The booming development of the domestic photovoltaic industry has led to a significant increase in the scale and quantity of photovoltaic power stations. The continuous development and maturity of the industry have also put forward higher requirements for power plant design. The previous extensive design can no longer meet today's development needs. The refined design of photovoltaic power plants requires every detail to improve the system efficiency of the power plant in order to win the recognition of owners and investors.
During the construction and installation process of photovoltaic power plants, different photovoltaic technologies and system designs have different requirements for tilt angle and orientation. To ensure the best power generation effect, the "optimal tilt angle" is often referred to. What is the optimal tilt angle?
The angle between the surface of the photovoltaic module and the ground level is called the inclination angle. The Earth revolves around the Sun, and within one revolution period, the point of direct sunlight on the Earth moves back and forth between the Tropic of Cancer and the Tropic of Capricorn. So the total amount of radiation received by the surface plane of photovoltaic modules varies under different tilt angles. When designing power plants, we generally refer to the historical data of cumulative radiation at different tilt angles throughout the year and choose the angle with the highest radiation as the optimal tilt angle design.
According to the "Design Code for Photovoltaic Power Stations" GB 50797-2012, the optimal tilt angle is defined as the maximum annual total radiation. If the fixed photovoltaic array receives the maximum annual total radiation on the inclined surface at this tilt angle, then the tilt angle is called the optimal tilt angle (rather than the highest annual power generation); However, in some scenarios, the optimal tilt angle can also be the tilt angle corresponding to the highest annual power generation, the tilt angle corresponding to the highest yield, the tilt angle corresponding to the highest monthly power generation, and other optimal tilt angles calculated under various limiting conditions. This article mainly discusses the inclination angle with the highest annual total radiation.
Why do we need the optimal tilt angle?
The optimal tilt angle is designed primarily to receive more solar radiation. For a tilted photovoltaic array, the different angles of incidence of the sun on it will result in different amounts of normal solar radiation received per unit area. The larger the angle of incidence (the angle perpendicular to the normal of the photovoltaic array), the less normal solar radiation received (for the same radiation input). The change in the inclination angle of the photovoltaic array will cause a change in the incident angle of the sun, thereby affecting its radiation reception. Therefore, it is necessary to obtain the optimal inclination angle based on the annual radiation reception through theoretical calculations.
Schematic diagram of component receiving solar radiation
In the process of designing the optimal inclination angle in practice, it is also necessary to consider factors such as the geographical and natural environment of the project construction site. The impact of tilt angle on snow sliding; The impact of changes in tilt angle on the wind pressure and snow pressure resistance of components; At the same time, it is necessary to consider the impact of these factors on the selection of photovoltaic bracket materials and foundation weighting, as well as changes in the distance between the front and rear rows caused by excessively high angles, which increases land costs.
How to calculate the optimal tilt angle?
The calculation of the optimal tilt angle requires the local latitude and longitude to determine the altitude and azimuth of the sun at each moment, and the annual average radiation data over many years to determine the characteristics of local solar radiation. Based on radiation data and latitude and longitude calculations, the annual total radiation reception of photovoltaic arrays with different tilt angles is accumulated, and the tilt angle with the highest annual total radiation is selected as the optimal tilt angle. Generally, software such as PVsyst can be used to conveniently and quickly calculate the optimal tilt angle.
It is advisable to use a single variable comparison to compare the impact of different tilt angles on power generation. But generally, the inclination angle of the same power station component is the same angle and orientation, and there are many influencing factors when comparing power stations in different regions. Therefore, it is considered to use PV System design software to demonstrate it. The meteorological data of its software comes from NASA and Meteonorm meteorological databases, and through actual calculations, its accuracy rate is as high as 99%, which is referenceable.
What are the main factors affecting:
Latitude and Season: Determine the inclination and orientation based on the latitude and seasonal changes of the location, so that the photovoltaic modules can receive solar radiation to the maximum extent possible. Generally speaking, in the Northern Hemisphere, the inclination angle can be set as the latitude angle minus 10 to 15 degrees, and the orientation can be set as due south.
Solar altitude angle: The solar altitude angle refers to the height of the sun in the sky, which varies with time and seasons. By studying the changes in solar altitude angle, selecting the inclination and orientation, photovoltaic modules can receive solar radiation to the maximum extent at different time periods.
Shadow occlusion: Shadow occlusion can reduce the power generation efficiency of photovoltaic modules. When choosing the inclination and orientation, it is necessary to consider the shading caused by buildings, trees, or other objects. Avoid or minimize shadow obstruction to improve the power generation efficiency of photovoltaic power plants.
