Electro Pulse Boring: An Experimental Rock-breaking Technology for Low-cost Access to Ubiquitous, Inexhaustible, Autonomous, Ultra-deep (5-10 km) Geothermal Heat

W.C. Leighty
The Leighty Foundation,
United States

Keywords: energy, CO2-emission-free, baseload, geothermal, ubiquitous


Deep geothermal heat is Humanity's only potential benign, baseload, inexhaustible, Earth-ubiquitous, and potentially-affordable energy source for all purposes. But we cannot afford to bore deep enough with today's prevailing rotary, abrasive, prevailing technology. "Electro Pulse Boring" (EPB), a novel rock-breaking technology, uses very high voltage, high power, short electric pulses (500-700 kV, 10 ns, ~1,500 J, 10-20 pps, average power ~ 25 kW) to fracture rock, to enable low-cost, distributed, deep (5-10 km) geothermal heat harvest anywhere on Earth. These deep EPB boreholes drive baseload electricity generation plants, with byproduct hot water for district heating and cooling (DHC). Off-peak electricity may be converted to Gaseous Hydrogen (GH2) and / or Anhydrous Ammonia (NH3) C-free fuels for low-cost energy storage, for later use or sale, in local mini- and micro-grids and / or export in underground pipelines. The complete renewable energy system would be optimized for maximum cash flow and minimum Long-term COE. Very low cost storage is now available at << $1.00/kWh capex: 1. GH2 in deep, solution-mined salt caverns at ~90 GWh each, where geology is available, and at no cost by "packing" pipelines to MAOP; 2. Liquid NH3 at 10 bar in common steel "propane" tanks of all sizes, and in large refrigerated "atmospheric" tanks at ~ 200 GWh each; 3. Thermal energy in underground, insulated, massive pipefields. If EPB achieves its cost goal of € 100 per meter for a 50 cm diam hole, 6 to 9 km deep, for sites easily-accessible to the compact EPB system (costs are higher for remote systems: Alaska villages), then: a. Baseload geothermal energy at 90 C out - 20 C return can be produced for < $ 0.01 / kWht; b. Baseload ORC generators can produce electricity at < $ 0.02 / kWhe from branched holes; < $ 0.05 / kWhe from single holes; c. Boring costs will be lower for conventional two-borehole EGS, for lower long-term COE; d. Thermal and electrical micro- and macro-grids may be established in remote areas, serving several communities and many people from a single branched or unbranched borehole; e. The abundant associated lower-grade heat may be used for DHS and DHW, crop-drying, greenhouses. Prof. Arild Rodland, principal EPB technical researcher and inventor, reported to AASI in 2016: a. EPB challenges, not obstacles, are: the bit concept, solids removal, performance level, among others; b. Diagonal boring at < 65 deg angle is well established and should work for multi-branch EPB holes; c. The confidential SINTEF performance study shows annual production, 90-20 deg C out/in: • 50 cm borehole, 6km: 8 GWht • 50 cm borehole, 9km: 28 GWht • 4-branch array at 4-9km to 9km from mother hole: 449 GWht