Research on Solar Photovoltaic-Building Integration

There are two major energy priorities in the new energy technology of the 21st century: solar photovoltaic power generation and nuclear fusion. Solar photovoltaic power generation is the longest-lived and cleanest power generation technology to date. The two areas where photovoltaic power generation will make a significant contribution to the world's energy needs are providing electricity for households and for large central power stations. The former will have a significant impact on the development of buildings. The solar photovoltaic power generation system only involves semiconductor packaging devices, does not consume conventional energy, has no moving mechanical parts, is pollution-free, noise-free, easy to maintain, and the power generation capacity can be selected at will.

Building-in-Platform Photovoltaics (BIPV) proposes a new concept of “buildings generating energy”, that is, the integration of buildings and photovoltaic power generation, where photovoltaic arrays are deployed on the surface of the building’s exterior envelope to generate electricity.

BIPV systems can be divided into two forms: photovoltaic roof structure (PV-ROOF) and photovoltaic wall structure (PV-WALL). BIPV systems are generally composed of photovoltaic arrays (solar panels), walls (roofs), cooling air ducts, brackets, etc.

For a complete BIPV system, there should be other equipment: load, battery, inverter, system control, filter protection, etc. When a BIPV system is connected to the grid, it does not need batteries, but it needs a device to connect to the grid.

1. Forms and characteristics of building integrated photovoltaic (BIPV)

In the 1980s, photovoltaic ground systems were widely used in remote areas without electricity, nomadic families, navigation lighthouses, power supply for residents on isolated islands and some special fields, and have begun to enter the general individual users, networked users and commercial buildings. After entering the 1990s, with the increasing cost of power generation caused by the depletion of conventional energy and the increasing environmental awareness of people, some countries have begun to implement and promote BIPV systems.

There are two ways to combine photovoltaics with buildings: one is to combine buildings with photovoltaic systems; the other is to combine buildings with photovoltaic devices.

1Combination of buildings and photovoltaic systems

The packaged photovoltaic modules (flat or curved panels) are installed on the roof of residential houses or buildings, and then connected to inverters, batteries, controllers, loads and other devices. The photovoltaic system can also be connected to the public power grid through certain devices.

2Combination of architecture and photovoltaic devices

The further combination of architecture and photovoltaics is to integrate photovoltaic devices with building materials. The outer protective surface of general buildings is painted, decorated with tiles or curtain wall glass, the purpose is to protect and decorate the building. If photovoltaic devices are used to replace some building materials, that is, photovoltaic modules are used to make the roof, exterior walls and windows of the building, it can be used as a building material and also for power generation, which can be said to be the best of both worlds. For buildings with frame structures, the entire enclosure structure can be made into a photovoltaic array, and appropriate photovoltaic modules can be selected to absorb both direct sunlight and reflected sunlight. At present, large-scale colored photovoltaic modules have been developed, which can achieve the above purposes and make the appearance of the building more attractive.

When photovoltaic devices are used as building materials, they must meet several requirements of building materials: durability, thermal insulation, waterproof and moisture-proof, and appropriate strength and rigidity. If used in windows, skylights, etc., they must be able to transmit light, that is, they can generate electricity and collect light. In addition, factors such as safety performance, appearance, and ease of construction must also be considered.

By replacing some building materials with photovoltaic devices, the production scale of photovoltaic modules will increase with the expansion of the surface in the future. The cost of photovoltaic modules can be reduced from the perspective of economies of scale, which is conducive to the promotion and application of photovoltaic products. Therefore, there is a huge potential market.

