Q5Non-Conventional Energy Sources

(a) Wind Energy Conversion System - Basic Principle, Applications, Site Selection

A wind energy conversion system (WECS) converts the kinetic energy of moving air into mechanical energy (via a rotor with aerodynamically shaped blades that experience lift and/or drag forces as wind flows past them, causing the rotor to spin) and subsequently into electrical energy (via a generator coupled to the rotor shaft, typically through a gearbox to match the rotor's relatively low rotational speed to the generator's required higher speed, though modern direct-drive designs eliminate the gearbox). The power available in the wind is proportional to the cube of wind speed and to the swept area of the rotor blades, meaning that even modest increases in average wind speed at a site translate into substantially larger increases in extractable power, which is the fundamental reason wind farm siting places such heavy emphasis on identifying locations with the highest sustained average wind speeds.

• Applications of wind energy: grid-connected electricity generation (utility-scale wind farms), standalone/off-grid rural electrification, water pumping (mechanical wind pumps for irrigation and livestock watering), battery charging for remote telecommunication and monitoring stations, and hybrid wind-diesel or wind-solar systems for reliable off-grid power supply.

• Average wind speed and wind speed distribution at the site, obtained through long-term (at least one year, preferably several years) meteorological measurement, since power output depends on the cube of wind speed.
• Absence of obstructions (buildings, trees, hills) that could cause turbulence or wind shadowing, reducing effective wind speed and increasing mechanical fatigue loading on the turbine.
• Terrain and elevation - hilltops, ridgelines, and coastal/offshore locations generally experience higher, more consistent wind speeds than sheltered valleys or inland plains.
• Grid connectivity and proximity to transmission infrastructure, to minimize the cost and losses of transmitting the generated power to load centers.
• Environmental and social factors, including impact on local bird and bat populations, noise impact on nearby residents, and land-use/ownership considerations.

(b) Basic Geothermal Steam Power Plant

A geothermal steam power plant extracts naturally occurring high-temperature steam (or, in a dry steam plant specifically, steam that already exists in essentially pure vapor form within the underground geothermal reservoir) directly from production wells drilled into a geothermal reservoir, passes this steam through a conventional steam turbine coupled to a generator (exactly as in a fossil-fuel steam plant, but without any boiler or fuel combustion, since the steam is provided directly by the Earth's internal heat), and exhausts the spent, lower-pressure steam to a condenser, with the resulting condensate typically reinjected back into the geothermal reservoir through injection wells to help sustain reservoir pressure and support the long-term sustainability of the resource.

• Advantages: continuous, reliable, weather-independent baseload power generation (unlike solar and wind); very low greenhouse gas emissions per unit of electricity generated; small land footprint relative to output capacity compared to solar or wind farms of equivalent capacity; and long operational plant life once developed.

• Disadvantages: geographically limited to regions with accessible high-temperature geothermal resources (typically near tectonically active zones); high upfront exploration and drilling risk and cost (since well productivity cannot be perfectly predicted before drilling); potential for reservoir depletion or declining steam pressure/temperature over the plant's operational life if reinjection and reservoir management are not carefully managed; risk of induced seismicity in some geothermal development contexts; and potential for release of trace hydrogen sulfide and other dissolved gases originally present in the geothermal fluid, requiring appropriate gas abatement equipment.

The power output of a wind turbine as a function of wind speed follows a characteristic curve with three distinct regions: below the cut-in wind speed (typically around 3-4 m/s) the turbine produces no power at all, since the available wind energy is too low to overcome mechanical friction and generator losses; between cut-in and the rated wind speed the power output rises rapidly, following approximately the cube-of-wind-speed relationship, until the rated (nameplate) power is reached; and between the rated wind speed and the cut-out wind speed (typically around 25 m/s) the turbine's pitch or stall control mechanism actively limits power output to the rated value to avoid overloading the generator and drivetrain, until the cut-out speed is reached, at which point the turbine is deliberately shut down and its blades feathered to avoid structural damage in excessively high winds.

Beyond dry steam plants, geothermal resources are also exploited through flash steam plants, which are used where the geothermal reservoir produces high-temperature water under pressure rather than pure steam - as this pressurized hot water rises to the surface and the pressure drops, a portion of it spontaneously flashes (vaporizes) into steam within a separator vessel, with this flashed steam directed to the turbine while the remaining hot water (brine) is either flashed again at a lower pressure in a second stage (double-flash plant, extracting additional energy) or reinjected into the reservoir - flash steam plants are considerably more common worldwide than pure dry steam plants, since naturally occurring dry steam reservoirs (such as at The Geysers in California) are geologically rare.

India's own geothermal resource potential, while modest compared to leading geothermal nations such as Iceland, the United States, or Indonesia (all located along more active tectonic boundaries), includes identified low-to-medium temperature sites such as Puga valley in Ladakh, Tattapani in Chhattisgarh, and various hot spring locations along the west coast, most of which are currently considered more suitable for direct-use applications (space heating, greenhouse heating) or small-scale binary-cycle power generation rather than large-scale dry-steam electricity generation, reflecting the generally lower geothermal gradient found across most of the Indian subcontinent outside the Himalayan and northeastern seismically active belts.

The five site-selection factors highlighted in this question - average wind speed, obstruction/turbulence avoidance, terrain/elevation, grid connectivity, and environmental/social impact - are typically evaluated together through a formal wind resource assessment process that can span one to several years of on-site measurement before a final site and turbine-layout decision is made, reflecting the very large capital investment at stake in a utility-scale wind farm project and the correspondingly strong incentive to reduce wind resource uncertainty as much as practically possible before committing to construction.

Geothermal steam power plants, discussed in the second part of this question, share an important commonality with wind power site selection in that both technologies are fundamentally geographically constrained by the underlying natural resource's location - just as a wind farm can only be economically built where genuinely strong, consistent wind resource exists, a geothermal steam plant can only be built where accessible high-temperature geothermal resource exists (typically near tectonically active regions), meaning both of these non-conventional technologies, unlike solar photovoltaic power (which can be deployed, with varying but generally still-useful efficiency, across a very wide range of geographic locations), are considerably more geographically selective in where they can be economically deployed at all.