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Advantages and disadvantages of vacuum tube solar collector and flat plate solar collector

Views:7     Author:Site Editor     Publish Time: 2019-05-05      Origin:Site

I. Several kinds of plate collectors for flat panel solar water heater:

Copper-aluminium composite anodized plate-core collector; all-copper selective coating plate-core collector; all-copper titanium nitride coating plate-core collector.  

2. Fabrication methods of flat panel solar collectors:

The plate core of flat solar collector and its manufacturing method: the plate core is composed of two metal sheets overlapped together, and joined together by a seam-biting process around the plate core, the plate heat absorber is made, with galvanized plate and insulating cotton pad at the bottom, glass plate covering at the top and rubber strip sealing around the plate core. The groove bottom of the groove on the light receiving panel is connected with the back panel stamping and transverse and longitudinal fluid channels interconnected are formed.

3. The characteristics of flat panel solar energy:

3.1. Flat-panel solar energy has been invented and applied in the 1970s. 

Since the invention of vacuum tube solar energy in the 1980s, flat-panel solar energy has been gradually withdrawn from the market in the whole industry (in the provinces like Guangdong, Yunnan, Hainan etc., Flat-panel solar energy is still prompted and used). Solar water heaters have also experienced  the process of development: from steaming solar energy, flat-panel solar energy, vacuum tube solar energy to vacuum tube solar energy.  

3.2. The working principle of flat panel solar energy is to use the principle of glass greenhouse effect to heat hot water. 

The low efficiency of flat panel solar energy can be seen from the way it is made. Some solar companies show its high thermal efficiency, such as high absorption rate: as > 92%, low emissivity:εh≤10%, and daily average thermal efficiency ηd≥55%. It's a sign of irresponsibility. As a kind of heat collector, it can absorb heat and dissipate heat at the same time. There are only three ways of heat transfer: radiation, conduction and convection. The three heat dissipation and heat transfer modes of flat panel solar energy are obvious, and the emissivity increases with the increase of water temperature in the collector. In fact, the thermal efficiency of flat panel solar collectors is less than 54%.  

3. 3 Service life of flat panel solar energy: 

Copper-aluminium composite process is adopted, copper runner and aluminium endothermic fins are formed after rolling, and selective endothermic coating is formed on the surface of plate core by anodizing treatment, or high-quality selective coating or electroplated black chromium coating is adopted. A. Because the coating materials are exposed to sunlight and oxidized by oxygen in the air, they begin to age in three to five years and become light white, as can be seen from the example of flat panel solar energy project installed. B. The copper tube of collector is easy to produce copper green under the action of water. It becomes thinner under the erosion of water, especially the welded joint, which is easy to perforate after several years. It is also an indisputable fact that flat solar energy and heat pump heat exchangers using copper tube are the same. C. Flat-plate solar collector is metal tube-plate type of structures, which usually have a life of 5 to 8 years and often has problems of water leakage and lower efficiency. The so-called futures like stable and reliable quality, maintenance-free are the performance of the early installation. The company who announces it has long life of fifteen years is an industry cheater.

3.4. The impact of various environments: 

Fast heat dissipation, poor heat preservation effect, no freezing resistance; flat panel solar water heater has futures as large resistance to typhoon and oppose to typhoon poorly; large external impact on the glass plane, poor hail resistance; What is so-called suitable for use in Guangdong, Fujian, Yunnan, Guangxi, Hainan and other areas should be understood as being able to deceive customs clearance. Because in the above areas, the winter which is about four months need the most energy-saving. While they went on strike when save energy is needed.   

3.5. Different application industries have different effects. 

Hotels that supply hot water all day have lower thermal efficiency because they require hot water supply all day. This requires solar collectors to operate at relatively high temperatures and dissipate more heat. It is better to use solar collectors in factories, schools and other places where hot water is regularly supplied at night, because cold water can be supplied in the morning so that solar energy system can be used. Relative to working at low temperature, the efficiency is higher than operating at high temperature, but the thermal efficiency of the system is less than 36% under any conditions.

