Building photovoltaic engineering design points
(1) Constant load of building photovoltaic For buildings under construction, the load problem of photovoltaic system has generally been considered in advance, here mainly introduces the load problem of completed buildings. For the roof photovoltaic system, when the roof is installed for the roof, after the installation of photovoltaic modules, due to the lack of activity space, it can be regarded as a non-human roof, the use of the roof property from the human to the non-human, the resulting photovoltaic module installation load margin of 1.417kN/m2, usually can meet the installation needs of photovoltaic modules. When the installed roof is a non-human roof, the installed photovoltaic modules increase the constant load of the roof, then the bearing capacity of the roof needs to be carefully checked, if the roof does not have enough bearing capacity margin, direct installation will pose a threat to the structural safety of the building. In this case, for the building structure with a small span, the photovoltaic bracket is usually directly rooted in the frame column to avoid its association with the roof, so as to avoid the increase of constant load on the roof; For building structures with large spans, roofing reinforcement is generally adopted, but the cost of this method is high.
(2) The wind load of building photovoltaics is very important for the design of wind resistance of building photovoltaic systems and photovoltaic arrays. When installing a photovoltaic system on an existing building, the photovoltaic array often does not want to be “rooted and installed” when designing the combination of the photovoltaic array and the building, and the photovoltaic installation of the existing building is often designed as a counterweight wind resistance or a centralized support form. After the use of suitable support form, in order to ensure the safety of building photovoltaic, in the building wall installation or roof support installation, the wind load of the photovoltaic system should be designed according to the national standard GB50009-2001 “Building structure Load Code” (2006 edition), and should consider: The wind load of the separated photovoltaic panel should be included in the wind load on the windward side and the wind load on the lee side. The wind load of the support should be included in the wind load from the panel and the wind load directly borne by the support; The all-in-one panel system should be divided.
(3) Requirements for installation convenience In order to combine with the building and install easily, solar cells are generally made into solar cell tiles, and the component structure and installation method are no different from ordinary building tiles; For the components applied to the photovoltaic curtain wall, the frame structure is also required to be the same as the module of the building curtain wall, and the installation method should also be consistent with the ordinary curtain wall glass. If ordinary photovoltaic modules are used, special brackets or rails need to be made to facilitate the installation of ordinary solar cells on them; In addition, solar cells are often made into bezel-less components, and the junction box is usually mounted on the side of the component for easy installation. In some special applications, the shape of the solar cell component will be required, no longer just the conventional square, such as the circular roof requires the solar cell to be round, the building with a hypotenuse requires the solar cell component to have a hypotenuse, and the arch roof requires the solar cell component to have a certain degree of curvature.
(4) As we all know, the general design life of concrete buildings is more than 50 years, but the life of ordinary photovoltaic modules is only 25 years, especially the components using EVA glue, compared with the life of PVB packaged components will be relatively long. Photovoltaic grid-connected inverters, the key equipment in the building photovoltaic system, usually have a life of only 8 to 10 years, so in order to ensure that the photovoltaic system is consistent with the life of the photovoltaic building, it is necessary to consider the regular replacement of photovoltaic grid-connected inverters. Most of the connection lines of the ordinary photovoltaic system are open in the atmosphere, the air convection is sufficient, the temperature is low, most of the connection lines in the BIPV building system are in the curtain wall column, beam and other closed structures, the temperature is not easy to scatter, the life of the wire and cable is also affected, so the requirements for the wire in the BIPV building system are higher. To sum up, it is necessary to consider the various components in the design of the building photovoltaic system, so that its service life is coordinated with the building itself, or it is easy to replace.
The photovoltaic characteristics of building photovoltaic
(1) Considering the cost of electrical design, it is still recommended to use a centralized grid-connected inverter; For BIPV systems, due to the diverse installation angles of photovoltaic modules and the scattered installation locations of battery modules, it is generally recommended to use low-power inverters or series inverters. All cables used in the building should be flame retardant cables. In some cases of greater stress, armored cables should be used. When the cable used for photovoltaic power generation needs to be laid in the same slot, hole and bridge with the building distribution cable, it is appropriate to choose the cable with the same material as the building distribution cable. In the laying of cables that can be reached by hands, the temperature of the cable sheath should not be higher than 70 ° C. In a cold environment, outdoor cables are required to be resistant to low temperature. When the cable wiring needs to pass through the wall, it is easy to cause “cold bridge”, and special bridge breaking and insulation construction should be done. For a low-voltage 380V access to the mains system, the biggest factor affecting the distribution network is the increase in the terminal voltage of the distribution network, especially when there is reverse power, this voltage increase will be more obvious. If the voltage rises beyond the limit, it will cause damage to the electrical equipment. If the irreversible grid-connection mode is used, reverse power protection should be set.
(2) Monitoring communication design photovoltaic building integration project communication usually adopts wireless and wired two ways. Wireless mainly includes: Zigbee and GPRS for RS485, WIFI for Ethernet; Cable mainly includes: twisted pair for RS485 and Ethernet, coaxial cable for Ethernet and video signals, optical fiber for Ethernet. For photovoltaic building integration projects, the main locations of monitoring are usually intelligent photovoltaic junction boxes, inverters, multifunctional meters and environmental monitors. For projects requiring increased pressure, a microcomputer integrated automation system is also included. Microcomputer integrated automation system is generally used in substation. Each high voltage switchgear in the station is an independent monitoring subsystem. These subsystems integrate relay protection functions and monitoring functions to achieve local data acquisition and local control, and provide remote channels.
Conclusion
In short, building photovoltaic integration is not a simple “stacking” of buildings and photovoltaic modules, but the organic combination of building characteristics and photovoltaic characteristics in building photovoltaic, building photovoltaic system gives full play to the architectural characteristics of the photovoltaic array and green power characteristics, providing an innovative way for the development of energy-saving buildings and photovoltaic power.
