... 4% 1. GoodWe GW4000-SS Advantages1) High quality of power generation connected to the grid: THDi < 1%.2) Maximize Solar ... Energy: High MPPT Efficiency > 99.5%.3) ... -1-1/A1, RD1663, ENEL, G83,G59, SAAAC grid frequencyAccording to VDE 0126-1-1/A1, RD1663, ENEL, ... Standard warranty[years]5/10( optional) GW4000-SS grid tie inverter china