Technical and Economic Feasibility study on Repowering of Wind Farms

Objectives: The main objective of the paper is to perform a repowering assessment of an old wind farm consisting of 2 bladed turbines located at Gudimangalam near Coimbatore in Tamil Nadu which is a good wind potential site. Methods/Statistical Analysis: Repowering refers to the replacement of first generation small capacity wind turbines with modern multi megawatt wind turbines that can produce more energy than before from the same site. Technical analysis of the site is done using WAsP software with the help of wind data collected from a met mast at the site and includes the calculation of Net Annual Energy Production and Wake losses. Net Annual Energy Production and Wake losses are the primary indicators for selecting the best options for repowering. The option selected is further supported by calculating the economic performance indices. The total repowering has been accomplished through partial repowering executed in three stages. Partial repowering refers to the replacement of only few of the turbines from the existing wind farm rather than replacing the whole farm. The economic feasibility of every repowering option has been studied based on the calculation of the economic performance indices like ALCoG, Payback Period and IRR. Findings: The study mainly results in framing a procedure for performing total repowering for any site through the optimization of best possible partial repowering options. The existing site comprises 18 turbines of 450 kW rating and is having a net AEP of 14.5 GWh with a wake loss of 3.82%. The Plant Load Factor (PLF) is obtained to be 20.44%. The best possible total repowering option is found to be producing a net AEP of 65.287 GWh with a wake loss of 2.36% and included 9 Suzlon S95 2.1 MW turbines which are four times the AEP of the existing farm. The three stages of partial repowering also include replacement of 6 old turbines by 3 new turbines in each stage. Finally the total repowering is reached through the execution of partial repowering options in three stages and it results in close proximity to the best possible total repowering option in both technical and economic aspects. The final repowering eventually attained results in a net AEP of 65.28 GWh with a wake loss of 2.36% which is the exact match of the best possible total repowering option found in the beginning. The total repowering also leads to an improvement in PLF i.e. almost doubles the PLF to 39.42%. Application/Improvements: This procedure can be very useful where the initial investment is an important factor. The study infers that performing total repowering through optimization process is more beneficial than performing partial repowering randomly.