Systems and methods for split-cell and multi-panel photovoltaic tracking control
Split-cell and multi-panel photovoltaic backtracking control systems and methods allow for increased total power generation during low sun elevation conditions by shading a percentage of panel modules, thereby allowing for a lower angle of incidence on unshaded modules. The control systems and methods involve determining a sun elevation angle, a traditional backtracking angle, a split-cell or multi-panel backtracking angle, a single-cell or single-panel relative light transmission (RLT) based on the single-cell or single-panel backtracking angle, and a split-cell or multi-panel RLT based on the split-cell or multi-panel backtracking angle. If twice the single-cell or single-panel RLT is greater than the split-cell or multi-panel RLT, the split-cell or multi-panel backtracking angle is used; otherwise, the single-cell or single-panel backtracking angle is used. The control systems and methods may further involve determining a diffuse fraction index (DFI) and, if the DFI is greater than a DFI limit, using a DFI tracking angle.
1. A method of controlling a single-axis solar tracker comprising:
determining a sun elevation angle;
determining a single-cell or single panel solar array backtracking angle based on the sun elevation angle;
determining a split-cell or multi-panel solar array backtracking angle based on the sun elevation angle;
determining a first relative light transmission (RLT) based on the single-cell or single panel solar array backtracking angle;
determining a second RLT based on the split-cell or multi-panel solar array backtracking angle;
determining that the first RLT and the second RLT satisfy a predetermined relationship; and
in response to determining that the first RLT and the second RLT satisfy the predetermined relationship, controlling the single-axis solar tracker to rotate the solar array to the split-cell or multi-panel solar array backtracking angle.
2. The method of claim 1 , further comprising:
determining that the first RLT and the second RLT do not satisfy a predetermined relationship; and
in response to determining that the first RLT and the second RLT do not satisfy the predetermined relationship, controlling the single-axis solar tracker to rotate the solar array to the single-cell or single-panel solar array backtracking angle.
3. The method of claim 1 , wherein the predetermined relationship is that twice the first RLT is greater than the second RLT.
4. The method of claim 1 , further comprising:
determining a diffuse fraction index (DFI);
determining that the DFI is greater than a DFI limit; and
in response to determining that the DFI is greater than a DFI limit, controlling the single-axis solar tracker to rotate the solar array to the DFI backtracking angle instead of the split-cell or multi-panel backtracking angle.
5. The method of claim 1 , wherein determining a single-cell or single panel solar array backtracking angle includes evaluating the following expression:
θ
t
=
θ
S
-
cos
-
1
(
cos
(
θ
S
)
G
C
R
)
where θ s is the sun elevation angle relative to the horizon, θ t is the backtracking angle relative to the zenith, and GCR is a ground coverage ratio.
6. The method of claim 1 , wherein determining a split-cell or multi-panel solar array backtracking angle includes evaluating the following expression:
θ
t
=
2
tan
-
1
(
tan
(
θ
S
)
-
1
-
4
(
1
G
C
R
)
2
+
tan
2
(
θ
S
)
2
G
C
R
+
1
)
where θ s is the sun elevation angle relative to the horizon, θ t is the backtracking angle relative to the zenith, and GCR is a ground coverage ratio.
7. The method of claim 6 , wherein the GCR is a span or width of the solar array divided by the pier-to-pier distance between rows of piers.
8. A solar tracker system, comprising:
a first solar array including a first segment and a second segment, the first solar array rotatably coupled to a first support pier and a first motor for driving the rotation of the first solar array;
a second solar array including a first segment and a second segment, the second solar array rotatably coupled to a second support pier and a second motor for driving the rotation of the second solar array;
a controller coupled to the first motor and the second motor, the controller configured to:
determine a sun elevation angle;
determine a single-cell or single panel solar array backtracking angle based on the sun elevation angle;
determine a split-cell or multi-panel solar array backtracking angle based on the sun elevation angle;
determine a first relative light transmission (RLT) based on the single-cell or single panel solar array backtracking angle;
determine a second RLT based on the split-cell or multi-panel solar array backtracking angle;
determine that the first RLT and the second RLT satisfy a predetermined relationship; and
in response to determining that the first RLT and the second RLT satisfy the predetermined relationship, control the first motor to rotate the first solar array to the split-cell or multi-panel solar array backtracking angle.
9. The solar tracker system of claim 8 , wherein the controller is further configured to:
determine that the first RLT and the second RLT do not satisfy a predetermined relationship; and
in response to determining that the first RLT and the second RLT do not satisfy the predetermined relationship, control the first motor to rotate the first solar array to the single-cell or single-panel solar array backtracking angle.
10. The solar tracker system of claim 8 , wherein the predetermined relationship is that twice the first RLT is greater than the second RLT.
11. The solar tracker system of claim 8 , wherein the controller is further configured to: determine a diffuse fraction index (DFI);
determine that the DFI is greater than a DFI limit; and
in response to determining that the DFI is greater than a DFI limit, control the first motor to rotate the first solar array to a DFI tracking angle.
12. The solar tracker system of claim 8 , wherein determining a single-cell or single panel solar array backtracking angle includes evaluating the following expression:
θ
t
=
θ
S
-
cos
-
1
(
cos
(
θ
S
)
G
C
R
)
where θ s is the sun elevation angle relative to the horizon, θ t is the backtracking angle relative to the zenith, and GCR is a ground coverage ratio.
13. The solar tracker system of claim 8 , wherein determining a split-cell or multi-panel solar array backtracking angle includes evaluating the following expression:
θ
t
=
2
tan
-
1
(
tan
(
θ
S
)
-
1
-
4
(
1
G
C
R
)
2
+
tan
2
(
θ
S
)
2
G
C
R
+
1
)
where θ s is the sun elevation angle relative to the horizon, θ t is the backtracking angle relative to the zenith, and GCR is a ground coverage ratio.
14. The solar tracker system of claim 13 , wherein the GCR is the span of the first solar array divided by a distance between the first support pier and the second support pier.
15. The solar tracker system of claim 8 , wherein the first solar array is a split-cell solar array, a multi-panel-in-landscape solar array, or a multi-panel-in-portrait solar array.