The simplest collector is a water-filled metal tank in a sunny place. The sun heats the tank. This was how the first systems worked. The challenge is to limit the heat loss. ICS or batch collectors reduce heat loss by thermally insulating the tank. This reflects heat lost from the tank back towards the tank.
In a simple way one could consider an ICS solar water heater as a water tank that has been enclosed in a type of 'oven' that retains heat from the sun as well as heat of the water in the tank. Using a box does not eliminate heat loss from the tank to the environment, but it largely reduces this loss. Standard ICS collectors have a characteristic that strongly limits the efficiency of the collector: a small surface-to-volume ratio.
Cylindrical objects such as the tank in an ICS collector have an inherently small surface-to-volume ratio. Collectors attempt to increase this ratio for efficient warming of the water.
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Variations on this basic design include collectors that combine smaller water containers and evacuated glass tube technology, a type of ICS system known as an Evacuated Tube Batch ETB collector. ETSCs can be more useful than other solar collectors during winter season. ETCs can be used for heating and cooling purposes in industries like pharmaceutical and drug, paper, leather and textile and also for residential houses, hospitals, nursing home, hotels, swimming pool etc.
An ETC can operate at a range of temperatures from medium to high for solar hot water, swimming pool, air conditioning and solar cooker. Floating pool covering systems and separate STCs are used for pool heating. Pool covering systems, whether solid sheets or floating disks, act as insulation and reduce heat loss.
Much heat loss occurs through evaporation, and using a cover slows evaporation.
Solar Variability Over the Past Several Millennia | SpringerLink
STCs for nonpotable pool water use are often made of plastic. Pool water is mildly corrosive due to chlorine. Water is circulated through the panels using the existing pool filter or supplemental pump. In mild environments, unglazed plastic collectors are more efficient as a direct system. In cold or windy environments evacuated tubes or flat plates in an indirect configuration are used in conjunction with a heat exchanger. This reduces corrosion. A fairly simple differential temperature controller is used to direct the water to the panels or heat exchanger either by turning a valve or operating the pump.
Once the pool water has reached the required temperature, a diverter valve is used to return water directly to the pool without heating. The collector panels are usually mounted on a nearby roof, or ground-mounted on a tilted rack.
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Due to the low temperature difference between the air and the water, the panels are often formed collectors or unglazed flat plate collectors. Adding solar collectors to a conventional outdoor pool, in a cold climate, can typically extend the pool's comfortable usage by months and more if an insulating pool cover is used.
An active solar energy system analysis program may be used to optimize the solar pool heating system before it is built. The amount of heat delivered by a solar water heating system depends primarily on the amount of heat delivered by the sun at a particular place insolation. In the tropics insolation can be relatively high, e.
Even at the same latitude average insolation can vary a great deal from location to location due to differences in local weather patterns and the amount of overcast. Calculators are available for estimating insolation at a site. Below is a table that gives a rough indication of the specifications and energy that could be expected from a solar water heating system involving some 2 m 2 of absorber area of the collector, demonstrating two evacuated tube and three flat plate solar water heating systems.
Certification information or figures calculated from those data are used. With most solar water heating systems, the energy output scales linearly with the collector surface area. Many thermosiphon systems have comparable energy output to equivalent active systems. The efficiency of evacuated tube collectors is somewhat lower than for flat plate collectors because the absorbers are narrower than the tubes and the tubes have space between them, resulting in a significantly larger percentage of inactive overall collector area.
Some methods of comparison  calculate the efficiency of evacuated tube collectors based on the actual absorber area and not on the space occupied as has been done in the above table. Efficiency is reduced at higher temperatures. In sunny, warm locations, where freeze protection is not necessary, an ICS batch type solar water heater can be cost effective.source
Solar Variability Over the Past Several Millennia
This increases initial costs, but not life-cycle costs. The biggest single consideration is therefore the large initial financial outlay of solar water heating systems. Payback times can vary greatly due to regional sun, extra cost due to frost protection needs of collectors, household hot water use etc.
For instance in central and southern Florida the payback period could easily be 7 years or less rather than the The payback period is shorter given greater insolation. However, even in temperate areas, solar water heating is cost effective. The payback period for photovoltaic systems has historically been much longer. Australia operates a system of Renewable Energy Credits, based on national renewable energy targets.
Chapter 006, Solar Radiation
The Toronto Solar Neighbourhoods Initiative offers subsidies for the purchase of solar water heating units. The source of electricity in an active SWH system determines the extent to which a system contributes to atmospheric carbon during operation. Active solar thermal systems that use mains electricity to pump the fluid through the panels are called 'low carbon solar'. However, PV-powered active solar thermal systems typically use a 5—30 W PV panel and a small, low power diaphragm pump or centrifugal pump to circulate the water. This reduces the operational carbon and energy footprint.
Alternative non-electrical pumping systems may employ thermal expansion and phase changes of liquids and gases. Recognised standards can be used to deliver robust and quantitative life cycle assessments LCA.
LCA considers the financial and environmental costs of acquisition of raw materials, manufacturing, transport, using, servicing and disposal of the equipment. Elements include:. The main energy-related impact is emissions. The energy used in manufacturing is recovered within the first 2—3 years of use in southern Europe. By contrast the energy payback time in the UK is reported as only 2 years.
This figure was for a direct system, retrofitted to an existing water store, PV pumped, freeze tolerant and of 2.
For comparison, a PV installation took around 5 years to reach energy payback, according to the same comparative study. In terms of CO 2 emissions, a large fraction of the emissions saved is dependent on the degree to which gas or electricity is used to supplement the sun. Using the Eco-indicator 99 points system as a yardstick i. This calculation assumes that the solar system produces about half of the hot water requirements of a household. But because methane CH 4 emissions from the natural gas fuel cycle  dwarf the greenhouse impact of CO 2 , the net greenhouse emissions CO 2 e from gas-driven systems are vastly greater than for solar heaters, especially if supplemental electricity is also from carbon-free generation.
Maintenance was identified as an emissions-costly activity when the heat transfer fluid glycol-based was replaced. However, the emissions cost was recovered within about two years of use of the equipment. In Australia, life cycle emissions were also recovered. Analysing their lower impact retrofit freeze-tolerant solar water heating system, Allen et al.
From Wikipedia, the free encyclopedia. Renewable energy portal Environment portal. See also: Solar power in China.
Related Chapter 006, Solar Radiation
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