use local version of pveducation iv curve plot

Author: kandersolar

Tutorial 4 - Model a Module's Performance.ipynb

@@ -166,7 +166,7 @@
     "\n",
     "Continuous IV curve models like the CEC, PVsyst, and DeSoto models yield a relation between current and voltage called an IV curve, and therefore yield a continuous set of (V, I) points spanning from Isc to Voc and beyond. The domain of the IV curve is in quadrants 1, 2, and 4 where voltage is on the horizontal and current is on the vertical axis. The figure below from [PV Education PVCDROM](https://www.pveducation.org/pvcdrom/welcome-to-pvcdrom) shows an IV curve of an \"ideal\" cell.\n",
     "\n",
-    "[![IV curve](https://www.pveducation.org/sites/default/files/PVCDROM/Modules/Images/NONIDEAL.gif)](https://www.pveducation.org/pvcdrom/modules-and-arrays/mismatch-effects)\n",
+    "[![IV curve](images/t4_PVEducation_IVCurve.PNG)](https://www.pveducation.org/pvcdrom/modules-and-arrays/mismatch-effects)\n",
     "\n",
     "Attribution: [PV Education, UNSW, ASU, _et al._](https://www.pveducation.org/pvcdrom/modules-and-arrays/mismatch-effects)"
    ]