EE535: Renewable Energy:
Systems, Technology &
Hydroelectric Power
Intro to Hydro
• Hydroelectricity is electricity generated by hydropower, i.e., the
production of power through use of the gravitational force of falling
or flowing water
• It is the most widely used form of renewable energy – Particularly in
• Once a hydroelectric complex is constructed, the project produces
no direct waste, and has a considerably lower output level of the
CO2 than fossil fuel powered energy plants
• Worldwide, an installed capacity of 777 GWe supplied 2998 TWh of
hydroelectricity in 2006. This was approximately 20% of the world's
electricity, and accounted for about 88% of electricity from
renewable sources.
Hydro Plant Schematic
Most hydroelectric power comes
from the potential energy of
dammed water driving a water
turbine and generator.
the energy extracted from the
water depends on the volume and
on the difference in height between
the source and the water's outflow
This height difference is called the
head. The amount of potential
energy in water is proportional to
the head. To obtain very high head,
water for a hydraulic turbine may
be run through a large pipe called
a penstock.
Pumped Storage
Pumped storage hydroelectricity produces electricity to supply high peak
demands by moving water between reservoirs at different elevations.
At times of low electrical demand, excess generation capacity is used to
pump water into the higher reservoir. When there is higher demand, water is
released back into the lower reservoir through a turbine.
Pumped storage schemes currently provide the only commercially important
means of large-scale grid energy storage and improve the daily load factor
of the generation system.
Hydroelectric plants with no reservoir capacity are called run-of-the-river
plants, since it is not then possible to store water.
A tidal power plant makes use of the daily rise and fall of water due to tides;
such sources are highly predictable, and if conditions permit construction of
reservoirs, can also be dispatchable to generate power during high demand
Calculating the amount of available
• A simple formula for approximating electric
power production at a hydroelectric plant is: P =
• where P is Power in watts, ρ is the density of water (~1000
kg/m3), h is height in meters, r is flow rate in cubic meters
per second, g is acceleration due to gravity of 9.8 m/s2, and
k is a coefficient of efficiency ranging from 0 to 1.
• Efficiency is often higher (that is, closer to 1)
with larger and more modern turbines.
• Annual electric energy production depends on
the available water supply. In some installations
the water flow rate can vary by a factor of 10:1
over the course of a year.
• The Dinorwig pumped storage station in
Wales has a water capacity of 7x106 m3,
which can be released for generating
electricity over a 5 hour period. If the
effective head is 500m, and the generator
efficiency is 90%, calculate the average
power output and the total electrical
energy produced in 5 hours.
Generating flow rate r = 7x106 / (5 *60 *60)
r = 388.9 m3/s
P = ρhrgk
P = 1000 x 0.9 x 388.9 x 9.81 x 500
P = 1.72GW
• Energy Output = 5 x 1.72 = 8.6 GWh
Follow – On Question
• It takes 6.5 hours to refill the reservoir.
Because of frictional drag, the effective
head when pumping is 530m. For pumps
having an energy efficiency of 90%,
calculate the input power to the pumps,
the total electrical energy required for
pumping, the overall energy efficiency of
the pumped storage plant.
• Pumping flow rate = 7x106 / (6.5 *60 *60)
• Pumping flow rate = 299.1m3/s
• Pumping power required = 1000 x 299.1 x 9.81 x 530 =
• Pumps are 90% efficient, so input power to pumps =
1.56/.9 = 1.73GW
• Energy Input = 6.5 x 1.73 = 11.2GWh
• Overall efficiency = output/input = 8.6 / 11.2 = 77%
• Check out:
• http://www.sei.ie/Renewables/REIO_Library/Case_
• http://www.spiritofireland.org/solution.php
• http://en.wikipedia.org/wiki/Hydroelectric_energy_s