CN107563903A - A kind of cloud layer blocks method for establishing model to ground photovoltaic plant - Google Patents

Abstract

Method for establishing model is blocked to ground photovoltaic plant the invention provides a kind of cloud layer, it includes：Calculate solar azimuth and determine sunshine and photovoltaic array incidence relation；Calculate photovoltaic plant, cloud cluster, the spatial relation of the sun；Establish cloud layer and model is blocked to ground photovoltaic plant.Technical scheme provided by the invention constructs photovoltaic plant location, cloud cluster position, the space polar coordinate model of position of sun, realizes cloud layer projection and the accurate description of ground photovoltaic plant spatial relationship, is laid a good foundation for photovoltaic minute level power prediction.

Description

A method for establishing a cloud cover model for ground photovoltaic power plants

technical field

The invention relates to the technical field of photovoltaic power generation and distribution, in particular to a method for establishing a cloud cover model for a ground photovoltaic power station.

Background technique

Photovoltaic power station refers to a photovoltaic power generation system that uses solar energy and uses special materials such as crystalline silicon panels, inverters and other electronic components to connect to the grid and transmit power to the grid. Photovoltaic power station is currently the most encouraged green power development energy project in the world. It can be divided into independent power generation system with battery and grid-connected power generation system without battery. Solar power generation is divided into photothermal power generation and photovoltaic power generation. The commercialization of solar power in the current period refers to solar photovoltaic power generation.

Photovoltaic power generation products are mainly used in three aspects: one is to provide power for non-electric places; This has been implemented on a large scale in developed countries.

As large-scale photovoltaic power plants are connected to the grid in recent years, the randomness and volatility of photovoltaic power have affected the security, stability and economic operation of the grid, and the research on the factors affecting photovoltaics has received increasing attention. The determinant of photovoltaic power is solar irradiance. Among the many influencing factors of irradiance, clouds have the most significant and dynamic influence on irradiance. Therefore, it is necessary to construct a model for the shielding of ground photovoltaic power plants by clouds.

Contents of the invention

In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides a method for establishing a cloud cover model for ground photovoltaic power plants. Ground irradiance is one of the most important factors in the output power variation of photovoltaic power plants, and its uncertainty directly leads to Randomness and volatility of output power. The cloud cover is the key to cause the change of radiation intensity. Construct the spatial model of the location of the photovoltaic power station, the position of the cloud cluster, and the position of the sun to realize the accurate description of the spatial relationship between the cloud projection and the ground photovoltaic power station, and lay the foundation for the power prediction of the photovoltaic power station under the cloud cover.

The solution adopted to achieve the above purpose is:

A method for establishing a cloud cover model for a ground photovoltaic power station, the establishment method comprising:

(1) Calculate the sun orientation and determine the incident relationship between sunlight and photovoltaic array;

(2) Calculate the spatial position relationship of photovoltaic power plants, clouds, and the sun;

(3) Establish the shielding model of the ground photovoltaic power station by the cloud layer.

Preferably, said step (1) includes:

(1-1) Take the photovoltaic power station as the axis, take the north direction of the photovoltaic power station as the starting point, rotate clockwise, and measure the solar azimuth β;

(1-2) Measure the angle between the sun's rays and the ground, that is, the sun altitude angle α, the sun altitude angle α and the sun zenith angle θ _Z are complementary, and the sine expression of the sun altitude angle α is:

sinα＝cosθ _z ＝sinδsinφ+cosδcosφcosω

In the formula: ω is the hour angle, δ is the declination angle, and φ is the latitude;

(1-3) For a photovoltaic array with an inclination angle to the horizontal plane, the sun incident angle θ _i is the angle between the sun incident ray and the normal line of the inclined surface, and its size changes with the position of the sun. The sun incident angle θ _i The formula for calculating the cosine value is:

cosθ _i =cosβsinδsinφ+cosβcosφcosδcosω+sinβsinγcosδsinω

+sinβsinφcosδcosωcosγ-sinβcosγsinδcosδ

Where: β is the inclination angle of the photovoltaic array panel, and γ is the azimuth angle of the photovoltaic array panel.

Preferably, said step (2) includes:

Note that the sun altitude angle is α, and the cloud layer height is H, then the ground projection distance R corresponding to the cloud layer blocking the observation point is:

R=H×cot(α).

Preferably, the step (3) includes: taking a certain point P in the cloud as an object, assuming that the projection of P on the ground is P′, the calculation formula of the offset of P′ relative to P is as follows:

Δx＝-z×tan(θ _Z )×sinβ

Δy=-z×tan(θ _Z )×cosβ

z: the vertical distance from point P in the cloud to the ground;

θ _Z : Sun zenith angle;

Δx: the east-west component of the offset of shadow P′ relative to P, and eastward is positive;

Δy: The north-south component of the shadow P′ relative to the P offset, and the north is positive;

Calculate the projection position of the cloud, the formula is as follows:

x ₁ ＝x ₀ +Δx＝x ₀ -z×tan(θ _Z )×sinβ

y ₁ =y ₀ +Δy=y ₀ -z×tan(θ _Z )×cosβ

In the formula, x ₀ and y ₀ are the coordinate position of point P in the cloud cluster, and x ₁ and y ₁ are the coordinate position of point P′ in the cloud cluster projection.