Temperature effect: High temperatures can lead to a decrease in the efficiency of photovoltaic modules. Appropriate inclination and orientation can help dissipate heat from components and reduce the impact of temperature effects on power generation efficiency.
Ground utilization: When selecting the inclination and orientation, consider the ground utilization of the photovoltaic power station. Determine the appropriate inclination and orientation based on the available land or building space to achieve maximum power generation efficiency.
Optimize the tilt angle and orientation of photovoltaic modules to improve the power generation efficiency of photovoltaic systems.
Tilt angle optimization:
Seasonal adjustment: Adjust the tilt angle of photovoltaic modules according to the seasonal changes in the location. In winter, increasing the tilt angle appropriately can increase the contact area between the photovoltaic panel and direct sunlight, and improve the power generation efficiency in winter; In summer, the tilt angle is reduced to minimize the potential overheating of photovoltaic panels caused by direct sunlight during high temperatures.
Latitude adjustment: Determine the optimal inclination angle based on the latitude of the location. Generally speaking, subtracting about 15 degrees from the latitude angle is a reasonable inclination setting that allows photovoltaic modules to receive maximum solar radiation energy.
Towards optimization:
Southward orientation: In the northern hemisphere, the photovoltaic modules are oriented towards the south to maximize the reception of solar radiation. Southward orientation ensures that photovoltaic modules receive maximum sunlight exposure for most of the time.
East West Orientation: In some situations where it is necessary to balance the power generation in the morning and afternoon, the photovoltaic modules are oriented in both directions, increasing the power generation through the slanting sun in the morning and evening.
Tracking system: Use a tracking system to automatically adjust the orientation of photovoltaic modules according to the movement of the sun, maximizing the reception of solar radiation. Tracking systems are usually divided into two types: single axis tracking and dual axis tracking. Dual axis tracking can more accurately follow the movement of the sun, but the cost is higher.
Shadow analysis and optimization:
Avoid Shadows: Avoid the photovoltaic modules from being obstructed by the shadows of surrounding buildings, trees, and other objects, ensuring that the photovoltaic modules can fully receive sunlight all day long.
Regularly trim trees: Trim surrounding trees regularly to reduce their shadow impact on photovoltaic modules.
Shadow analysis and optimization techniques are crucial in the design and operation of photovoltaic power plants.
Is the optimal tilt angle fixed and unchanging? Is it certain that photovoltaic power plants will have the highest revenue at the optimal tilt angle?
The optimal tilt angle means high radiation reception, but it also means a relatively large footprint. For example, in a limited site area, as the optimal inclination angle decreases, the installed capacity will continue to increase. Lowering the inclination angle will reduce the power generation, while increasing the installed capacity will increase the power generation. Therefore, further technical and economic comparisons based on external conditions are needed to determine which inclination angle ultimately yields the highest returns. The installation angle of a general cement flat roof is recommended to be greater than 10 degrees, which is beneficial for the self-cleaning of rainwater components.
The optimal power generation tilt angle is not fixed, in fact, it is closely related to the array spacing. The larger the array spacing, the closer the value of the optimal power generation tilt angle is to the optimal radiation tilt angle. In theory, if the spacing is large enough to be unobstructed throughout the year, the values of the two are the same.
Due to the uncertainty of climate, the optimal inclination angle can only be referred to as the relative optimal inclination angle based on historical data. Firstly, the optimal inclination angle varies depending on the historical radiation data. There are some differences between the optimal inclination angle calculated using 5-year historical data and 10-year historical data; Secondly, historical average data represents a high probability of local radiation characteristics, but for a given year, it may not necessarily be the optimal choice.
Summary:
(1) The optimal tilt angle is related to the local geographic latitude. As the geographic latitude gradually increases towards the poles of the Earth with the equator as the reference point, the corresponding optimal inclination angle also gradually increases.
(2) When the tilt angle increases from horizontal (0 °) to the optimal tilt angle, the amount of radiation received by the surface increases accordingly, and the maximum amount of radiation is received when the optimal tilt angle is reached; As the tilt angle continues to increase, the amount of radiation received by its surface begins to decrease again, corresponding to a gradual decrease in power generation.
(3) The influence of radiation on power generation is relatively small when the tilt angle is within ± 5 ° of the optimal tilt angle.
(4) Whether to design the optimal inclination angle needs to be comprehensively evaluated based on the installation site conditions and the economic feasibility of the plan, and should not be blindly designed.
(5) By optimizing the spacing and inclination angle, the economy and power generation of the power station can be significantly improved.