Alternate Sources of Energy - Solar, Wind, Geo-Thermal & Ocean-Thermal Energy Sources

Wind power

Wind Energy - Introduction

• The wind has been used for thousands of years as a source of energy.

• Sailors capture it in the sails of their ships, and weather has therefore had important historical consequences, for example, the Spanish Armada was defeated with the help of stormy weather around the British Isles.

• The Netherlands are famous for the use of windmills with four cloth sails. These were used for pumping water to drain polders forming agricultural land.

• In the UK, Norfolk borrowed this Dutch expertise to do the same, leaving distinctive features on the flat lowland landscape.

Wind Turbine

• The yaw drive is an important component in horizontal axis wind turbines. To ensure the wind turbine is producing the maximal amount of electrical energy at all times, the yaw drive is used to keep the rotor facing into the wind as the wind direction changes.

• The wind turbine is said to have a yaw error if the rotor is not aligned to the wind.

Wind Turbine

Wind Power Generation

• Before setting up a wind turbine generator, the availability of wind - the wind speed and direction for a ten minute average is checked.

• Since the winds on the sea coast are of high speed and vary in speed, wind turbine generators are usually not installed in these areas.

• The preferred wind speed for optimum power generation is around 12 m/sec (40-50 km per hour) above which the turbines have to be switched off to avoid damage.

• The average height of the wind turbine is 200 meters while the blades could span 80 meters.

Factors to be taken into account• Before setting up a wind turbine generator, the availability of

wind - the wind speed and direction for a ten minute average is checked.

• Since the winds on the sea coast are of high speed and vary in speed, wind turbine generators are usually not installed in these areas.

• The preferred wind speed for optimum power generation is around 12 m/sec (40-50 km per hour) above which the turbines have to be switched off to avoid damage.

• The average height of the wind turbine is 200 meters while the blades could span 80 meters.

Wind Power Status• At the end of 2008, worldwide wind farm nameplate capacity

was 121 GW, representing an increase of 28.8 percent during the year, and wind power produced some 1.3% of global electricity consumption.

• Wind power accounts for approximately 19% of electricity use in Denmark, 9% in Spain and Portugal, and 6% in Germany

World wide wind power capacity

Wind power capacity in India

Wind power in India

• The development of wind power began in the 1990s.

• 5th largest in wind power installed capacity

• Tax benefits: 80% depreciation in the first year and 10 year tax holiday, many of the highest tax payers in the country invest their money in wind farms

• Wind power accounts for 6% of India's total installed power capacity, and it generates 1.6% of the country's power

• Despite the high installed capacity, the actual utilization of wind power in India is low because policy incentives are geared towards installation rather than operation of the plants. This is why only 1.6% of actual power production in India comes from wind although the installed capacity is 6%. The government is considering the addition of incentives for ongoing operation of installed wind power plants

• Vestas, Suzlon and Enercon are the major suppliers of wind power equipment in India

• In February 2009, Shriram EPC bagged INR 700 million contract for setting up of 60 units of 250 kW (totaling 15 MW) wind turbines in Tirunelveli district by Cape Energy

Wind power - Disadvantages

• The major disadvantage of wind power farms are the low load factors of 20-30% .

• They are not reliable since wind patterns keep changing.

• Seasonal variability introduces a challenge in integration of wind power into electricity grids, requiring balancing with other technologies such as hydropower and pumped-storage hydroelectricity.

• Also, the area required is large, a 225MW plant may take up an area of size 35 km by 5 km.

• Other allegations (not proven) are that the wind turbine cause droughts and affect bird life

Solar power

Solar Energy - Introduction

• Solar energy, indirectly is the main source of biological energy cycle – photosynthesis

• There are three processes for converting solar energy heliochemical: the photosynthesis process heliothermal: heating of a secondary fluid (solar thermal) helioelectrical: photovoltaics (solar cells)

Solar Collection Systems• There are three general categories of solar-energy collection systems:

direct conversion of sun rays to electricity with solar cells (photovoltaics),

flat-plate systems producing low-temperature (<150°F) thermal energy for heating and cooling of buildings; the thermal energy generated in the collector is usually removed by either air or an ethylene glycol-water solution, and

concentrating solar collection systems that produce high temperature thermal energy for the generation of electricity.

Solar Photovoltaics• Solar photovoltaic (solar cell) is a direct conversion of the

sun's electromagnetic radiation to electricity, and is not limited by Carnot cycle efficiency considerations.

• Photovoltaic (PV) cells employ a solid-state diode structure with a large area on a silicon wafer. The surface layer is very thin and transparent so that light can reach the junction region of the silicon sandwich. In that region the photons are absorbed, releasing charges from their atomic bonds. These charges migrate to the terminals, raising the potential.

• A single cell has an open circuit the voltage of approximately 0.6-1.0 volts and a short circuit current of a few mA.

• In order to increase both current and voltage, the individual cells are placed into (solar) arrays where cells may be connected in series to raise the voltage and current output can be raised by parallel connection of cells.

• A more efficient conversion (15%) of solar energy to electrical energy is provided by photovoltaic (PV) cells.

Solar Photovoltaics

Solar Thermal• Solar thermal is the use of a vapor power cycle that requires the concentration of solar energy to reach high temperatures and reasonable thermal efficiency.

• Solar thermal, energy concentration devices include parabolic mirrors and arrays of focused mirrors (heliostats)

Solar Thermal

Solar Thermal Collectors

Solar Thermal System - Classification

• large point focus: power tower systems with heliostats. Molten salts and liquid metals are used as the working fluid that then boils water for use in a Rankine cycle. Sizes of 100 kWe to 100 MWe.

