The project owner is National Energy Group Shanghai Electric Power Co., Ltd. The project is located in a commercial office building on Plot 2 (West) in Changfeng District, developed by Shanghai Tianhong Real Estate Investment Co., Ltd., with a total installed capacity of 48kWp.This system mainly consists of photovoltaic modules and their brackets, string inverters, 0.4kV photovoltaic grid connected cabinets, monitoring communication, lightning protection grounding, AC/DC cables, civil engineering and other related auxiliary materials.

Equipment Selection

Crystalline silicon solar cells are widely used in large-scale grid connected photovoltaic power station projects due to their mature manufacturing technology, stable product performance, long service life, and relatively high photoelectric conversion efficiency.

This project comprehensively considers factors such as technology, efficiency, and cost, and adopts 500Wp monocrystalline silicon modules.

One 40 kW inverter is selected for this project. This inverter is equipped with functions such as grid voltage over and under voltage protection, grid frequency over and under frequency protection, anti islanding effect protection, inverter overload and overheating protection, inverter ground leakage protection, inverter anti back discharge protection, anti reverse connection protection, overvoltage protection, anti surge protection, and low voltage crossing. It has the characteristics of intelligence, efficiency, safety, and reliability.

design scheme

String design principles:

(1) The range of voltage variation at the output end of a series of solar cell components must match the input voltage range of the inverter. The maximum output voltage of the solar cell string must be less than the maximum input voltage allowed by the inverter, and the minimum output voltage of the solar cell string must be greater than the minimum input voltage allowed by the inverter.

(2) The total power of all solar cell strings connected in parallel should be slightly greater than the rated power of the inverter.

(3) After the solar cell modules are connected in series to form a photovoltaic string, the maximum output voltage of the photovoltaic string shall not exceed the maximum allowable system voltage required by the solar cell module itself.

String design of solar cell modules:

The maximum allowable input voltage of the inverter is 1100V, and the full load MPPT working range is 200-1000V.

According to the formula and the photovoltaic power demand, the number of modules in series for this project is determined to be 6-19 modules connected in series to form a string.

String array design:

On each roof, place each single crystal silicon solar cell module horizontally in a regular row, and reserve maintenance channels during this period. A sub array is formed using photovoltaic modules as an installation unit, and the entire roof is composed of multiple sub arrays. Channels are reserved between the arrays for later maintenance, depending on the roof situation.

Support structure scheme:

Due to the good bearing capacity of concrete roofs, traditional solutions only use concrete strip or block foundations for concrete roofs. The supports are made of Q235B steel and hot-dip galvanized (with an average thickness of not less than 65 um). The components can be adjusted to the optimal inclination angle of 25 degrees through the steel supports, improving power generation efficiency and achieving high economic benefits.

The photovoltaic modules on the concrete roof are installed on steel brackets, and a concrete strip foundation is prefabricated on the roof, which serves as the foundation for the bracket. When constructing on the roof, minimize the damage to the waterproof and insulation layers of the roof as much as possible. If there is any damage, it should be repaired to ensure the normal use of the original structure.

Access system scheme

The photovoltaic modules are installed on the roof of the enterprise, and the energy generated by the modules is converted into AC energy with the same frequency, phase, and amplitude as the 0.4kV voltage by the inverter, which meets the requirements of national power quality standards. A new photovoltaic grid cabinet is built and connected to the 0.4kV busbar of the distribution room through a 0.4kV cable.

The access scheme refers to the XGF380-Z-2 scheme in the "Typical Design Scheme for Distributed Photovoltaic Power Generation Access System of State Grid Corporation of China"

Power generation analysis

Efficiency analysis of photovoltaic power generation system:

The overall efficiency of grid connected photovoltaic power generation systems consists of three parts: the efficiency of photovoltaic arrays, the efficiency of inverters, and the efficiency of AC grid connection. After comprehensive calculation, the system efficiency is 80%.

Annual power generation considering attenuation rate:

Photovoltaic modules will experience attenuation when used in light and conventional atmospheric environments, and manufacturers generally guarantee that the efficiency of photovoltaic modules will exceed 80% after 25 years. Considering the efficiency attenuation of conventional crystalline silicon battery components, the attenuation rate is 2.5% in the first year, and the average annual attenuation rate is 0.6% in the second to 25th years. The total attenuation of the entire life cycle components is 15.7%.

According to PVsyst software calculation, the first year's online power generation was 50400 kWh, and the average annual online power generation for 25 years was 46700 kWh. The total online power generation in 25 years is 1.1677 million kWh.

Power Station Safety Protection

Roof load review

The original design of the concrete roof of this project has considered a photovoltaic load of 0.2 kN/㎡, meeting the newly added photovoltaic load requirement of 0.15 kN/㎡. After preliminary verification, the roof meets the requirements after arranging the photovoltaic panels. Therefore, it is feasible to use the original roof to support the solar photovoltaic array on the roofs of each factory building selected for this project construction, without the need for reinforcement.

