Solar Hot Water Systems Components
Most solar water-heating system have three main parts: (1) a solar collector and (2) a solar storage tank or a pool/tub (3) Plumbing and Solar Control System. Until recently the most common collector used in solar hot water systems was the flat panel collector. However with the advance in technology, solar vacuum tube technology is rapidly becoming the method of choice as its energy output is much higher and takes up less space per square foot.Mass production of solar tubes has driven the cost down to allow widespread use of vacuum tubes.
Solar water heaters use the sun to heat either water or a heat-transfer fluid in the collector. Heated water is then held in the storage tank ready for use or directly circulated in an open mass such as pool or hot tub. The tank can be as simple as a modified standard water heater, but more specific solar water tanks are also available. Most solar water tanks will also feature a back up electric element built into the unit.
One of the most overlooked aspect of a solar system is the Plumbing and Control System.This includes all items required to make the system function optimallyand safely. Items such as temperature controllers, pumps, expansion vessels, pressure safetyvalves, fill and drain spouts are all part of a properly installed solar system.
ACTIVE or PASSIVE System
Solar water heating systems can be either active or passive, but the most common are active systems. Northern Lights Solar Solutions designs application based around active system with pumps andand digital controllers designed specifically for the solar industry.
/ Active Direct-circulation (open loop systems) use pumps to circulate potable water through the collectors. These systems are appropriate in areas that do not freeze for long periods and do not have hard or acidic water. These systems may require a recirculation freeze protection (circulating warm tank water during freeze conditions) and this in return requires electrical power for the protection to be effective.An open loop system operatesat atmospheric pressure. A pool uses this method as it is generally not operated in freezing months. In an open loop system the usable hot water is directly circulated through the heating system./ Active Indirect-circulation (closed loop) uses a heat-transfer fluid (water or a diluted antifreeze fluid) to collect heat and a heat exchanger to transfer the heat to the potable water indirectly. Heat exchangers transfer the heat from the heated fluid to the potable water (or other fluid). Some indirect systems have "overheat protection" by-pass which removes the heat that cannot be used. This protects the collector and the glycol fluid from becoming super-heated when the load is low and the solar intensity of incoming solar radiation is high.The heat transfer fluid is usually a glycol-water mixture with the glycol concentration depending on the expected minimum temperature. The glycol is usually food-grade Propylene glycol because it is non-toxic. This system is typically used in hot water heating and radiator or in floor home/commercial heating. Because the system is closedtothe atmosphere, pressure can build up asthe temperature rises. Such systems will incorporate pressure reliefvalves and expansion tanks for safety purposes
/ Passive solar water heaters systems move household water or a heat-transfer fluid through the system without pumps. They rely on gravity and the tendency for water to naturally circulate as it is heated (warm water is lighter and rises). Because they contain no electrical components, passive systems though simpler, haveveryminimal control for home use. Passive storage systems consist of one or more storage tanks placed in an insulated box with a glazed side facing the sun.These solar collectorsare suited for areas where temperatures rarely go below freezing. They are also good in households with significant daytime and evening hot-water needs; but they do not work well in households with predominantly morning draws because they lose most of the collected energy overnight.
Common Solar Heating System Applications
In Japan an estimated 10,000,000 homes use this technology to heat their homes. In North America solar water heating is quickly growing as the price of solar collectors fall and governments support the use of clean energy, financially. A hot water system is in most cases done using a close loop system with glycol mixture running through the primary side of a heat exchanger. Special solar water tanks are now available that have the heat exchanger built directly inside the system, An existing hot water system can also be quickly adapted by using a primary storage hot water tank before the existing secondary tanks. Using a heat exchanger and solar systemwould heat the primary storage tank. Water would then be drawn into the existing water tank as needed. This is perhaps the most common type of home water heating as the current system is left in place and solar water compliments the system. When installing a hot water system, a controller and pump are required. There should also be proper pressure release valves used.