• small point focus: use parabolic hemispherical dishes to reflect light to a focal point on each individual dish. These are for remote stand-alone systems (5-25 kWe), and

• line focus systems: use parabolic shaped troughs, and have lower efficiency.

Solar Power in India

• India is both densely populated and has high solar insolation, providing an ideal combination for solar power in India.

• Much of the country does not have an electrical grid, so one of the first applications of solar power has been for water pumping, to begin replacing India's four to five million diesel powered water pumps, each consuming about 3.5 kilowatts, and off-grid lighting

• Some large projects have been proposed, and a 35,000 km² area of the Thar desert has been set aside for solar power projects, sufficient to generate 700 to 2,100 GW

• The amount of solar energy produced in India is merely 0.5% compared to other energy resources. The Grid-interactive solar power as of June 2007 was merely 2.12 MW

• The cost of production ranges from Rs 15 to Rs 30 per unit compared to around Rs 2 to Rs 6 per unit for conventional thermal energy

Solar power – Advantages & Disadvantages

• The advantages of solar energy include its nonpolluting nature; it is nondepletable, reliable, and free fuel.

• The disadvantages of solar energy are The solar energy concentration is very dilute, so collectors

with large surface area are needed. In addition, solar radiation is neither constant nor

continuous for terrestrial applications (i.e., low capacity factor).

The solar energy received depends on

Geo-thermal power

Geo-thermal Energy - Introduction

• Geothermal energy is thermal energy generated and stored in the Earth.

• Hot springs have been used for bathing at least since paleolithic times. The oldest known spa is a stone pool on China’s Lisan mountain built in the Qin dynasty in the 3rd century BC.

• In 1892, America's first district heating system in Boise, Idaho was powered directly by geothermal energy, and was copied in Klamath Falls, Oregon in 1900. 

Geo-thermal Energy - Status

• The largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California, United States.

• As of 2004, five countries (El Salvador, Kenya, Philippines, Iceland, and Costa Rica) generate more than 15% of their electricity from geothermal sources.

• Worldwide, geothermal plants have the capacity to generate about 10 GW as of 2007, growing annually by 3%

• More than half of the geothermal energy is used for space heating, and another for one third for heated pools. The remainder supports industrial and agricultural applications.

• India has a geothermal potential of 10 GW

Geo-thermal power sites – loactions, 2005

Geo-thermal energy - conversion• Geothermal power uses the heat of magma below the Earth's

crust, which comes from radioactive decay Direct use Electricity generation Geothermal heat pumps

Geo-thermal Electricity• Geothermal electric power generation generally uses higher

temperature geothermal resources (above 110°c) Vapor dominated sources – direct steam conversion Liquid dominated sources – to separate steam from

geothermal fluid Low quality resources – using binary power plant

• Electricity generation requires high temperature resources that can only come from deep underground. The heat must be carried to the surface by fluid circulation, either through magma conduits, hot springs, hydrothermal circulation, oil wells, drilled water wells, or a combination of these.

• Away from tectonic plate boundaries the geothermal gradient is 25-30°C per km of depth in most of the world, and wells would have to be several kilometers deep to permit electricity generation.

• The quantity and quality of recoverable resources improves with drilling depth and proximity to tectonic plate boundaries.

Geo-thermal – Electricity Generation

Geo-thermal Heat Pump• The GHP energy-conversion process works much like a

refrigerator, except that it is reversible, that is, the GHP can move heat either into the earth for cooling or out of the earth for heating, depending on whether it is summer or winter.

• GHP can be used instead of or in addition to direct uses of geothermal energy for space or industrial process heating (or cooling), but the shallow resource used by

• GHP is available essentially anywhere, constrained principally by land use and economics, especially initial installation costs.

Sustainability• Geothermal power is considered to be sustainable because the heat extraction is small compared to the Earth's heat content, but extraction must still be monitored to avoid local depletion.

• Although geothermal sites are capable of providing heat for many decades, individual wells may cool down or run out of water.

Geo-thermal sources in India

Geo-thermal – Environmental Impacts

• Fluids drawn from the deep earth carry a mixture of gases, notably carbon dioxide (CO2) and hydrogen sulfide (HS2). These pollutants contribute to globalwarming, acid rain, and noxious smells.

• Existing geothermal electric plants emit an average of 122 kg of CO2 per megawatt-hour (MWh) of electricity, a small fraction of the emission intensity of conventional fossil fuel plants

• In addition to dissolved gases, hot water from geothermal sources may contain trace amounts of dangerous elements such as mercury, arsenic, and antimony which, if dumped into rivers, is hazardous.

• Plant construction can adversely affect land stability. (subsidence and earthquake)

• Geothermal has minimal land and freshwater requirements. Geothermal plants use 1-8 acres per MW versus 5-10 acres per for nuclear operations and 19 acres per MW for coal power plants. They use 20 litres of freshwater per MWh versus over 1000 litres per MWh for nuclear, coal, or oil

Ocean thermal power

Ocean thermal power - Introduction• Ocean thermal energy conversion (OTEC) uses the difference between

cooler deep and warmer shallow or surface ocean waters to run a heat engine and produce useful work, usually in the form of electricity.

•  In 1881, Jacques Arsene d'Arsonval, a French physicist, proposed tapping the thermal energy of the ocean. D'Arsonval's student, Georges Claude, built the first OTEC plant, in Matanzas, Cuba in 1930.

 The system generated 22 kW of electricity with a low-pressure turbine.

Global distribution of ocean thermal energy. The temperature difference (°C) shown is that between the surface and a depth of 1000 m [data from US National Renewable Energy Laboratory in RIS99]

Ocean thermal power generation

Ocean thermal power generation

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