Statistical analysis of ramp rates of solar photovoltaic system connected to grid

Penetration of Photovoltaic (PV) power to the grid is increasing very rapidly. Ramp rate (RR) of the PV power is important to determine the capacity of the energy storage for dispatching smoothed PV power to the grid. This paper focuses on determination of ramp RR of the PV generated power due to irradiance and temperature fluctuation. In order to investigate the smoothing effect of geographically distributed PV stations, global horizontal irradiance (GHI) and temperature (°C) with 5 min resolution at four sites across the Colorado State were converted to PV power by proper design of 0.5MW grid-connected PV plant. The ramp rates (RRs) of the stations are calculated by exploiting the moving average. Smoothing effect of geographically distributed PV stations is shown by comparing the histogram of the RRs of the sites. Also the cumulative distribution functions (CDF) are employed for this analysis. The Pearson correlation of PV power of each of the sites increases with geographic proximity of the sites. The analysis shows that the RR and PV power fluctuation is reduced after averaging the generated power of four stations. Also, statistical analysis of RR is advantageous in understanding the extent of variability of PV power.