Method for positioning a single-axis solar tracker during overcast periods

Abstract

Method for positioning a single-axis solar tracker during overcast periods, comprising using a radiation-detecting sensor in the vicinity of the single-axis solar tracker to measure values of global horizontal irradiance (GHI) of the sun during a time interval; determining an estimation of a diffuse horizontal irradiance (DHIapx) based on measured values of global horizontal irradiance (GHI); determining an estimation of a global tilted irradiance (GTIapx) also based on measured values of global horizontal irradiance (GHi); comparing the diffuse horizontal irradiance (DHIapx) with the global tilted irradiance (GTIapx); and obtaining a maximum tracking angle (p) based on said comparison, such that when the diffuse horizontal irradiance (DHIapx) is greater than the global tilted irradiance (GTIapx) the rotation of the single horizontal axis (10) is limited to the maximum tracking angle (p).

Description

[0001] DESCRIPTION

[0002] Method for positioning a single-axis solar tracker during cloudy periods

[0003] TECHNICAL SECTOR

[0004] The present invention relates to a method for positioning a single-axis solar tracker during cloudy periods to maximize the solar irradiance received.

[0005] PRIOR STATE OF THE ART

[0006] The solar irradiance received by photovoltaic panels is converted into electrical energy. The electrical energy generated by photovoltaic panels is proportional to the solar energy striking the active surface of the panels; the greater the solar irradiance, the more energy is generated.

[0007] Solar trackers allow you to follow the sun's path to maximize the solar irradiance received by photovoltaic panels. Among solar trackers, single-axis trackers are particularly efficient. A single-axis tracker comprises a single horizontal axis operatively coupled to a drive mechanism and a plurality of photovoltaic panels arranged on this single horizontal axis. The single horizontal axis can rotate through various tracking angles to position the photovoltaic panels in different normal tracking positions to follow the sun throughout the day between sunrise and sunset from east to west.

[0008] Solar tracking presents a significant drawback: it results in reduced performance under certain weather conditions, particularly during cloudy periods, which are the source of diffuse solar radiation. Diffuse solar radiation occurs when direct solar radiation is scattered by clouds and atmospheric particles, leading to light diffraction by the clouds and various molecules suspended in the atmosphere. Under such conditions, it is known that it is better to position photovoltaic panels horizontally to the ground than to place them in standard tracking positions to follow the sun. To determine whether solar tracking is preferable during cloudy periods, decision-making systems are used that incorporate data from multiple sensors measuring irradiance at different locations around the solar tracker site, and / or complex weather forecasting systems.

[0009] EP3940951A1 shows a method for controlling a single-axis solar tracker that involves measuring the solar irradiance on a tracking plane of a panel of the single-axis solar tracker and also measuring the solar irradiance on a horizontal plane using solar plant sensors deployed along a solar plant, and comparing the irradiance levels to bring the panels to a 0 position o when there is a higher level of irradiance in the horizontal plane than in the tracking plane.

[0010] US20180152134A1 shows a method for controlling the orientation of a single-axis solar tracker based on the processing of images obtained with a skycam to predict weather evolution.

[0011] EXPLANATION OF THE INVENTION

[0012] The object of the invention is to provide a method for positioning a single-axis solar tracker during cloudy periods, as defined in the claims.

[0013] The invention relates to a method for positioning a single-axis solar tracker during cloudy periods, wherein the solar tracker comprises a single horizontal axis operatively coupled to a drive mechanism and a plurality of photovoltaic panels arranged on the single horizontal axis, the single horizontal axis being rotatable through various tracking angles to position the photovoltaic panels in different normal tracking positions to follow the sun during the day between sunrise and sunset from East to West;

[0014] The method comprises: using a radiation detection sensor in the vicinity of the single-axis solar tracker to measure global horizontal irradiance (GHI) values ​​of the sun at the location of the single-axis solar tracker over a time interval; determining, based on the global horizontal irradiance (GHI) values ​​measured with the radiation detection sensor, an estimate of the diffuse horizontal irradiance (DHI). apx representative of the diffuse irradiance incident at the location of the solar tracker during that time interval; determine, based on the global horizontal irradiance (GHI) values ​​measured with the radiation detector sensor, an estimate of the global inclined irradiance (GTI). apx representative of the global irradiance incident on the photovoltaic panels during that time interval; compare the diffuse horizontal irradiance DHI apx with the tilted global irradiance GTI apxAnd obtain a maximum tracking angle based on this comparison, so that when the diffuse horizontal irradiance DHI apx is greater than the tilted global irradiance GTI apx The rotation of the single horizontal axis is limited to the maximum tracking angle.

