SOLAR SERDAR – TYPES OF THERMAL SOLAR COLLECTORS

SOLAR SERDAR

There are basically three types of thermal solar collectors: flat-plate, evacuated-tube and concentrating.

Flat-Plate collectors comprise of an insulated, weatherproof box containing a dark absorber plate under one or more transparent or translucent covers. Water or heat conducting fluid passes through pipes located below the absorber plate. As the fluid flows through the pipes it is heated. This style of collector, although inferior in many ways to evacuated tube collectors, is still the most common type of collector in many countries.

Evacuated Tube solar water heaters are made up of rows of parallel, glass tubes. There are several types of evacuated tubes (sometimes also referred to as Solar Tubes).

Type 1 (Glass-Glass) tubes consists of two glass tubes which are fused together at one end. The inner tube is coated with a selective surface that absorbs solar energy well but inhibits radiative heat loss. The air is withdrawn (“evacuated”) from the space between the two glass tubes to form a vacuum, which eliminates conductive and convective heat loss. These tubes perform very well in overcast conditions as well as low temperatures. Because the tube is 100% glass, the problem with loss of vacuum due to a broken seal is greatly minimized. Glass-glass solar tubes may be used in a number of different ways, including direct flow, heat pipe, or U pipe configuration. Apricus uses a high efficiency heat pipe and heat transfer fin design to conduct the heat from within the evacuated tube up to the header. For more information about heat pipes,click solarserdar@gmail.com.

Type 2 (Glass-Metal) tubes consist of a single glass tube. Inside the tube is a flat or curved aluminium plate which is attached to a copper heat pipe or water flow pipe. The aluminium plate is generally coated with Tinox, or similar selective coating. These type of tubes are very efficient but can have problems relating to loss of vacuum. This is primarily due to the fact that their seal is glass to metal. The heat expansion rates of these two materials. Glass-glass tubes although not quite as efficient glass-metal tubes are generally more reliable and much cheaper.

Type 3 (Glass-glass – water flow path) tubes incorporate a water flow path into the tube itself. The problem with these tubes is that if a tube is ever damaged water will pour from the collector onto the roof and the collector must be “shut-down” until the tube is replaced.

Concentrating collectors for are usually parabolic troughs that use mirrored surfaces to concentrate the sun’s energy on an absorber tube (called a receiver) containing a heat-transfer fluid, or the water itself. This type of solar collector is generally only used for commercial power production applications, because very high temperatures can be achieved. It is however reliant on direct sunlight and therefore does not perform well in overcast conditions.

Types of Solar Water Heating Systems

Solar water heating systems (SWHS) can be either active or passive. An active system uses an electric pump to circulate the fluid through the collector; a passive system has no pump and relies on thermo-siphoning to circulate water. The amount of hot water a solar water heater produces depends on the type and size of the system, the amount of sun available at the site, installation angle and orientation. SWHS are also characterized as open loop (also called “direct”) or closed loop (also called “indirect”). An open-loop system circulates household (potable) water through the collector. A closed-loop system uses a heat-transfer fluid (water or diluted antifreeze) to collect heat and a heat exchanger to transfer the heat to the household water. A disadvantage of closed looped system is that efficiency is lost during the heat exchange process.

Active Systems

Active systems use electric pumps, valves, and controllers to circulate water or other heat-transfer fluids through the collectors. They are usually more expensive than passive systems but generally more efficient. Active systems are often easier to retrofit than passive systems because their storage tanks do not need to be installed above or close to the collectors. If installed using a PV panel to operate the pump, an active system can operate even during a power outage.

Open-Loop Active Systems
Open-loop active systems use pumps to circulate household potable water through the collectors. This design is efficient and lowers operating costs but is not appropriate if water is hard or acidic because scale and corrosion will gradually disable the system. Open-loop active systems are popular in regions that do not experience subzero temperatures. Flat plate open-loop systems should never be installed in climates that experience sustained periods of subzero temperatures. The ApricusTM AP solar water heater can be installed in an open loop in areas that experience sub-zero temperatures as long as the solar controller has a low temperature fuction.

Closed-Loop Active Systems
These systems pump heat-transfer fluids (usually a glycol-water antifreeze mixture) through the solar water heater. Heat exchangers transfer the heat from the fluid to the water that is stored in tanks. Double-walled heat exchangers or twin coil solar tanks prevent contamination of household water. Some standards require double walls when the heat-transfer fluid is anything other than household water. Closed-loop glycol systems are popular in areas subject to extended subzero temperatures because they offer good freeze protection. However, glycol antifreeze systems are more expensive to purchase and install and the glycol must be checked each year and changed every few years, depending on glycol quality and system temperatures.

