The connection between the flat solar collector and the system is a metal connection, which is less affected by the environment and can ensure the stability of the entire system, resulting in good thermal performance of the product. Flat panel solar collectors and hot water systems are safe and reliable, with a large effective lighting area and high thermal efficiency.
- Advantages of Flat Plate Solar Collectors
1.1 High thermal efficiency
Firstly, in terms of daily average efficiency, flat plate solar collectors are superior to vacuum tube solar collectors. At present, the thermal efficiency of flat plate solar collectors is generally 60%, while the thermal efficiency of vacuum tube solar collectors is generally 50%. When the water temperature inside the collector is below 50 ℃, the instantaneous thermal efficiency of the flat plate collector is greater than that of the vacuum tube collector. The temperature of ordinary solar collectors is generally medium or low, so the instantaneous efficiency of flat plate collectors is higher than that of vacuum tube collectors during operation.
The average daily efficiency of flat solar water heaters is between 48% and 58%; The average daily efficiency of all glass vacuum tube solar water heaters is between 45% and 55%. The thermal efficiency of flat solar water heaters is about 5% higher than that of all glass vacuum tube solar water heaters. Even in winter in the south, under the same conditions, the average daily efficiency of flat plate solar water heaters is about 4% higher than that of all glass vacuum tube solar water heaters. So within a year, under the same conditions, a flat plate water heater can provide more hot water, even in the cold winter, using a flat plate water heater can achieve good results.
1.2 Beneficial for the use of circulatory systems
At present, solar water heaters in China mainly use compact natural circulation systems, which are characterized by simple manufacturing and low prices. But if we look at the weight, ease of use, safety, and operability of solar water heaters, the separated forced circulation system can better meet people’s requirements. Flat plate collectors are generally made of metal, and the connection between the collector and the water storage tank is made of metal, which can withstand high water pressure and has good sealing performance. The connection between the heat collection pipe and the storage tank of a vacuum tube water heater is generally sealed with plastic or rubber, which results in poor pressure and sealing performance. In a flat plate solar collector, the heat transfer medium can flow unobstructed between the collector and the heat exchanger in the storage tank, heating the water in the storage tank through the heat exchanger and completing the dual circulation of the system. This is also the obvious advantage of flat plate solar water heaters. In addition, flat plate solar collectors are mainly made of metal materials such as copper and aluminum, and their product materials have a high recycling rate.
1.3 Good Pressure Bearing Performance
Good pressure resistance is a development trend of solar water heaters. A significant advantage of flat panel solar water heaters is their excellent pressure bearing performance. Flat plate solar collectors can withstand pressure, have a long lifespan, and are easy to form secondary circuit systems. Most foreign solar water heaters have a dual circuit pressure bearing split structure. If the vacuum tube solar water heater is made into a pressure bearing split structure product, its cost will be significantly higher than that of flat plate products. Relatively speaking, flat solar water heaters will be more popular among users.
1.4 Stable Performance When Forming A Large System
For some large places, such as hotels, swimming pools, schools, factories, hospitals, etc., when using solar water heaters, it is often necessary to use many solar collectors to form a large-scale water supply system.
The connection between the flat solar collector and the system is a metal connection, which is less affected by the environment and can ensure the stability of the entire system, resulting in good thermal performance of the product.
- Flat panel solar collectors and hot water systems are safe and reliable, with a large effective lighting area and high thermal efficiency.
Based on the many advantages of flat plate solar collectors and fully drawing on foreign experience and technological innovation, China has developed high-performance selective absorption coatings and high-performance new flat plate collectors and water heaters with independent intellectual property rights. This is of great significance for completing China’s renewable energy plan and achieving the phased goals of energy conservation and emission reduction.
Currently, most flat panel solar water heaters on the market adopt EU standards. At present, the world’s most advanced fourth generation high-efficiency flat plate solar hot water system can withstand a static load of 1500 kilograms and a free fall impact of 1040 grams of steel balls at a height of 0.6 meters. The unit effective lighting area can be increased by more than 40% compared to vacuum tube solar energy, and the heat collection efficiency is as high as 80%. Its service life is twice that of domestic vacuum tube pressure bearing products.
