Solar radiation
Solar energy panels are devices that convert solar energy into electrical energy, and the intensity of radiation directly affects the amount of solar power generation. The solar radiation data in various regions can be obtained through the NASA meteorological data query website or through photovoltaic design software such as PV-SYS and RETScreen.
The tilt angle of solar energy panels
The data obtained from meteorological stations generally refer to the solar radiation on a horizontal plane, which needs to be converted into the radiation on the inclined plane of the photovoltaic array to calculate the power generation of the photovoltaic system. The optimal tilt angle is related to the latitude of the project location.
The conversion efficiency of solar energy panels
The photovoltaic component is the core factor that affects the amount of electricity generated. In February 2015, the General Office of the National Energy Administration of China issued the “Opinions on Soliciting Market Role to Promote Technological Progress and Industrial Upgrading of Photovoltaics” which stipulated that the photovoltaic components and grid-connected inverters used in photovoltaic power generation projects enjoying national subsidies should meet the relevant index requirements of the “Photovoltaic Manufacturing Industry Normative Conditions”.Β
The conversion efficiency of polycrystalline silicon solar cell modules should not be less than 15.5%, and that of monocrystalline silicon solar cell modules should not be less than 16%. Currently, the conversion efficiency of first-line brand polycrystalline silicon modules on the market generally exceeds 16%, and that of monocrystalline silicon is generally above 17%.
System loss
Like all products, the efficiency of photovoltaic power plants and the performance of electrical components will gradually decrease during the 25-year service life, and the power generation will decrease year by year. In addition to these natural aging factors, there are also quality problems with components and inverters, as well as various factors such as circuit layout, dust, series and parallel losses, and cable losses.
In general, the financial model of photovoltaic power plants reduces the system’s power generation by about 5% per year for three years, and the power generation decreases to 80% after 20 years.
Combination loss
Where there is the series connection, there will be current loss due to the difference in current between the components; where there is a parallel connection, there will be voltage loss due to the difference in voltage between the components. The combination loss can reach more than 8%, and the China Engineering Construction Standardization Association stipulates that it should be less than 10%. Therefore, to reduce combination losses, attention should be paid to:
- Strictly select components with consistent currents in series before installing the power plant.
- The attenuation characteristics of the components should be as consistent as possible.
Dust cover
Among all the various factors that affect the overall power generation capacity of photovoltaic power plants, dust is a major killer. Dust mainly affects photovoltaic power plants in the following ways:
- By blocking the light from reaching the components, thereby affecting the power generation capacity;
- Affects heat dissipation, thus affecting conversion efficiency;
- Dust with acidic and alkaline properties will deposit on the surface of the component for a long time, corrode the surface of the plate, and make the plate rough and uneven, which is conducive to further accumulation of dust while increasing the diffuse reflection of sunlight.
Therefore, solar panel components need to be cleaned regularly. Currently, there are three main methods of cleaning photovoltaic power plants: sprinkler trucks, manual cleaning, and robots.
Temperature Characteristics
When the temperature rises by 1Β°C, the output power of a crystalline silicon solar cell decreases by 0.04%, the open circuit voltage decreases by 0.04% (-2mV/Β°C), and the short-circuit current increases by 0.04%. In order to minimize the impact of temperature on power generation, good ventilation conditions should be maintained for the modules.
Line and Transformer Losses
The line losses of the DC and AC circuits in the system should be controlled within 5%. To achieve this, wires with good electrical conductivity and sufficient diameter should be used in the design. Special attention should be paid to the firmness of the connectors and wiring terminals during system maintenance.
Inverter Efficiency
Due to the presence of inductive transformers and power devices such as IGBTs and MOSFETs, inverters will produce “conduction losses” during operation. The efficiency of a general string inverter is 97-98%, that of a central inverter is 98%, and that of a transformer is 99%.
Shadowing and Snow Cover
In distributed power plants, surrounding tall buildings may cause shadows on the modules, which should be avoided as much as possible during the design. According to circuit principles, when the modules are connected in series, the current is determined by the one with the lowest output, so if one module is shadowed, it will affect the power generation of the entire series of modules. Snow accumulation on the modules will also affect power generation and must be cleared as soon as possible.
