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Home of Photovoltaic Storage | How to design a PV plant based on a roof
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Distributed commercial and industrial photovoltaic projects have become a target for everyone due to the relatively high price of electricity, the relative synchronisation of photovoltaic power generation and load electricity consumption, the high proportion of self-generation and self-use, and the high return on investment.
Not every roof is suitable for the installation of photovoltaic power station, first of all, to determine the business situation, housing ownership, electricity prices; secondly, we must explore the roof conditions, to confirm the roof bearing can meet the requirements of the installation of photovoltaic power station, roof equipment, whether there are fans, air windows, light belt, air conditioning, whether there is a daughter wall, the height of the daughter wall to the actual measurement of the site shall prevail. Whether there are high-rise buildings around the plant, a small amount of shadow shading will lead to a decrease in system output, and the plant's grid environment, power supply and distribution facilities, etc.
1, the building situation, including the building's property rights, life, orientation, load, etc., need to field exploration, the use of aerial photographs, to understand the roof orientation inclination and the site has no shade. First of all, the aerial photograph needs at least five different angle pictures and surround video, two high overhead pictures to effectively prevent distortion when photographing the roof, one side picture at an angle of 45 degrees from east to west and one front view close to the house to get a comprehensive understanding of the various conditions of the roof.
(1) Ownership of the building
If the investor is not the owner of the building, pay attention to the ownership of the building, if it is a public building such as government agencies, schools, hospitals, stations, etc., the ownership is clear and uncontested, it is suitable for development; if it is a leased factory building, it is necessary to sign a contract with the owner to confirm, if there is no formal property certificate, the investment risk is relatively large.
(2) The life span of the building roof
Photovoltaic power stations need to operate for 25 years, and it generally takes about 8-10 years to recover the full cost. When developing a project, you need to know the number of years the roof can be used, which is too short to be suitable for development, generally more than 20 years.
(3) Orientation of the building roof
From the perspective of power generation, the best tilt angle and south-facing direction is undoubtedly the best, but most roofs do not meet this condition, the survey needs to measure the azimuth of the roof, roof tilt angle and the height of the surrounding shade such as the daughter wall, using PV simulation software to calculate the power generation and revenue before deciding whether to invest.
(4) Building Roof Loads
Roof loads are divided into constant loads and variable loads. Constant load refers to the self-weight of the structure and dust load, etc. PV power station needs to operate for 25 years, and its self-weight belongs to the constant load. Usually a PV system installed on a steel workshop will add 15 kg per square metre and a brick and mortar roof will add 80 kg per square metre. During the project visit, it is important to check the design values of the constant load in the building design specifications and to ensure that, in addition to the self-weight of the roof, there are no additional loads, such as pipes, suspended equipment, roof appendages, etc., and that the constant load has a margin to allow for the installation of a PV plant.
Variable loads are loads that are temporarily applied to the roof under consideration of limit conditions and are divided into wind, snow, earthquake and live loads, which cannot be occupied. Under special circumstances, live load can be used as an option to share the load of the PV plant, but it cannot be taken up too much and needs specific analysis.
(5) User electricity consumption and price of electricity consumption
High investment value of commercial and industrial PV power generation. Commercial and industrial electricity prices are high, the proportion of self-generation and self-use is high, so we should examine the electricity consumption and electricity costs of enterprises, the annual, monthly and daily average electricity consumption of enterprises, the electricity consumption during the daytime when PV power is generated, whether there is electricity consumption on holidays and how much electricity is used. The balance of the grid is fed using the local FGD tariff.
(6) Quality of the grid in the building
The PV grid-connected inverter is connected to the grid, and the quality of the grid will have an impact on the operation of the inverter. If there are cranes, welding machines, gantry mills, arc furnaces and other high-power inductive equipment, between start-up and shutdown, accompanied by a large number of harmonics, it will have an impact on the inverter. PV systems installed in places with poor quality require additional equipment for power quality correction, such as active filters APF, static reactive generators SVG, etc. The grid connection point of the inverter is as far away as possible from the electricity-using equipment, e.g. by directly stepping up to medium voltage 10kV to avoid the risk of harmonics and other power quality risks.
2、Roof of the building
There are mainly colour steel tiles, ceramic tiles and steel mixed roofs, etc. Colour steel tiles are divided into upright locking edge type, nibble type, snap type and fixed piece connection type. The first two require special adapters, and the last two require perforated fixing; ceramic tile roofing can use special adapters, and can also not be fixed with the roof, using self-weight and roof slope attached to it; steel mixed structure roofing needs to make bracket foundation, considering roof waterproofing, wind load resistance, roof design load and other factors.
There are three common types of roofing, colour steel tile roofing, concrete roofing and tile roofing.
(1) Colour steel tile roofing:
To confirm the colour steel tile tile type (angle chi type, ladder type, upright lock edge type, etc.), colour steel tile roofing broken, corrosion and rust, waterproof situation. Color steel plate roof structure load-bearing capacity of 20KG/㎡, such as roof does not meet the load-bearing capacity requirements, the original building reinforcement and then photovoltaic component installation; color steel plate has no serious rust, rain leakage and broken situation, has been used for no more than 3 years. There are also professional companies that can replace the colour steel tiles to install PV.
(2) Concrete roofing:
The concrete roof structure has a load-bearing capacity of 40~60KG/㎡. If the roof does not meet the load-bearing capacity requirements, the original design should be adjusted to use a lighter bracket scheme or reduce the installation capacity of the PV system before PV installation; the overall structure of the house has not been seriously affected by the deformation of the building safety; the waterproof layer of the roof has not been seriously damaged and there is no water leakage, otherwise the waterproofing needs to be redone first.
(3) Tile roofing:
Various types of tiles with hooks can be used: barrel tiles, flat tiles, Roman tiles, etc. Choose different hooks according to the type of shingle. Linoleum asphalt tiles: need to use a professional bracket structure to install. Small green tiles: traditional Chinese green tiles, not recommended for installation, too weak in terms of waterproofing, or you can simply replace the roof tiles and use a recessed system for installation.
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