The invention allows verifying the performance of energy over time of any photovoltaic or wind solar plants whose value of energy produced is made available on computers accessible through a public data communication network and monitoring the operation thereof. Energy production values of a plant over time (even from the plant start up) are collected by computers connected to the Internet public network which present them in a hypertext structure of accessible documents, the current ones from an energy meter inserted downstream of the plant and the historical and current weather ones from computers also connected to the Internet public network. The result obtained is the automatic production, i.e. in almost zero processing time, of operating reports that include the energy produced, the revenues and a performance index over time with energy performance measurements, graphs, analysis and alerts of photovoltaic solar and wind plants.