Renewable Energy Sources: Geothermal, Wind, and Hydraulic Power

Geothermal Reservoirs

Hydrothermal Deposits

Hydrothermal deposits contain fluid, primarily water, within the Earth. This water originates from surface sources like rain, snowmelt, and rivers, seeping into the ground through various cracks and fissures. Depending on the pressure (P) and temperature (T) within the reservoir, the water can exist in either gaseous or liquid form.

The surface of a hydrothermal deposit typically consists of:

  • A heat source (e.g., magma)
  • Impermeable rock surrounding the heat source

The heat from the source raises the temperature of the water, leading to increased pressure. If the temperature rises significantly, the water can vaporize, generating even higher pressure. This high-pressure steam or water can then escape through cracks in the impermeable rock, reaching the surface and potentially being harnessed for geothermal energy.

Geopressured Deposits

Geopressured deposits are similar to hydrothermal deposits, but the water or steam is trapped at greater depths and under higher pressure. These deposits are typically found at temperatures around 200°C. They often contain natural gas, offering three potential energy sources: the heat from the water, the pressure of the water, and the chemical energy of the natural gas.

Hot Rock Deposits

Hot rock deposits consist of hot, impermeable rock that can reach temperatures up to 300°C. These deposits typically lack fluid within the rock. The primary challenge with hot rock deposits is the impermeability of the rock, which prevents water from flowing through and extracting heat effectively.

Wind Energy

Wind is generated by several factors:

  • Uneven solar heating: The sun heats the air unevenly, causing warmer air to rise and cooler air to rush in, creating wind.
  • Weather conditions: Local weather patterns, such as pressure differences, influence wind speed and direction.
  • Earth’s rotation: The Earth’s rotation affects wind patterns through the Coriolis effect.

Classification of Wind Machines

Horizontal Axis Wind Turbines

Horizontal axis wind turbines (HAWTs) are the most common type, thanks to their technological maturity and commercial viability. They consist of a vertical tower with blades mounted on a horizontal rotor that faces the wind. The wind drives the blades, which in turn rotate a generator to produce electricity.

Low-power HAWTs (up to 50 kW): These turbines typically have a high number of blades (up to 24) and are often used in rural areas for water pumping or providing electricity to individual homes.

High-power HAWTs (over 50 kW): These turbines usually have three blades with aerodynamic profiles similar to aircraft wings. They require wind speeds above 5 m/s to operate and achieve maximum efficiency at wind speeds around 15 m/s. Multiple high-power turbines are often grouped together to form wind farms.

Vertical Axis Wind Turbines

Vertical axis wind turbines (VAWTs) are less common than HAWTs, but their use is expected to increase in the future. The most common types of VAWTs are:

  • Darrieus wind turbine
  • Savonius wind turbine

Types of Hydraulic Power

Captive Hydraulic Power

Captive hydraulic power plants have a capacity of less than 10 MW. They have historically been a primary source of electricity for small towns and businesses located near rivers.

Grand Central Hydraulic Power

Grand central hydraulic power plants have a capacity exceeding 10 MW. They are typically located in river basins with high water flow.

Pumped-Storage Hydroelectricity

Pumped-storage hydroelectric plants utilize two reservoirs at different elevations. During periods of high electricity demand, water is released from the upper reservoir to the lower reservoir, driving turbines to generate electricity. During periods of low demand, surplus electricity is used to pump water from the lower reservoir back to the upper reservoir, effectively storing energy for later use.

Mixed Pumped-Storage Hydroelectricity

Mixed pumped-storage plants function similarly to conventional pumped-storage plants but can also operate without pumping water back to the upper reservoir. This is possible if the upper reservoir is fed by a river, allowing water to be pumped only when there is surplus energy or low river flow.

Cogeneration Systems

Many industries utilize cogeneration systems to generate electricity and heat simultaneously, improving overall energy efficiency. Two common types of cogeneration systems are:

Cogeneration using Diesel Cycle Engine

This type of cogeneration system uses a standard diesel engine coupled to an alternator to generate electricity. The waste heat from the engine is captured and used for heating or other purposes, rather than being dissipated through a radiator or fan.

Cogeneration using Gas Turbine (Steam)

This type of cogeneration system operates similarly to a jet engine. It is typically used for applications requiring more than one megawatt of power and can utilize various fuels, including natural gas, biogas, and kerosene. The system captures both electrical and thermal energy, maximizing efficiency.

Ways to Save Energy

Heating

  • Insulate walls and roofs.
  • Keep doors and windows closed when heating or cooling.
  • Ventilate rooms briefly (e.g., 10 minutes) by opening windows, rather than leaving them open for extended periods.
  • Install double-glazed windows to reduce heat loss.

Lighting

  • Unplug transformers and chargers when not in use.
  • Turn off lights and appliances when they are not needed.

Formulas

P = 9.8 · Q · h

P = theoretical power in kW

Q = water flow in m3/s

h = height in meters

E = P · t = 9.8 · Q · h · t

E = theoretical energy in kWh

t = time in hours

Q = K · t · S

K = solar radiation constant

t = time in minutes

S = section or area in cm3

Q = heat in calories

Pwind = 0.37 · S · v3

P = power in watts

S = section in m2

v = wind speed in m/s

Q = Pc · m

E = Ce · m · (Tf – Ti)

Pc (real) = Pc · p · [273 / (273 + Ta)]

Esupplied = Pc (real) · V

Euseful = m · Ce · (Tf – Ti)

Efficiency = Eu / Es