Solar power comes from the sun, where hydrogen atoms fuse together to form helium in a process called nuclear fusion. This reaction releases enormous amounts of energy, which travels 93 million miles to Earth as light and heat. We capture that energy using two main technologies: photovoltaic panels that convert sunlight directly into electricity, and solar thermal systems that use the sun’s heat to generate steam and drive turbines.
How the Sun Produces Energy
The sun is essentially a giant fusion reactor. Deep in its core, where temperatures reach about 27 million degrees Fahrenheit, hydrogen nuclei collide with enough force to fuse into helium. Each fusion reaction converts a tiny amount of mass into energy, and the sheer volume of reactions happening every second produces more power than anything humans have managed to replicate on Earth for a sustained period.
That energy radiates outward from the core and eventually leaves the sun’s surface as electromagnetic radiation: a mix of visible light, infrared radiation (heat), and ultraviolet rays. Over half the solar energy reaching Earth is infrared, while only 2 to 3 percent is ultraviolet. Above Earth’s atmosphere, sunlight arrives at an intensity of roughly 1,380 watts per square meter, a figure known as the solar constant. By the time it passes through the atmosphere and reaches the ground, that drops to about 1,000 watts per square meter on a clear summer day at noon. The difference is energy absorbed or scattered by air, water vapor, and clouds.
How Solar Panels Turn Light Into Electricity
Most solar panels use the photovoltaic effect, a process where light particles (photons) knock electrons loose inside a semiconductor material, typically silicon. A solar cell is built with two layers of silicon that have been treated to carry different electrical charges: one layer is positive (called the p-type) and one is negative (the n-type). Where these two layers meet, they form a boundary called a p-n junction.
When a photon with enough energy strikes the silicon, it knocks an electron free from its atom, leaving behind a “hole” where the electron used to be. The electric field at the junction acts like a one-way gate: it pushes freed electrons toward the negative layer and holes toward the positive layer. This separation of charges creates a voltage difference between the two sides of the cell. Connect a wire between them, and electrons flow through it as electric current, no external power source needed. Each absorbed photon of visible light frees one electron, so stronger sunlight means more photons and more current.
The electricity coming out of a solar panel is direct current (DC), which flows in one direction. Your home and the electrical grid run on alternating current (AC), which reverses direction many times per second in a smooth, repeating wave pattern. A device called an inverter handles the conversion, reshaping the DC output into a clean sine wave that matches the grid’s frequency and voltage. Without this step, the electricity from your panels could damage household appliances built to operate on AC power.
What Solar Panels Are Made Of
Silicon is the foundation of most solar panels. About 12 percent of all silicon metal produced worldwide goes into making the high-purity polysilicon used for solar cells. The silicon is processed into thin wafers, then wired with silver, which serves as the conductive pathway that channels electrons into usable current. Ten percent of the world’s silver production now goes toward solar panels. Aluminum frames provide structural support and are sourced from bauxite, a mineral found near Earth’s surface. Copper wiring connects the cells and carries electricity out of the panel.
Solar Thermal: Capturing Heat Instead of Light
Not all solar power systems use photovoltaic cells. Concentrating solar-thermal power (CSP) plants take a fundamentally different approach: they use mirrors to focus sunlight onto a receiver, generating intense heat that produces steam to spin a turbine. These plants look more like traditional power stations than rooftop solar installations.
The biggest advantage of solar thermal technology is built-in energy storage. One common design uses two tanks of fluid, often molten salt. During the day, the fluid circulates through the solar receiver, heats up, and flows into a high-temperature storage tank. When electricity is needed (including after sunset), the hot fluid passes through a heat exchanger to create steam, then returns to a low-temperature tank to be reheated the next day. This cycle allows CSP plants to generate electricity for hours after the sun goes down, solving one of solar energy’s core challenges.
Several storage configurations have been tested since 1985. Two-tank direct systems use the same fluid for both heat collection and storage. Two-tank indirect systems use separate fluids for each job, adding flexibility in material choice. A simpler alternative, the single-tank thermocline system, stores heat in a solid material like silica sand inside one tank, with hot material sitting on top of cooler material, separated by a temperature gradient. Each approach balances cost, efficiency, and engineering complexity differently.
From Sunlight to Your Outlet
Whether through photovoltaic panels or thermal systems, the chain is the same: fusion in the sun’s core produces electromagnetic radiation, that radiation crosses space and filters through Earth’s atmosphere, and technology on the ground converts it into electricity compatible with the grid. A rooftop solar system compresses this chain into something remarkably direct. Photons that left the sun about eight minutes ago strike silicon, free electrons, and push current through a wire. An inverter cleans up the signal, and the electricity powers your lights.
The roughly 28 percent of solar energy lost between the top of the atmosphere and the ground, combined with the conversion efficiency of current panels (most residential panels convert 18 to 22 percent of incoming light into electricity), means only a fraction of the sun’s original output becomes usable power. But that fraction, spread across enough panels, is substantial. The sun delivers more energy to Earth’s surface in one hour than humanity uses in an entire year.