Sensors and methods for monitoring soiling on monofacial and bifacial photovoltaic panels

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.

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.