From the perspective of architecture, technology and technology, photovoltaic-building integration has the following advantages: ① The photovoltaic array of the networked system is generally installed on an idle roof or wall, without the need for additional land or the construction of other facilities, and is suitable for use in densely populated areas. This is especially important for urban buildings where land is expensive. ② It can generate electricity and use electricity on site, which can save the investment in power stations to transmit electricity to the grid within a certain distance. For networked household systems, the electricity generated by the photovoltaic array can be supplied to the load of the building or sent to the grid. On rainy days, at night or when the light intensity is very low, the load can be powered by the grid. Since the photovoltaic array and the public grid jointly supply electricity to the load, the reliability of power supply is increased. ③ In summer, when it is sunny, the use of a large number of refrigeration equipment forms a peak in power grid electricity consumption. This is also the time when the photovoltaic array generates the most electricity. In addition to ensuring its own building electricity consumption, the BIPV system can also supply electricity to the grid, thereby alleviating peak power demand. ④ Since the photovoltaic array is installed on the external protective structure such as the roof and wall, it absorbs solar energy and converts it into electricity, which greatly reduces the outdoor comprehensive temperature, reduces the heat gain of the wall and the indoor air conditioning cooling load, which not only saves energy but also helps to ensure indoor air quality. ⑤ It avoids air pollution and waste pollution caused by the use of general fossil fuels for power generation, which is even more important today and in the future when environmental protection requirements are strict. ⑥ Due to the modularization of photovoltaic cells, photovoltaic arrays are easy to install and the power generation capacity can be selected at will. ⑦ Installing photovoltaic arrays on building envelopes can promote the large-scale production of PV components, thereby further reducing the market price of PV components, which has a great driving effect on the widespread application of BIPV systems.

2. Development trend of BIPV system

Driven by energy and environmental pressure, solar photovoltaic technology has gradually become one of the preferred technologies for sustainable development in the world. Facts have proved that for systems below a few kW, solar photovoltaic power generation is the most ideal. In addition to traditional single-user and special field applications, photovoltaic (PV) technology is developing towards high-level and large-scale. BIPV grid-connected power generation has become the main direction and hotspot of PV applications in recent years. A recent survey report released by the United Nations Energy Agency shows that BIPV will become a market hotspot in the 21st century, and the solar energy construction industry will be one of the most important emerging industries in the 21st century. Countries have been vigorously reducing the manufacturing cost of photovoltaic cells and improving their power generation efficiency by improving processes, expanding scale, and opening up markets.

In recent years, the global photovoltaic market has undergone great changes: from independent operation (water lifting, lighting, etc.) and communication equipment, health care, navigation buoys and other fields in the past to grid-connected power generation and conventional power supply combined with buildings; and from being a supplementary energy to an alternative energy. Now let's introduce the development of different countries.

1United States

In June 1993, the U.S. Department of Energy and the National Renewable Energy Laboratory signed a five-year contract to implement the "PV: BONUS" program, spending $25 million to develop photovoltaic products integrated with buildings, namely building curtain wall photovoltaic devices and large rooftop photovoltaic modules.

In order to promote the rapid development of the U.S. photovoltaic industry, reduce the cost of photovoltaic power generation, save energy and protect the environment, former U.S. President Clinton announced at the United Nations Special Session on Environment and Development on June 26, 1997 that the United States would implement the "Million Solar Roofs" plan, which aims to install 1 million solar energy systems, including photovoltaic systems and solar thermal collectors, on the roofs of residential, commercial buildings, schools and federal government office buildings across the country by 2010, which can supply electricity and hot water. To this end, the U.S. government's photovoltaic funding increased by 30% in fiscal year 1998.

2Japan

Japan attaches great importance to the technology of combining photovoltaics with architecture. In the 1990s, the government funded some universities, research institutes and companies to carry out research and development. For example, Sanyo Electric Company launched several products that combine amorphous silicon cells with building materials (Sanyo is world-class in amorphous solar cell technology): one is made into a curved tile shape, each with an area of ​​305 square centimeters and an output power of 2.7 WP, which is relatively expensive; the other is a 90cm×35cm flat amorphous silicon cell module, which has "feet" on the back of the module for easy installation and is generally used as roofing material. Sanyo Electric Company has also launched translucent and opaque amorphous silicon glass modules for vertical curtain walls of commercial buildings. The light transmittance of its translucent module is 30%, which can be used as window lighting and for power generation (Germany also has similar products). The above photovoltaic modules have been installed in office buildings such as Sanyo Electric Company and Fsukasa Power Company.

In 1997, the Ministry of International Trade and Industry announced the implementation of the "70,000 Rooftops" plan and installed 37 MWP rooftop photovoltaic systems. The plan made Japan the world's largest photovoltaic module market that year. The Japanese government planned to install 400 MW of photovoltaic power generation systems by 2000 and 4,600 MW by 2010.

