Geothermal energy is heat derived from within the earth's subsurface. It is a renewable resource because its source is the almost unlimited heat generated by the earth's core. Hot water or steam carry geothermal energy to the surface. Geothermal energy can be used directly for heating applications or indirectly to generate electricity. Common methods to harness geothermal energy include geothermal power plants that use steam or binary cycle systems, as well as geothermal heating systems and geothermal absorption cooling.

1. Geothermal Energy
• Geothermal energy is heat derived within the sub-surface of
the earth.
• Geothermal energy is a renewable resource, because its
source is the almost unlimited amount of heat generated by the
Earth's core
• Hot water or steam carry the geothermal energy.
• Geothermal energy - the most promising form of
renewable energy which has been proven to be reliable, clean
and safe,

2. GEOTHERMAL Resource Requirements
• A geothermal resource requires fluid, heat and
permeability in order to generate electricity:
• Fluid—Sufficient fluid must exist naturally or be pumped
into the reservoir.
• Heat—The earth's temperature naturally increases with
depth and varies based on geographic location.
• Permeability—In order to access heat, the fluid
directly exchange heat from heated rock, either via
natural fractures or through stimulating the rock.

3. GEOTHERMAL ENERGY
• Heat energy of the earth, generated by various natural
processes, such as:
1. Direct use of Geothermal Energy
i. Hot springs use geothermal pumps.
ii. Heating water at fish farms,
iii. Hot water near the earth's surface is piped and circulated around the
buildings to provide heat.
2. Indirect use of Geothermal Energy
i. Electricity generation;
ii. Absorption Cooling System

4. Geothermal Energy
• Geothermal energy - thermal energy within the earth’s interior.
• Geothermal - energy renewable energy source because heat is
continuously transferred from within the earth to the water recycled by
rainfall. geothermal energy.
• Classification of Geothermal resources - based on thermal and
compositional characteristics.
i. Hydrothermal : high temperature water in steam, mixture, or liquid
phases.
ii. Geo-pressurized: hot liquid water at 150°C to 180°C at very high
pressures (up to 600 bar) but highly corrosive, thus very difficult to
harvest and use.
iii. Magma : molten rock, e.g., active volcanoes at temperatures above
650°C.

5. iv . Enhanced heat recovery:
• Hot, dry rock geothermal systems but
not natural geothermal resources.
• Water is injected into the hot rock
formation at high pressure, and then
the resulting hot steam is brought
back to the surface (Fig.).
• The system involves drilling of
injection and deep production wells
( 3 to 5 km.)
• The temperature of the hot rock at
this depth ~ 250°C.
Operation of enhanced geothermal
systems

6. Common classification of geothermal resources
is based on resource temperature.
i. High temperature resource: T > 150°C
ii. Medium temperature resource:
90°C < T < 150°C
i. Low temperature resource: T < 90°C
• Quality of a geothermal
resource depends on its phase
(and temp.) in the reservoir.
• The higher the quality, the
higher the work potential.
Quality of a geothermal resource

7. GEOTHERMAL APPLICATIONS
• Several options for utilizing the geothermal energy are;
• Electricity generation, space heating/cooling, cogeneration, and
geothermal heat pumps.
• Natural utilization of geothermal energy include, water
supply, growing plants and crops (greenhouses), drying of
wood, fruits and vegetables, sunbathing, desalination,
and fish farming.
• A cogeneration system utilizing geothermal energy and
producing electricity and heat and/or cooling occur
simultaneously.

8. • USA generates maximum geothermal electricity in the world > 3.5 gigawatts
which is sufficient to supply energy to ~ 3.5 million homes.

9. GEOTHERMAL HEATING COST ESTIMATION
• Many residential and commercial areas are effectively heated in
winter by low-cost geothermal heat in many parts of the world.
• Some of the largest district heating installations are in China,
Sweden, Iceland, Turkey, and the United States.
• Almost 90 percent of buildings in Iceland (a relatively small country)
are heated in winter by geothermal heat.
• The annual amount of space heating supplied in the world is
estimated to be about 360,000 TJ as of 2015.
• Noting that 1 terajoule (TJ) = 1013 J,
• This is approximately equivalent to kg of natural gas at a heating
value of 50,000 kJ/kg which depend @ its burning efficiency.

