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Table of Contents

A. Availability of fuel

B. Conventional Binary-Cycle Power Plant

C. Ideas To improve Geothermal Power Plant

D. Capacity & installed Resources Comparison

E. Cost & Efficiency Comparison

F. Environmental Impact

G. Conclusion

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A. Availability of fuel

Geothermal energy is energy from the heat of the earth. Geothermal resources consist of thermal

energy from the Earth’s interior stored in both rock and trapped steam or liquid water.

3Km Depth 5 Km Depth Within 10 km Depth

Stored Thermal Energy 43x 106 EJ 139.5 x 106 EJ 403 x 106 EJ

In theory, it is possible to tap into this resource almost everywhere, even accessing the extremely

hot temperature of the magma, the earth’s molten rock core. It is particularly easy to tap this

energy in countries where there is existing volcanic activity, such as the hot springs in Iceland,

Japan, New Zealand etc.

In practice geothermal plants can only utilize a portion of the stored thermal energy due to

limitations in drilling technology and rock permeability. Commercial utilization to date has

concentrated on areas in which geological conditions create convective hydrothermal reservoirs

where drilling to depths up to 4 km can access fluids at temperatures of 180°C to more than 350°C.

The total thermal energy contained in the

Earth is of the order of 12.6 x 1012 EJ and

that of the crust of the order of 5.4 x 109 EJ

to depths of up to 50 km.

The main sources of this energy are due to

the heat flow from the Earth’s core and

mantle, and that generated by the

continuous decay of radioactive isotopes in

the crust itself.

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B. Conventional Binary-cycle Power Plant

Binary cycle power plant is a type of geothermal power plant that allows

cooler geothermal reservoirs to be used than with dry steam and flash steam plants.

Main features:

Power generation by means of closed thermodynamic cycle

Geothermal fluid loop and power cycle are completely separated

Nearly zero emission plant (for all-liquid geo fluid)

It can operate using fluids at temperatures as low as 58° C

Suitable for integration with other energy sources (solar, biomass, waste....)

Binary Power system relies on relatively low temperature and requires a shallower well.

Hence, it has the widest potential for development.

Fig:

Schematic Diagram of a Binary-Cycle Power Plant

Geothermal binary power

generation systems utilize a

geothermal resource (steam or

hot water)as a heating source to

evaporate a low boiling point

fluid, which drives a turbine. Such

a system is called a “Binary Power

Generation system” because it

uses two different kinds of fluids,

geothermal fluid and low boiling

point fluid.

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C. Ideas to improve Geothermal Power Generation

1. Thermoelectric Generator (TEG): This device convert heat (temperature differences) directly into electrical energy, using a

phenomenon called the “Seebeck effect” .

“If heat is applied to a circuit at the junction of two different conductors, a current will be

generated.”

So replacing conventional turbine and generator in our geothermal plant with

thermoelectric generator (TEG) will improve the efficiency by saving the energy lost in

mechanical conversion of heat into electricity

TEG has almost all of the advantages of PVs (Photo Voltaic) and moreover the lower

limit temperature for generating electricity using TEG may be 30℃.

With this advantage, much more geothermal resources might be used and much more

power might be generated using TEG technology.

2. Co-produced Geothermal Power from Oil and Gas Fields There is a huge amount of geothermal resource associated with oil and gas reservoirs

for power generation and other purpose. There are 164,076 oil and gas wells (2005 data)

in China. 76,881 wells have been abandoned, about 32% of the total. These

abandoned wells may be served as geothermal wells. The potential geothermal resource in

the reservoirs holding these oil and gas wells is huge. Texas has thousands of oil and gas

wells that are sufficiently deep to reach temperatures of over 121°C and sometimes

204°C.

So we can use existing oil and gas fields to co-produce geothermal power and reduce the

cost. Coproduced geothermal resources can deliver near-term energy savings, diminish

greenhouse gas emissions, extend the economic life of oil and gas fields, and profitably

utilize oil and gas field infrastructure.

The main advantage of the co-produced geothermal power is the lower cost than that of

EGS because the infrastructure, including wells, pipes, roads, and even grid, is already there.

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3. EGS (Enhanced Geothermal System) :

An Enhanced geothermal system (EGS) generates geothermal electricity without the need

for natural convective hydrothermal resources. EGS attempts to artificially reproduce the

conditions of naturally occurring hydrothermal reservoirs by fracturing impervious hot rocks

at 3 to 10 kilometers depth, pumping fluid into the newly porous system, and then

extracting the heated fluid to drive an electricity-generating turbine

Artificially creating hydrothermal reservoirs gives EGS greater siting flexibility than

traditional geothermal power plants, which can only be developed at sites with naturally

occurring hydrothermal resources that may be limited in their size and their proximity to

end-users of electricity.

