Components Solar water heating

1 components

1.1 collector

1.1.1 flat plate
1.1.2 evacuated tube


1.2 pump

1.2.1 pv pump
1.2.2 bubble pump


1.3 controller
1.4 tank

1.4.1 insulated tank

components
collector

solar thermal collectors capture , retain heat sun , use heat liquid. 2 important physical principles govern technology of solar thermal collectors:

any hot object returns thermal equilibrium environment, due heat loss conduction, convection , radiation. efficiency (the proportion of heat energy retained predefined time period) directly related heat loss collector surface. convection , radiation important sources of heat loss. thermal insulation used slow heat loss hot object. follows second law of thermodynamics (the equilibrium effect ).
heat lost more rapidly if temperature difference between hot object , environment larger. heat loss predominantly governed thermal gradient between collector surface , ambient temperatures. conduction, convection , radiation occur more rapidly on large thermal gradients (the delta-t effect).


flat-plate solar thermal collector, viewed roof-level


flat plate

flat plate collectors extension of idea place collector in oven -like box glass directly facing sun. flat plate collectors have 2 horizontal pipes @ top , bottom, called headers, , many smaller vertical pipes connecting them, called risers. risers welded (or connected) thin absorber fins. heat-transfer fluid (water or water/antifreeze mix) pumped hot water storage tank or heat exchanger collectors bottom header, , travels risers, collecting heat absorber fins, , exits collector out of top header. serpentine flat plate collectors differ harp design, , instead use single pipe travels , down collector. however, since cannot drained of water, serpentine flat plate collectors cannot used in drainback systems.

the type of glass used in flat plate collectors low-iron, tempered glass. such glass can withstand significant hail without breaking, 1 of reasons flat-plate collectors considered durable collector type.

unglazed or formed collectors similar flat-plate collectors, except not thermally insulated nor physically protected glass panel. consequently, these types of collectors less efficient. pool heating applications, water heated colder ambient roof temperature, @ point lack of thermal insulation allows additional heat drawn surrounding environment.

evacuated tube

evacuated tube solar water heater on roof

evacuated tube collectors (etc) way reduce heat loss, inherent in flat plates. since heat loss due convection cannot cross vacuum, forms efficient isolation mechanism keep heat inside collector pipes. since 2 flat glass sheets not strong enough withstand vacuum, vacuum created between 2 concentric tubes. typically, water piping in etc therefore surrounded 2 concentric tubes of glass separated vacuum admits heat sun (to heat pipe) limits heat loss. inner tube coated thermal absorber. vacuum life varies collector collector, 5 years 15 years.

flat plate collectors more efficient etc in full sunshine conditions. however, energy output of flat plate collectors reduced more etcs in cloudy or extremely cold conditions. etcs made out of annealed glass, susceptible hail, failing given golf ball -sized particles. etcs made coke glass, has green tint, stronger , less lose vacuum, efficiency reduced due reduced transparency. etcs can gather energy sun day long @ low angles due tubular shape.

pump
pv pump

one way power active system via photovoltaic (pv) panel. ensure proper pump performance , longevity, (dc) pump , pv panel must suitably matched. although pv-powered pump not operate @ night, controller must ensure pump not operate when sun out collector water not hot enough.

pv pumps offer following advantages:

simpler/cheaper installation , maintenance
excess pv output can used household electricity use or put grid.
can dehumidify living space.
can operate during power outage.
avoids carbon consumption using grid-powered pumps.

bubble pump


the bubble separator of bubble-pump system

a bubble pump (also known geyser pump) suitable flat panel vacuum tube systems. in bubble pump system, closed htf circuit under reduced pressure, causes liquid boil @ low temperature sun heats it. steam bubbles form geyser, causing upward flow. bubbles separated hot fluid , condensed @ highest point in circuit, after fluid flows downward toward heat exchanger caused difference in fluid levels. htf typically arrives @ heat exchanger @ 70 °c , returns circulating pump @ 50 °c. pumping typically starts @ 50 °c , increases sun rises until equilibrium reached.

controller

a differential controller senses temperature differences between water leaving solar collector , water in storage tank near heat exchanger. controller starts pump when water in collector sufficiently 8–10 °c warmer water in tank, , stops when temperature difference reaches 3–5 °c. ensures stored water gains heat when pump operates , prevents pump excessive cycling on , off. (in direct systems pump can triggered difference around 4 °c because have no heat exchanger.)

tank

the simplest collector water-filled metal tank in sunny place. sun heats tank. how first systems worked. setup inefficient due equilibrium effect: heating of tank , water begins, heat gained lost environment , continues until water in tank reaches ambient temperature. challenge limit heat loss.

the storage tank can situated lower collectors, allowing increased freedom in system design , allowing pre-existing storage tanks used.
the storage tank can hidden view.
the storage tank can placed in conditioned or semi-conditioned space, reducing heat loss.
drainback tanks can used.

insulated tank

ics or batch collectors reduce heat loss thermally insulating tank. achieved encasing tank in glass-topped box allows heat sun reach water tank. other walls of box thermally insulated, reducing convection , radiation. box can have reflective surface on inside. reflects heat lost tank towards tank. in simple way 1 consider ics solar water heater water tank has been enclosed in type of oven retains heat sun heat of water in tank. using box not eliminate heat loss tank environment, largely reduces loss.

standard ics collectors have characteristic limits efficiency of collector: small surface-to-volume ratio. since amount of heat tank can absorb sun largely dependent on surface of tank directly exposed sun, follows surface size defines degree water can heated sun. cylindrical objects such tank in ics collector have inherently small surface-to-volume ratio. collectors attempt increase ratio efficient warming of water. variations on basic design include collectors combine smaller water containers , evacuated glass tube technology, type of ics system known evacuated tube batch (etb) collector.