[0015] The proposed method avoids the loss of energy production caused by tracking the sun during cloudy periods when diffuse irradiance predominates, as well as preventing energy waste from unnecessary panel movements. Furthermore, by reducing these movements, the lifespan of the solar tracker can be extended.

[0016] Furthermore, the method requires minimal resources for its on-site application, since the decision to track the sun or not is based on information provided by a radiation detector sensor, which is a simple sensor that only measures global horizontal irradiance (GHI) values ​​of the sun at the location of the solar tracker, and diffuse horizontal irradiance (DHI). apx and also the global tilted irradiance (GTI) apx These values ​​are estimated from simple measurements of global horizontal irradiance (GHI). The method does not require complex calculations of data provided by various sensors mounted on solar trackers, sensors located at different points in the solar plant, or complex weather forecasting systems. These and other advantages and features of the invention will become apparent from the figures and the detailed description of the invention.

[0017] DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 shows a schematic of the solar irradiance produced at the site of a solar tracker.

[0019] Figures 2a and 2b show an example of a single-axis solar tracker.

[0020] Figure 3 shows a flowchart of an example method for positioning a single-axis solar tracker during cloudy periods according to the invention.

[0021] Figure 4 shows a block diagram of a system for carrying out the method.

[0022] Figure 5a shows a graph of the tracking angle adopted by the photovoltaic panels of the single-axis solar tracker during a sunny day with cloudy periods.

[0023] Figure 5b shows a graph of the tracking angle adopted by the photovoltaic panels of the single-axis solar tracker during a cloudy day.

[0024] Figure 6a shows a set of single-axis solar trackers with the photovoltaic panels in normal tracking positions pointing towards the sun, while Figure 6b shows said photovoltaic panels during a cloudy period not pointing towards the sun.

[0025] DETAILED EXPLANATION OF THE INVENTION

[0026] Figure 1 shows a schematic of the solar irradiance produced at the site of a solar tracker showing a global horizontal irradiance (GHI), direct (or beam) normal irradiance (DNI), diffuse horizontal irradiance (DHI), and global inclined irradiance (GTI).

[0027] Global horizontal irradiance (GHI) is the total amount of radiation received from the sky by a surface horizontal to the ground. GHI includes direct normal irradiance (DNI) and diffuse horizontal irradiance (DHI). Direct normal irradiance (DNI) is the solar radiation that arrives in a straight line from the sun based on the sun's current position in the sky, while diffuse horizontal irradiance (DHI) is the solar radiation that does not come directly from the sun but has been scattered by molecules and particles in the atmosphere (especially clouds) and comes from all directions.

[0028] Figure 1 and also Figures 2a and 2b show an example of a single-axis solar tracker 1 having a single horizontal axis 10 operatively coupled to a drive mechanism 11 and a plurality of photovoltaic panels 12 arranged on the single horizontal axis 10. The drive mechanism 11 may comprise a motor for rotating the single horizontal axis 10. The single horizontal axis 10 may be composed of sections operatively coupled to each other.

[0029] As can be seen in Figure 1, the global tilt irradiance GTI is the total amount of radiation received on the active surface of the photovoltaic panels 12 of the single-axis solar tracker 1.

[0030] The unique horizontal axis 10 can rotate through various tracking angles To position the 12 photovoltaic panels in different normal tracking positions to follow the sun throughout the day between sunrise and sunset from East to West. For example, the single-axis solar tracker 1 may include a tracking algorithm that has a plurality of normal tracking positions depending on the tracking angles to follow the sun during the day.

[0031] For example, the tracking algorithm can calculate the tracking angle based on data such as a GPS position of solar tracker 1 and the UTC date and time.

[0032] A tracking angle This is a set angle with respect to a horizontal plane parallel to the ground that allows the active surface of the photovoltaic panels 12 to be positioned perpendicular to the solar radiation coming in a straight line from the sun (see Figure 4). For example, the drive mechanism 11 can rotate the single horizontal axis 10 throughout the day using these tracking angles from the tracking algorithm, which are predetermined angles based on the sun's position to maximize the direct irradiance received by the photovoltaic panels 12. The photovoltaic panels 12 can rotate at least 45 degrees from the horizontal towards the East and at least 45 degrees from the horizontal towards the West, although other angles are possible depending on the location of the solar tracker. Preferably, and as can be seen in Figures 5a and 5b, the photovoltaic panels 12 can rotate between 60 and -60 degrees.