Compared with the closest prior art, the technical solution of the present invention has the following beneficial effects:

The present invention constructs the spatial polar coordinate model of the position of the photovoltaic power station, the position of the cloud cluster, and the position of the sun, realizes the accurate description of the spatial relationship between the cloud layer projection and the ground photovoltaic power station, and lays the foundation for the minute-level power prediction of photovoltaics. The invention has clear physical meaning, simple calculation method and reliable calculation result, can obtain accurate cloud shadow position, is applicable to any region in the world, and is easy to popularize and apply in engineering.

Description of drawings

Fig. 1 is the space polar coordinate provided by the present invention.

Fig. 2 is a schematic diagram of the cloud projection position offset relationship provided by the present invention.

Detailed ways

The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Cloud cover will cause changes in radiation intensity, which in turn will cause rapid fluctuations in the power of photovoltaic power plants. According to the relative relationship between the position of the sun, the position of the cloud layer and the position of the photovoltaic power station, the shielding range of the cloud layer to the photovoltaic power station can be predicted; the type and thickness of the cloud are reflected by the texture characteristics and grayscale of the satellite cloud image, so the change of grayscale can reflect the impact of the cloud layer on the photovoltaic power station. Therefore, it is necessary to construct a spatial model of the location of the photovoltaic power station, the location of the cloud, and the location of the sun. On this basis, a projection model of the cloud layer on the ground is established.

1. Spatial models of the sun, clouds, and photovoltaic power plants

1.1 Calculate the sun orientation

The solar altitude angle is the elevation angle when we observe the sun, that is, the angle between the sun's rays and the ground. Due to the rotation of the earth, the sun rises in the east and sets in the west, and the altitude angle of the sun changes continuously within a day; when the sun is at the mid-heaven at noon (local time is 12 o'clock), the altitude angle of the sun reaches the maximum value H, and we take the sun at this time The altitude is called the noon solar altitude for that day. When the sun's altitude angle is 90°, the solar radiation intensity is the largest at this time; when the sun obliquely hits the ground, the solar radiation intensity is small.

The solar azimuth is based on the true north direction of the target object (same as the north direction of the central meridian in the same geographical division/zone) as the starting direction, that is, 0 degrees. Its value ranges from 0 to 360 degrees, and the calculation method of rotation is: take the target as the axis and the north direction of the target as the starting point, rotate clockwise for one circle, and the azimuth gradually increases to 360°. Therefore, the azimuth of the sun is generally an angle measured clockwise with the north direction of the target as the starting direction and the incident direction of sunlight as the ending direction.

First of all, regardless of the weakening effect of the atmosphere on the solar radiation intensity, the factor that affects the radiation intensity of a certain point on the earth is only the angle between the point and the sunlight, which is manifested as the influence of the sun's altitude angle in geography.

The solar altitude angle is complementary to the solar zenith angle, and its function expression is:

α＝90- _θZ (1)

In the formula: α is the altitude angle of the sun, θ _Z is the zenith angle

sinα＝cosθ _z ＝sinδsinφ+cosδcosφcosω (2) In the formula: ω is the hour angle, δ is the declination angle, and φ is the latitude.

The solar energy received by the ground changes with the position of the sun relative to the ground plane. Generally speaking, photovoltaic arrays are not placed horizontally, and have a certain inclination angle relative to the ground plane. For photovoltaic arrays with an inclination angle to the horizontal plane, the sun The angle of incidence _θi is the angle between the incident ray of the sun and the normal of the inclined surface, and its size changes with the position of the sun. The calculation formula is:

Where: β is the inclination angle of the photovoltaic array panel, and γ is the azimuth angle of the photovoltaic array panel.

1.2 Calculate the distance between the sun and the earth

The earth revolves around the sun in an elliptical orbit, and the distance between the earth and the sun varies every day of the year. The average distance between the sun and the earth is 149 597 892 ± 500km, and the solar irradiance corresponding to this distance is the standard solar irradiance. On other dates, the solar irradiance between the upper boundary of the atmosphere and the solar irradiance must be corrected, and the correction adopts the sun-earth The distance correction factor d _m , which is defined as:

d _m =d ₀ /d

d _m : Sun-Earth distance correction factor;

d ₀ : the average distance between the sun and the earth;

d: distance between the sun and the earth.

1.3 Spatial model of photovoltaic power station, cloud cluster and sun position

The relative position relationship between the position of the sun and the cloud is closely related to whether the cloud covers the photovoltaic power station. Generally, the altitude and azimuth of the sun are used to describe the position of the sun.