Drainback systems use water as the heat-transfer fluid in the collector loop. A pump circulates the water through the solar water heater. When the pump is turned off, the solar water heater drains of water, which ensures freeze protection and also allows the system to turn off if the water in the storage tank becomes too hot. A problem with drainback systems is that the solar water heater installation and plumbing must be carefully positioned to allow complete drainage. The pump must also have sufficient head pressure to pump the water up to the collector each time the pump starts. Electricity usage is therefore slightly higher than a sealed closed or open loop.

SOLAR SERDAR collectors are ideal for use in active (open or closed) systems.

Passive Systems

Passive systems move household water or a heat-transfer fluid through the system without pumps. Passive systems have the advantage that electricity outage and electric pump breakdown are not issues. This makes passive systems generally more reliable, easier to maintain, and possibly longer lasting than active systems. Passive systems are often less expensive than active systems, but are also generally less efficient due to slower water flow rates through the system.

Thermosiphon Systems
A thermosiphon system relies on warm water rising, a phenomenon known as natural convection, to circulate water through the solar absorber and to the tank. In this type of installation, the tank must be located above the absorber tubes/panel. As water in the absorber heats, it becomes lighter and naturally rises into the tank above. Meanwhile, cooler water in the tank flows downwards into the absorber, thus causing circulation throughout the system. This system is widely used with both flat plate and evacuated tube absorbers. The disadvantages of this design are the poor aesthetics of having a large tank on the roof and the isses with structural integrity of the roof. Often the roof must be reinforced to cope with the weight of the tank.

Batch Heaters
Batch heaters are simple passive system consisting of one or more storage tanks placed in an insulated box that has a glazed side facing the sun. Batch heaters are inexpensive and have few components, but only perform well in summer when the weather is warm. Evacuated tube solar collectors are now an affordable and much more efficient alternative to either batch or flat plate collectors.

SOLAR SERDAR

solarserdar@gmail.com

About CROATIAN CENTER of RENEWABLE ENERGY SOURCES

CROATIAN CENTER of RENEWABLE ENERGY SOURCES (CCRES)• was founded in 1988 as the non-profit European Association for Renewable Energy that conducts its work independently of political parties, institutions, commercial enterprises and interest groups, • is dedicated to the cause of completely substituting for nuclear and fossil energy through renewable energy, • regards solar energy supply as essential to preserve the natural resources and a prerequisite for a sustainable economy,• acts to change conventional political priorities and common infrastructures in favor of renewable energy, from the local to the international level, • brings together expertise from the fields of politics, economy, science, and culture to promote the entry of solar energy, • provides the opportunity to play a part in the sociocultural movement for renewable energy by joining the association for everyone, • considers full renewable energy supply a momentous and visionary goal - the challenge of the century to humanity. CCRES Željko Serdar Head of association solarserdar@gmail.com
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2 Responses to SOLAR SERDAR – TYPES OF THERMAL SOLAR COLLECTORS

  1. solarserdar says:

    SOLAR SERDAR
    • was founded in 1988 as the non-profit European Association for Renewable Energy that conducts its work independently of political parties, institutions, commercial enterprises and interest groups,

    • is dedicated to the cause of completely substituting for nuclear and fossil energy through renewable energy,

    • regards solar energy supply as essential to preserve the natural resources and a prerequisite for a sustainable economy,

    • acts to change conventional political priorities and common infrastructures in favor of renewable energy, from the local to the international level,

    • brings together expertise from the fields of politics, economy, science, and culture to promote the entry of solar energy,

    • provides the opportunity to play a part in the sociocultural movement for renewable energy by joining the association for everyone,

    • considers full renewable energy supply a momentous and visionary goal – the challenge of the century to humanity.

    SOLAR SERDAR
    solarserdar@gmail.com

  2. solarserdar says:

    Solarni vakumski kolektor s vakumskim cijevima najnovije tehnologije omogućuje grijanje vode čak i tijekom zimskih mjeseci ili po potpuno oblačnom vremenu te predstavlja odličan izbor za grijanje tople vode u pasivnim kućama. Visoki vakum u vakumskim cijevima solarnog vakumskog kolektora čini solarni vakumski kolektor višestruko učinkovitijim od klasičnog kolektora. Konstrukcija solarnog vakumskog kolektora predstavlja najnoviju tehnologiju izrade vakumskih cijevi promjera 100mm i suhog spoja unutar kolektora. Solarni vakumski kolektor svojim učinkom nadmašuju sve ostale tipove kolektora čak i zimi. Najnovija 4. generacija solarnog vakumskog kolektora maksimalno je učinkovita tijekom cijele godine, ne samo tijekom ljetnih mjeseci.