[0033] As can be seen in the flowchart in Figure 3, the method for positioning a single-axis solar tracker 1 during cloudy periods comprises: using a radiation detection sensor 2 in the vicinity of the single-axis solar tracker 1 to measure global horizontal irradiance (GHI) values ​​from the sun at the location of the single-axis solar tracker 1 during a time interval T; and determining, based on the global horizontal irradiance (GHI) values ​​measured with the radiation detection sensor 2, an estimate of a diffuse horizontal irradiance (DHI). apx representative of the diffuse irradiance incident on the site of solar tracker 1 during said time interval T; determine, based on the global horizontal irradiance values ​​GHI measured with radiation detection sensor 2, an estimate of a global inclined irradiance GTI apxrepresentative of the global irradiance incident on the photovoltaic panels 12 during said time interval T; compare the diffuse horizontal irradiance DHI apx with the tilted global irradiance GTI apx and obtain a maximum tracking angle p based on this comparison, so that when the diffuse horizontal irradiance DHI apx be greater than the tilted global irradiance GTI apx , the rotation of the single horizontal axis 10 is limited to the maximum tracking angle p.

[0034] In this way, the solar irradiance received on the photovoltaic panels 12 is maximized, since when the global irradiance inclined GTI apx is predominant, the single horizontal axis 10 rotates according to the tracking angles to place the photovoltaic panels 12 in normal tracking positions pointing towards the sun (see figure 6a) and when the diffuse horizontal irradiance DHI apxIt is predominant, the rotation of the single horizontal axis 10 is limited to arranging the panels 12 at an angle no greater than the tracking angles (see figure 6b).

[0035] The estimation of the tilted global irradiance (GTI) apx and the diffuse horizontal irradiance DHI apx It is determined using simple mathematical expressions that do not require large resources for their calculation, so they can be implemented in a device with low computational capacity, such as a microcontroller, thus allowing the calculation to be implemented locally without the need to connect to external computing devices.

[0036] The estimation of the tilted global irradiance (GTI) apx It is determined from the following expression: where:

[0037] G m is the average of the global horizontal irradiance (GHI) values ​​measured during that time interval T; a mis the average of the solar elevation angle at n adopted by the sun during that time interval T; kl is a constant between 2 and 4, and k2 is a constant between 0 and 1.

[0038] The solar elevation angle is the zenith angle of the sun, i.e., the angle between the direct rays of the sun and the vertical direction above the ground.

[0039] Estimation of diffuse horizontal irradiance (DHI) apx It is determined from the following expression: where:

[0040] G m is the mean of the global horizontal irradiance (GHI) values ​​measured during that time interval T; k3 is a constant between 2 and 4, and k4 is a constant between 0 and 1. For example, the mean G m can be determined according to the following expression: where: n is the number of times the global horizontal irradiance GHI is measured during the time interval T.

[0041] For example, the average at m can be determined according to the following expression: where: n is the number of times the global horizontal irradiance GHI is measured during the time interval T; n is the solar elevation angle at each time n during the time interval T.

[0042] Preferably, the method additionally comprises:

[0043] - Obtain an RTD ratio by comparing the diffuse horizontal irradiance (DHI). apx with the tilted global irradiance GTI apx according to the following expression: where:

[0044] DHI apx is the estimate of the diffuse horizontal irradiance during that time interval T; and

[0045] GTIapx es Yo a estimation of the global tilted irradiance during said time interval T;

[0046] - compare the RTD ratio with decision ranges, where each decision range corresponds to a maximum tracking angle p, and obtain a maximum tracking angle p based on this comparison, so that when the RTD ratio is greater than 1, the rotation of the single horizontal axis 10 is limited to the maximum tracking angle p.

[0047] Accordingly, when the RTD ratio is greater than 1, it means that the sky is at least partially cloudy and that the photovoltaic panels 12 are not arranged in their normal tracking position, but rather the rotation of the single horizon axis 10 is limited according to the maximum tracking angle p.

[0048] The decision ranges and, therefore, the maximum tracking angle p for each decision range are specially calculated to maximize the energy obtained by the 12 panels under diffuse light conditions.

[0049] For example, when the RTD ratio is greater than 1 and less than or equal to 2, the rotation of the single horizontal axis 10 is limited to a maximum tracking angle p1 of less than 35°.

