“Thermographic imaging is commonly part of the preventive maintenance schedule of PV power plants, but when it comes to the replacement of defective modules, no firm decision algorithm exists”, explains Dr. Robin Hirschl, managing director of the ENcome group, a pan-European technical service provider for PV power plants.
The newly developed method aims to replace common rules of thumb as “from five degree over-temperature replace a module” which is often applied. The problem of such simplistic methods is, that wind, thermography view angle, and irradiance influence the estimation of cell temperatures. Neither does this rule account for the financial implication of replacing one or multiple modules.
Starting point is a previous thermal model for PV modules, developed by a consortium led by the Austrian Institute of Technology (AIT): Based on environment conditions, IR-radiation of ground and sky, illumination, module layering and other impacts, the module layers’ temperature distribution can be calculated, and at the same time the electric production. This model can be used in an inverse way to estimate the heat source in the cell area, based on the front module temperature and the environmental conditions. By comparing the heating power of a hot cell to its known ideal conditions under the environment, the energy balance delivers the electrical underachievement, and hence the monetary gain by replacing the module. To obtain the quantitative frontal module temperatures for such an investigation is not an easy task, as outdoor thermography images are often perturbed by reflections, and angle dependence of thermal emission changes the originally obtained “temperatures” of upper rows. Hence it is necessary to correct for this effects, before one can cast a raster on the modules to extract individual cell temperatures. This is also done automatically.
“ENcome Energy Performance thus has an objective methodology at hand to determine the financial impact of a hot-spot and decide on facts whether the replacement of a module is indicated”, concludes Robin Hirschl. While IR measurements of modules are part of the standard preventive maintenance program offered by ENcome, also individual IR assessments or evaluation of single pictures are possible.
The ENcome group is a pan-European leading and independent provider for the operation of photovoltaic power plants with focus on technical Operation and Maintenance (O&M), technical Asset Management (TAM) and the compilation of technical expertise. At present ENcome operates power plants with a nominal capacity of several hundred megawatts in different countries. Well skilled engineers ensure the best yield for every renewable energy park in any grid environment. Furthermore ENcome offers other services along the asset lifecycle of photovoltaic installations partnering amongst others with renown law firms, tax advisers and security centres.