STRATEGIES TO IMPROVE SOLAR PLANT PERFORMANCE
In last three years, Indian has achieved in installation of 1.5 GW and developers are striving hard to boost their plant performance to remain competitive and maximize their profits. Recent data released by MNRE justifies that the solar plant CUF can be as high as 24.5 % which gives developers confidence to invest in solar PV technology. It is important for EPC developers O&M service providers to consider various options/ strategies to increase their plant yield at a minimal cost.
In order to improve the plant performance the operators should focus on 5 Basic parameters right at the plant design stage to achieve optimized plant performance. These option includes reduced DC cable layout losses, shadow losses, inverter losses, AC wiring losses and module miss-match losses.
We have explain in detail about the above losses in our previous articles and not like to repeat the same in this article, however, major inspiration in this article is to focus on plant performance to improve data management.
We believe that most of the plat owner collect data right at the string level to the inverter level, however, this data is not analyzed by the plant operators and successful strategies remain unidentified to improve plant performance. Typically, most of the solar project owner install SCADA system and fed the data in that at their control room and headquarter. Most of the project developer analyses the plant data in term of specific yield (kWh/ MW), CUF and performance ratio. While performance ratio is universally accepted as overall indicator of plant performance, the further improvement in performance ratio can only be done if the data collected by a SCADA system is analyzed right at string level. For example, the string level generation can be separately analyzed for the day and weakest string can be identified to check specific losses at string level. If any of the string is not performing in line with other string it may be due to module mismatch losses, wiring losses or shadow loss which needs to be analyzed by physically visiting specific string once you have analyzed overall data.
Apart from string losses, it is observed that significant losses occur at inverter level. The losses at inverter level may be because of a faulty system design or inverter is not matching with the connected PV generator. While system sizing, it is important that inverter is selected by considering operating temperature of the location and string size is determined considering the input voltage window of the inverter. Some of the latest inverters have option to operate in a master and slave mode as well as in reversible master and slave mode so that the inverter loading can be optimized to reduce the losses at inverter level. The losses in inverter are also function of operating temperature of inverter and many times project developers over EPC not focus on proper ventilation for the cooling level of inverter which leads to higher losses in the inverter.
Selecting a right cable size is equally important and conducting of cable together may reduce the Ampacity of cable which may lead to higher losses in the plant. In fact operating temperature of DC cable is equally important and cable routing should be done in a separate cable tray having slotted holes for proper ventilation to dissipate heat generated through DC cable. While most of the developers focus on controlling the losses on the DC side of the plant. It is equally important to control the losses of AC side of the plant and in this regards selection of transformer, RMU (Ring main units), LT and HT switchgears is critical.
Losses due to shading are underestimated, at least in India. Some people consider the liner shading losses but in actual, effect of shading is not liner to the generation. Solar panel especially crystalline technology reduce their output even by 50% with just 10-15% of shading. In a typical solar plant inverter room, control are the main building which become reason of shading. It is true that shading cannot be avoided but motive is to optimize the design so that losses due to shading can be minimized.
It has also been seen in some plants that one string is putting shadow on the next string. So, one should take care of structure design and while selecting structure, designer should give special attention to thermal expansion of the material used and site maximum temperature.
Module miss-match losses cannot be zero down as there will defiantly be some manufacturing alteration in one module to another. This alteration is known as Module power tolerance. While selecting a module one should take care that these tolerance limit is minimum. Now days, good quality manufactures are providing modules with module power tolerance as less as 3%. Please read article for more information on Power tolerance by following the link: http://firstgreenconsulting.wordpress.com/2013/07/20/effect-of-solar-pv-module-tolerance-on-your-pocket/