This work experimentally studies the energy consumption of multiple-antenna MIMO 802.11 devices. Our measurements reveal an increase in power consumption and speed with the number of antennas. State of the art proposals have limitations to save energy in MIMO 802.11 networks. First, they focus on either maximizing speed or minimizing power consumption. Second, they only seek to minimize energy for the receiver side of mobile devices. As a result, they present limitations to utilize MIMO speed gains and to save energy in MIMO 802.11 infrastructure. To this end, we design Collaborative MIMO Energy Save (CMES), which seeks to identify the transmitter-receiver most energy efficient antenna setting, at runtime. Our experiments with commodity MIMO 802.11n testbeds confirm that CMES can provide energy savings in real scenarios.