# PV array spacing calculation principle

- Dec 24, 2018-

According to the "Design Code for Photovoltaic Power Stations" (GB50797-2012), the calculation of the PV array spacing is aimed at "guaranteeing the PV array winter solstice sunshine duration of 6 hours/day". (ie guarantee 6 hours of sunshine on the winter solstice, below: to ensure that the sunshine duration of the PV array on the winter solstice is referred to as: the duration of sunshine).

At present, the ground photovoltaic power plants constructed at different latitudes inChinahave completed the calculation of the PV array spacing according to the specification. The radiation and power generation caused by the change of the PV array distance are not considered due to the difference in latitude and sunshine duration. This change caused the difference in the area and investment of photovoltaic power plants.

This paper will study the above situation and analyze the relationship between power generation loss and investment change, and propose the recommended sunshine duration for different latitude photovoltaic power plants. Calculate the spacing according to the classic formula, the following formula:

In this paper, based on the above formula, the time period of the day-to-day PV array is occluded under different sunshine durations, and the amount of radiation received by the ground level can be calculated. Therefore, the radiation rate of the photovoltaic array inclined surface can be utilized throughout the year (ie, the power generation rate).

At the same time, according to the above formula, the PV array spacing under the above constraints can be obtained, thereby obtaining the MWp footprint of the photovoltaic power plant. Changes in floor space will cause changes in part of the PV power plant investment (eg cable investment), land cost changes, etc.

In order to simplify the calculation of investment changes, the principle of the value of PV power plants is as follows:

1) In addition to changes in equipment and materials investment caused by land occupation, other investments remain unchanged;

2) The unit price of the PV module is 4.5 RMB/Wp, and the unit price of the inverter is 0.5 RMB/Wp. Other material prices are based on the electricity rating price;

3) Do not consider investment changes caused by terrain changes;

4) The land acquisition is calculated separately according to the paid and unpaid methods, and the land price is 0.5 million RMB/mu.

Combining Table 1 with Figures 1 to 2, analyzing the above calculation results, the following conclusions can be drawn:

1) Under the conditions of different sunshine durations, the ratio of the radiation value and the proportion of the power generation in the low-latitude power stations can be significantly changed. However, the ratio of the radiation value and the proportion of the power generation that can be used in power stations in high latitudes are not obvious. And the investment difference of power stations in low latitudes is small; and the investment in power stations in high latitudes is significantly different. It can be seen that as the latitude increases, the power plant area increases, resulting in a significant increase in power plant investment.

2) Under the same conditions of sunshine duration, the proportion of power generation in high-latitude power stations is higher than that in low-latitude regions. The proportion of power generation in the power station is positively correlated with the latitude.

3) When the latitude is lower than 25?, the increase of the proportion of power generation is higher than the increase of investment ratio; on the contrary, when the latitude is higher than 30?, the increase of investment ratio is higher than the increase of the proportion of power generation. Therefore, it is recommended that the sunshine duration of photovoltaic power stations in low latitudes should increase to 7-8 hours, and the sunshine duration in high latitudes should be reduced to less than 6 hours.

4) When the latitude is between 25 and 30, when the duration of sunshine is 6 to 7 hours, the increase in the proportion of investment is basically the same as the increase in the proportion of power generation. Therefore, it is recommended that the number of hours of sunshine at this time can be 6 to 7 hours.

5) It is analyzed from Fig. 2 that as the sunshine duration increases, the intersection of the power generation proportional curve and the investment ratio curve shifts to a low latitude. From this, the best sunshine duration curve for each latitude is obtained, as shown in Fig. 3.

According to the above conclusions, taking the photovoltaic power station with a latitude of 40? as an example, the duration of sunshine is 6 hours: theoretically, the power generation rate of the power station is 99.19%, and the power station covers 28.47 acres; if it takes 5 hours according to the sunshine duration in Figure 3: Theory The power generation rate of the power station is 99.67%, and the power station covers an area of 25.58 acres. The power generation rate of the power station is reduced by 0.48%, and the power plant area is reduced by 2.89 mu (10.15%). According to the cost principle mentioned above, the power station reduced the investment by about 85,700 RMB (10.13%) and 71,300 RMB (10.13%) according to the paid and unpaid land. It can be seen that the photovoltaic power station has a significant benefit after selecting the best sunshine duration.

To sum up: the calculation of PV plant array spacing should be analyzed and demonstrated based on the latitude and investment level. If there is already measured optical resource data in the region, it should be combined with optical resource data for analysis, in order to achieve the purpose of saving land, controlling investment, and improving the revenue of the power station.