Solar panels are devices that convert sunlight directly into electricity. Each panel contains dozens of solar cells made from semiconductor material, typically silicon, that generate an electrical current when light hits them. A standard residential panel measures about 5.5 feet by 3 feet, weighs 40 to 50 pounds, and converts roughly 20% of the sunlight it receives into usable power.
How Solar Panels Generate Electricity
When sunlight strikes a solar cell, one of three things happens: the light reflects off, passes through, or gets absorbed. It’s the absorbed light that does the work. The cell’s semiconductor material soaks up the light’s energy and transfers it to electrons within the material, knocking them loose. Those freed electrons flow through the material as an electrical current, which is drawn out through the thin metallic grid lines visible on the cell’s surface.
This process is called the photovoltaic effect, and it happens silently with no moving parts. A single solar cell produces a small amount of power on its own, so manufacturers wire 60 to 70 cells together inside a single panel to produce a useful amount of electricity. Multiple panels wired together form an array, and a typical home installation uses anywhere from 15 to 25 panels depending on the household’s energy needs and roof space.
What’s Inside a Solar Panel
A solar panel is a layered sandwich designed to protect fragile silicon cells from decades of weather. The sun-facing side is a sheet of tempered glass, which accounts for about 75% of the panel’s total weight. Beneath the glass, the solar cells are embedded in a polymer encapsulant that cushions them and seals out moisture. The back side is covered by a multilayer plastic backsheet made from weather-resistant fluoropolymers and polyester films that block humidity and provide structural support. An aluminum frame holds everything together and gives installers a sturdy edge to clamp onto mounting hardware.
Types of Solar Panels
Monocrystalline
Monocrystalline panels are the most common choice for home rooftops. They’re made by growing a single, continuous crystal of silicon from a molten vat, then slicing that crystal into thin wafers. Because the silicon has a uniform crystal structure, electrons move through it more efficiently. These panels typically achieve 17% to 22% efficiency, the highest of any widely available type. Their higher output per square foot makes them especially practical if your roof space is limited.
Polycrystalline
Polycrystalline panels use a simpler manufacturing process. Instead of growing a single crystal, molten silicon is cooled so that multiple crystals form together. This is faster and produces less waste, which brings the price down. The tradeoff is lower efficiency, typically 15% to 17%, because the boundaries between crystals slightly impede electron flow. If you have plenty of roof space and want to keep upfront costs low, polycrystalline panels can still be a solid option, though monocrystalline has increasingly dominated the residential market.
Thin-Film
Thin-film panels deposit a very thin layer of photovoltaic material onto glass or flexible backing. They’re lighter and can conform to curved surfaces, which makes them useful in commercial buildings, portable setups, and situations where traditional rigid panels won’t work. Their efficiency is generally lower than crystalline silicon panels, so they require more surface area to produce the same amount of power.
Bifacial Panels
A newer design called bifacial panels can capture light on both sides. The front absorbs direct sunlight as usual, while the back picks up light reflected off the ground or nearby surfaces. Testing by the National Renewable Energy Laboratory found that bifacial panels produced up to 9% more energy than traditional one-sided panels, and the gains were even higher over reflective surfaces. Snow cover, for instance, dramatically boosts the reflected light hitting the back side. Brown grass, crushed rock, and light-colored ground coverings also improve performance. These panels are increasingly popular in ground-mounted commercial installations where the surface below can be optimized.
How the Rest of the System Works
Solar panels produce direct current (DC) electricity, but your home and the electrical grid run on alternating current (AC). An inverter bridges that gap. It’s one of the most critical components in any solar installation, converting the panel’s DC output into grid-compatible AC power. Modern inverters do more than convert electricity. They monitor system performance, communicate with home networks, and manage how power flows between your panels, your home, and the grid.
If your system includes battery storage, the inverter also coordinates charging and discharging the batteries. During a power outage, an advanced inverter paired with batteries can keep your home running independently from the grid. Under normal conditions, inverters are designed to ride through small fluctuations in grid voltage or frequency, only disconnecting if a disruption is large or prolonged enough to pose a safety risk.
The physical mounting system, while less glamorous, matters too. Roof-mounted systems use racking hardware bolted to rafters, angled to maximize sun exposure for your latitude. Ground-mounted systems offer more flexibility in positioning but require dedicated yard space.
How Long Solar Panels Last
Solar panels are remarkably durable. Most manufacturers back them with 25-year performance warranties, but the panels themselves often keep producing well beyond that. A large-scale study analyzing data from 53 solar plants over roughly a decade found annual power degradation of less than 0.29%. That means after 25 years, a panel might still be producing over 93% of its original output. With no moving parts and cells sealed behind tempered glass, there’s very little that wears out mechanically. The main enemies are prolonged moisture exposure and extreme temperature cycling, which the encapsulant and backsheet layers are specifically engineered to resist.
What Happens When Panels Are Retired
Because glass makes up about 75% of a panel’s weight, and glass recycling is already a mature industry, recovering that material is straightforward. The aluminum frame, copper wiring, and plastic junction box are also easily recyclable through existing streams. The silicon cells and trace metals inside are harder to recover economically. Current recycling processes can separate the glass, aluminum, and copper, but the remaining materials, including the cells themselves, are sometimes incinerated rather than reclaimed. As millions of panels installed in the 2010s approach the end of their warranties in the coming decades, the recycling infrastructure is expected to scale up significantly.
What’s on the Horizon
Perovskite solar cells represent the biggest shift in solar technology in years. These cells use a different crystal structure than silicon and can be manufactured at lower temperatures with cheaper materials. Their efficiency has climbed from about 3% in 2009 to over 26% on small lab devices. When layered on top of a traditional silicon cell in a “tandem” configuration, the combined cell has reached nearly 34% efficiency, far beyond what either technology achieves alone. The catch is that perovskite cells aren’t yet manufactured at scale. They face significant hurdles around long-term stability, since they degrade faster than silicon when exposed to moisture and heat, along with challenges in scaling up production while maintaining performance. These are solvable problems, but commercial availability at meaningful volumes is still some years away.