Lecture 27 Hydro : Part 1

Summary

What hydropower is and how it works

Hydropower, also called hydroelectric power, converts the potential or kinetic energy of water into mechanical energy and then into electricity:

1. Water flows or falls, often from a reservoir at a height.
2. The moving water turns a hydraulic turbine.
3. A shaft connects the turbine to a generator, which produces electricity.

Water may flow through rivers and channels or through pipes and penstocks from a reservoir. Hydropower uses water’s energy rather than consuming the water itself.

Benefits and uses

Hydropower is a major renewable electricity source, accounting for about 14% of global electricity generation. Its benefits include:

• Low-emission, renewable generation: It can produce substantial electricity without the direct greenhouse-gas emissions associated with fossil-fuel power plants.
• Reliability and flexibility: Hydropower can provide dependable output and ramp up quickly when demand rises.
• Grid support and energy storage: Pumped-storage plants can use surplus electricity to pump water to an upper reservoir, then release it later to generate electricity. This can help balance variable wind and solar generation, regulate grid frequency, and reduce blackout risk.
• Water management: Reservoirs can help regulate downstream flows, reduce flood risk, support irrigation, and store water for other uses, including drinking-water supply.

Hydropower potential

The lecture distinguishes three levels of hydropower potential:

• Gross theoretical potential: The maximum physical energy available from water flows and elevation changes, assuming idealized conversion. The lecture estimates this at 40,000–52,000 TWh per year globally.
• Technical potential: The portion that could realistically be captured with available technology and given structural and geographic constraints. The estimate is 15,000–20,000 TWh per year.
• Economically exploitable potential: The portion that can be developed cost-effectively without major environmental disruption. The estimate is 8,000–10,000 TWh per year.

The lecture gives global installed hydropower capacity as about 1,456 GW, including roughly 1,300 GW of conventional hydropower and 160 GW of pumped storage. Global hydropower generation is given as about 4,578 TWh per year—approximately 45% of the midpoint of the estimated economically exploitable potential.

Substantial untapped potential remains in parts of Sub-Saharan Africa, Southeast Asia, and Latin America. The lecture names China, Brazil, the United States, Canada, and India as leading hydropower-producing countries. China is described as the largest by capacity and a major driver of recent construction. The United States and Canada are also focusing on upgrades and rehabilitation of older facilities.

Historical development

The lecture traces hydropower’s development through several broad stages:

• Ancient times through the 1700s: Water wheels were used for mechanical work, including grinding grain and crushing ore.
• 1800s: Turbine designs advanced. James Francis developed the Francis turbine in 1849, and Pelton developed the Pelton wheel in the 1870s. The Francis turbine is widely used, while the Pelton wheel is suited to high-head sites.
• Late 1800s: Hydroelectric schemes began generating electricity. A small scheme in England powered an arc lamp, and a commercial hydroelectric plant began operating in Appleton, Wisconsin, in 1882.
• Early to mid-1900s: Large dams and major hydroelectric projects expanded. The lecture cites Hoover Dam on the Colorado River as a prominent example.
• Modern era: Projects such as China’s Three Gorges Dam illustrate the scale of more recent development. Current priorities increasingly include sustainability, pumped storage, and integration with intermittent renewable sources.

Hydropower in India

The lecture states that India’s first hydroelectric station was established at Shivanasamudra Falls on the Kaveri River in Karnataka in 1905. It places India fifth globally by installed hydropower capacity and gives a total of about 56.58 GW as of March 2026: approximately 51 GW of large hydro and 5.17 GW of small hydro.

Areas with substantial potential include the northeastern states, Himalayan states such as Uttarakhand and Himachal Pradesh, and the Western Ghats. Major projects mentioned include Tehri Dam, the Koyna hydroelectric project, and the Sardar Sarovar Dam.

Hydropower equation and calculation method

Water stored at height (h) has potential energy:

[ E_p = mgh ]

Power is the rate of energy conversion. For continuous flow, mass per unit time is the mass-flow rate, (\dot m). Since (\dot m = \rho Q), where (\rho) is water density and (Q) is volumetric flow rate:

[ P_{\text{hydraulic}} = \rho g Q h ]

This is the theoretical hydraulic power. Accounting for the overall turbine-generator efficiency, (\eta), gives electrical output:

[ P_{\text{out}} = \eta \rho g Q h ]

Where:

• (\rho) = water density, approximately (1{,}000\ \text{kg/m}^3)
• (g) = gravitational acceleration, approximately (9.81\ \text{m/s}^2)
• (Q) = flow rate or discharge, in (\text{m}^3/\text{s})
• (h) = effective head, in metres
• (\eta) = overall system efficiency

For a channel with flow velocity (V) and cross-sectional area (A):

[ Q = VA ]

Using (\rho = 1{,}000) and (g = 9.81), the lecture gives:

[ P_{\text{out}}(\text{kW}) = 9.81\,\eta Qh ]

Modern hydropower plants typically achieve overall efficiencies of about 80–95%, higher than the comparison ranges given for several other generation technologies. The lecture attributes this to water’s high density, efficient turbines, low mechanical losses, and the absence of intermediate heat-generation stages.

Worked example

Given:

• Channel area (A = 100\ \text{m}^2)
• Water velocity (V = 2\ \text{m/s})
• Effective head (h = 10\ \text{m})
• Overall efficiency (\eta = 0.80)
• (\rho = 1{,}000\ \text{kg/m}^3)
• (g \approx 10\ \text{m/s}^2)

1. Calculate discharge:

[ Q = VA = 2 \times 100 = 200\ \text{m}^3/\text{s} ]

1. Calculate electrical power:

[ P_{\text{out}} = 0.80 \times 1{,}000 \times 10 \times 200 \times 10 = 16{,}000{,}000\ \text{W} ]

The estimated electrical output is 16 MW.

Speakers and sources

• Speaker: One lecturer presents the material; the subtitles do not identify the lecturer by name.
• Other voices: None clearly identifiable. The lecture mentions historical figures James Francis and Pelton, but they are discussed rather than appearing as speakers.