Collector solar systems: how to organize heating and water supply at home with their help?

The idea of ​​​​a solar col­lec­tor is very sim­ple — the sun’s rays heat the liq­uid flow­ing through the tubes, which are made of a mate­r­i­al that absorbs heat well. In this way, it is pos­si­ble to effec­tive­ly obtain hot water for domes­tic sum­mer needs. Such solar sys­tems work espe­cial­ly suc­cess­ful­ly in sum­mer. At this time, an ordi­nary black plas­tic tank can also cope with the role of a solar sys­tem for obtain­ing hot water, which many sum­mer res­i­dents use, build­ing, for exam­ple, an impromp­tu show­er from such tanks. But solar ener­gy can be used more effi­cient­ly.

How is a solar collector system arranged?

Mod­ern col­lec­tor solar sys­tem is arranged as fol­lows. The sun’s rays heat the coolant in the col­lec­tor. This liq­uid cir­cu­lates from the col­lec­tor to the heat exchang­er in the heat­ing device — a water boil­er. Cir­cu­la­tion is car­ried out using a pump. The solar sys­tem also includes a con­trol unit (con­troller) that reg­u­lates the oper­a­tion of the pump, includes pro­tec­tion against over­heat­ing and per­forms some oth­er tasks.

Types of collectors-solar panels

The most impor­tant node is solar col­lec­tors. They account for most of the cost of the sys­tem. There are sev­er­al options for the device of solar pan­els, which can be reduced to two types. Each of these types has its own advan­tages and dis­ad­van­tages that deter­mine their scope.

flat

In them, tubes with a heat-car­ri­er liq­uid are placed under a cop­per absorber plate and enclosed in a com­mon hous­ing. From above, the absorber plate is closed with pro­tec­tive glass, from below, under the tubes, there is a lay­er of ther­mal insu­la­tion.

Flat-plate col­lec­tors are 20–30% cheap­er and less effi­cient, since tubes with coolant have worse ther­mal insu­la­tion (part of the heat goes into the atmos­phere). Para­dox­i­cal­ly, this short­com­ing turns into a virtue, for exam­ple, dur­ing snow­fall.

Tubular

In them, each tube with a coolant is mount­ed in a sep­a­rate cylin­dri­cal glass case with a reflec­tive coat­ing. The air from the case is pumped out, hence the name — “vac­u­um col­lec­tors”.

Tubu­lar col­lec­tors prac­ti­cal­ly do not heat up due to vac­u­um, and the snow does not melt on them. Worse tubes tol­er­ate hail, they are more frag­ile. In gen­er­al, tubu­lar col­lec­tors are good in ide­al cli­mates, where hail is rare and snow does not occur. Tubu­lar col­lec­tors pro­vide an almost con­stant sup­ply of heat through­out the day, this is due to the fact that the sun’s rays illu­mi­nate the sur­face of the glass cylin­der in the same way, regard­less of the posi­tion of the sun in the sky.

The pipelines of the solar sys­tem are laid in such a way that com­plete removal of air is ensured.

Comparison of properties of flat and tubular collectors

Prop­er­ty flat Tubu­lar
Work dur­ing the day Effi­cien­cy varies great­ly dur­ing the day depend­ing on the angle of inci­dence of the sun’s rays. Effi­cien­cy is almost con­stant through­out the day
Snow­fall impact Snow on the pan­el melts by itself due to par­tial heat leak­age The snow does not melt, it needs to be cleaned
Dura­bil­i­ty, impact resis­tance High Medi­um
windage High (needs a stronger base) Medi­um

Collector selection criteria

When choos­ing a col­lec­tor, pay atten­tion to the qual­i­ty of solar pan­els, sys­tem com­po­nents and the life of the absorber (sur­face exposed to sun­light).

The cost of a solar sys­tem depends on its per­for­mance, which is deter­mined by the col­lec­tor area, geo­graph­ic lat­i­tude, time of year, and a num­ber of oth­er char­ac­ter­is­tics. The cheap­est are Chi­nese, Ger­man pan­els are more expen­sive, but their ser­vice life is usu­al­ly high­er, and they can be rec­om­mend­ed for impor­tant tasks, for exam­ple, year-round hot water sup­ply.

An accu­rate cal­cu­la­tion of the sys­tem should be done by an expe­ri­enced spe­cial­ist. Sim­plis­ti­cal­ly, we can assume, for exam­ple, that a sys­tem with a col­lec­tor with a usable area of ​​3 m² in the mid­dle zone and in win­ter can pro­vide the prepa­ra­tion of approx­i­mate­ly 150 liters of hot water (with a tem­per­a­ture of about 50 ° C) in 2–3 hours in 2–3 hours. Prac­tice shows that for a small fam­i­ly (two or three peo­ple) a solar sys­tem with a col­lec­tor area of ​​​​2–4 m² and a boil­er with a capac­i­ty of 200–300 liters is enough. Such a sys­tem will cost about 100–300 thou­sand rubles. The cost of one mod­ule (with an area of ​​approx­i­mate­ly 2 m²) of the col­lec­tor ranges from 200–250$. (Chi­nese man­u­fac­tur­ers) up to 50–600 $. (Aris­ton, Buderus, Viess­mann and oth­er Euro­pean man­u­fac­tur­ers); anoth­er 40–600 $. you will have to pay for the boil­er and 10–200 $. for the con­troller, pump and mate­ri­als need­ed for instal­la­tion.