Cable fire protection

This project is a DC cable, and it is difficult to cut off the DC current, which can easily cause a fire. This project follows the electrical fire protection regulations and national fire protection regulations, and has complete fire protection measures: all cables are flame-retardant cables, cable trenches are forked, and firewalls are installed at the entrance and exit of the house. The cables on both sides of the firewall are coated with fireproof paint, and the holes under the screen cabinet are sealed with fireproof partitions and fireproof materials.

Overvoltage protection

In this project, lightning rods will not be installed separately in the battery panel station area, and the original roof lightning rods will be used.

An overvoltage protector is installed in the incoming circuit of the inverter to prevent direct lightning strikes and induced lightning waves from cascading to other battery panel circuits, quickly releasing lightning waves and protecting other battery panels from damage caused by lightning waves.

Overvoltage protectors are installed on both the AC and DC sides of the inverter, and lightning arresters are installed on the low-voltage busbar. It can prevent lightning wave intrusion and overvoltage during operation.

Lightning protection and grounding

Install lightning rods in the photovoltaic array, and the shadow of lightning rods has a significant impact on the performance of photovoltaic modules. According to the relevant provisions of the "Guidelines for Overvoltage Protection of Photovoltaic (PV) Power Generation Systems", it is planned to no longer install lightning rods in the photovoltaic array of this power station. The main method of direct lightning protection is to connect the battery modules and brackets to the grounding grid in the factory area through the solar cell array.

The photovoltaic array forms a grounding grid according to the layout of the power station. The grounding grid is welded to the foundation steel bars of the photovoltaic cell module for grounding, and the sub array grounding bodies are welded into a mesh, and each sub array grounding body is connected to each other.

In order to ensure the safety of equipment and personnel, the grounding network of the entire station mainly adopts horizontal grounding bodies, and fully utilizes civil metal foundation steel reinforcement brackets as natural grounding bodies, with a grounding resistance not exceeding 4;, The grounding grid should be closed in a circular arc, and all electrical equipment should be grounded. The main grounding grid should be laid below the permafrost layer. The grounding resistance of the grounding grid meets the requirements of DL/T621 "Grounding of AC Electrical Equipment", and limits the contact potential and step potential to safety values. Vertical grounding electrodes are installed at each distribution room for better current dissipation. Each battery panel is connected to a horizontal grounding grid.

Protection configuration of photovoltaic power station grid connection points

A fault disconnection device is installed on the grid connected circuit breaker side (i.e. the photovoltaic grid connected cabinet side), equipped with low cycle, low voltage, high cycle, and high voltage disconnection functions. Low voltage disconnection should have the function of judging short circuits and blocking AC voltage disconnection.

Anti islanding protection

Photovoltaic power plants should have the ability to quickly monitor isolated islands and immediately disconnect from the power grid.

Operation and maintenance

Safety management work

The director of a photovoltaic power plant is the first person responsible for the safety production of the photovoltaic power plant, and is fully responsible for the safety of the photovoltaic power plant. The safety officer is responsible for daily safety training and inspection of safety measures in various maintenance work. While strictly implementing the "two tickets and three systems", photovoltaic power stations actively promote the "pre control of dangerous points" and "process card" systems to ensure strict and meticulous safety production work. Gradually standardize maintenance procedures, achieve procedural operations, and eliminate illegal operations.

Repair and maintenance work

① On the basis of the "Maintenance Manual" provided by various equipment manufacturers of the photovoltaic power station, combined with the specific situation of the project location, corresponding maintenance content is added, and routine maintenance is arranged during periods with weak lighting. This not only facilitates maintenance work, but also reduces energy loss.

② On the premise of digesting and absorbing contents such as the "Maintenance Manual" and "Operation Manual", starting from practice, compile the "Operation Guide" and "Field Operation Regulations" for photovoltaic power plants, move from inspection based maintenance to procedural maintenance, formulate maintenance standards and standardize maintenance steps, and achieve the goal of "necessary and necessary maintenance, and must be done well".

③ In troubleshooting, improve maintenance quality, shorten fault time, and reduce downtime. And by using the "barcode" inspection method, not only can the inspection be carried out in place, but also it has changed from "managing people with people" to "managing people with technology", urging employees to inspect in place, timely grasp the operation status of equipment, detect hidden dangers early, handle them in a timely manner, and effectively avoid the expansion of faults.

Other measures taken

① Drawing on the operating experience of other photovoltaic power plants that have already been in operation, the most difficult task for photovoltaic power plants is to deal with inverter faults. One reason is that these devices occupy a large amount of funds and are not easy to prepare; The second is that once a malfunction occurs, there will be a significant loss of electricity. In response to this issue, we adopt a regular inspection method to identify problems as early as possible, "prepare to fight", and eliminate accidents in the bud.

② Promote the application of technical supervision in the photovoltaic power generation industry. According to the 9 technical supervision standards of the power industry, technical supervision work is carried out in photovoltaic power plants to ensure the normal working status of all equipment and avoid the occurrence of malignant events.

③ Regularly clean the light receiving surface of the solar cell to increase its battery level.