3.6. Reasons for promoting the type of flat plate:

Collectors are easy to produce and manufacture; when supporting solar energy projects, there is no need for connecting boxes, underpinnings and other supporting facilities of vacuum tubes, the cost is low. Under the same price of two kinds of solar energy, higher interests can be pursued; under the premise that the vacuum tube is easy to break, solar energy enterprises can avoid more maintenance; and most customers can be utilized when the concept of heat saving is not clear to households, only promote the concept of solar energy, such as environmental protection, energy saving, safety and other concepts, without installing energy meters, water meters... Uses various methods to promote customer acceptance and acceptance; in Guangdong, often several large solar energy companies unite with each other in the promotion and marketing process, using certificates issued by Guangdong Solar Energy Association (not scientific basis) to surround monopoly customers; in Guangdong, Fujian, Hainan and other areas, the enterprises who use solar energy are liable to be deceived, then accepted.

3.7. The application status of flat panel solar energy: 

In China only accounts for less than 5% of the total. In the international community, except for a few developed countries and regions, due to paying more attention to aesthetics and other factors, especially large investment, installing large areas to meet the needs of use. In addition, the factors like vacuum tube solar energy was invented in China, and so on, flat panel solar energy has been promoted abroad so far.

3.8. Examples of the application of flat panel solar energy in engineering (respectively, the flat panel solar hot water projects of the larger solar companies in Guangdong Province) and the harm they bring: 

As far as I know,.

A. The 1800 students of Shimen Experimental School in Nanhai, Foshan, installed 1200 square meters with flat panel solar energy. As a result, they consumed 210,000 litres of oil annually, more than 50,000 litres of energy than those who directly used oil-fired boilers.   

B. The flat panel solar energy installed in Shenzhen No. 1 Rehabilitation-through-Labor Institution has only been used for three years because of its high energy consumption with electric auxiliary, and has been discontinued for six years.   

C. South China Sea China-US Toy Factory, after using flat panel solar energy, all of them were demolished that year, with an investment of 400,000 yuan, and finally only 30,000 yuan.   

D. Danzao Town Middle School in South China Sea, when bidding for solar hot water project, 12 families were promoting flat-panel solar energy, only one Snowball promoted vacuum tube solar energy, and finally installed flat-panel solar energy, resulting in energy consumption of about 40,000/month (only about 1400 students) in winter 2006 (less rain and sufficient sunshine). In that year, Shenzhen Pingdi Yaosheng Shoe Factory adopted Snowball vacuum tube solar energy. 600 workers consume only 1600 yuan per month.   

E. The use of flat-panel solar energy in hotels: for example, Huatong Building Hotel in Futian, Shenzhen, uses 900 tons of water per month, or 30 tons per day, installs 720 square meters of flat-panel solar energy and 35 tons of water tank, and finally consumes about 30,000/month in summer and 50,000/month in winter in 2006. Flat-panel solar energy has little effect. Luyin four-star hotel in Jungqi, Shunde, uses flat-panel solar energy with little energy-saving effect. More hotels use flat-panel solar energy because of the unsatisfactory energy-saving effect many eventually were demolished.   

F. Official Hill Hotel in Xiqiao, South China Sea has installed flat-panel solar energy. In the past four years, the installation company has only received 30% of the first installment due to the discovery that solar energy is not energy-efficient by private enterprises. The installation company wants to use Guangdong Solar Energy Association to solve the problem, but in the end, because it can not change the fact of non-energy-saving, it still can not be done till now.   

G. Because of the disadvantages of flat panel solar energy, it has no energy-saving effect in high-demand industries such as hotels. In the promotion process, flat panel solar energy is often installed in a large number of state enterprises and institutions, regardless of the energy-saving effect. As for hotels and private enterprises, they seldom accept it. Many of them show that they are victims of solar energy, or even excluded. That's why oil prices are high and solar energy is not widely used by enterprises. The irresponsible promotion of solar energy enterprises is the fundamental reason for the slow development of hot water project in Guangdong Solar Hotel.   

H. Because flat solar energy has great shortcomings compared with vacuum tube solar energy, before 2006, every large solar energy enterprise in Guangdong tried to promote flat solar energy in a large part of the company's website to elaborate the advantages of flat solar energy, but now, when they publicize the advantages of flat solar energy on the website, they only downplay it, which proves that flat solar energy. It's really going to be eliminated.   