Note that the sun altitude angle is α, the azimuth angle is β, and the cloud layer height is H, then the ground projection distance R corresponding to the cloud layer blocking the observation point is:

R＝H×cot(α) (4)

The coordinates of the ground projection point are:

Different cloud systems generally fall within specific altitude ranges, and Table 5-1 shows the typical altitude ranges for various operations. Since the information provided by geostationary satellite cloud images is relatively limited, it is impossible to determine the height of the cloud layer, so the present invention assumes that the cloud layer is at different typical heights.

Table 1 Characteristics of different cloud layers

2. Projection model of clouds on the ground

The projection position of the cloud is related to the position of the cloud, the height of the cloud and the orientation of the sun. Taking a certain point P in the cloud as the object, let the projection of P on the ground be P′, the calculation formula of the offset of P′ relative to P is as follows

Δx＝-z×tan(θ _Z )×sinβ

Δy=-z×tan(θ _Z )×cosβ

z: the vertical distance from point P in the cloud to the ground;

θ _Z : Sun zenith angle;

Δx: the east-west component of the offset of shadow P′ relative to P, and eastward is positive;

Δy: the north-south component of the offset of shadow P′ relative to P, positive to the north.

Among them, β is the azimuth of the sun, which is defined as the angle measured clockwise with the north direction of the target as the starting direction and the incident direction of sunlight as the ending direction. For the Chinese region, the solar azimuth angles in the morning, middle and evening are about 90°, 180°, and 270°, respectively.

The projection offset relationship of the cloud cluster is shown in Figure 2 below:

On this basis, the projection position of the cloud can be calculated, and the formula is as follows. In the formula, x ₀ and y ₀ are the coordinate position of point P in the cloud cluster, and x ₁ and y ₁ are the coordinate position of point P′ in the cloud cluster projection:

x ₁ ＝x ₀ +Δx＝x ₀ -z×tan(θ _Z )×sinβ

y ₁ =y ₀ +Δy=y ₀ -z×tan(θ _Z )×cosβ

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application rather than to limit the scope of protection thereof. Although the present application has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: After reading this application, those skilled in the art can still make various changes, modifications or equivalent replacements to the specific implementation methods of the application, but these changes, modifications or equivalent replacements are all within the protection scope of the pending claims of the application.

Claims (4)

1. a kind of cloud layer blocks method for establishing model to ground photovoltaic plant, it is characterised in that the method for building up includes：

(1) calculate solar azimuth and determine sunshine and photovoltaic array incidence relation；

(2) spatial relation of photovoltaic plant, cloud cluster and the sun is calculated；

(3) establish cloud layer and model is blocked to ground photovoltaic plant.

2. method for building up as claimed in claim 1, it is characterised in that the step (1) includes：

(1-1), with the north of photovoltaic plant to for starting point, rotates, measured using photovoltaic plant as axle center in the direction of the clock Solar azimuth angle beta；

(1-2) measures angle between sunray and ground both sun altitude α, sun altitude α and solar zenith angle θ_ZIt is Complementary, sun altitude α sinusoidal expressions are shown below：

Sin α=cos θ_z=sin δ sin φ+cos δ cos φ cos ω

In formula：ω is hour angle, and δ is declination angle, and φ is latitude；

(1-3) is for having the photovoltaic array at inclination angle, solar incident angle θ with horizontal plane_iBetween sun incident ray and inclined plane normal Angle, its size changes with the change of position of sun, solar incident angle θ_iCosine value calculating formula is：

cosθ_i=cos β sin δ sin φ+cos β cos φ cos δ cos ω+sin β sin γ cos δ sin ω

+sinβsinφcosδcosωcosγ-sinβcosγsinδcosδ

Wherein：β is the inclination angle of photovoltaic array plate, and γ is the azimuth of photovoltaic array plate.

3. method for building up as claimed in claim 1, it is characterised in that the step (2) includes：

Note sun altitude is α, ceiling of clouds H, then cloud layer observation station is formed block corresponding to floor projection distance R it is as follows Shown in formula：

R=H × cot (α).

4. method for building up as claimed in claim 1, it is characterised in that the step (3) includes：The certain point P using in cloud cluster as Object, if P is as follows relative to P offset calculating formula in the P ' that is projected as on ground, P '：

Δ x=-z × tan (θ_Z)×sinβ

Δ y=-z × tan (θ_Z)×cosβ

z：Vertical range of the P points to ground in cloud cluster；

θ_Z：Solar zenith angle；

Δx：Shade P ' relative to P offsets East and West direction component, eastwards for just；

Δy：Shade P ' relative to P offsets north-south component, northwards for just；

Calculate the projected position of cloud, such as following formula：

x₁=x₀+ Δ x=x₀-z×tan(θ_Z)×sinβ

y₁=y₀+ Δ y=y₀-z×tan(θ_Z)×cosβ

X in formula₀、y₀For the coordinate position of P points in cloud cluster, x₁、y₁The coordinate position of P ' in being projected for cloud cluster.