To　evaluate　the　performance　of　photovoltaic　(PV)　power　plants,　it　is　necessary　to　effectively　monitor　PV　power　plants.　An　online　monitoring　system　based　on　open-source　platform　is　presented　for　monitoring　and　managing　the　PV　power　plant　effectively　and　economically.　The　proposed　monitoring　system　consists　of　data　acquisition,　transmission　part,　data　gateway,　and　on-line　monitoring　center.　A　PV　diagnosis　approach　based　on　FFA-SVM　for　array　fault　is　implemented　in　the　gateway.　The　on-line　monitoring　center　based　on　the　platform　ubidots　is　designed　for　displaying　the　data　and　monitoring　PV　arrays.　Experiment　results　show　that　the　system　can　realize　abundant　data　visualization　and　accurate　PV　fault　diagnosis.　Copyright　(C)　2018　The　Authors.　Published　by　Elsevier　Ltd.