Hydropower is the conversion of energy embodied in moving
water into useful power. People have been harnessing the
power of water for thousands of years for irrigation and
operation of mechanical equipment and more recently for
electricity generation. In fact, hydroelectric power now
supplies about 19 percent of the world’s electricity.
In the United States, hydropower accounts for only 7 percent
of the total electricity production, but over 70 percent
of the total installed renewable energy capacity.
Most industrialized nations have developed
their hydropower potential, but undeveloped resources remain
in countries such as China, India, Brazil, and regions of Africa
and Latin America. In some countries with access to large untapped
hydro resources, the resources are located far from electric
load centers, posing a problem for transmission of electricity
over long distan\ces. Solving this technological problem and
providing efficient transmission of electric power from off-grid
hydropower plants is a major opportunity for investment and
leadership in many countries around the world.
Hydropower plants are a clean, emission-free
source of electricity. The natural hydrological cycle replenishes
the resource, but also making it vulnerable to droughts. Competition
for scarce water resources for agriculture, recreation, and
fishing can affect the availability of water for power production.
However, the potential for small hydro project development for
rural electrification remains high in countries with concentrations
of rural populations living near rivers and streams.
Large hydropower plants with capacities in
the tens of megawatts are typically impoundment systems and
require a dam that stops or reduces a river’s flow to
store water in a reservoir. Penstocks carry water from the reservoir
to water turbines, which in turn drive electric generators.
Impoundment systems offer the advantage of controlled power
output and other benefits such as water recreation associated
with reservoirs, irrigation, and flood control. However, dams
negatively impact fish populations by interfering with migration
patterns. Water quality both in the reservoir and downstream
of the dam can be affected by changes in water flow and dissolved
Large new hydropower projects often require
planning to remove communities from areas that will be flooded
after a dam is built and other measures to manage environmental
impact. Recent research has also raised concern about the possible
effect of large reservoirs on atmospheric concentrations of
Small hydropower plants with capacities ranging
from a few kilowatts to several megawatts, are typically diversion
systems, which divert some water from a river through a canal
or penstock to a turbine. Small hydropower plants can provide
electricity for isolated rural populations. These systems range
in size from household-sized systems to ones that can supply
power to entire villages and commercial or industrial loads.
Diversion systems, also called run-of-river systems, do not
require dams or reservoirs, are suitable for small hydropower
projects, and have less impact on the environment.