In recent years, with the increasingly mature photovoltaic market, industrial and commercial photovoltaic continues to promote, more and more plant roofs are equipped with photovoltaic, using clean energy. However, the large, flat, well oriented, unobstructed cement or color steel roof resources are less and less, and the remaining ones that have not been developed may be complex roofs with multiple angles, multi orientations and sheltered structures. Facing the increasingly complex roof resources, how to design photovoltaic power plants on these complex roofs? It is the most concerned issue for every PV designer and investor to control the cost, ensure the power generation and be safe and reliable.

01- multi angle, multi facing roof

According to the basic principle of circuit series, the current size is determined by the smallest component in the same circuit, which is the barrel effect principle we know well. Therefore, when designing the string, the number of strings should be kept as consistent as possible for the module model and installation angle of each circuit of each inverter. Each MPPT circuit of inverter is independent and does not interfere with each other, so different MPPT circuits can be different.

When facing the complex roof, the design scheme of multiple inverters or multiple MPPT inverters can be selected according to the number of components with local consistency. At present, inverter technology is very mature, and the harmonic suppression problem of parallel connection of multiple inverters has been solved. There are no problems for inverters with different power at the power grid. In the project with high photovoltaic power, the inverter with high single power and multiple MPPT can be selected to further reduce the loss of series parallel mismatch under complex roof conditions.

10-way MPPT design, maximizing and reducing the loss of group string mismatch

In some more complex scenarios, it is possible to have three-phase grid connection and single-phase grid connection at the same time. At this time, the three-phase inverter and single-phase inverter can also be combined. According to the current national standard "code for design of low voltage distribution", there are three types of low-voltage distribution system, namely it system, TT system and TN system. It system has no zero line, TT system and TN system have zero line. In industrial and commercial and civil systems, most of them are TN systems. The grid connected inverter is connected to the grid, and the three-phase inverter is three-phase five wire. The single-phase inverter is a fire line, a zero line and a ground wire. Therefore, in the case of three-phase and single-phase simultaneous grid connection, there is no problem in the electrical connection.

★ note: when single-phase inverter is connected to three-phase power grid, attention should be paid to the problem of three-phase imbalance. Therefore, it is necessary to connect single-phase inverter to the phase with the largest load. If it is a multi-phase model, it is necessary to distribute it on three phases equally.

02- shaded roof

The shadow of photovoltaic power plant can be divided into temporary shadow, environmental shadow and system shadow. Many factors will cause temporary shadows on photovoltaic arrays, such as snow, leaves, bird manure and other forms of pollutants; Generally, the inclination of photovoltaic modules larger than 12 ° is more favorable for the self-cleaning of photovoltaic arrays.

The shadow of the system itself is mainly the occlusion of the components in front and back row. During design, the array spacing can be calculated according to the installation angle and the size of the components, so as to ensure that the sun is not blocked at 9:00-15:00 on the winter solstice day.

In the process of photovoltaic power station construction, environmental shadows are common. The high buildings, air buildings, roof height differences or trees around the floor will shadow the photovoltaic modules, which will cause the loss of the power generation of the PV group. If the installation conditions are limited, solar modules must be installed in shaded places, the following methods can be adopted to minimize losses:

(1) Solar irradiation is the strongest around noon every day. The power generation at 10:00 to 15:00 accounts for more than 80%, while the light in the morning and evening is weaker. The installation angle of the components can be adjusted to avoid the peak time of power generation, so as to reduce some losses.

(2) Make the components with possible shadows concentrate on an inverter or on an MPPT circuit, so that the shaded components will not affect the normal components.

03- installation inclination is not the best item

The installation angle of photovoltaic module includes two angles: inclination angle and azimuth angle. Inclination angle (height angle): the angle between photovoltaic module and horizontal ground. Azimuth: the angle between the orientation of photovoltaic module and the direction of the south. Whether the change of inclination angle or azimuth will affect the power generation of photovoltaic project.

Assuming that the efficiency of the components at the optimum installation angle is 100%, if the inclination is not correct, the loss of power generation will be relatively large, for example, the efficiency is only 59% when the vertical installation is conducted. For a photovoltaic array slope, the different incidence angle of the sun on it will lead to the different normal solar radiation received per unit area. The change of installation inclination of the photovoltaic array will change the incidence angle of the sun, thus affecting the radiation reception, and then the module power generation will be reduced.

For the cement floor type plants, most of them can adopt the best inclination angle for array design. According to the previous engineering experience, the optimum installation angle is generally less than 5 ° to 10 ° of local latitude.

For industrial color steel workshop, the inclination angle of color steel tile is only about 10 degrees. If the PV module is installed according to this angle, the overall efficiency is relatively low and the loss is relatively large. If it is possible to use the angle solar support of color steel tile, the installation angle can be increased appropriately to improve the efficiency of photovoltaic system. But in the design, we should pay attention to some points: in coastal areas, typhoon should be noticed, because the angle will generate negative wind pressure, and the wind resistance design of the support should exceed the local strongest typhoon load; In the northern region, the influence of snow should be paid attention to, and the snow load and the design of snow melting channel should be calculated.

04- roof with insufficient load

At present, there are several difficulties in industrial and commercial projects: some of the enterprises with good benefits may be old roofs, and the floor can not meet the requirements of bearing load. The installation of photovoltaic should be strengthened separately, which increases a lot of costs; Some airports, shopping malls and other roofs are glass roofs, and the owners want to install photovoltaic and do not want to destroy the previous glass structure. How to solve the installation pain of such roof?

The BIPV component, which is currently available on the market, can solve this problem. From the perspective of load limit and installation difficulty restriction conditions of buildings, BIPV components require more stringent requirements for light and flexibility, and lower weight can reduce the load-bearing pressure of the building to the greatest extent. Its own weight is far lower than that of conventional components. Some of them only have one quarter of the weight of conventional components, which can effectively reduce the load limit of old floor, Suitable for installation on the roof with insufficient load. The component and colored steel tile are connected with building structural adhesive instead of traditional fixed supports, which can reduce the overall cost of the system by more than 20%. It can also be used for glass roof, and can be glued on with structural adhesive, and it is easy to install and no additional load-bearing is added.

Under the background of more and more strict carbon emission control and increasing social demand for electricity, more and more enterprises begin to participate in the construction of industrial and commercial photovoltaic projects. However, the good roof resources are always limited. In the face of more and more complex photovoltaic roofs, we can solve the photovoltaic installation problems of complex roofs from equipment selection and system design, More and more owners will be using clean energy.