Sensors and methods for monitoring soiling on monofacial and bifacial photovoltaic panels
Systems and methods for monitoring soiling of one or more photovoltaic (PV) modules. A sensor is provided that includes a measure chamber and a clean chamber. Cells in the measure chamber allow a measurement to be taken that accounts for soiling. Reference cells in the clean chamber can be exposed to incident light outside of the clean chamber. Measurements taken when the reference cells are outside of the clean chamber allow a clean output to be determined that is not subject to soiling. Comparing the output of the reference cell and the cells in the measure chamber allows a soiling loss to be determined.
1 . A sensor for monitoring soiling of photovoltaic modules, the sensor comprising:
at least one measurement cell that is arranged to generate a measurement signal, wherein the at least one measurement cell is subject to soiling over time;
a first reference cell, wherein the first reference cell is arranged to receive at least incident radiation;
a controller;
wherein the controller is configured to transition the first reference cell from a protected state to a measurement state, to perform a measurement using the first reference cell, and to transition the first reference cell back to the protected state,
wherein a soiling loss of a photovoltaic module associated with the sensor is determined based on an output of the first reference cell and an output of the at least one measurement cell; and
a second reference cell, wherein the second reference cell is positioned near the first reference cell, wherein the second reference cell is transitioned between the protected state and the measurement state, and wherein the measurement state allows the first reference cell to receive incident radiation and allows the second reference cell to receive reflected radiation.
2 . The sensor of claim 1 , wherein the controller does not expose the first reference cell or perform the measurement using the first reference cell when an output of the at least one measurement cell indicates that the first reference cell should not be exposed or when external conditions would subject the first reference cell to soiling.
3 . The sensor of claim 1 , wherein the controller is configured to compare an output of each of the at least one measurement cell with the output of the first reference cell to determine information on a non-uniform nature of the soiling.
4 . The sensor of claim 1 , wherein the output of the at least one measurement cell and the output of the first reference cell is used to calculate the soiling loss based on a ratio of signals from each of the at least one measurement cell and a signal from the first reference cell.
5 . The sensor of claim 1 , further comprising a clean chamber, wherein the clean chamber is resistant to at least water and dust, and wherein the first reference cell is inside the clean chamber in the protected state.
6 . The sensor of claim 5 , wherein the at least one measurement cell comprises a second measurement cell, wherein the soiling loss of the photovoltaic module associated with the sensor is further determined based on an output of the second reference cell and an output of the second measurement cell.
7 . The sensor of claim 5 , wherein the clean chamber comprises a resealable opening, wherein the first reference cell and the second reference cell are transitioned from the protected state to the measurement state using the resealable opening to transition to the measurement state to operate in a measurement mode and to the clean chamber to operate in a rest mode, wherein the clean chamber is closed when the first and second reference cells are inside the clean chamber.
8 . The sensor of claim 7 , wherein the first reference cell and the second reference cell are configured to be in unison or independent when transitioned between the protected state and the measurement state.
9 . The sensor of claim 1 , wherein the first reference cell is used to determine a first soiling loss associated with a first surface of the photovoltaic module associated with the sensor and the second reference cell is used to determine a second soiling loss associated with a second surface of the photovoltaic module associated with the sensor.
10 . A measurement system, comprising:
a sensor associated with a string of photovoltaic modules, the sensor comprising:
a first reference cell, wherein the first reference cell is arranged to measure at least incident radiation;
a clean chamber;
a controller, wherein the controller is configured to transition the first reference cell from a first position relative to the clean chamber where the first reference cell is protected from soiling to a measurement position relative to the clean chamber where the first reference cell is exposed to incident light, to perform a measurement using the first reference cell, and to transition the first reference cell back to the first position relative to the clean chamber;
a second reference cell configured to receive reflected light and positioned near the first reference cell, wherein the second reference cell is transitioned relative to the clean chamber between the first position and the measurement position,
wherein the measurement position allows the second reference cell to receive the reflected light;
a measurement circuit, wherein the measurement circuit is configured to measure a power of a selected photovoltaic module within the string of photovoltaic modules,
wherein the controller is configured to determine a soiling loss associated with the selected photovoltaic module by:
determining a maximum power that could have been generated by the selected photovoltaic module based on an output of the first reference cell; and
comparing the power of the selected photovoltaic module with the maximum power to determine the soiling loss of the selected photovoltaic module.