    Korištenjem tehnologije suhe grijačeg spoja unutar vakumske cijevi, solarni vakumski kolektor osigurava nam korištenje zagrijane tople vode čak i zimi, po oblačnim danima kad su drugi solarni kolektori neupotrebljivi.

    Srce svakog solarnog vakumskog kolektora je staklena vakumska cijev. U njoj je namješteno pet osnovnih dijelova kojima je zadaća da absorbiraju solarno zračenje i pretvaraju ga u toplinu.Više na solarserdar@gmail.com.

    Kondezator
    Na vrhu Heta Pipe cijevi nalazi se kondezator koji se suhim spojem spaja s toplinskim kolektorom
    Heat Pipe (toplinska cijev)
    Heat Pipe je cijev koja se prostire po cijeloj duljini absorbera. To je toplinski element s visokim stupnjem toplinske vodljivosti 4000 – 8000 više od srebra, kovine koja najbolje prenosi toplinu. Toplina se iz absorbera prenosi na Heat Pipe u kojem se nalazi specijalan medij koji ima svojstvo da se može konstantno pretvarati iz plinovitog u tekuće stanje i obratno čak i pri nižim temperaturama. Kad se medij zagrije visoka temperatura putuje gore prema kondezatoru koji zagrijava vodu u toplinskom kolektoru, koji se nalazi na vrhu kolektora i u kojem su uronjene Heat Pipe cijevi.
    Absorber
    Izraden je iz čistog aluminija visoke kvalitete. Namijenjen je upijanju i prijenosu sunčeve energije. Apsorber je tretiran aluminij-nitridnim selektivnim premazom kako bi se postigla najviša učinkovitost prijenosa topline. Premaz se nanosi pomoću magnetske tehnike raspršivanja. Ovaj posebni optički premaz transformira više od 92% dolaznog zračenje u toplinu.
    Staklena cijev
    Izrađena je iz borosilikatnog stakla koji ima veliku otpornost na udarce i tuču. Niska količina željeza omogućava visoki postotak prolaska sunčevog zračenja kroz staklo.
    Visoki vakum
    Da bi se smanjio gubitak topline konvekcijom, staklene cijevi su evakuirane u vakuumu pod pritiskom <10-5 mbar. Solarni vakumski kolektori 4. generacije koriste patentiranu tehniku korištenja visoke temperature i pritiska da se osigura nepropustan spoj stakla na metal vakuumske brtve. Kako bi zadržali stabilnost vakuuma za dugi period koristi se barijev tzv. "živi oganj". Evakuiranjem zraka iz staklene cijevi apsorbera sav materijal i selektivni premaz su zaštićeni od korozije i drugih utjecaja okoline.

    Apsorber i Heat Pipe cijevi su instalirani u visoko stabilnu borosilikatnu vakuumsku staklenu cijev. To spriječava oštećenje i gubitak topline koji se javlja u konvencionalnim solarnim kolektorima.Više na solarserdar@gmail.com.

    Kako bi se osigurala visoka učinkovitost apsorpcije, a pogotovo za oblačnih dana. Absorber je tretiran aluminij-nitridnim selektivnim premazom.
    Solarni vakumski kolektori absorbiraju veliki dio sunčeve energije pri niskom intezitetu svjetlosti, npr. Kod 200Wm2 kolektori ce lako osigurati 58% učinkovitosti i podignuti temperaturu medija preko 20°C iznad vanjske temperature.

    Solarni vakumski kolektori odlikuju se dugotrajnim zadržavanjem topline. Solarni vakumski kolektori imaju cijevi koje su visokovakumirane te sprjecavaju gubitak topline iz cijevi. Emisijski gubici su minimalni. Vakumske cijevi su opremljene toplinskom diodom koja potpuno sprjecava povratak topline iz toplinskog kolektora nazad prema absorberu.

    SOLAR SERDAR
    CENTAR ALTERNATIVNIH IZVORA ENERGIJE
    solarserdar@gmail.com

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