, lifespan and warranty
We do not print a panel price, because quotes vary. Panels are only part of the cost. Labor, inverter, racking, permits and roof work add the rest. Compare quotes using the cost per watt guide.
Higher-efficiency, all-black, bifacial or n-type panels usually sit higher in price. They pay off most when roof space is tight.
For life, the DOE cites a Berkeley Lab survey putting average panel life at 25–35 years in 2025. NLR says panels often lose less than 1% a year. The warranty is your real protection. The example panel carries a 25-year product warranty and a 30-year performance warranty.
The IRS says the federal 25D homeowner credit is not available for property placed in service after 31 December 2025.
How panels get installed
A licensed installer handles the work. The steps are similar in most places.
- Site visit: roof condition, shade, direction and structure.
- Design: panel model, layout and an annual kWh estimate.
- Permits: building and electrical permits from your city or county.
- Utility application: interconnection approval to connect to the grid.
- Install: flashing and racking go on the roof, then panels clamp to the rails.
- Wiring: an electrician connects panels to the inverter and your electrical panel.
- Inspection and permission to operate: the inspector and utility sign off.
See solar panel installation for what each step involves.
Panel care
Panels need little care. Rain washes most dust away. Check your app monthly and compare to the same month last year.
If dirt, pollen or bird droppings build up, book a pro. Our cleaning guide covers when it is worth it. Do not use pressure washers or climb on the roof.
Keep branches trimmed back from the array. After a big storm, look from the ground for damage.
Warning signs and when to call a pro
Call your installer if you see any of these. Many are warranty claims.
- Cracked or shattered glass.
- Brown spots, burn marks or bubbles on the cells.
- A scorched or cracked junction box.
- Loose panels or bent frames after wind.
- One panel making much less than the others in your app.
- Animals nesting under the array and chewing wires.
Safety rule
Panels are live whenever light hits them. Never unplug connectors or touch a damaged panel. Call a licensed installer.
Standards and codes for solar panels
Product standards. Panel data sheets list the tests they passed. The example panel lists IEC 61215:2016 (design and performance tests) and IEC 61730:2016 (safety tests), with a fire rating based on ANSI/UL 61730. Ask for these on any panel you are offered.
Electrical code. Panel wiring follows Article 690 of the National Electrical Code (NFPA 70). The 2023 edition updated rapid shutdown and other PV rules, per IAEI. Your area chooses the edition.
Building code. Roof attachment and fire setbacks follow the adopted building code. South Carolina enforces the 2021 state codes based on the 2021 IRC and IBC.
Misconceptions about solar panels
- Myth A higher-watt panel always gives a cheaper system.
- Reality Bigger panels need fewer pieces, but cost per watt and fit on the roof decide value.
- Myth Panels stop working after the warranty ends.
- Reality They usually keep producing, at reduced output.
- Myth Panels work best on the hottest days.
- Reality Heat lowers output. Bright, cool days are best.
- Myth Panels make AC you can plug into.
- Reality They make DC. An inverter is needed.
- Myth Hail destroys most panels.
- Reality Panels are tested for impact and load; the example panel lists a 5,400 Pa push test load 2. Severe storms can still break glass.
Solar panels in SC, GA and VA
Panels are the same across states, but who installs them and how you are paid differ. In South Carolina, "Solar Panel Installer" is a Residential Specialty registration with the Residential Builders Commission 11.
In Virginia, residential solar of 25 kW DC or less is exempt from state and local property tax 12. Georgia Power caps residential renewable systems at 10 kW 13.
How to choose panels
Use these rules of thumb when comparing quotes:
- Small roof: favor higher efficiency to fit more watts.
- Hot climate: favor a smaller temperature coefficient.
- Snow or high wind: check the design load rating.
- Any home: check the IEC/UL tests, product warranty and performance warranty.
- Close quotes: compare cost per watt and the annual kWh estimate, not just brand.
Next steps
Questions about solar panel
Is a solar module the same as a solar panel?
Yes. "Module" is the industry and code term; "panel" is the everyday one. Data sheets, permits and warranties usually say module. A "solar array" is different: it is a group of panels wired together.
What does the junction box on a solar panel do?
It is where the cell circuits connect to the output cables. It holds the bypass diodes that let current route around a shaded or failed section of the panel. A good data sheet lists its sealing rating, such as IP68.
How long do solar panels last?
Many last decades. The DOE cites a Berkeley Lab survey putting average life at 25–35 years in 2025. The Qcells line above promises output declining no more than 0.33% a year after year 1 under a 30-year performance warranty. Panels usually keep producing after the warranty ends.
How many watts is a typical home solar panel?
Ratings vary by model and size. The Qcells line used on this page is sold from 435 to 450 W. The rating is printed on the label on the back and on the data sheet. Your quote should list the exact model and wattage.
Do solar panels produce AC or DC?
DC. An inverter, either one central unit or a microinverter behind each panel, converts it to the AC your home uses. Some "AC modules" come with the microinverter already attached.
How efficient are solar panels?
Most home panels turn about a fifth of sunlight into electricity. The DOE puts factory silicon modules at 20%–22%. The example panel is rated at 21.8% or more. Efficiency matters most when roof space is tight.
How much do solar panels weigh?
It depends on the model. The example Qcells panel weighs 20.9 kg (about 46 lb). Racking adds more. An installer checks that your roof can carry the load before installing.
Can solar panels withstand hail?
Most are built and tested for hail and heavy loads. The example panel lists a 5,400 Pa push test load and a 3,600 Pa design load. Very large hail can still crack glass. Check your home insurance covers the panels.
Do solar panels need cleaning?
Usually not often. Rain clears most dust. Heavy pollen, dust or bird droppings can lower output. If your app shows a drop that weather does not explain, book a pro cleaning. Do not climb on the roof.
What certifications should a solar panel have?
Look for IEC 61215 for design and performance and IEC 61730 or UL 61730 for safety. They appear on the data sheet. Your inspector and utility may also need the panel to be listed for use in the US.
Sources
- US EIA, Solar explained: Photovoltaics and electricity, retrieved .
- Qcells, Q.TRON BLK S-G3R.12+/BFG 435–450 W data sheet (2025-08 Rev04), retrieved .
- US DOE Solar Energy Technologies Office, Solar Photovoltaic System Design Basics, retrieved .
- US DOE Solar Energy Technologies Office, Solar Photovoltaic Technology Basics, retrieved .
- US DOE Solar Energy Technologies Office, Crystalline Silicon Photovoltaics Research, retrieved .
- National Laboratory of the Rockies (NLR), Photovoltaic Lifetime Project, retrieved .
- US DOE Solar Energy Technologies Office, End-of-Life Management for Solar Photovoltaics, retrieved .
- IRS, Residential Clean Energy Credit (§25D), retrieved .
- IAEI Magazine, John Wiles, 2023 National Electrical Code and Photovoltaic Power Systems (23 Mar 2023), retrieved .
- SC Building Codes Council, code adoption, retrieved .
- SC LLR, Residential Specialty Contractor registration (Solar Panel Installer), retrieved .
- Code of Virginia §58.1-3661 (solar equipment tax exemption), retrieved .
- Georgia Power, Behind-the-Meter Interconnection Summary for Residential Customers (rev. 15 Aug 2025), 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: Every component, rating, load, certification and warranty is copied from one manufacturer’s current data sheet and labelled as such; it illustrates the rows to read, not a product recommendation.
Lifespan and aging are from DOE and NLR. The temperature example is arithmetic on the published coefficient. State facts are from sc-local/facts.js and verified VA/GA rows.
Suggest a correction. We fix errors and say what changed.