Hydro-electric power plants convert the kinetic energy contained in
falling water into electricity.
The energy in flowing water is ultimately derived from the sun, and is
therefore constantly being renewed. Energy contained in sunlight
evaporates water from the oceans and deposits it on land in the form of
rain. Differences in land elevation result in rainfall runoff, and allow
some of the original solar energy to be captured as hydro-electric power
Hydro power is currently the world's largest renewable source of
electricity, accounting for 6% of worldwide energy supply or about 15% of
the world's electricity.
The majority of these power plants involved large dams which flooded vast
areas of land to provide water storage and therefore a constant supply of
electricity. In recent years, the environmental impacts of such large
hydro projects are being identified as a cause for concern. It is becoming
increasingly difficult for developers to build new dams because of
opposition from environmentalists and people living on the land to be
The two vital factors to consider are the flow and the head of the stream
is the volume of water which can be captured and re-directed to turn the
is the distance the water will fall on its way to the generator.
The larger the flow –i.e. the more water there is, and the higher the head
– i.e. the higher the distance the water falls
– the more energy is available for conversion to electricity.
Double the flow and double the power, double the head and double the power
where power is measured in Watts, head in metres, flow in litres per
second, and acceleration due to gravity in metres per second per second.
The acceleration due to gravity is approximately 9.81 metres per second
per second – i.e. each second an object is falling, its speed increases by
9.81 metres per second (until it hits its terminal velocity).
Therefore it is very simple to calculate how much hydro power you can
generate. Let’s say for example that you have a flow of 20 litres per
second with a head of 12 metres.
Put those figures in the equation and you will see that:
12 x 20 x 9.81 = 2,354 Watts
Efficiencies of around 70% can be expected which is to say that 70% of the
hydraulic energy of the flowing water can be turned into mechanical energy
spinning the turbine generator. The remaining 30% is lost. Energy is again
lost in converting the mechanical energy into electrical energy
(electricity) and so at the end of the day you can expect a complete
system efficiency of around 50-60%. In our previous example where 2.3kW of
power was available – we can therefore expect to generate around 1.1-1.4kW
High head hydro-electric commercial power plants
Plants can generally be divided into two categories. "High head" power
plants are the most common and generally utilize a dam to store water at
an increased elevation. The use of a dam to impound water also provides
the capability of storing water during rainy periods and releasing it
during dry periods. This results in the consistent and reliable production
of electricity, able to meet demand. Heads for this type of power plant
may be greater than 1000 m. Most large hydro-electric facilities are of
the high head variety. High head plants with storage are very valuable to
electric utilities because they can be quickly adjusted to meet the
electrical demand on a distribution system.
Low head hydro-electric commercial power plants
are power plants which generally utilize heads of only a few meters or
less. Power plants of this type may utilize a low dam or weir to channel
water, or no dam and simply use the "run of the river". Run of the river
generating stations cannot store water, thus their electric output varies
with seasonal flows of water in a river. A large volume of water must pass
through a low head hydro plant's turbines in order to produce a useful
amount of power. Hydro-electric facilities with a capacity of less than
about 25 MW (1 MW = 1,000,000 Watts) are generally referred to as "small
hydro", although hydro-electric technology is basically the same
regardless of generating capacity.
A low head site has a head of below 10 metres. In this case you
need to have a good volume of water flow if you are to generate much
A high head site has a head of above 20 metres. In this case you
can get away with not having a large flow of water, because gravity will
give what you have an energy boost.
The Australian Renewable Energy Agency is supporting a feasibility study
into the construction of a pumped storage hydroelectric power plant at the
disused Kidston Gold Mine in North Queensland.
Located 280km north west of Townsville, the project has the potential to
generate up to 330 MW of rapid response, flexible power for delivery into
Australia’s National Electricity Market.
Electricity generation in a pumped storage system works much like a
conventional hydroelectric scheme:
in periods of high demand, electricity is generated by releasing
water from an upper reservoir through reversible turbine-generators
and into a lower reservoir.
However, unlike a conventional hydro scheme, water is not then
discharged from the lower reservoir but pumped back to the upper
reservoir during off-peak hours using electricity from the grid.
This process is similar to the Wivenhoe Pump Storage scheme and Snowy’s
Tumut 3 scheme.