In 1998, three Japanese companies (Shimizu Corporation, Sharp, and Kawasaki Steel) cooperated to develop a new type of building material, which was to install solar cells in the building material and make it into three types as needed for use as roofs and exterior walls.

3. Germany

The “One Thousand Roofs Project” was first implemented in 1990 to promote household networked photovoltaic systems with a capacity of 1 to 5 kWP on the roofs of private homes.

In terms of combining photovoltaic devices with buildings, several companies affiliated with ASE have launched a variety of photovoltaic modules, including large-size (1.5 m×2.5 m) frameless amorphous silicon modules, each with a power of up to 360Wp, which can be used for vertical exterior walls and sloping roofs; they have also launched amorphous silicon opaque modules with a size of 1 m×0.6 m, which can be used for roofs, vertical curtain walls and windows respectively.

Currently the world's largest solar rooftop photovoltaic system is installed at the new Munich Trade Fair Center.

4. India

India has made great efforts to promote solar energy in recent years and has achieved great results. Among developing countries, India's photovoltaic industry and application market are in a leading position; according to reports, it has become the second largest producer of monocrystalline silicon solar cells after the United States. There are 400,000 photovoltaic systems in the country for various applications. In addition, the government is organizing some research and production institutions to carry out research and development of photovoltaic devices combined with buildings.

On December 18, 1997, the Indian government announced that it would promote 1.5 million solar roofs across the country by 2002.

5. China

China's solar photovoltaic technology has also reached a certain scale. According to statistics, by the end of 1997, the installed capacity of solar photovoltaic power generation systems that had been completed and normally used in my country was 10-15MW, mainly used for power supply to residents in remote areas. With the transformation of the photovoltaic power generation field, the research and development of BIPV systems in my country has made great progress. During the "Ninth Five-Year Plan" period, my country successfully built 17kWp and 7kWp photovoltaic power generation roofs in Shenzhen and Beijing respectively and achieved grid-connected power generation. With the support of the World Bank's donation and bilateral or multilateral technical cooperation, it is expected that the annual sales volume of my country's photovoltaic market will grow at an annual rate of 20%, and is expected to exceed 10MW by 2010.

It was recently learned that in order to support environmental protection, the Hong Kong Special Administrative Region Government, through the Hong Kong Industry Department, recently allocated HK$1.7 million to the Hong Kong Polytechnic University to establish the first "photovoltaic building" experimental system to provide part of the building's electricity with solar energy.

There is data that has statistically analyzed the photovoltaic demand between 1984 and 1994, and predicted the PV capacity that can be installed by 2010. The results are shown in Table 1.

Various research and development work has been carried out intensively in developed countries to reduce the cost of photovoltaic power generation. In terms of photovoltaic systems, photovoltaic modules with micro inverters have been developed, which will bring revolutionary changes to the installation of photovoltaic systems and their integration with buildings.

The development of BIPV is currently a major research hotspot for large-scale use of photovoltaic technology for power generation in the world, and Western developed countries are actively carrying it out as a key project. In addition to installing photovoltaic panels on roofs, products that install photovoltaic cells in tiles have been launched.

In the rapidly developing intelligent building (IB), the building automation system (BAS) is an important component. The BIPV system is essentially a building equipment, but it has not been included in the current information about BAS. The author believes that the BIPV system should be included in the BAS. In order to prepare for a rainy day, the laying device of the photovoltaic array should be reserved in the actual construction; in the integrated wiring system (PDS), the access port and line box of the photovoltaic equipment should be preset to prepare for the future combination of photovoltaic components and building equipment. With the widespread application of photovoltaic components and the sharp drop in prices, the intelligent buildings in the future must be equipped with BIPV systems, which is also an important supplement to IB.

It can be predicted that the combination of photovoltaics and buildings will be one of the most important areas of photovoltaic applications in the future. It has broad development prospects and huge market potential.

Due to factors such as price and regulations, BIPV systems are unlikely to be popularized on a large scale in the short term. However, with the increasing depletion of conventional energy, people's increasing awareness of environmental protection, and the resulting innovation in manufacturing processes and technological development, BIPV will surely show strong vitality.