In a small house, solar ener­gy makes it pos­si­ble to pro­vide up to 60% of the ener­gy need­ed to pro­duce hot water.

How to install the collector

Heliopo­lis should be locat­ed on the unshad­ed side: fac­ing the south side or with the loca­tion west — east. If such an arrange­ment is not pos­si­ble, a cor­rec­tion fac­tor is intro­duced into the cal­cu­la­tions. It is also desir­able that there are no tall trees near­by. The angle of incli­na­tion of the col­lec­tors rel­a­tive to the hor­i­zon­tal sur­face is select­ed accord­ing to the geo­graph­ic lat­i­tude and cli­mat­ic con­di­tions, the opti­mal angle depend­ing on the sea­son of peak use. If, for exam­ple, we design a solar sys­tem for prepar­ing hot water in a cot­tage on the Black Sea coast with a May-Sep­tem­ber sea­son­al­i­ty, this angle will be 20–25 °. But if there is a need to sup­port heat­ing with this solar sys­tem, the angle should be 40–45 °.

Solar sys­tems are placed on the roof in such a way as to max­i­mize the use of solar ener­gy to heat the heat car­ri­er. For the North­ern Hemi­sphere, this would be the south side of the slope of the roof.

Solar col­lec­tor pan­els are placed in an inclined plane so that dur­ing the day they are pro­vid­ed with an angle of inci­dence of the sun’s rays as close to direct as pos­si­ble. The opti­mal slope of the col­lec­tor plane cor­re­sponds to the geo­graph­ic lat­i­tude of the area and is, for exam­ple, 57° for world. The direc­tion the pan­el is fac­ing in the North­ern Hemi­sphere should be south. And of course, the solar col­lec­tor should not be blocked from the sun by oth­er objects. It is not always pos­si­ble to with­stand all con­di­tions, there­fore, when mount­ing col­lec­tors, pre­fab­ri­cat­ed or weld­ed met­al struc­tures are wide­ly used, which can be mount­ed both on the roof and on stand-alone stands.

Choosing a boiler for a solar system

For solar sys­tems, spe­cial boil­ers with a built-in heat exchang­er are used, do not con­fuse them with the usu­al stor­age water heaters. Since the pro­duc­tion of hot water by the solar sys­tem is uneven depend­ing on the time of day, these boil­ers are cho­sen with a mar­gin of capac­i­ty in order to accu­mu­late heat with their help. There­fore, con­tain­ers with a vol­ume of 300 liters or more are often used. Sim­i­lar biva­lent water heaters are avail­able from Aris­ton, Buderus, Viess­mann and oth­er man­u­fac­tur­ers. In addi­tion to the solar ther­mal prepa­ra­tion of hot water, these boil­ers usu­al­ly pro­vide for the pos­si­bil­i­ty of addi­tion­al heat­ing from the heat­ing boil­er.

Do not for­get that if the heat is not removed to heat the water in the boil­er, then it is nec­es­sary to pro­vide a way to some­how dump the excess heat.

How to avoid overheating

A seri­ous prob­lem with the irreg­u­lar use of solar sys­tems is over­heat­ing of the col­lec­tor. Over­heat­ing can be dealt with in sev­er­al ways. The eas­i­est option is to use water as a coolant. When water boils, steam is dis­charged through a spe­cial valve, and then the lack of water is tak­en from the water sup­ply sys­tem. This method is bad because the water freezes, so it can only be used where frost is rare (in this case, the sys­tem is sup­ple­ment­ed with frost pro­tec­tion with forced heat­ing of the coolant).

Anoth­er option — drain­ing the coolant and fill­ing the col­lec­tor with air when the pump is turned off (Drain Back sys­tem) — requires a com­pe­tent cal­cu­la­tion of the sys­tem, slopes and pipe vol­umes. There is also the pos­si­bil­i­ty of adjust­ing the tem­per­a­ture of the coolant by chang­ing the oper­at­ing modes of the sys­tem by the con­troller. For exam­ple, the con­troller starts a pump at night, which pumps the heat­ed coolant through a flat col­lec­tor; the sys­tem works in reverse. This method is good in the pres­ence of a flat col­lec­tor (tubu­lar ones are not suit­able) and a capa­cious boil­er. Anoth­er inter­est­ing devel­op­ment was pro­posed by Viess­mann. Its col­lec­tors use mate­r­i­al with vari­able reflec­tiv­i­ty. When the tem­per­a­ture ris­es (say, above 90 °C), the absorp­tion capac­i­ty of the mate­r­i­al decreas­es sev­er­al times, and the coolant stops heat­ing up.

In some cas­es, a mal­func­tion of the solar sys­tem can be guessed from the appear­ance of the col­lec­tor. So, the appear­ance of frost on the tubu­lar col­lec­tor indi­cates a vio­la­tion of the tight­ness of the glass cylin­der. It has no ther­mal insu­la­tion, and this sec­tion of the col­lec­tor pro­duces very lit­tle heat.

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