10. • A common operating mode for
geothermal space heating systems.
• Temperature values are
representative.
Where,
• m - mass flow rate of geothermal water,
• cp - specific heat of geothermal water, and
• Tsupply and Treturn
Efficiency of the heating equipment.
Energy cost = (Energy consumption) X (Unit price of energy)

11. EXAMPLE: A residential area is currently heated by natural gas heaters in winter with an
average efficiency of 85 percent. The price of natural gas is $1.30/therm (1 therm = 100,000
Btu). It is proposed to heat this area by geothermal water. On an average winter day, hot
geothermal water is supplied to the district at 200°F at a rate of 55 lbm/s and returns at 130°F
after giving its heat to the area.
How much revenue can be generated per year if the winter period can be taken to be
equivalent to 2800 h of these average conditions, and geothermal heat is sold at a discount of
25 percent with respect to natural gas.
SOLUTION:
• Specific heat of water at room temperature: cp = 1.0 btu/lbm⋅°F.
• The rate of geothermal heat supplied to the area can be determined from
• Rate of useful heat supplied for the given efficiency of natural gas heaters = 85 %
• The corresponding consumption of natural gas during a winter period of 2800 h can
be determined;

12. • Geothermal heat is sold at a discount of 25%, the potential revenue that can be
generated by selling geothermal heat is,

13. EXAMPLE : 2
Consider a house with an overall heat loss coefficient of Koverall = 0.5 kW/°C
and a heating degree-days of 2500°C-days. Determine the annual heating
energy consumptions for the following heating systems;
• Solution:
• When heating degree-days are available for a given location, the amount of energy
consumption for the entire winter season can be determined from

16. • For a cost comparison, the cost of energy for each system can be obtained by
multiplying energy consumption by the unit price of energy.

17. Degree-Day (DD) Method for Annual Energy Consumption
• The simplest and most intuitive method to estimate the annual energy
consumption of a building is the degree-day (or degree-hour) method, which is
a steady-state approach.
• DD is based on constant indoor temperature during the heating or cooling
season and assumes the efficiency of the heating or cooling equipment is not
affected by the variation of outdoor temperature.

18. • Outdoor temperature To drops below the indoor temperature Ti at which the
thermostat is set,
• The heater will turn on to compensate the heat losses from the building until the
outdoor temperature drops below a certain value.
• The outdoor temperature above which no heating is required is called the balance
point temperature Tbalance (or the base temperature) and is determined by;
where Koverall - the overall heat transfer coefficient of the building in W/°C or Btu/h ⋅ °F.
where ηheater is the efficiency of the heating system, which is equal to 1.0 for electric resistance
heating systems, coefficient of performance(COP) for the heat pumps, and boiler or heater
efficiency (about 0.6 to 0.95) for fuel-burning heaters.
COP is defined as the relationship between the power (kW) that is drawn out of the
heat pump as cooling or heat, and the power (kW) that is supplied to the compressor.

19. • If Koverall, Tbalance, and ηheater are taken to be constants, the annual energy
consumption for heating can be determined by integration (or by summation over
daily or hourly averages) as
where DDheating is the heating degree-days. The + sign “exponent” in the Equation indicates that
only positive values are to be counted, and the temperature difference is to be taken zero when To
> Tbalance. The number of degree-days for a heating season is determined from
where To,avg,day is the average outdoor temperature for each day (without considering
temperatures above Tbalance),

20. • When heating degree-days are available for a given location, the amount of energy
consumption for the entire winter season can be determined from
• If the heating is accomplished by a heat pump, ηheater needs to be replaced by
heating COP (coefficient of performance) of the heat pump.,
• Electrical energy consumed can be determined, by following equation;

21. EXAMPLE : (Annual Energy Consumptions for Different Heating Systems)
Consider a house with an overall heat loss coefficient of Koverall = 0.5 kW/°C and a heating
degree-days of 2500°C-days. Determine the annual heating energy consumptions for the
following heating systems.
(a)Coal heater, hheater = 0.75, Heating value of coal = 30,000 kJ/kg
(b) Natural gas heater, hheater = 0.85
(c) Heat pump, COP = 2.5
SOLUTION The annual heating energy consumption for each heating system is
determined as follows:

23. GEOTHERMAL COOLING :
Geothermal heat may be supplied to an absorption
refrigeration system for space cooling applications.
Absorption Cooling System:
• Absorption cooling becomes economical, if the
source is inexpensive energy at a temperature
of 100 to 200°C.
• Inexpensive thermal energy sources include
geothermal energy, solar energy, and waste
heat from cogeneration or process steam
plants, and even natural gas, or waste energy
at a relatively low price.
• A cogeneration plant may involve electricity
generation and absorption cooling.

