In this study, a novel renewable double-energy system, coupling activated biochar production and thermoelectric generation, is conducted and demonstrated. In the installed 13 thermoelectric modules (TEMs), they are partitioned into three groups of 3, 4, and 6 TEMs. The temperature difference across the TEMs depends upon the number of TEMs and is ranked as 3 TEMs > 4 TEMs > 6 TEMs. By harvesting the waste heat from the carbonization of water chestnuts, the greatest mean output power of single TEMs is 14.1 W and the mean output power of the installed 13 TEMs at the carbonization time of 10-30 min is 8.8 W. The higher heating value of produced activated biochar is 28.17 MJ kg(-1), accounting for 42.7% improvement in the calorific value when compared to its untreated counterpart. The analysis also suggests that heavy metals contained in this coal-like renewable solid fuel are fairly low. The activated biochar possesses high hydrophilicity and specific surface area (430 m(2) g(-1)), and a large portion of pore sizes is smaller than 2 nm. The analyses of attenuated total reflectance spectrometry, X-ray diffractometry, and thermogravimetry also clearly indicate the impact of carbonization on the biomass structure. Overall, the produced activated biochar is suitable for an alternative fuel, absorbent, and soil amendment.