4. Characteristics of vacuum tube solar collectors:

The structure of vacuum tube solar collector is divided into inner and outer tubes with mercury coating on the inner tube wall, endothermic coating on the outer wall of the inner tube, and vacuum layer between the inner and outer tubes. The outer tubes are transparent glass, and the inner and outer tubes are made of high hardness borosilicate glass; one end has an inlet and outlet, and the other end is closed.   

4.1. Flat-panel solar energy has been invented and applied in the 1970s. Since the invention of vacuum tube solar energy in the 1980s, flat-panel solar energy has slowly withdrawn from the market in the whole industry, which now accounts for less than 5% of the total market in China. Solar water heaters have also experienced the development of steaming solar energy, flat-panel solar energy, vacuum tube solar energy and vacuum tube solar energy in the 1960s. Three high vacuum tubes and vacuum heat pipe vacuum tubes have been developed in vacuum tubes.   

4.2. The working principle of solar energy in vacuum tube is to absorb sunlight by using heat absorbing coating of inner tube, heat water in Inner tube, exchange with water tank or connecting tank, and raise water temperature. As a kind of heat collector, it can absorb heat and dissipate heat at the same time. There are only three ways of heat transfer: radiation, conduction and convection. The three ways of heat dissipation and heat transfer of vacuum tube solar energy are very small, the mercury coating of inner tube prevents heat radiation, the vacuum layer between inner tube and outer tube prevents heat conduction, and the convective heat emission of vacuum tube solar energy is almost zero. The thermal efficiency is 93.5% higher than that of flat panel solar energy by 50-80%.

4.3. The service life of vacuum tube solar energy: because its material is high borosilicate glass, and the inner and outer coatings are not oxidized in the vacuum environment, the service life of vacuum tube solar energy is more than 20 years without external force.   

4.4. The influence of various environments: small heat dissipation, good heat preservation effect, strong anti-freezing ability (excellent performance in Antarctica); small resistance to typhoon and strong anti-typhoon ability of vacuum tube; circular shape of vacuum tube is small by external impact, strong anti-hail ability.   

4.5. The thermal efficiency of the vacuum tube solar tube is 93%, and that of the system is 46%. Snowball vacuum tube solar energy technology system thermal efficiency can reach 75%, so that boiled water can be directly produced.   

4.6. Reasons for popularizing vacuum tubes: new technology, high efficiency.   

4.7. The application status of vacuum tube solar energy: in our country, it accounts for more than 95%, and in the world, the export of vacuum tube solar energy is absolutely superior to that of flat plate solar energy.   

4.8. The engineering application of vacuum tube solar energy and its harm: it is the mainstream in the whole country and the development direction of solar hot water.

Schedule 1: Comparison of instantaneous heat gain and temperature rise between flat plate collector and U-tube collector:


Schedule 2: Comparisons between Vacuum Tube and Plate Solar Energy:


Flat panel solar energy

Vacuum tube solar energy

Efficiency of Vacuum Tube Circulation System

Efficiency of Vacuum Tube Constant Temperature System

thermal efficiency





Invention time





Service life





Freeze proof and windproof





Application ratio

Now 5%


More than 99%

Very seldom

Use area

Small area

Throughout the country

Throughout the country

Throughout the country

technical requirement

Simple and easy




Leakage and Maintenance

Less in the early stage and no remedy in the later stage

When the temperature difference between water and temperature is large (glass properties)

Less skilled

High technology and less

Endothermic area

Front and rear shielding affected by installation position

Front and rear shielding affected by installation position

Front and rear shielding affected by installation position

A plane, full use

Debugging situation




Technical requirements

Schedule 3: Performance comparison between vacuum tube collector and flat plate coll-ector

Serial number


Vacuum tube collector

Flat plate collector



More than 95%

Less than 80%


Heat loss rate

Less than 6%

More than 20%


Total thermal efficiency

More than 85%

Less than 60%


Air drying temperature




Maximum water temperature

125 Temperature (hot gasification)



Use area

Limit the tropics to any latitude.

Subtropical Region (South of Yangtze River)


Application scope

It can be used in high temperature state.

For cryogenic forms only



Simple and convenient

Require professional and technical personnel


Breakage treatment

Partially replaceable

Need to be repaired as a whole


Scaling during service life

20 years, scaling easy to clean

5-8 years, efficiency decay fast




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