Fig: EGS Schematic Diagram with Explanantion

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D.Capacity & Installed Resources Comparison

Fig: Different Resource Capacity around the world

Fig: Installed power all around the world

Fig: Installed global power capacity Comparison (yearly)

As we can see in the graph, Geothermal

has the largest resources among the

four types of renewable energies

The change of the installed global

power capacity with time for

geothermal, PV, and wind is shown in

Figure. One can see that PV’s power

change rate was the maximum,

followed by wind power and

geothermal line is almost constant.

Of all the energy sources used for

electricity generation, renewable

or not, geothermal energy is

probably the most neglected and

has so far commanded the least

public attention. It deserves

consideration.

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E. COST AND EFFICIENCY COMPARISON

Table: Comparison of cost, payback time, and construction period

Fig: Cost comparison for per kWh Energy Generation (left) and Construction Period (Right)

Points to be Noted:

The cost of geothermal energy is very close to wind energy but much less than PV.

Cost for power generation from hydro is less than geothermal but construction period of

hydro plant is too high compared to geothermal.

As compared to wind energy, Geothermal Power is a Reliable Power providing continuous

source of clean energy, 7 days a week regardless of changing weather. In this sense, they are

far superior to wind and solar energy systems, which both suffer from relatively low

efficiency and unpredictable down times.

Renewable

Non-Renewable

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Fig: Capacity Factor(CF) and Efficiency

Geothermal power has the highest capacity factor over 90%

Efficiency of Geothermal Power plant can be improved using new technology as stated

above in this document like TEG

* (Since Coal and gas are not eco-friendly and Non-renewable resources, so we are not taking

them into account.)

Capital Cost

Capital costs are the upfront costs to construct the plant and major maintenance work that needs to be

carried out during the lifetime of the plant beyond typical operating expenses.

Fig: Capital cost Comparison of different power plants

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F. Environmental Impacts

One of the main advantage of using geothermal energy since it does not create any pollution and

help in creating clean environment. Being the Renewable source of energy, geothermal energy has

helped in reducing global warming and pollution.

The distinction between open- and closed-loop systems is important with respect to air emissions.

In closed-loop systems, gases removed from the well are not exposed to the atmosphere and are

injected back into the ground after giving up their heat, so air emissions are minimal.

So we are using a closed loop binary cycle-power plant.

Geothermal power plants involve no combustion, unlike fossil fuels plants, so they emit very

low levels of greenhouse gases. Binary geothermal plants, along with flash/binary plants, produce

nearly zero air emissions. Even dry-steam plants are considered environmentally being compared

with fossil fuels. Geothermal heat pumps, which are used to heat and cool buildings, are

also considered to be one of the most efficient heating and cooling systems available – because of

their very low electricity demand, their use greatly reduces emissions resulting from power

generation. Additionally, geothermal energy has a very small land-use footprint – among the

smallest, per kilowatt of ANY power generation technology, including coal, nuclear, and other

renewables.

If we compare emission from open loop geothermal plant to coal-fired plant, it is considerably low

as shown in fig below.

1014

622

46 39 18 17 15 14

0

200

400

600

800

1000

Comparison of Life cycle Emissions Tons of carbon Dioxide(CO2) Equivalent per Gigawatt-hour

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G. Conclusion

1) Geothermal power has been left behind wind and solar in terms of

both growth rate and installed capacity. The main reasons may

be high initial investment, long payback time and construction

time, difficulty to assess resource and difficulty to modularize.

2) Some of the solutions and directions to speed up geothermal

growth may be development and utilization of new technologies

such as :

a) TEG

b) Co-produced geothermal power from oil/gas fields

c) EGS.

3) It is a limitless energy resource with no fuel costs

4) It is very scalable , a small plant can easily be built to supply a rural

village at relatively low capital cost.

5) Geothermal heat is obtainable almost everywhere on earth.

6) Exploiting the co-generation from existing oil wells would greatly

reduce drilling costs.

7) Heat from shallow ground has multiple industrial uses that include

heating greenhouses, fish farms, pasteurizing milk, etc.

8) Capital cost, though high, is comparable to that required to build

other energy facilities.

9) Geothermal power has the potential to grow exponentially in the

future.