[0050] 1 < RTD <=2; maximum tracking angle ±35°

[0051] For example, when the RTD ratio is greater than 2 and less than or equal to 3, the rotation of the single horizontal axis 10 is limited to a maximum tracking angle p2 of less than 20°.

[0052] 2 < RTD <=3; maximum tracking angle ± 20°

[0053] For example, when the RTD ratio is greater than 3 and less than or equal to 4, the rotation of the single horizontal axis 10 is limited to a maximum tracking angle p3 less than 10°.

[0054] 3 < RTD <=4; maximum tracking angle ± 10°

[0055] For example, when the RTD ratio is greater than 4, the rotation of the single horizontal axis 10 is limited to a maximum tracking angle p4 of less than 5 o .

[0056] 4 < RTD; maximum tracking angle ± 5 o

[0057] For example, when the RTD ratio is less than 1, no maximum tracking angle is set and the single horizontal axis 10 is rotated through the various tracking angles p n to position the 12 photovoltaic panels in the different normal tracking positions.

[0058] 0 < RTD <= 1 ; tracking angle 0 n The method can be repeated continuously throughout the day between sunrise and sunset from East to West, and several time intervals T can be established during the day. Preferably, a time interval T is at least 30 minutes long.

[0059] Preferably, the radiation detection sensor 2 is a pyranometer positioned horizontally near the solar tracker 1 to measure only the global horizontal irradiance (GHI) values ​​of the sun at that location. For example, an SR05-D1A3 pyranometer from Hukseflux.

[0060] Figure 4 shows an example of a system for carrying out the positioning method of a single-axis solar tracker 1 during cloudy periods. The system comprises a single-axis solar tracker 1 and a radiation detection sensor 2, as described above, and an NCU control unit to carry out the method described above.

[0061] The NCU control unit receives global horizontal irradiance (GHI) values ​​measured by radiation detector sensor 2 during a time interval T and tracking angle values ​​adopted by the single horizontal axis 10 during that time interval T, and determines based on these values ​​an estimate of the diffuse horizontal irradiance (DHI). apx and an estimate of the tilted global irradiance (GTI) apx during that time interval T, and compares both estimates to obtain a maximum tracking angle p, such that when the diffuse horizontal irradiance DHI apx be greater than the tilted global irradiance GTI apx , the rotation of the single horizontal axis 10 is limited to the maximum tracking angle p.

[0062] When the diffuse horizontal irradiance DHI apx is greater than the tilted global irradiance GTI apxThe maximum tracking angle p obtained is sent to a tracker control unit TCU of the single-axis solar tracker 1, which generates a signal S to drive the drive mechanism motor 11 to rotate the single horizontal axis 10 until the maximum tracking angle py is reached when the global irradiance tilted GTI apx is greater than the diffuse horizontal irradiance DHI apx , the follower control unit TCU generates a signal S to drive the drive mechanism motor 11 to rotate the single horizontal axis 10 through the various tracking angles? n to position the 12 photovoltaic panels in the different normal tracking positions. The NCU control unit may include a microcontroller to calculate the diffuse horizontal irradiance (DHI). apx and the tilted global irradiance GTI apxbased on the global horizontal irradiance (GHI) values ​​and the solar elevation angle values ​​at n and using the simple mathematical expressions described above.

[0063] For example, the NCU control unit may have an algorithm to calculate the solar elevation angle. n based on data such as a GPS position of solar tracker 1 and the UTC date and time.

[0064] The TCU follower control unit may also comprise a microcontroller comprising the tracking algorithm having a plurality of normal tracking positions according to the tracking angles p n to track the sun during the day, so that the commands of the NCU control unit prevail to limit the rotation of the single horizontal axis 10 in diffuse conditions.

[0065] NCU and TCU control units may comprise a controller, a processor, a microcontroller, an FPGA, or any other computing-capable device.

[0066] Figures 5a and 5b show graphs of the tracking angle p nThe images show the movement of the photovoltaic panels 12 of the single-axis solar tracker 1 during a sunny day with cloudy periods and during a cloudy day, respectively. In these figures, the dashed line represents the normal rotation of the single horizontal axis 10 to track the sun, positioning the photovoltaic panels in the normal tracking position, while the solid line represents the rotation of the single horizontal axis 10 according to the proposed invention, limiting the rotation of axis 10 during cloudy periods. As can be seen, during sunny periods the two lines overlap, but during cloudy periods, the rotation of the axis is limited. In Figure 5b, where there are more cloudy periods, the movement of the panels is less than in Figure 5a, where there are fewer cloudy periods. Therefore, the method allows for a reduction in the energy used to move the solar tracker and maximizes its efficiency.