24. GEOTHERMAL ELECTRICITY GENERATION SYSTEM:

25. Geothermal Steam power plants:
• uses Geo- hydrothermal fluid,
• Geo-Steam flows directly to a turbine, which
drives a generator to produce electricity.
• Geo-Steam eliminates the burning of fossil
fuels to operate turbines,
• Flash steam i.e., high-pressure hot water from
deep well is converted to steam due to
pressure reduction.
• Most geothermal power plants are flash steam
plants,
• When used steam condenses to water and
injected back into the ground to be used again.

26. Binary cycle power plants
• Heat from the geothermal fluid causes the secondary fluid to flash to vapor,
which then drives the turbines and subsequently, the generators.
• Binary cycle power plants are closed-loop systems, and virtually nothing
(except water vapor) is emitted to the atmosphere.

28. Tidal Energy

29. • All technologies to capture energy from natural resources
(directly or indirectly) originate from the Sun, e.g., fossil fuel,
hydroelectric, biofuel, wave, geothermal, wind, and solar etc.
• Tides are caused due to gravitational interaction with Moon
and Sun and Earth's rotation, and this interaction will remain
for ever.
• Tidal power is practically inexhaustible and classified as
a renewable energy resource,
Tidal Energy - Sustainable Resource

30. • Large tidal currents are used to turn turbines just like
hydroelectric power plants.
• Only about 20 locations have good inlets and a large enough
tidal range- about 10 feet- to produce energy economically.
• The largest daily tidal ranges in the world range between 23-
38 meters

31. Principle - Variation of tides over a day
• Tides formation is periodic due to
cosmic reasons exerted on the
coastline.
• The forces are created corresponding
motions or currents, in sea level.
• The magnitude and character of tides
• varies as the path to water changes
due to rotation of moon, elliptic shape
of the Earth around the Sun.
• Tidal power technologies are
developed according to orbital system
of Earth–Moon–Sun.
Basic Concepts in Physical
Oceanography: Formation of Tides

32. • Tidal streams based Tidal Power Plants

33. • Tidal Power or Tidal Energy
• Tidal action in the oceans is converted to electric
power.
• Tides possess K.E., rotational, cyclic and wake’s
energy.
• Tidal energy is used to produce clean and
pollution free electricity.
• Ocean thermal energy conversion (OTEC) -
an additional energy due to temp. differences
(thermal gradients) between ocean surface waters
and deep ocean waters.
• (Sun heats up ocean’s surface water)
A tidal range is the difference
between the high tide and low
Red color displays areas with larger and
stronger tidal ranges.
Blue color indicates weaker tidal ranges.

34. Different tidal power plants
•Single basin-one-way cycle. This is the simplest form of tidal power
plant.
•Single-basin two-way cycle. In this arrangement, power is generated
both during flood tide as well as
•Single –basin two-way cycle with pump storage.
•Double basin natural flow.
•Double basin with pumping system.
• Tidal power plants are, usually constructed in the tidal area.
• During an incoming high tide, (water level rises) and flows over
the turbines,
• When water flows back (low tide) and passes through the turbines,
• The turbines are connected to generators which produces electricity.
How does a tidal power plant work?

35. Technology to Harness Tidal Energy
• A dam is constructed to separate tides from the sea water
level between the basin and sea.
• The constructed basin is filled during high tide season
and fast-flowing water through the channels, rotates
turbine and generator respectively
• There are 3 different ways to get tidal energy:
• (i) Tidal streams, (ii) barrages, (iii) tidal lagoons.
• Tidal streams
• Tidal energy is produced by the surge of ocean waters during the rise
and fall of tides.
• There are very few commercial-sized tidal power plants operating in
the world.

36. Tidal Power Plants

37. Barrage Type Tidal Power Plant,
A tidal barrage is a dam-like structure used to capture the energy from the water
moving in and out due to tidal forces.

38. • Tidal lagoons would function much like a barrage.
• Unlike barrages, offshore tidal lagoons are constructed along the
natural coastline.
• A tidal lagoon power plant could also generate
continuous power. The turbines work as the lagoon is filling and
emptying.
Tidal Lagoons Power Plant
Lagoons is a small lake near sea, larger lake or river

39. Double Lagoons Tidal Power Plant

40.  Tidal power has not yet been operational in Pakistan compared to other renewable
energy technologies.
 In Sindh, 2 sites, on Indus delta of 170 km and two to five meters tidal heights at the
Korangi Creek, are available to exploit the tidal energy