Methods, systems, and devices for wireless communications are described. An energy transmitter device may transmit an energy signal to an energy receiver device for energy harvesting by the energy receiver device. To communicate channel state information (CSI) of a channel between the energy transmitter device and the energy receiver device, the energy transmitter device may transmit a first signal to the energy receiver device. In response, the energy receiver device may transmit a second signal to the energy transmitter device that is indicative of the CSI, where the CSI is based on the first signal. The energy transmitter device may transmit additional signals to the energy receiver device whose transmission characteristics are based on the CSI.