Self-contained blockchain mining and high-energy-density computing systems have a low temperature heat engine (LTHE) with a working fluid loop extended between a heat source and a heat sink; a biockchain mining device connected to receive electricity generated from the LTHE; a heat exchanger on the working fluid loop; and a coolant loop extended between the blockchain mining device and the working fluid loop (heat exchanger). A self-contained high-energy-density computing data center (HEDC) system is disclosed comprising: a low temperature heat engine (LTHE) with a working fluid loop extended between a heat source and a heat sink; an HEDC device connected to receive electricity generated from the LTHE; a heat exchanger on the working fluid loop; and a coolant loop extended between the HEDC device and the working fluid loop (heat exchanger). A method is also disclosed comprising: generating electricity using a low temperature heat engine (LTHE); operating an HEDC device, using electricity generated by the LTHE, to carry put computer processes; and cooling the HEDC device by heat exchange with working fluid of the LTHE.