The discussion of photovoltaic power station technology is based on the "Design Code for Photovoltaic Power Stations" (GB50797-2012). The calculation of the photovoltaic array spacing is based on the goal of "ensuring 6 hours of sunshine per day on the winter solstice for the photovoltaic array". (That is, ensuring 6 hours of sunshine on the winter solstice. In the following text, the sunshine duration of the photovoltaic array on the winter solstice is simply referred to as "sunshine duration").
Currently, all ground-mounted photovoltaic power stations built at different latitudes in China have completed the calculation of the photovoltaic array spacing according to this standard, without considering the reduction in radiation and power generation caused by the change in photovoltaic array distance due to different latitudes and sunshine durations; at the same time, they have not considered the differences in the land area and investment of photovoltaic power stations caused by this change.
This paper will study the above situation and analyze the relationship between the resulting power generation loss and investment changes, proposing recommended sunshine durations for photovoltaic power plants at different latitudes. The spacing is calculated using the classical formula:
This paper first uses the above formula to calculate the time periods during which the photovoltaic array is shaded each day of the year under different sunshine duration conditions, and then calculates the amount of radiation received by the horizontal ground each day of the year. Thus, the annual usable radiation rate (i.e., power generation rate) of the tilted surface of the photovoltaic array is obtained.
Simultaneously, based on the above formula, the photovoltaic array spacing under the aforementioned constraints can be obtained, thus yielding the land area per MWp of the photovoltaic power station. Changes in the land area will lead to changes in some material investments (e.g., cable investment) and land costs for the photovoltaic power station.
To simplify the calculation of investment changes, the principles for determining the cost of a photovoltaic power plant are as follows:
1) Except for changes in equipment and material investment due to land occupation, the other investments in the power plant remain unchanged;
2) The unit price of photovoltaic modules is 4.5 yuan/Wp, and the unit price of inverters is 0.5 yuan/Wp. Prices of other materials are based on the electricity quota price.
3) Investment changes due to terrain variations are not considered;
4) Land acquisition and occupation shall be calculated separately for compensated and uncompensated methods, with the land price set at 0.5 million yuan/mu.
Based on Table 1 and Figures 1-2, and analyzing the above calculation results, the following conclusions can be drawn:
1) Under different sunshine durations, the proportion of usable radiation and the proportion of power generation for power plants vary significantly in low-latitude regions. However, the changes in these proportions are not significant in high-latitude regions. Furthermore, investment differences for power plants are smaller in low-latitude regions, while significant differences exist in high-latitude regions. This indicates that as latitude increases, the land area required for power plants increases, leading to a significant increase in investment.
2) Under the same sunshine duration, the proportion of electricity generated by power plants in high-latitude regions is higher than that in low-latitude regions. The proportion of electricity generated by power plants is positively correlated with latitude.
3) When the latitude is below 25°, the increase in the proportion of electricity generated exceeds the increase in the proportion of investment; conversely, when the latitude is above 30°, the increase in the proportion of investment exceeds the increase in the proportion of electricity generated. Therefore, it is recommended that the sunshine duration of photovoltaic power plants in low-latitude areas be increased to 7-8 hours, while the sunshine duration in high-latitude areas should be reduced to less than 6 hours.
4) When the latitude is between 25° and 30°, and the sunshine duration is 6 to 7 hours, the increase in the investment ratio is basically consistent with the increase in the power generation ratio. Therefore, it is recommended that the sunshine duration be 6 to 7 hours in this case.
5) Analysis of Figure 2 shows that as the sunshine duration increases, the intersection point of the power generation ratio curve and the investment ratio curve shifts towards lower latitudes. Therefore, the optimal sunshine duration curves for each latitude are derived, as shown in Figure 3.
Based on the above conclusions, taking a photovoltaic power station built at latitude 40° as an example, with 6 hours of sunshine per day, the theoretical power generation rate is 99.19%, and the power station occupies 28.47 acres. If the sunshine duration is taken as 5 hours as shown in Figure 3, the theoretical power generation rate is 99.67%, and the power station occupies 25.58 acres. The power generation rate decreases by 0.48%, and the power station's land area decreases by 2.89 acres (10.15%). According to the cost principles mentioned above, the power station reduces investment by approximately 85,700 yuan (10.13%) and 71,300 yuan (10.13%) respectively, depending on whether the land is paid or not. It is evident that selecting the optimal sunshine duration for a photovoltaic power station yields significant benefits.
In summary, the calculation of the array spacing for photovoltaic power plants should be analyzed and demonstrated based on different latitudes and investment levels. If there is already measured solar resource data for the region, it should also be analyzed in conjunction with the solar resource data to achieve the goals of saving land, controlling investment, and increasing power plant revenue.
Disclaimer: This article is a reprint. If there are any copyright issues, please contact us promptly for deletion (QQ: 2737591964). We apologize for any inconvenience.