Through optimized design, the flat solar water heater can achieve separation of collection and storage, with each component installed independently. The hot water storage tank can also be hidden in the basement, attic, or stairwell, solving problems such as waterproofing, aesthetics, and load-bearing capacity. It greatly meets the requirements of integrating solar energy with buildings and can be extended to more than 20 solutions that are integrated with buildings, such as embedded, curtain wall, balcony wall mounted, floor standing, tiled, and gallery style.
The series of practical examples from the current weak market situation to the development against the trend show that China’s solar thermal utilization market is gradually showing a trend of centralization. Retail may no longer be a large proportion module for enterprise sales, and the engineering market will become popular. Overseas exports will also become an important aspect to make up for the insufficient domestic sales. In these aspects, high-performance and high-quality flat solar products are obviously more favored than vacuum tube solar products. Many solar energy manufacturing companies have also started to invest in flat panel projects, giving birth to a group of professional enterprises that produce flat panel solar energy. By observing the market and predicting the development of various solar energy companies, the changing market environment may usher in a new opportunity for the development of flat panel solar energy in China in all aspects.
2.The Development Direction Of Flat Plate Solar Collectors
The key to the development of flat panel solar energy is technological innovation, developing products that meet consumer needs. Improving technology and reducing costs are important avenues for the development of flat panel solar energy. To meet consumer demand for flat panel solar products, four technical issues need to be addressed: cover plate technology; Efficient heat absorption technology; Improve insulation and sealing performance; Reduce heat loss technology; Develop process equipment, achieve industrial production, improve efficiency, and reduce costs. We need to carefully study market development trends and consumer demands, and innovate in product development
- Develop balcony wall mounted flat panel solar energy. Balcony wall mounted flat panel solar energy split installation, easy to construct, can solve the problem of insufficient rooftop area in high-rise buildings; Users are not limited by floor, suitable for retail promotion; In line with the trend of integrating solar energy and buildings, it can enjoy policy support.
- Develop a combination product of flat panel and condensing gas boiler. This is the commonly used hot water system in Europe, which can meet the dual needs of hot water and heating. Buildings with heating needs in the Yangtze River Basin and cold northern regions of China can choose the system combination of flat panel solar water heaters and condensing gas boilers.
This product has product differences caused by functional complexity, and there is successful experience to draw on, which can form a performance differentiation from other tablet products and is more suitable for terminal retail promotion. The application form of the combination product of flat panel and condensing gas boiler is manifested in that multi story and high-rise buildings can choose to connect the balcony mounted flat panel solar energy and condensing boiler in series; Villas or sloping buildings can use flat split solar energy and condensing gas boilers in parallel, with dual coil heat exchange water tanks for separate heating; Public and commercial places can choose a combination of floor standing condensing gas boilers and flat panel solar centralized systems.
In response to the technological and quality gap between domestic flat plate collectors and foreign ones, the following measures should be taken to improve the performance and quality of flat plate collectors:
1) Research and develop selective coatings suitable for flat solar collectors, which should have high absorption, low infrared emissivity, excellent heat, moisture, and weather resistance, and suitable processing costs;
2) Widely used is low iron high transmittance cover glass. At present, multiple glass manufacturers have started producing low iron glass suitable for solar collectors, and the quality gap between domestic and foreign glass is becoming smaller and smaller;
3) Emphasize the optimization design of collectors, improve manufacturing processes, ensure structural tightness, and reduce heat dissipation losses of collectors;
4) Using tempered glass as the cover plate for the collector to improve the quality of collector components, adopting optimized structural design to ensure that the collector can withstand performance tests such as hail, rain, air exposure, pressure resistance, and thermal shock, thereby increasing the lifespan of the collector and reducing system maintenance costs;
5) To meet the special requirements of cold regions, solar heating and air conditioning, and industrial heating, efficient flat plate collectors should be developed. Accelerate the industrialization of technologies such as double-layer cover plates and transparent honeycomb, and improve their cost-effectiveness to make high-efficiency flat plate collectors more competitive in the market;
6) Track advanced technologies and processes of flat plate collectors abroad, develop new solar systems for flat plate collectors, and increase market share of flat plate collectors.
In the next article, we will discuss the application prospects of flat panel solar collectors.
