A solar collector is a device that captures solar radiation and uses it to generate heat, whether to cook food, heat water or generate electricity.
Solar collectors are not new: they have been used since the 18th century as solar ovens and since the 19th century to produce steam and electricity.
What is a solar collector?
A solar collector is a device that collects and/or concentrates solar radiation from the Sun. These devices are mainly used for active solar heating and are used to heat water for personal use. These sensors are usually roof mounted and need to be very durable as they are exposed to various weather conditions.
Using these solar collectors offers an alternative to traditional domestic water heating using a water heater, potentially reducing energy costs over time. In addition to the domestic sphere, a large number of such collectors can be combined into a whole and used to generate electricity in solar thermal power plants.
Solar collectors can be unfocused or focused. The difference between them is that the concentration collectors have a larger interceptor than the absorber, while the non-concentration collectors have both with the same size. Flat plate and evacuated tube solar collectors are used for domestic purposes, such as heating, hot water or cooling.
Types of solar collectors.
A solar collector can cost billions of euros to bring electricity to entire cities or less than 100 euros to bring it to a campsite. But the physics behind the technology is more or less the same.
Before the advent of photovoltaic cells to convert light energy from the sun directly into electricity, solar collectors absorbed heat to cook food.
In 1768, the Genevan naturalist and physicist Horace de Saussure created a solar oven which raised the temperature to 111°C.
Solar ovens are still used today around the world as a convenient way to cook food without electricity or combustion.
Wood and other biofuels, such as peat, remain the main sources of cooking fuel for nearly half of the world’s population. Replacing wood with solar ovens avoids deforestation: a single solar oven avoids the felling of one ton of wood per year.
Cooking with the heat of the sun also reduces carbon emissions from burning wood and reduces indoor air pollution.
Solar water heaters are usually small black panels mounted on the roof. Panels can be confused with solar photovoltaic panels, but homes often only need one or two panels to service a water heater.
Solar collectors can also be configured as a series of black collector tubes, which generally act in the same way: the panels and tubes have materials that absorb heat and conduct it to the water supply. Often, as pictured, 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 quickly became popular, especially in sunny climates like California and Florida, but the industry was crippled by the incentives from electricity companies to switch customers to gas and electric water. radiators.
The reintroduction of solar water heaters can combat climate change. Depending on the climate zone, it is estimated that solar water heaters can meet more than 81% of a region’s annual hot water demand and reduce greenhouse gas emissions from water heating by more than 81%. by 89%.
- flat plate collectors. These collectors are simply metal boxes that have a form of transparent glazing as a lid on a dark colored absorbent plate. The sides and bottom of the collector are usually covered with insulation to minimize heat loss to other parts of the collector. The solar radiation passes through the transparent material of the glazing and reaches the absorber plate which heats up and transfers the heat to the water or the air retained between the glazing and the absorber plate. Sometimes these absorbent plates are painted with special coatings designed to absorb and retain heat better than traditional black paint. These plates are usually made of a good conductive metal, usually copper or aluminum.
- Evacuated tube collectors. This type of solar collector uses a series of vacuum tubes to heat water for use. These tubes use a vacuum, or evacuated space, to capture the sun’s energy while minimizing heat loss to the environment. They have an inner metal tube that acts as an absorber plate, which is connected to a heat pipe to carry collected heat from the Sun to the water. This heat pipe is essentially a pipe in which the contents of the fluid are subjected to a very specific pressure. At this pressure, the “hot” end of the tube contains boiling liquid while the “cold” end contains vapor which condenses. This allows heat energy to move more efficiently from one end of the pipe to the other. Once the heat from the sun moves from the hot end of the heat pipe to the condensing end, the thermal energy is carried to the water which is heated for use.
- Linear focus solar collectors. These collectors, sometimes called parabolic troughs, use highly reflective materials to collect and concentrate thermal energy from solar radiation. These collectors consist of parabolic shaped reflective sections connected in a long channel. A pipe carrying water is placed in the center of this channel, so that sunlight collected by the reflective material is concentrated on the pipe, heating the contents. They are very high power collectors, so they are typically used to generate steam for solar thermal power plants and are not used in residential applications. These collectors can be very efficient at generating heat from the Sun, especially those that can be rotated, following the Sun across the sky to ensure maximum sunlight collection.
Residential electricity generation.
Among the small-scale collectors available at the residential scale are parabolic solar collectors, which are shaped like a large satellite dish but contain mirrors and not antennae.
They generate electricity by directing sunlight onto a Stirling engine. Unlike an internal combustion engine or a thermal power plant, such as a nuclear or fossil fuel power plant, a Stirling engine does not emit greenhouse gases or release steam, so it loses little water during the production of electricity. And with few moving parts and zero emissions, they can be used safely in a garden or on a roof.
Beyond the direct benefit of emission reductions, distributed energy resources, such as local solar collectors, can help reduce the total costs of electricity generation and distribution.
Because solar collectors are close to the source of electricity demand, there is little or no transmission cost to get electricity to customers.
Homeowners can enjoy energy independence, store their own electricity to keep lights on even during power outages, and reduce the need for utilities to build new transmission lines to bring electricity from power plants distant.
Industrial scale solar collector.
On a large scale, solar collectors are used in concentrated solar power plants (CSP) to produce hundreds of megawatts of electricity.
They use a wide array of mirrors to direct sunlight onto a central tower containing solar collectors, generating huge amounts of heat.
The heat produces steam to drive a turbine and create electricity. In a closed circuit, almost all of the water used to produce the steam is cooled, recovered and reused.