Claims

CLAIMS 1. Method for positioning a single-axis solar tracker during cloudy periods, wherein the single-axis solar tracker (1) comprises a single horizontal axis (10) operatively coupled to a drive mechanism (11) and a plurality of photovoltaic panels (12) arranged on the single horizontal axis (10), the single horizontal axis (10) being rotatable through various tracking angles ( ? n ) for positioning the photovoltaic panels (12) in different normal tracking positions to follow the sun during the day between sunrise and sunset from East to West; characterized in that the method comprises: - use a radiation detection sensor (2) in the vicinity of the single-axis solar tracker (1) to measure global horizontal irradiance (GHI) values ​​of the sun at the location of the single-axis solar tracker (1) during a time interval (T); - determine, from the global horizontal irradiance (GHI) values ​​measured with the radiation detector sensor (2), an estimate of a diffuse horizontal irradiance (DHI) apx ) representative of the diffuse irradiance incident on the location of the single-axis solar tracker (1) during said time interval (T); - determine, from the global horizontal irradiance (GHI) values ​​measured with the radiation detector sensor (2), an estimate of a global tilted irradiance (GTI) apx ) representative of the global irradiance incident on the photovoltaic panels (12) during said time interval (T); - compare the diffuse horizontal irradiance (DHI) apx ) with the tilted global irradiance (fiTI) apx and - obtain a maximum tracking angle (p) based on this comparison, such that when the diffuse horizontal irradiance (DHI) apx) is greater than the tilted global irradiance (GTI) apx ), the rotation of the single horizontal axis (10) is limited to the maximum tracking angle (p).

2. Method according to claim 1, wherein the estimation of the tilted global irradiance (GTI) apx ) is determined from the following expression: where: G m is the average of the global horizontal irradiance (GHI) values ​​measured during that time interval (T); a m is the average of the solar elevation angle (a n ) adopted by the sun during that time interval (T); kl is a constant between 2 and 4, and k2 is a constant between 0 and 1.

3. Method according to claim 1 or 2, wherein the estimation of the diffuse horizontal irradiance (DHI) apx ) is determined from the following expression: where: G mis the average of the global horizontal irradiance (GHI) values ​​measured during that time interval (T); k3 is a constant between 2 and 4, and k4 is a constant between 0 and 1.

4. Method according to any of the preceding claims, wherein the method further comprises: - obtain a ratio (RTD) by comparing the diffuse horizontal irradiance (DHI) apx ) with the tilted global irradiance (GTI) apx ) according to the following expression: - compare the ratio (RTD) with decision ranges, each decision range corresponding to a maximum tracking angle (p), and obtain a maximum tracking angle (p) based on this comparison, so that when the ratio (RTD) is greater than 1, the axis rotation single horizontal (10) is limited to the maximum tracking angle (p).

5. The method according to the preceding claim, wherein: when the ratio (RTD) is greater than 1 and less than or equal to 2, the rotation of the single horizontal axis (10) is limited to a maximum tracking angle (p1) of less than 35°; when the ratio (RTD) is greater than 2 and less than or equal to 3, the rotation of the single horizontal axis (10) is limited to a maximum tracking angle (p2) of less than 20°; when the ratio (RTD) is greater than 3 and less than or equal to 4, the rotation of the single horizontal axis (10) is limited to a maximum tracking angle (p3) of less than 10°; when the ratio (RTD) is greater than 4, the rotation of the single horizontal axis (10) is limited to a maximum tracking angle (p4) of less than 5°. o , and when the ratio (RTD) is less than 1, no maximum tracking angle (p) is set and the single horizontal axis (10) rotates through the various tracking angles (p nto position the photovoltaic panels (12) in the different normal tracking positions.

6. Method according to any of the preceding claims, wherein when the rotation of the single horizontal axis (10) is limited to the maximum tracking angle (p), the single horizontal axis (10) rotates through the various tracking angles (p n ) until reaching the maximum tracking angle (p).

7. Method according to any of the preceding claims, wherein the time interval (T) is at least 30 minutes.

8. Method according to any of the preceding claims, wherein the radiation detector sensor (2) is a pyranometer arranged horizontally in the vicinity of the solar tracker (1) to measure only global horizontal irradiance (GHI) values ​​of the sun at said location.

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