In the more than a decade of the 21st century, energy shortages and environmental degradation have become increasingly prominent. Developing renewable energy instead of traditional energy is the only way to solve the above problems. Due to its huge reserves, clean use, and wide distribution, solar energy has become the most popular renewable energy source in recent years. All major countries in the world have made the photovoltaic industry one of the research focuses and have launched their own plans. For example, California is fully promoting the Million Roof Project, the EU White Paper for Renewable Energy Project, and the German Solar Energy Access Subsidy Program.
In China, due to the support of national policies, the industrial application of solar photovoltaic industry has also been rapidly developed. The Golden Sun demonstration project and the solar photovoltaic building application project led by the Energy Development Bureau of the National Development and Reform Commission and the Ministry of Housing and Urban-Rural Development, and the distributed power generation plan launched at the end of 2012, and the new energy development quota target have been Five "planning.
China's future will focus on the development of BIPV
At present, China's solar energy industry has ranked first in the world. It should be noted that for the eastern coastal economic zone in the economically active areas, energy shortage after urbanization, building accumulation, and small land are not conducive to the development of large-scale ground-based photovoltaic power plants, but it is very suitable for the development of BIPV. Although the scale of a single BIPV project is small, it drowns the sea and supplements the shortage of electricity on the spot, and it also solves the long-distance transmission problem of the loss of photovoltaic power plants.
After years of development of domestic photovoltaic applications, no matter whether it is industrial development orientation or actual policy effect, from this year onwards, the transition from large-scale ground power station applications to distributed generation mode has gradually begun, and distributed generation based on buildings has entered the golden decade development cycle.
The BIPV power generation model will become the key development direction of China's solar energy applications with its advantages of “low space cost, low power transmission and transformation costs, and low integrated installation cost†and the following characteristics.
After many years of industrial progress, building materials photovoltaic products are now mature and able to meet the current market demand.
In terms of price, building-material photovoltaic products (such as thin-film modules for photovoltaic curtain walls and photovoltaic tiles) have obvious comparability and feasibility compared with other similar high-grade materials, and they are in terms of size, color, strength, power safety, and construction. Aesthetics and other aspects can also meet the special requirements of building applications, product light transmittance, color, structure can be customized according to building requirements for production.
The additional type (BAPV) applications of industrial plants will be phased out due to low integration with the buildings.
The roof of a large number of industrial plants adopts a colored steel structure rather than a concrete structure, which makes the roof bearing and the age of use very risky. As we all know, the service life of the roof of the Caigang structure is limited to 15 years (it has been less than 15 years since the construction of the photovoltaic project), but the agreement signed by the PV generation is 25 years, and the two do not match at all.
The residential roof is a concrete structure that can effectively avoid this problem. The principle of roof photovoltaic applications in industrial enterprises is to use high-energy-consumption and self-use power grids. After entering the “Twelfth Five-Year Plan†period, the transformation of industrial structure in coastal developed areas will determine that such enterprises will become less and less, and high-energy-consuming industrial enterprises are not the direction that the state encourages to develop. In addition, due to the stability of industrial roofs and the requirements of bearing weight, etc. With regard to the restrictions, the shortage of industrial roof resources has suddenly emerged, which has also led to the ever-increasing use of photovoltaic space on the roofs of industrial enterprises.
The application of residential roofs can effectively avoid many key constraints in the application of industrial roofs. It is more feasible to analyze the feasibility of projects and business models. It takes up to 25 years for the power purchase agreement signed between the company and the roof owner, and the ownership of the residential property is clear and stable. There are no uncertain risks in the operations, changes, reconstructions, etc. of the photovoltaic power plant application project, so the risk of its business model is small. The stable income from electricity bills is a good type of project that actively explores and promotes demonstration of photovoltaic applications in China.
Commercial buildings, with their advantages of high power generation efficiency, large installed capacity, small use loss, long retention time, good demonstration effect, etc., will be the key demonstration directions for provinces and cities.
Since different orientations have a greater impact on power generation, rooftop projects are the most efficient BIPV location, while commercial buildings are known for their large roofs and are mostly idle roofs. For example, commercial buildings such as the Yiwu Small Commodity Market have a roof area of ​​more than 10,000 square meters and an installed capacity of more than 1MWP. This is a big asset in the BIPV project.
In addition, large and large businesses generally rely on power supply lighting, and their business hours are mostly daytime and without interruptions. They can be used without electricity storage equipment, which reduces investment, and do not require long-distance transmission. Local consumption is small.
