What Is a Solar Collector? Why Is It Important? Overview and Types

Solar collectors are devices that collect the Sun's radiation and use it to generate heat, either for cooking food, heating water, or generating electricity. Solar collectors are not new—they have been used since the 18^th century as solar ovens and since the 19^th century to generate steam and electricity.

Types of Solar Collectors

A solar collector can cost billions of dollars to bring electricity to entire cities or less than $100 to bring with you on a camping trip. But the physics behind the technology is more or less the same.

Solar Ovens

Before the advent of photovoltaic (PV) cells to convert the Sun's light energy (photons) directly into electricity (volts), solar collectors were absorbing heat to cook food. In 1767, the Genevan naturalist and physicist Horace de Saussure created a solar oven that raised temperatures up to 230 degrees F (110 degrees C). Solar ovens are still used around the world today as a practical way to cook food without electricity or combustion.

Wood and other biofuels like peat are still the primary fuel sources for cooking for nearly half of the world's population. Replacing wood with solar ovens can help prevent deforestation: a single solar cooker prevents a ton of wood per year from being harvested, according to Solar Cookers International. Cooking with the sun's heat also reduces the carbon emissions from burning wood and reduces indoor air pollution.

Water Heaters

Solar water heaters are often small black panels mounted on a roof. The panels might be mistaken for PV solar panels, but homes usually only need one or two panels to maintain a water heater.

Solar collectors can also be configured as a series of black collector tubes, which act in generally the same manner: both panels and tubes have heat-absorbing materials that conduct heat to a water supply. Often, as in the photo here, the water heater is attached to panels on the roof to reduce heat loss and maximize water pressure. Solar water heaters can also be used to heat swimming pools.

Commercially, solar water heaters have been around since Clarence Kemp introduced the Climax in 1891. They soon became popular especially in sunny climates like California and Florida, but the industry was crippled by utility companies giving incentives for customers to switch to gas and electric water heaters.

Reintroducing solar water heaters can combat climate change. Depending on the climate zone, solar water heaters have been estimated to be able to meet more than 80% of the annual hot water demand of a region and reduce greenhouse gas emissions from heating water by more than 90%.

Residential Electricity Generation

Small-scale collectors available on a residential scale include parabolic solar collectors that are shaped like a large satellite dish but contain mirrors, not antennae. They generate electricity by directing sunlight toward a Stirling engine. Unlike an internal combustion engine or a thermal power plant like a nuclear or fossil fuel plant, a Stirling engine emits no greenhouse gases and releases no steam, thus loses little water in producing electricity. And with few moving parts and no emissions, they are safe to use in a backyard or on a roof.

Beyond the direct benefit of reduced emissions, distributed energy resources like local solar collectors can help reduce the total system costs of electricity generation and distribution. Since solar collectors are close to the source of the electricity demand, the transmission cost of bringing the electricity to customers is minimal to none. Homeowners can enjoy energy independence, store their own electricity in order to keep their lights on even during power outages, and reduce the need for utility companies to build new transmission lines to bring power from faraway power plants.

Utility-Scale Solar Collectors

At their grandest scale, solar collectors are used in concentrated solar power (CSP) plants to produce hundreds of megawatts of electricity. They use a large array of mirrors to direct sunlight to a central tower containing solar collectors, thereby generating massive amounts of heat. The heat produces steam to drive a turbine and creates electricity. In a closed-loop, nearly all of the water used to produce the steam is cooled, recaptured, and reused.

Large-scale projects such as the Ivanpah Solar Electric Generating System complex in the Mojave Desert have met with mixed success, and the development of new projects in the United States has dried up. During rolling blackouts in California in 2020, the Ivanpah complex was unable to operate at full capacity. And while CSP plants promise to provide clean, renewable electricity when operating fully, Ivanpah still requires the burning of natural gas to ramp up into operation each morning. Worldwide, CSP projects have been few and far between.