11 . The measurement system of claim 10 , wherein the clean chamber is resistant to at least water and dust, and wherein the first position relative to the clean chamber is inside the clean chamber.
12 . The measurement system of claim 10 , wherein the controller is further configured to determine a second soiling loss associated with a second selected photovoltaic module of the string of photovoltaic modules by:
determining a second maximum power that could have been generated by the second selected photovoltaic module based on an output of the second reference cell; and
comparing the power of the second selected photovoltaic module with the second maximum power that could have been generated by the second selected photovoltaic module to determine the soiling loss of the second selected photovoltaic module.
13 . The sensor of claim 10 , wherein the clean chamber comprises a resealable opening, wherein the first reference cell and the second reference cell are transitioned from the first position in a protected state to the measurement position in an exposed state using the resealable opening to operate in a measurement mode and are transitioned to the clean chamber to operate in a rest mode, wherein the clean chamber is closed when the first and second reference cells are inside the clean chamber.
14 . The measurement system of claim 13 , wherein exposure of the first reference cell and the second reference cell are configured to be in unison or independent.
15 . The measurement system of claim 10 , wherein the first reference cell is used to determine a first soiling loss associated with a first surface of the selected photovoltaic module and the second reference cell is used to determine a second soiling loss associated with a second surface of the selected photovoltaic module.
16 . A measurement system comprising:
a sensor associated with a string of photovoltaic modules, the sensor comprising:
a first reference cell, wherein the first reference cell is arranged to measure at least incident radiation;
a first controller;
a mechanism wherein the first controller is configured to transition the first reference cell between a first state where the first reference cell is protected from soiling and a measurement state where the first reference cell is exposed to incident light, to perform a measurement using the first reference cell, and to transition the first reference cell back to the first state; and
a second reference cell configured to receive reflected light, wherein the second reference cell is positioned near the first reference cell, wherein the second reference cell is transitioned by the mechanism between the first state and the measurement state;
wherein the measurement state allows the first reference cell to receive incident light and allows the second reference cell to receive the reflected light;
a measurement circuit, wherein the measurement circuit is configured to measure a measured short circuit current of the string of photovoltaic modules that have been disconnected from an inverter; and
a second controller configured to determine a soiling loss associated with the string of photovoltaic modules by:
determining a short circuit current that could have been generated by the string of photovoltaic modules based on an output of the first reference cell; and
comparing the short circuit current of the string of photovoltaic modules with a maximum short circuit current based on the output of the first reference cell.
17 . The measurement system of claim 16 , wherein the sensor further comprises a clean chamber, wherein the clean chamber is resistant to at least water and dust and wherein the first state is inside the clean chamber.
18 . The measurement system of claim 16 , wherein the second controller is further configured to determine the soiling loss associated with the string of photovoltaic modules by comparing the short circuit current of the string of photovoltaic modules with a second maximum short circuit current based on an output of the second reference cell.
19 . The sensor of claim 17 , wherein the clean chamber comprises a resealable opening, wherein the first reference cell and the second reference cell are transitioned from a protected state to an exposed state using the resealable opening to transition to the measurement state to operate in a measurement mode and to the clean chamber to operate in a rest mode, wherein the clean chamber is closed when the first and second reference cells are inside the clean chamber.
20 . The measurement system of claim 16 , wherein transitions of the first reference cell and the second reference cell are configured to be in unison or independent, wherein the first reference cell is used to determine a first soiling loss associated with first surfaces of the string of photovoltaic modules and the second reference cell is used to determine a second soiling loss associated with second surfaces of the string of photovoltaic modules.