Introduction,How do hydropower schemes work, Current status, How much electricity do they produce, Economics, Social implications, Environmental aspects, Conclusions
This industry has been around for many years now and has been optimised in Scotland. It has been said that any new schemes would only be on a small scale. This method of generation supplies around 10% of the electricity generated in Scotland, supplying base load and being able to respond quickly to surges in demand.
There are many implications of building a hydroelectric scheme. These are mainly environmental and disrupt the ecosystem around the dam.
An Example of a Hydroelectric scheme,
Sourced: www.tva.gov
Hydro schemes use the kinetic energy of moving water to produce electricity. This water is put through a turbine, which in turn drives a generator that creates electricity. Although there are different forms of hydroelectric schemes, they all are based on the following components:
·A Dam
·Penstocks
·Forebay
·Turbine(s)
·Generator(s)
The dam raises the level of the water to create a hydrostatic head, in the same way as a tidal barrage; this is the difference between the level of the water in the dam and the level where it flows out from the scheme. This acts to trap the water and can be released when necessary, enabling the water held to become stored energy. The height of water necessary to exploit the resource varies from a few metres up to 2000m; the best results have come from heights of 120m.
The construction of the dam requires large investment and has been a stumbling block for some schemes. But once running, the scheme will generate electricity with no fuel costs. Maintenance and running costs will be small, and again as with tidal barrages, it is safe to assume that the turbines will last for many years.
Hydroelectric scheme, sourced: www.edf.fr
The penstocks are pressurised pipes that take the water to the turbine. The
forebay controls the rate of the flow, ensuring that adequate levels are attained
in accordance with the turbine controls. This pressurised water then drives
the turbine that in turn drives a generator and creates electricity.
There are three main types of hydroelectric schemes, these are:
· Run of the River
· Diversion
· Pumped Storage
In the Run of the River type of scheme, the turbine and generator are located either in the dam or found along side it. The dam uses the flow of the river to create the hydrostatic head, this method can also be applied to tidal barrage systems.
A Diversion scheme is where the supply of water is taken from a dammed river or lake to a remote powerhouse containing the turbine and generator. A Canal or low-pressure tunnel transports the water to this end point and then back to the river to continue its course.
Pumped storage is a scheme that incorporates two reservoirs. At times of low demand, generally when electricity is cheap like at night, electricity is bought to pump water from the lower to the upper basin. This extra water can then be released to create power at a time when demand is high and prices high. This means that the company make money on their investment of electricity for pumping. This enables the scheme to perform with greater efficiency when matching supply and demand. This type of scheme is also similar to pumping for tidal barrages to increase supply and income.
How much electricity a scheme can produce is really dependant on how much water falls through it, and how far it falls. The further the water falls, the more power it has, as with the amount of water falling which is also directly proportional to the power.
The amount of power supplied to the turbine by the water can be calculated using the following equation:
Where, P = Power Supplied to the turbine (kW)
r = Specific mass (tonne/cubic metre)
Q = Volumetric discharge (cubic metres per second)
h = Net head of water (m)
m = Mass flow rate (tonne/second)
g = Gravity = 9.81
For examples of hydro schemes that go into greater detail, see the HydroPower Case Studies.
Hydro schemes generally involve a huge civil engineering effort, which requires a sizeable investment. The payback on this investment can be a lengthy process so therefore it is mainly governments or large corporations who fund these schemes.
There will be local economic benefits during construction due to the amount of people who will have to live and work in the area. The loch created by the dam will have recreational possibilities that can also add to the tourism in the area and therefore the economic prosperity.
The nature of tidal schemes means that they will always produce almost cost free electricity. There are no fuel costs and pumping can facilitate generation at a small cost.
Hydro schemes are often built in remote areas away from centres of population. They can be a valuable source of employment to that area during construction and operation. They will however, cause an increase in traffic to the area during construction, which will be a long and noisy process. This will affect what might be an otherwise peaceful area.
There are many environmental effects that a hydroelectric scheme will cause. Firstly, the flow of the river will be changed for the life of the scheme, affecting all the aquatic life in the river. This affects the quality of the water, which all plant and wildlife are dependant on in one way or another, and the local ecology of the site. The right balance is maintained by controlling the flow of water to ensure a suitable amount is available.
Before a dam can be built the ecosystem surrounding the dam is flooded to aid construction by keeping the actual site dry, but this can be accounted for and careful planning can reduce these effects. After flooding, replanting can be done where necessary and the area can become an attractive place for walking and tourism.
Hydro Power is an integral part of the generation of electricity in Scotland. It is not a new technology and therefore has been optimised in this country. The way forward is no longer increasing the number of schemes, but instead to ensure efficient management and modernisation of the schemes. Optimising Pumped Storage wherever possible is also an important step towards hydropower realising its full potential.