The energy efficiency of various OFDM systems, such as optical, mobile, Wireless and WiMaX systems, has been analyzed in this paper. High peak to average power ratio that may appear in modulation process is one of the main problems in OFDM systems. The influence of subcarriers number and modulation techniques to the peak-to-average power ratio in different OFDM based systems has been studied. The results of analysis are presented in numerous figures and tables. The main goal is to provide a comparative study that can be used for an optimal system selection with predefined power consumption requirements.