Solar Air Heater
Solar space heaters use solar air panels to collect and heat buildings. An example of a solar air panel is shown to the left. They can function as add-ons to already installed ventilation systems because air is the heating medium. Solar air panels come in two main types: glazed and unglazed. Glazed solar collectors are usually used in the residential sector for space heating. Air is heated through a solar air panel and is directed through the building. For proper circulation, the solar space heating system penetrates into the building in at least two places to create flow, and the air in the solar collector is warmer than the building room temperature. A diagram of the air flow in a solar air heater is shown below to the left. Unglazed solar collectors are used in commercial, industrial, and institutional buildings to pre-heat make-up ventilation air with a high ventilation load.[24] The unglazed solar air collectors are walls with an external painted perforated metal solar heat absorber that conducts heat from the absorber surface into a thermal boundary layer of air 1 mm thick between the perforated absorber and inside wall. With fans, the heated boundary layer of air is pulled through a perforation into the building’s ventilation system. [18]
Another type of solar space heater is called a trombe wall, as shown in the picture below to the right. A trombe wall is a passive solar heating and ventilation system that functions similar to other solar space heaters. It is made up of a thermal mass that stores heat from the sun and heats up the boundary layer of air to promote ventilation. The difference is there are vents at the top and bottom of the wall which allows the boundary layer of air to circulate in and out of the building. Throughout the day, sunlight heats up the thermal mass and warms the boundary layer of air causing circulation through the top and bottom vents. After ventilation, the trombe wall radiates the stored heat from the day. [19]
Another type of solar space heater is called a trombe wall, as shown in the picture below to the right. A trombe wall is a passive solar heating and ventilation system that functions similar to other solar space heaters. It is made up of a thermal mass that stores heat from the sun and heats up the boundary layer of air to promote ventilation. The difference is there are vents at the top and bottom of the wall which allows the boundary layer of air to circulate in and out of the building. Throughout the day, sunlight heats up the thermal mass and warms the boundary layer of air causing circulation through the top and bottom vents. After ventilation, the trombe wall radiates the stored heat from the day. [19]
Solar Water Heater
According to the National Renewable Energies Laboratory, solar water heaters can be used to produce at least half or more of the hot water needed for residential and commercial use in the US. Solar water heater systems are similar to the large scale solar thermal power plants, but without the array of mirrors to concentrate sunlight. These water heater systems are made up of a collector that holds heat-transfer fluid to collect and pass heat to the usable water in the water heater storage tanks. Solar water heater systems are divided into two categories: active and passive. The main operational difference between active and passive solar water heating systems is that the active solar water heater uses a pump to pump cooler heat-transfer fluid from the storage tank into the collector, whereas the passive solar water heating system relies on water’s natural inclination to rise when it is warm and sink when it is cooler. Therefore passive solar water heating systems do not have to install pump to move heat-transfer fluid from the storage tank to the collector, but installers have to be mindful of the roof design with respects to where to install the heavy storage tank in the water heating system. [15]
One of the main components of the solar water heater systems is the collector. There are three types of solar collectors used for residential applications: flat-plate collector, integral collector-storage systems, and evacuated-tube solar collector. Flat-plate collectors are dark absorber plates. They come glazed or unglazed. Glazed flat-plate collectors have the dark absorber plates in insulated, weatherproofed boxes under a glass or plastic cover, whereas the unglazed collector has none of these features. Integral collector-storage systems also known as a batch system has one or more black tanks or tubes in an insulated, glazed box. Cold water passing through the solar collector heats up and continues into a conventional backup water heater, providing a reliable source of hot water. Lastly, evacuated-tube solar collectors are parallel rows of transparent glass tubes, each containing a glass outer tube and metal absorber tube attached to a fin. The fin has a unique coating that absorbs solar energy but inhibits radiative heat loss. [18]
While these systems can provide clean carbon-free hot water, they are not perfect systems. These solar water heating systems almost always require a backup system for cloudy days and when hot water demand is high. However, solar water heater systems can also be good for heating pools. In fact, solar pool heating is the most cost-effective use of solar energy in many climates, according to DOE. Similar to a solar water heater system, the solar pool heating system includes: a solar collector, a filter, a pump, and a flow control valve. Pool water is pumped through the filter and through the solar collector to be heated before returning to the pool, providing heated pool water. In addition, circulating pool water through the collector at night can also cool the pool. The cost to install either a solar water heater or a solar pool heater comes out to be between $4,000-$6,000 to buy and install, but the cost will be paid back in 1-7 years. According to the DOE, on average a solar water heater system will drop water heating bills by 50% to 80%.