This paper presents a detailed measurement study of the electrical energy consumption of commercial Multiple Input Multiple Output (MIMO) Power Line Communications (PLC) modems. Based on these measurements, we propose a linear model that can be used to predict the energy consumed for different communication states and different operation modes of MIMO PLC modems (idle, standby, transmission, reception, variable data rates and variable Ethernet frame sizes). A multiple regression analysis is used to estimate the model parameters. Such an experimental campaign provides valuable data for benchmarking the energy consumption of MIMO PLC modems and gives insights on which energy improvements can be evaluated