Presented by: William Murray March 28, 2007 Geothermal Energy Presented by: William Murray March 28, 2007

What is Geothermal Energy? Defined: Energy that is generated by converting hot water or steam from deep beneath the Earth’s surface into electricity. Unique renewable Natural Energy Flow Heat Mining Enthalpy -Geothermal is the only form of renewable energy that is independent of the sun, having its ultimate source within the earth. -Small in comparison to the massive amount of solar heating of the earth that drives the atmospheric and hydrological cycles. -Heat mining because the heat is being removed faster than it’s being replaced at no fault of humans. Non-renewable outside the scale of human existence. -Enthalpy is the heat content of a substance per unit mass.

The Heat Source Tiny quantities of radioactive isotopes liberate heat as they decay Core heat transfer through convection Accessible in locations where heats interior is brought within reach Lithospheric Plates Significant heat flow Volcanic activity =Radioactive heat accounts for half of the surface energy, remainder attributed to the Motion of hot deformable solids, transferred through convection =Convection is the vertical transfer of heat energy =Core heat transferred through conduction (transfer of heat through materials) =Boundaries of plates where Extension and compression of lithospheric plates where heat flow reaches a maximum

Gradient heat distribution Convection visible from core to outer layers

Movement of these lithospheric plates referred to as plate tectonics

Basically the heat transfer from the magma heats the IMPERMEABLE rock through CONDUCTION. This super heated rock then transfers it’s heat energy to the cold water stored in the permeable water table aquifer generating steam and super heated water. Steam and hot water then escape from the reservoir through fault lines in the CAPROCK (Insulating properties). In accessible regions it’s possible to drill down to the aquifer. Figure 9.5 on page 350 ROCK MUST BE POROUS AND INTERCONNECTED TO ALLOW FLOW. Although, the caprock must be firm and impermeable to allow for steam and heat build up. More specific numbers and calculation are available in the book. VOLCANOES: rising magma is halted. The pressure of overlying rocks decrease encouraging the separation of gasses that increase density. FIGURE 9.7 HOT SPRING, GEYSER, FUMAROLE, STEAM WELL

The Heat Source Cont’d High enthalpy systems are divided into two categories Vapor Dominated Best and most productive Free of liquids Liquid Dominated Relies on water at boiling point Often results in steam “flash” Two-phase zone Wairakei feild in New Zealand Famous for it’s two phase system. Only top 6km of the earths crust considered for geothermal potential

Geothermal Potential Nature of the resource Economies of Scale Fluid Temperature Salinity Fluid Pressure Gas Content Economies of Scale Maximum efficiency Nature of the resource Fluid Temperature Salinity - Varying concentrations and boiling points Fluid Pressure Gas Content - Volatile and intermittent

Four Main Types Dry steam power plant Single flash steam power plant Binary cycle power plant Double flash power plant

Dry Steam Power Plant Dry Steam Plants produce electricity directly from the steam that emerges at the earths surface. The steam drives turbines. Ideal for vapor dominated resourced where there is no water contamination. Hot Dry Rocks (HDR)

Single/Double Flash Steam Flash Steam Power Plants are the most common form of geothermal power plant. The hot water is pumped under great pressure to the surface. When it reaches the surface the pressure is reduced and as a result some of the water changes to steam. This produces a ‘blast’ of steam. The cooled water is returned to the reservoir to be heated by geothermal rocks again. Double flash steam power plants include an additional drop in pressure after the initial flash to help power the circulatory pumps and others that contribute to power loss. 20-25% power increas with only 5% more cost. Have additional

Binary Cycle Power Plant If the water that reaches the surface is not hot enough to produce steam, it can still be used to produce electricity by feeding it into a Binary Power Plant. The hot water is fed into a heat exchanger. The heat from the water is absorbed by a liquid such as isopentane which boils at a lower temperature. The isopentane steam is used to drive turbines, producing electricity. The isopentane then condenses back to its liquid state and is used again.

Ground Source Heat Pump 40% reduction in CO2 emissions vs. competing heating and cooling technologie. Used to extract heat from warm shallow groundwater to supply a single domestic dwelling. In the winter heat is removed from the earth and delivered in a concentrated form via the heat pump. Because electriity is used to increase the temperature of the heat, not to produce it, Ground source pumps can deliver three to four times more energy as heat than the energy content of the electricity it consumes.

Global Capacity Worldwide use of geothermal 9.3GW 28 GW used directly for heating 100GWt through ground-source heat pumps Potential for 65-138GW MIT claims 100GWe by 2050 0.3% of US energy consumption Nuclear power plant has 4GW potential

Environmental Impact Gaseous emissions Land use Noise Less than 1/10th of coal-fired carbon emissions Dissolved gasses Land use Noise Potential ground subsidence small amounts of ammonia, hydrogen, nitrogen, methane and radon, and minor quantities of volatile species of boron, arsenic, and mercury. 0.2 lb/kWh * A pressure drop in the reservoir as a result of fluid withdrawal * The presence of a highly compressible geological rock formation above or in the upper part of a shallow reservoir * The presence of high-permeability paths between the reservoir and the formation, and between the reservoir and the ground surface

Geothermal Usage Iceland generates 26.5% of energy from geothermal .1% Fossil fuels 73% Hydro In the US Alaska (1 Plant) California (4.8% of electrical energy, 2.4GW installed capacity) Hawaii (30MW on largest island, 20% of electrical energy) Nevada(15 plants, 254MW) Utah (reconstructed developing plants)

Applications in Belize Belize is the only country in Central America that does not have the potential for geothermal energy according to the US Department of Energy

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