Solar energy is one of the most important renewable energy resources available to mankind and it can be harnessed in many ways. Active vs passive solar energy systems are discussed in this article.
Solar Energy for both residential and commercial systems can be harnessed through both active and passive solar energy systems. A passive solar system optimizes the use of solar energy through the design, architecture, orientation, and placement of the building.
Whereas active solar systems use devices to convert solar energy into a more usable form, such as hot water or electricity. Both technologies complement each other when used simultaneously.
Active solar systems involve some kind of adaptable technology (like PV panels or solar water heaters) to harness solar energy. Active solar systems can be divided into two main types.
Photovoltaic (PV) panels or solar cells are active systems in which solar radiation is used to generate electric power through silicon semiconductor wafers. This is called the photoelectric effect. It is a fairly efficient means to utilize solar energy sources. The panels are of two main types: monocrystalline and polycrystalline panels. They are used according to the climate and efficiency required.
Commercially available solar panels such as a 2000 watt kit are up to 22.5 percent efficient at converting sunlight into electricity in optimal conditions, but even in partly cloudy weather, they can operate at 80 percent of their maximum output.
PV systems can be connected to the electric transmission grid or they are capable of operating as a standalone system to power your fridge and other appliances.
Solar thermal technology utilizes heat energy from the sun’s rays rather than light and can be used in multiple ways.
Active Solar Space Heating works on the principle of thermal conduction. The sun’s thermal energy is captured through specialized air collectors or liquid-based collectors which use the air or liquid as a heat exchanger medium which is then distributed through the building via electric fans or water pumps.
Collectors can be of two types. Concentrating collectors and non-concentrating collectors. Non-concentrated collectors are mostly used in space heating.
The costs for these systems range from $3,000 to $10,000 depending on the size of the space. With savings in electricity or natural gas, they can pay for themselves in 7 to 10 years.
Solar Water Heaters are used to heat water for domestic or commercial use through the thermal energy of the sun’s radiations. These systems are very popular due to their cost-effectiveness and relatively simple installation. Conventional gas or electric water heaters may still be needed as a backup for unusual circumstances (cloudy days). A constant water supply is also needed in this setup.
Although initial home installation costs range from $1,500 to $3,000, which is at least double that of conventional heaters, the reduction in gas or electric bills can cover the costs in 15-20 years.
Concentrated Solar Power (CSP) is an active solar system with the ability to function as a utility-scale power plant. Solar rays are concentrated through fields of mirrors into channels containing heat-responsive fluid. This results in excitation of the fluid due to high temperature to a level where it can power a turbine or engine, which in turn runs an electric generator.
CSP requires a substantial initial investment, and it typically uses more land and water than other technologies.
In passive solar energy systems, solar energy is consumed passively through the intelligent and efficient designs and architecture of the building. It may also use some specialized materials to harness energy from the sun. The only source of energy is the sun, so you don’t need specialized equipment to harness energy. Five basic design elements are considered for passive systems in a building.
Aperture/Collector: The large glass area through which sunlight enters the building.
Absorber: The hard, darkened surface of the storage element.
Thermal mass: Use of materials (both solid and liquid) that retain or store the heat produced by sunlight.
Distribution: Methods by which heat is distributed from the collection and storage points to different areas of the building.
Control: The use of different techniques like roof overhangs to shade the aperture area during the summer months.
Passive methods can be used for both heating and cooling depending upon the season and climate of the region.
Passive solar heating systems maintain a comfortable room temperature by capturing the heat within the building’s elements and utilizing that heat during the unavailability of the sun. Sun-facing glass and thermal mass are the two primary elements of passive heating.
Passive heating can be done by direct and indirect gains. Direct gains involve solar collectors, heat absorbers, and a distribution system for heating. Indirect gains involve storing heat through glass-paned windows in the south-facing walls of the building.
Passive solar cooling systems reduce excessive heat gain during the day, provide non-mechanical airflow, exchange warm interior air for colder outdoor air where possible, and store nighttime coolness to moderate warm daytime temperatures. Basically, passive solar cooling systems comprise overhangs or curtains on sun-facing windows, shade trees, thermal mass, and cross ventilation to keep the temperature down in homes during the summer months.