22MEX01 Renewable Energy Sources

Unit IV Geothermal Energy and Ocean Energy

Geothermal Energy: Geothermal Resources-Structure of Earths Interior - Electricity Production - Conversion Technology - Challenges- Economics.

Ocean Energy: Ocean Thermal Plants - Types-Tidal Plants Types - Energy Estimation - Grid Interfacing of Tidal Power - Wave Energy Conversion Machines Types Buoy - Dolphin - Oscillating Water Column - Duck -Challenges - Economics

Geothermal Energy

• All the heat energy stored in earth’s crust above 15^oC to a depth of 10Km.
• Heat energy in earth core rises closer to the surface of earth due to cracks.
• Hot molten metal called “Magma” is present at the depth greater than 24 to 40 Km.
• Geothermal steam

- Magmetic steam

- Meteoritic steam

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Earth’s Interior Structure

• Crust
• Outermost solid layer (5–70 km thick).
• Contains rocks, groundwater, and geothermal reservoirs.
• Most accessible geothermal energy is extracted here.
• Mantle
• Extends up to ~2,900 km depth.
• Composed of hot, semi-solid rock (temperature ~500–4,000 °C).
• Heat transfer occurs through conduction and convection, driving magma movement.
• Magma intrusions near the crust act as heat sources for geothermal fields.
• Outer Core
• Liquid layer (~2,900–5,100 km deep).
• Made of molten iron and nickel, temperatures up to ~6,000 °C.
• Major source of Earth’s internal heat flow.
• Inner Core
• Solid metallic sphere (~5,100–6,371 km depth).
• Extremely hot (~6,000 °C+).
• Contributes to long-term geothermal heat through radioactive decay and residual formation heat.

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Types of Geothermal Resources

• Hydrothermal Resources
• Hot water and steam trapped in porous rocks.
• Commonly used in geothermal power plants.
• Geopressured Resources
• Hot brine water under high pressure with dissolved methane gas.
• Hot Dry Rock (HDR)
• Heat stored in dry, impermeable rocks at great depth.
• Requires artificial fracturing and water injection.
• Magma Resources
• Heat from molten rock deep in the Earth’s crust.
• Very high temperature potential but still experimental.

GEOTHERMAL SOURCES

• Hydrothermal Convective System

- Vapour-dominated fields

- Liquid-dominated system

- Hot-water fields

• Geo pressure resources.
• Petro-thermal
• Magma resources.
• Valcanoes.

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VAPOUR DOMINATED SYSTEM

LIQUID DOMINATED SYSTEM�(Flash Steam System)

Challenges in Geothermal Energy

• Resource Location & Depth – Geothermal reservoirs are site-specific and often deep, making exploration difficult.
• Drilling Difficulties – High cost and risk due to hard rock, high temperature, and corrosive fluids.
• Reservoir Management – Pressure decline and reduced steam production if extraction is not balanced with re-injection.
• Scaling & Corrosion – Dissolved minerals (silica, sulfides, carbonates) can clog pipes and damage equipment.
• Limited Resource Type – High-temperature vapor-dominated fields are rare.

TIDAL ENERGY

Basic Principle Of Tidal Energy

• Tides are period rise and fall of the water level of sea which are carried by the action of sun and moon on the water of the earth.

Components of tidal power Plants

• Power house
• Dam or barrage
• Sluice gates

Types of tidal energy utilization

• Single basin system

- Single ebb-cycle system

- Single tide-cycle system

- Double cycle system

• Double basin system

OCEAN THERMAL ENERGY CONVERSION (OTEC)

INTRODUCTION

• Conversion of solar energy stored in the ocean into electrical energy by making use of temperature difference between warm surface water and colder deep water.
• Types of OTEC system

1. Open cycle OTEC system

- Working fluid is Water

2.Closed cycle OTEC system

- Working fluid is ammonia or propane

Open cycle OTEC system

Closed cycle OTEC system

Wave Energy