1. Design principles of photovoltaic power plants

The design should be based on the requirements of the construction project, comprehensively analyze and demonstrate the technical, economic, resource, environmental and other conditions required for the construction project, and in line with the principles of "mature and advanced, safe and reliable, reasonable cost, energy saving and environmental protection", The activity of preparing construction engineering design documents. This is an important process for the overall planning of the construction project and the embodiment of specific implementation intentions. It is the link for the conversion of science and technology into productivity, the key link for dealing with the relationship between technology and economy, and the key stage for determining and controlling the project cost.

(1) Selection of photovoltaic power station construction

The annual total sunshine hours, sunshine percentage, annual total radiation, annual average temperature, annual frost days and other parameters are important basis for the site selection of photovoltaic power plants.

At present, according to the total amount of solar energy resources in each region, my country has divided the country into Class I, II, and III divisions, and implemented different benchmark electricity price subsidy policies. The total amount of solar energy resources in type I areas is relatively high, and the electricity price subsidy is relatively low; the total amount of solar energy resources in type III areas is relatively low, and the electricity price subsidy is relatively high. Class I electricity price areas are mainly concentrated in the northwest region, with a total annual radiation of 1500-2000 (kwh/m²); the vast central area is a Class II electricity price area, with an annual radiation total of 1000^2050 (kwh/m²); III class electricity price areas Mainly in the southeast coastal areas, the total annual radiation is 1000^1600 (kwh/m²). Obviously, the grid subsidy price of photovoltaic power plants in my country does not match the actual total solar energy resources, such as the total annual radiation in the second-level electricity price area, and the areas that exceed the annual radiation amount in the first-class electricity price area. Finding suitable investment areas in different electricity price areas is the key factor for obtaining income, that is, in relatively high electricity price subsidy areas, finding areas with good solar resource conditions to build photovoltaic power plants can obtain better income.

Before selecting a site for a new photovoltaic power station, the usable area of the area should be evaluated, and the overall construction scale should be drawn up. Generally speaking, a sufficiently large usable area is required to reach a certain total installed capacity. For example, the connection system line and access road construction of a new power station with a small scale, etc., the initial investment cost will greatly increase the unit cost, and if the later operation and maintenance does not have a large scale, the maintenance cost will also be increased, and the construction economy will be greatly reduced . Generally speaking, it is required that the construction scale be large, the access system lines be close, and the access roads be short.

The nature of the land selected for the photovoltaic power station, the status of use rights, and the inclusion of stones in the scope of land use regulations should be clarified; the address of the selected site should be ascertained, and the address structure, earthquake effects, landslide hazards, and flood discharge during flash floods should be reasonably evaluated Passages, etc.; know the hydrogeological conditions, flood control evaluation, and water conservancy protection in the vicinity of the plant site; be familiar with the cultural conditions around the plant site, transportation conditions, etc.; Nature reserves, military installation areas, etc., comply with the relevant regulations on natural environment protection. In general, it is necessary to confirm the nature of land use, find out the address situation, strengthen environmental protection, and avoid cultural relics and mineral deposits.

It is necessary to grasp the local industrial policy, understand the development space of the regional market, be familiar with the necessary conditions for project construction, complete the planning and site selection work, put forward planning and site selection suggestions through survey and research, carry out data collection and obtain professional title documents, and obtain approvals from various competent departments. Ensure that the project passes all evaluations smoothly.

(2) General layout of photovoltaic power station

According to the requirements of flood prevention, earthquake prevention, landslide prevention, fire protection, operation and maintenance, etc., the power station should be coordinated and arranged according to the scale of the proposed total installed capacity, so as to achieve safe operation without risk, fire protection and environmental protection without accidents, and more prominent economic benefits , Maintenance is more convenient. The general layout of photovoltaic power plants should be combined with the topography and landform to avoid large-scale re-planning. The production and management area of the power station is separated from the living area to ensure safe production and suitable life for personnel.

2. Design of solar array

(1) Selection of solar modules

It mainly considers the manufacturer's production scale, industry performance, manufacturing level, technology maturity, operational reliability, and future technology development trends. Consult the statistics of module attenuation rate, loss and annual power generation data of power stations that have been put into production, which can be used as an intuitive basis for analysis and judgment. A single photovoltaic module with the same area should be selected with a higher peak power to reduce the floor area, line loss, module installation, and integrated circuit usage and construction. At present, domestic power stations mainly use polysilicon high-efficiency components. The entire power station should try to select components from the same manufacturer, specification, and batch. In this way, the efficiency consistency is relatively good, and the decay rate of the components is basically stable. Anti-PID components must be used in high temperature and high humidity areas.

(2) Arrangement of solar modules

To determine the optimal inclination angle by calculation, the arrangement order of solar modules must take into account money, the shadow of the rear row, the distance between the solar module array and the building, the shadow of the maximum angle position, and the influence of terrain factors. The general determination principle is: during the time period from 9:00 am to 15:00 pm on the winter solstice day, the component array should not be blocked. When arranging, there should be a certain gap between the components as a ventilation channel.

According to the module's own characteristics and theoretical calculations, the horizontal arrangement of modules can increase the power generation by about 2%~5% compared with the vertical arrangement. There are generally 2 blocks arranged from top to bottom. However, the horizontal arrangement uses 20 tons more steel materials per megabyte than the vertical arrangement and the amount of later installation work; the horizontal arrangement will increase the occupied area by 20% compared with the vertical arrangement; the horizontal arrangement is slightly more difficult to install big.

(3) Stringing method of solar modules

According to the open circuit voltage of photovoltaic modules and the level of input voltage on the DC side of the inverter, combined with local solar radiation conditions, generally 18 or 20 strings form a basic power generation unit. When vertically arranged, the stringing methods mainly include: (I) the upper and lower layers form a string in order; (II) the upper half and the lower half form a string in order, and the other half forms another string in order; (III) Both the upper and lower layers are arranged in a string in the way of jumping, that is, 1, 3, 5~19. 20, 18~6, 4, 2. The amount of photovoltaic cables used in the three arrangement methods (I), (II), and (III). Relatively speaking, the arrangement method (III) is scientific and can reduce DC loss and increase power generation.

It is recommended to adopt the vertical (III) arrangement method for centralized large and medium-sized photovoltaic power stations; horizontal arrangement can be used for distributed small photovoltaic power stations such as agricultural greenhouses and rooftop photovoltaics when there are just available resources.