10 things you should know:
1. Hydro-power produces one fifth of all the world's electricity. In emerging economies hydro is used to generate one third of the electricity used.
2. Canada, the USA and China are the three largest generators of hydro electricity.
3. Even relatively flat countries can generate with hydro. Holland currently has 38MW of installed capacity, with about the same again economically feasible.
4. The world's largest operational hydro plant is the Itaipu project shared jointly by Brazil and Paraguay - it has 12,600 MW of installed capacity. There are, however, hundreds of run of river (no dams) hydro stations in the developing world of around 5 kW capacity - over 2.5 million times smaller!
5. Most large hydro stations have dams but thousands of small hydro stations have no dams - they are 'run of river' and make a minimal impact on the environment.
6. Hydro is the only renewable technology that can be used to store large quantities of energy in a clean environmentally friendly way. This is done by reservoir storage and pumped storage schemes.
7. Only hydro can produce over 200 times more energy from an installation than the energy needed to build and run the installation. This is ten times more than oil fired power stations - and with minimal atmospheric pollution.
8. Hydro installations can have a useful life of over 100 years - many such plants are in existence worldwide.
9. Gilbert Gilkes and Gordon Ltd of Kendal, England have manufactured hydro turbines for longer than any other company in the world.
10. A modern hydro turbine generator set can convert over 90% of the energy in the available water into electricity. This is more efficient than any other form of generation
Is the capture of the energy of moving water for some useful purpose. Prior to the widespread availability of commercial electric power, hydropower was used for irrigation, milling of grain, textile manufacture, and the operation of sawmills. The energy of moving water has been exploited for centuries; in Imperial Rome, water powered mills produced flour from grain, and in China and the rest of the Far East, hydraulically operated 'pot wheel' pumps raised water into irrigation canals. In the 1830s, at the peak of the canal-building era, hydropower was used to transport barge traffic up and down steep hills using inclined plane railroads. Direct mechanical power transmission required that industries using hydropower had to locate near the waterfall. For example, during the last half of the 19th century, many grist mills were built at Saint Anthony Falls, utilizing the 50 foot (15 metre) drop in the Mississippi River. The mills contributed to the growth of Minneapolis. Today the largest use of hydropower is for electric power generation, which allows low cost energy to be used at long distances from the watercourse.
The Hydrological Cycle -
Hydro, like all forms of renewable energy, is a result of the effect of the sun's rays on the Earth. Water rises from the sea under the action of the sun into the atmosphere where it forms clouds. These clouds are blown by the wind over the land where hills force the clouds to a higher colder level where the water vapour condenses back into liquid which falls as rain (or snow if it is cold enough). This rain runs off the hills and forms streams and rivers that run back into the sea.
This sequence..... water in the sea - clouds - rain on hills - rivers - back to water in the sea , is called the hydrological cycle.
The study of what happens to the water that falls as rain - because not all goes into the rivers, some being lost in evaporation, some taken up by plants, some stored in lakes and underground natural reservoirs - is called hydrology and is an essential element in the science of hydro-power.
Energy Potential of a Site -
The owner of a potential hydro site may ask the question 'how much power will my site produce?' The question should really be 'how much energy will my site produce?' since it is energy that we buy from or sell to the electricity supplier. Energy is a measure of the length of time we have used or produced a given amount of power. Thus a site on a river with a very variable flow may not have the potential to produce as much energy as a site on a river with a lower peak flow but a higher mean flow. The hydrologist can produce a 'flow duration curve' for a river by studying the recorded water flows (preferably the recorded flows for a number of years). This flow duration curve is a means of showing the probability in a graphical form of how many days in a year a particular flow will be exceeded.
The vertical axis of the flow duration curve shows the flow, the horizontal axis days (or % of time).
Curve A is for a river with a high flood flow for a short time,
Curve B is for a river with a more steady flow.
The area below the curve is a measure of the energy potential of the river.
Head, Flow and Power -
The power available in a volume of water Q is the mass of the water (Q x density) times the height or head (H) the water can fall. This is the theoretical power. In practice we must consider the losses due to imperfections in the design of machinery and pipelines. Internal friction in pipelines and channels as water travels towards the turbine causes a loss of head in the system. Hence the head used in calculations is the nett head - this is the head across the turbine system only. Similarly there are friction and heat losses in the turbine, the gearbox and the electric generator. These are catered for by the efficiency of the system. As a rule of thumb the 'water to wire' efficiency of a small hydro system may be taken as 70%
Hence combining efficiency and water density into one number we arrive at the simple formula :
Power in kilowatts = 6.9 x Q x H
Where Q = cubic metres per second
H = nett head in metres
The Energy produced is the power x the time for which it is produced. It is usually expressed in kilowatt hours (kWh).
Many types of turbine have been developed over the centuries. The water wheel (in one of its forms) is the ancestor of the modern turbine and is still used today to produce electricity - see the separate chapter on water wheels.
Turbines can be split into four main groupings (although they do of course overlap and experts may disagree on where one group starts and ends).
These are :
1. High head - above 100 m
Turbine types are - Pelton, Turgo, High head Francis.
2. Medium Head - 20m to 100m
Turbine types are - Francis, Cross Flow.
3. Low Head - 5m to 20m
Turbine types are - Cross Flow, Propeller, Kaplan.
4. Ultra Low Head - below 5m
Turbine types are - Propeller, Kaplan, Water wheel
The most common types of turbine are listed although variations on each type are produced.
All types except the simple propeller turbine can be fitted with mechanisms to enable the turbines to work at varying water flows without too great a loss of efficiency.
Turbines are usually tailor made for a particular site and it is down to the skill of the engineer to choose the most effective machine for a site - taking into consideration cost, variations in head, variations in flow, water quality, reliability.
Small hydro costs can be split into four segments :
This group includes the turbine, gearbox or drive belts, generator and the water inlet control valve.
2. Civil Works
This includes the intake and screen to collect the water, the pipeline or channel to carry the water to the turbine, the turbine house and machinery foundations, and the channel to return the water back to the river.
3. Electrical Works
The control panel and control system, the wiring within the turbine house.
4. External Costs
This could encompass the services of someone to design the installation, costs of obtaining a water licence, planning costs and the big one - cost of connection to the electricity network if you are exporting the energy produced.
The last two categories are largely dependent on the maximum power output of the installation. The connection cost is set by the local electricity distribution company and may cynically be said to be inversely proportional to how much they want your energy. More and more often the hydro developer is being made to make environmental and landscaping improvements as a condition of obtaining planning permission. This ecological blackmail is suffered by most energy developers.
The Civil Works are largely site specific. On high head sites the major cost will be the pipeline; on low head sites probably the water intake screens and channel.
Machinery costs again depend largely on site. High head machines have to pass less water than low head machines for the same power output and are therefore smaller. They also run faster and thus can be connected directly to the generator without the complication of gearbox or belts. Generally speaking, machinery costs for high head schemes are lower than for low head schemes of similar power