This article aims to give the reader an understanding into two areas of hydropower; large scale Hydroelectricity and micro scale Hydro Schemes. Unlike most of the other renewable forms of energy, hydropower has been a form of energy generation throughout history. Over time, energy generated by hydropower has been used for different needs, with the technology evolving from milling to electrical generation. The Galloway Hydroelectric Scheme in Scotland was the first major hydroelectric scheme built in the UK in 1935, and much like today, it was specifically designed to provide extra power when electrical energy demand was high. It has a total of 12 turbines with an output capacity of 109MW ¹. Hydropower schemes of both sizes can be applied to existing water courses where a previous watermill was once situated, or they can be applied ‘brand new’, such as the 3 Gorges Dam on the Yangtze River in China. Obviously new build schemes will have an impact on the local environment, and many issues arise from this.

Hydroelectricity

How It Works

Hydroelectricity involves transferring energy from water by allowing it to flow through a turbine. The turbine revolves and electrical energy is generated. We can increase the amount of energy content water has by effectively adding gravitational energy into it. By storing water at a height and then releasing it, the water in essence has now gained a vast amount of additional energy. The velocity of the water is increased and will therefore cause the turbine which it is flowing through, to revolve much faster, and thus create more energy.

Advantages

• In comparison to other power plant generations (such as Nuclear and Coal), Hydroelectric Dams can be turned on or off very quickly – beneficial for supplying energy when demand is high.
• Apart from the initial construction, Hydroelectric Dams produce no carbon emissions.
• Hydroelectric Dams (unlike wind or solar power) are not intermittent. They can produce electrical energy continuously and at a constant rate.
• The reservoir that stores the electricity can be used for water sports and other water activities.
• The water can also be used for irrigation.
• It can be used as a renewable intermittent power resource. For example, when demand is low and wind turbines are generating an excess amount of electricity that is not needed; this energy can be used to pump up water into the reservoir. When demand is high, and there is an intermittent period, the hydroelectric dam can be turned on and uses the water which was stored by the wind turbines electricity.
• Once initial costs of construction have been paid back, hydroelectricity is very cheap to generate (in comparison to other renewable and fossil fuel generation plants).
• Modern hydroelectric power plants generate 90% of the water’s energy. In comparison to coal which at best generates 50% of its fuel.

Disadvantages

• The local ecosystem around the area a dam is built will be permanently changed as well as the ecosystems downstream.
• The risk of flooding is greatly increased. If a dam were to burst, settlements downstream would be affected.
• A dam may cause earthquakes. An increase in pressure due to the mass of stored water can trigger this to happen.
• Dams that are built on a long distance river may affect other countries that also rely on the same river. I.e. the Ganges. When the dam’s water has been released in India it upsets the naturally occurring flooding in Bangladesh.
• Fish migratory courses may be affected.
• Its construction may cause drought further downstream.

Micro Hydropower

How It Works

Water is siphoned off from the river or stream by a dam or a weir. This enables a smooth collection of water into the canal and forebay. Usually, within the canal and forebay system a screen collects debris, as this will damage the turbine system. The forebay houses water which is then fed into, and through a penstock. The penstock will be only a few inches in diameter, and creates a jet of water through a nozzle onto the turbine. The turbine is housed inside a ‘powerhouse’. The powerhouse is enclosed to protect the alternator/generator/inverter from the elements, and also to act as a barrier to noise that is produced through generation. The tail race feeds the water back into the river or stream.

To estimate the maximum power that a river could produce, you will need to take an average (not maximum) flow rate for the year –measured in metres cube per second. I.e. an average sized stream is likely to have anywhere between 0.25 and 1 m³/s. You will also need to find out the head (height of the water from the top to the bottom), measured in metres. This is only a rough calculation:

Power (estimation) = Flow rate x Head x 5

The 5, denotes gravity divided by frictional losses within a system, and again, is a rough, rounded number.

Advantages

• It is very efficient and reliable.
• In winter months, when demand for energy is highest, a hydro powers resource is at its highest.
• It is a good power source for developing countries. Many places may not have a grid system supplying them with electricity. Hydro offers a cheap and reliable source of energy.
• It will often generate enough electricity for personal needs, and will often produce a large excess, which can be sold to the grid.
• Unlike hydroelectric dams, a big reservoir isn’t required as it works off of the run of the river and therefore has a minimal impact on the local ecology.

Disadvantages

• It is limited to the ‘power’ of the river.
• Feasibility is extremely site specific.
• Whereas demand is expected to be highest during the winter months, generation requirements are hindered during the summer months when the river does not produce such a large capacity of water.
• Fish migratory paths may be hindered, and therefore careful planning will be needed which still allows fish to migrate whilst temporarily extracting water for electrical generation.
• Freezing temperatures (particularly for the penstock) will need to be addressed, such as burying or insulating.

UK Micro Hydro Schemes

The UK’s feed-in-tariff levels for Micro Hydro Schemes start at 19.9p/kWh for projects under 5kW, and 17.8p/kWh for projects between 15 and 100kW. Both have a lifespan of 20 years. So, if a project is installed this year (2010/2011) the generator for a 5kW system will earn 19.9p/kWh every year for 20 years for the total that is generated, whether consumed or exported to the grid. For every 1kWh that is exported to the grid, the generator will also receive 3p/kWh.

The Local Planning Authority will need to be consulted on building a powerhouse and pipe work. The Environment Agency is in charge of watercourses in the UK, and you will need permission prior to installation and an abstraction of water licence. You will also need to assess the affects on river ecology and flooding.

There are many examples of Micro Hydro Schemes within the UK. Old water mill sites are also commonly used. Gants Mill in Somerset is one such example.

‘Old Walls’ Dartmoor, Devon: http://www.re4d.org/images/stories/pdf/re4d%20cs%20old%20walls.pdf

‘Gants Mill’ Bruton, Somerset: http://www.gantsmill.co.uk/hydropower.htm#tour

World Hydroelectricity

‘The International Energy Outlook 2000 predicts that the global consumption of electricity will be 76% higher in 2020 than it was in 1997. Electricity consumption will increase from 12,000TWh (1997) to 22,000TWh (2020).The worlds total feasible hydropower potential has been estimated at 14,370TWh/yr of which 8082TWh/yr is considered economically viable for development. In 2000, 2600TWh/yr was already in operation.’ (Hydropower and Dams, World Atlas and Industry Guide 2000)

China, India, Iran and Turkey are developing large scale hydro projects².’

More recently, the ‘Key World Energy Statistics 2007’ wrote that Hydroelectricity combined had a capacity of 836GW producing 2994 TWh of energy generation in 2005. With China being the highest contributor (13.3% – 397 TWh).

References

1. Boyle, G. 2004. Renewable Energy, Power for a Sustainable Future. 2^nd Ed. Oxford: Oxford University Press. Chapter 5. Hydroelectricity, The Galloway Hydros.

2. World Hydroelectricity. Information taken from: http://www.ieahydro.org/reports/Hydrofut.pdf