In addition, commercial buildings are generally permanent buildings. The design service life is generally 50 years. The development time is short. The actual plant life can be equal to or exceed the equipment life of the photovoltaic power station, and the concentration of people is more suitable for new products and new technologies. Promotion.
The government will also adopt certain mandatory and encouraging measures to vigorously promote the demonstration work of commercial buildings. Compulsory measures for developers include large-scale commercial buildings that need to meet the requirements of the construction green certification design and operation of the two-star or Samsung, and the incentives for the developers include While subsidizing the country’s green building, local governments can also provide incentive funds, and give certain incentives for land sales, project approval, and taxation. The functional departments can set development goals and encourage functional departments to actively coordinate the relationship between developers and power plant investment operators, and promote the development of commercial BIPV.
Attention in BIPV design
The battery pack form and specifications need to be diversified.
Component types include conventional monocrystalline silicon cells, polycrystalline silicon cells, microcrystalline thin-film cells, amorphous thin-film cells, and soft-film cells, as well as derivative products such as solar photovoltaic tiles. Crystal silicon battery components can be formatted according to a variety of architectural sizes, and can also be made of different light-transmitting plates according to architectural lighting and aesthetic requirements. There are many manufacturers of thin-film battery modules that can be adjusted in different sizes, and there are manufacturers who can cut any size of semi-finished products. These are all designed to meet the requirements of architectural design. In addition, we have also developed photovoltaic tiles and soft film batteries that have been directly made into traditional building materials.
With such a wide variety of batteries, it is important to choose how they are designed.
First of all, it is a photovoltaic module that meets building requirements and is used in ground-based photovoltaic power plants. As long as it passes the test of IEC 61215, it can meet the requirements of anti-130 km/h (2,400 Pa) wind pressure and 25 mm diameter hail 23 m/s impact resistance. The BIPV PV modules not only need to meet the performance requirements of the PV modules themselves, but also to meet the four-character experimental requirements of the curtain wall (wind pressure resistance, in-plane deformation performance, air tightness performance and watertightness performance) and building safety performance requirements. Have higher mechanical properties and adopt different structural methods.
Secondly, when selecting a crystalline silicon cell, if there is a partial blockage, the hot spot problem of the crystalline silicon component must be considered. At this time, the bypass diode does not work, although the degree of shadowing does not reach the reverse conduction voltage of the diode. Although the resulting hot-spot effect is not sufficient to damage the components, the battery components that have been in this state for a long time will be significantly damaged. Therefore, the thin-film battery components should be considered in the position where the sunlight incidence angle on the façade is poor and shaded. The voltage difference between crystalline silicon and thin-film battery assemblies is relatively large, and the voltages produced by different manufacturers are also different. Therefore, the electrical parts must be configured according to actual conditions.
Junction box needs to be miniaturized and diversified
Junction box as a battery and other equipment to connect the necessary equipment, and then combined with the curtain wall, the building's requirements for it is invisible, so the design of the junction box is gradually miniaturized, and hidden in the plate gap or inside the outer trim.
Short cable connector and combination of plates need multiple groups
Even if the efficiency of photovoltaic power generation is 0.1 percentage points higher, researchers are spending a lot of energy, time, and money, but the loss in cable transmission is nearly 1 percentage point. Therefore, how to reduce the loss of cables and other equipment is BIPV. Points to note in the design.
The application of the curtain wall must consider the appearance of indoor and outdoor, so the line must be exposed both indoors and outdoors. In addition, the plates increase the grouping of the solar panels through the combination of serial and parallel connections, and reduce the impact of the individual plate damage on the efficiency of the entire system.
The controller and inverter must be combined. The inverter needs to be miniaturized and modularized.
Now many of the controllers and inverters are designed together to facilitate overhaul of the equipment and reduce the chance of accidents. In addition, due to the damage of individual plates, the entire string of power will be affected, and more installed capacity will be lost. In some cases, due to changes in the sunshine conditions, too many inverter loads will be involved in the work and the efficiency will decline, which will restrict the efficiency of large-scale inverters. The improvement, so now need to consider the modular design of the inverter, and now manufacturers have adopted intelligent sleep technology, so that the maximum efficiency of the inverter to 98.6%, European efficiency increased to 97.6%, and the use of low voltage 50 ~ The 500kW capacity is freely combined, and it supports hot-plugging. It can be installed and maintained without shutting down the system. In addition, the perfect network communication function is easy to monitor the operation of the entire system. It is a better direction for BIPV in the future.