The Kidston Project would be a highly efficient form of large-scale energy
storage that helps to manage the growth of intermittent forms of renewable
energy such as solar and wind.
Intermittent generation can therefore be stored and dispatched to the grid
during periods of high demand.
The Kidston Project will be the first in the world to use two disused mine
pits for hydroelectric power generation.
The use of existing infrastructure from the old mining operation is also
expected to significantly lower construction costs.
Knowledge gained from this project may be used at other mine sites to
generate and store renewable energy.
Like other hydroelectric power plants, the facility will offer rapid
response to the demands of the grid, helping to restart other generators
and the electricity grid within seconds in the event of network shutdown.
Genex estimated the power facility will cost $282 milion and aims to
commence construction in 2017, with first year of operation scheduled for
The project will contribute to stability of the electricity grid by
combining renewable energy generation with large-scale energy storage
capability. It is also expected to help meet the growing demand for
electricity at peak times in Queensland, as well as help alleviate the
state’s peak power prices.
It may be possible as pumped storage hydrodevelops , to recharge the
system using excess alternative power , for example from solar arrays.
this would overcome the limitations of large scale battery storage and
provide a profitable use of excess alternative energy.
water, enters the steel drive pipe and flows through it by
gravitation until it reaches the RAM, passes through the RAM and out
through the pulse valve into the waste drain.
as the water flows, its velocity increases until the pulse valve is
no longer able to pass the volume of water flowing: at this point the
pulse value is suddenly closed.
Since outlet is now closed, the flow of water suddenly stops.
this produces a concussion of more or less severity in the body of
RAM according to the height and distance from which the water is
the result of this concussion is that a portion of the water in
the body of the RAM is forced upwards through the delivery valve
into an air cylinder.
at the same time the recoil allows the pulse valve to return to
its original open position.
so the outlet is reopened,
the water which was brought to rest by the closing of the pulse
valve starts flowing again through the RAM until it acquires
the necessary velocity to raise the pulse valve a second time, closing
the outlet, producing a concussion and forcing more water into the air
chamber through the delivery valve.
the water, which is forced into the air chamber, finds its way
through a pipe, known as the 'rising main', to the place where it is
required for use with a continuous flow being maintained so long as
the RAM remains working.
These steps are repeated from about b 40 to 90 times per minute, according
to the size of the hydraulic RAM, the fall of the water driving the RAM,
etc. The RAM will continue working automatically, the pulse valve rubber
and delivery valve rubber being the only moving parts.
The fall of water necessary to work a RAM may be as low as 500mm (20
inches) and with such a fall, water may be raised to 18m (60 feet). With
higher falls, such as from 2m (6.7 feet) to 7m (23.3 feet) and over, water
can be raised to upwards of 300m (1000 feet) or more in height and
distance is more or less unlimited: several of our ram installations pump
to over 5km (3.13 miles).
due to the action of the RAM, unless the conditions are unusually
severe, and provided the RAM is kept working and the water keeps
flowing,, the RAM will be unaffected by changes in temperature
especially low temperatures which might cause a conventional system to
'freeze up' unless some form of heat is provided.
the waste valve can be a spring-operated normally-open valve that
closes when the flow velocity generates sufficient drag. t
the water in the drive pipe, which is long and rigid (steel pipes
will generate higher pressure than pvc), has gathered significant
momentum (p=m*v) by that time.
when the valve closes, that momentum generates pressure, slamming
open the check valve and compressing the air in the reservoir.
the check valve closes again, the compressed air expands, pushing
water up the delivery pipe. The waste valve reopens and the process
the air reservoir stores the energy, absorbs the pressure pulses,
and provides continuous flow at the delivery pipe.
without the air, every time the waste valve closes, the two water
columns are in direct contact, one at full speed, the other at
that will cause either large pressure peaks (when they meet head
on), or large movement of the pump. At 30,000 times a day, they may
not last very long.
the fundamental difference between a pump with air reservoir and one
without is the efficiency: without reservoir, energy is transferred by
a perfectly inelastic collision: the water in the drive pipe and the
water in the delivery pipe have the same velocity after the
not only is that the collision where most energy is lost, the mass
in the drive pipe is also the largest mass, and will keep most of its
energy after the collision.
with a reservoir, most of the energy of the drive mass is
transferred to the reservoir, and all that energy is used to pump the
water in the delivery pipe.