There are two types of active solar water heating systems: Contact online >>
There are two types of active solar water heating systems:
Solar water heating (SWH) is heating water by sunlight, using a solar thermal collector. A variety of configurations are available at varying cost to provide solutions in different climates and latitudes. SWHs are widely used for residential and some industrial applications.[1][2]
A Sun-facing collector heats a working fluid that passes into a storage system for later use. SWH are active (pumped) and passive (convection-driven). They use water only, or both water and a working fluid. They are heated directly or via light-concentrating mirrors. They operate independently or as hybrids with electric or gas heaters.[3] In large-scale installations, mirrors may concentrate sunlight into a smaller collector.[original research?]
As of 2017, global solar hot water (SHW) thermal capacity is 472 GW and the market is dominated by China, the United States and Turkey.[4] Barbados, Austria, Cyprus, Israel and Greece are the leading countries by capacity per person.[4]
Records of solar collectors in the United States date to before 1900,[5] involving a black-painted tank mounted on a roof. In 1896 Clarence Kemp of Baltimore enclosed a tank in a wooden box, thus creating the first ''batch water heater'' as they are known today. Frank Shuman built the world''s first solar thermal power station in Maadi, Egypt, using parabolic troughs to power a 45 to 52 kilowatts (60 to 70 horsepower) engine that pumped 23,000 litres (6,000 US gal) of water per minute from the Nile River to adjacent cotton fields.
Flat-plate collectors for solar water heating were used in Florida and Southern California in the 1920s. Interest grew in North America after 1960, but especially after the 1973 oil crisis.
Solar power is in use in Australia, Canada, China, Germany, India, Israel, Japan, Portugal, Romania, Spain, the United Kingdom and the United States.
Israel, Cyprus and Greece are the per capita leaders in the use of solar water heating systems supporting 30%–40% of homes.[6]
In 2005, Spain became the world''s first country to require the installation of photovoltaic electricity generation in new buildings, and the second (after Israel) to require the installation of solar water heating systems, in 2006.[12]
After 1960, systems were marketed in Japan.[5]
Australia has a variety of national and state and regulations for solar thermal starting with MRET in 1997.[13][14][15]
Solar water heating systems are popular in China, where basic models start at around 1,500 yuan (US$235), around 80% less than in Western countries for a given collector size. At least 30 million Chinese households have one. The popularity is due to efficient evacuated tubes that allow the heaters to function even under gray skies and at temperatures well below freezing.[16]
The minimum requirements of the system are typically determined by the amount or temperature of hot water required during winter, when a system''s output and incoming water temperature are typically at their lowest. The maximum output of the system is determined by the need to prevent the water in the system from becoming too hot.
In some direct systems, collectors can be manually drained when freezing is expected. This approach is common in climates where freezing temperatures do not occur often but can be less reliable than an automatic system as it relies on an operator.
The third type of freeze protection is freeze-tolerance, where low-pressure water pipes made of silicone rubber simply expand on freezing. One such collector now has European Solar Keymark accreditation.
Notably, while the need for freeze protection has traditionally been a complicating factor, systems using evacuated tube collectors may be used in climates with moderate frosts without any need for drainback or antifreeze. This is because an evacuated tube system only has water in the thermally insulated header, not in the evacuated tubes themselves. Additional protection is also provided by the controller: if header temperature drops below a set value (typically 2 to 4''C) the circulating pump is automatically turned on for a short period to pass warmer water to the header.
When no hot water has been used for a day or two, the fluid in the collectors and storage can reach high temperatures in all non-"drainback" systems. When the storage tank in a "drainback" system reaches its desired temperature, the pumps stop, ending the heating process and thus preventing the storage tank from overheating.
Some active systems deliberately cool the water in the storage tank by circulating hot water through the collector at times when there is little sunlight or at night, losing heat. This is most effective in direct or thermal store plumbing and is virtually ineffective in systems that use evacuated tube collectors, due to their superior insulation. Any collector type may still overheat. High pressure, sealed solar thermal systems ultimately rely on the operation of temperature and pressure relief valves. Low pressure, open vented heaters have simpler, more reliable safety controls, typically an open vent.
The ''drain-back'' is another lower-maintenance concept.[18] No anti-freeze is required; instead, all the piping is sloped to cause water to drain back to the tank. The tank is not pressurized and operates at atmospheric pressure. As soon as the pump shuts off, flow reverses and the pipes empty before freezing can occur.
Residential solar thermal installations fall into two groups: passive (sometimes called "compact") and active (sometimes called "pumped") systems. Both typically include an auxiliary energy source (electric heating element or connection to a gas or fuel oil central heating system) that is activated when the water in the tank falls below a minimum temperature setting, ensuring that hot water is always available. The combination of solar water heating and back-up heat from a wood stove chimney[19] can enable a hot water system to work all year round in cooler climates, without the supplemental heat requirement of a solar water heating system being met with fossil fuels or electricity.
Direct or open loop systems circulate potable water through the collectors. They are relatively cheap. Drawbacks include:
The advent of freeze-tolerant designs expanded the market for SWH to colder climates. In freezing conditions, earlier models were damaged when the water turned to ice, rupturing one or more components.
Indirect or closed loop systems use a heat exchanger to transfer heat from the "heat-transfer fluid" (HTF) fluid to the potable water. The most common HTF is an antifreeze/water mix that typically uses non-toxic propylene glycol. After heating in the panels, the HTF travels to the heat exchanger, where its heat is transferred to the potable water. Indirect systems offer freeze protection and typically overheat protection.
Passive systems rely on heat-driven convection or heat pipes to circulate the working fluid. Passive systems cost less and require low or no maintenance, but are less efficient. Overheating and freezing are major concerns.
Active systems use one or more pumps to circulate water and/or heating fluid. This permits a much wider range of system configurations.
Pumped systems are more expensive to purchase and to operate. However, they operate at higher efficiency and can be more easily controlled.
Active systems have controllers with features such as interaction with a backup electric or gas-driven water heater, calculation and logging of the energy saved, safety functions, remote access and informative displays.
An integrated collector storage (ICS or batch heater) system uses a tank that acts as both storage and collector. Batch heaters are thin rectilinear tanks with a glass side facing the Sun at noon. They are simple and less costly than plate and tube collectors, but they may require bracing if installed on a roof (to support 400–700 lb (180–320 kg) lbs of water), suffer from significant heat loss at night since the side facing the sun is largely uninsulated and are only suitable in moderate climates.
A convection heat storage unit (CHS) system is similar to an ICS system, except the storage tank and collector are physically separated and transfer between the two is driven by convection. CHS systems typically use standard flat-plate type or evacuated tube collectors. The storage tank must be located above the collectors for convection to work properly. The main benefit of CHS systems over ICS systems is that heat loss is largely avoided since the storage tank can be fully insulated. Since the panels are located below the storage tank, heat loss does not cause convection, as the cold water stays at the lowest part of the system.
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