Thursday, March 5, 2015

PV Array (Solar Panel) Thermography

 Solar energy is a clean and inexhaustible energy source. According to the World Energy Outlook 2014, solar power has contributed significantly (18%) to the growth of renewable energy technologies in the recent decade, after the wind power (34%) and hydropower (30%). Solar energy is gaining popularity in many countries because the cost of solar energy is getting cheaper making it more competitively priced against generating electricity using fossil fuels. Many countries have achieved Grid Parity (when solar or other renewable power sources can generate electricity at costs equal or less than the conventional fossil fuel sources).  In some remote areas, solar energy has become one of the substantial alternative energy sources where the conventional electrical grid is hard to reach. 

The solar photovoltaic (PV) system converts sunlight into electrical energy using the photoelectric effect.  With continuous technology innovations and cost reduction aided by global subsidies, solar PV is becoming a fast growing industry.  
A solar PV system consists of several main components:
- Solar panels to absorb and convert the solar power to electricity
- Solar inverter to change the electrical current from DC to AC
- Mounting and cabling accessories that make up the system

A solar panel consists of a matrix of solar cells. The failure of any solar cell may lead to a drop in power generation causing output yield losses. A solar farm may consist of a few thousand solar panels. Testing each individual solar panel at the installation site using the direct wire connection for checking output is time consuming and cumbersome. A more effective method is using the thermography scan to detect if the solar cells is overheating due to shade or defective cells. When a cell is shaded or not working, the cell consumes power from the adjacent series of solar cells instead of generating power.  This causes the cell to overheat as seen in the thermal images indicated by the hotspots as shown in the following figures. To minimize the shading effect, the manufacturer normally installs bypass diodes to the solar panel. However, the bypass diodes can degrade or become defective, which will also create the similar problem of hotspots.  If the affected cells continue to heat up the adjacent cells, the power generated will be greatly reduced. 

The anomalies detected in the thermal image should be compared with a normal solar cell. It is recommended to further confirm the anomalies detected with relevant electrical testing. 

Figure 1 Thermography scan with thermal-visual side-by-side images using Keysight TrueIR Analysis and Reporting Tool showing multiple hotspots indicated in red detected on one of the solar panel

Figure 2 Picture-in-picture (fusion) mode in Keysight U5855A Thermal Imager enables user to identify the location of the abnormalities easily with a combination of IR and visible images