In addition, the micro-inverter works independently for each component, which is more conducive to improving the efficiency of the entire system. In particular, it is an excellent choice when there are many types of plates and the use position is complex. However, the cost of such a solution is high, and it needs comprehensive consideration. .
Reduce battery usage. Photovoltaic modules have their own power generation function and do not have the effect of storing electricity. The grid-connected electricity is sent directly to the national grid and does not require energy storage. It can be safely and seamlessly used through the anti-backflow device. Off-grid is used on its own. In the case of weak light or no sunlight at night, if electricity is needed, it depends on the battery section to provide power. The electricity generated by the photovoltaic modules during the day is used to charge the battery for use at night, thus requiring a higher cost to configure the energy storage device.
At present, the battery used in photovoltaic industry is mainly maintenance-free lead-acid battery, which has advantages of low cost, low cost, and easy maintenance. The disadvantage is that the capacity is low and the service life is short. There is also a lithium battery, which has the advantages of simple maintenance and high capacity. The disadvantage is that it has just been used in the photovoltaic industry, so the cost is high, and lead-acid batteries cannot be replaced for the time being. There is also an energy storage device, that is, a super capacitor. The advantage is that the capacity can be made very high, but the disadvantage is that it is still in the R&D stage and it is immature. Therefore, due to the high investment and high maintenance of the off-grid system due to energy storage, it is not the future direction of development. Therefore, we try to minimize the use of batteries during design.
Profiles for easy access and cable concealment
The installation of BIPV PV modules is much more difficult than the installation of ordinary modules. The general BIPV assembly has a high installation height and a small installation space. Taking into account the ease of installation, the photovoltaic modules and structures can be made into a unit structure to facilitate the installation and improve the installation accuracy of the curtain wall. For example, a modular photovoltaic wall can be used instead of a clear-frame curtain wall and a hidden-frame curtain wall. The author also developed a hidden channel system for the hidden frame and the bright frame curtain wall to solve the problem of photovoltaic cell component wiring. The inward-opening hidden line system was designed on the interior side to solve the problem of PV system line detection and overhaul, so that the connection lines of BIPV PV modules are all hidden in the curtain wall structure. We need to further improve this requirement in our future designs.
Continue to improve the efficiency of the module and improve the low light performance of the product.
The conversion efficiency of crystalline silicon cells commonly used in BIPV systems (13 to 16.5% for polysilicon and 16 to 18.5% for monocrystalline silicon) needs further improvement. Thin-film batteries for BIPV systems (11% to 13% for copper indium selenide and copper indium gallium selenide; 8 to 11% for cadmium telluride; 10 to 14% for gallium arsenide and polymers) have excellent relative low-light performance and good relative efficiency. The application of the curtain wall requires the battery module to have a good temperature coefficient and low light, and has a good absorption and conversion effect on infrared and ultraviolet rays. The photovoltaic panel is used on the facade of the curtain wall, which saves the use of the traditional panel of the curtain wall and has low reflectivity. No light pollution, with good economic and social benefits. In the future, the main economic indicators for R&D will be the price of BIPV in 2015, which will drop to RMB 14/W in 2015 (the current comprehensive cost will be about RMB 16/W)6. The system has a power generation efficiency of more than 80%.
Continue to improve the degree of integration with buildings
The building curtain wall is a complex of technology, art and function. Therefore, architects have higher requirements on material colors and specifications. Therefore, we need to further improve the degree of integration of photovoltaic and building, and develop more building materials components to provide beautiful appearance. Practical photovoltaic products further enhance the architectural taste.
Application of DC, integration
Photovoltaic cell power generation is currently a direct current. Therefore, practical DC loads should be considered in applications to reduce costs and losses. In addition, the integrated integration of photovoltaic and thermal insulation materials, integration of photovoltaic and electrochromic integration, integration of photovoltaic light and heat integration, integration of PV-LED integration is also the future direction of application.
Diversification of battery module specifications and colors, and increase industrialization and modular production level: Although the stability of traditional crystalline silicon battery is good, but the price is expensive, and the battery itself is not transparent, lighting needs to adjust the battery spacing to achieve, so you can go through in-depth development By increasing the industrialization rate and lowering the cost, it is also possible to develop new packaging methods and material-rich crystal silicon components.
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