Good Energy’s information on hydro electricity

Quick links: generate your own hydro power - Good Energy’s pioneering hydro generators

The UK has benefited from hydro electric power for well over a century. We have over 1,500MW of existing hydro electric generating capacity, accounting for around 24% of renewable electricity generated. Worldwide, hydro electric power enjoys a similar status as the world’s number one source of renewable electricity, and producing almost 20% of the total energy demand. Countries like Norway produce nearly all their electricity from hydro, and Austria over 70%. And there is plenty more to come – it is estimated that only a third of the potential hydro electricity capacity in the world has been exploited (New Scientist).

Large hydro electric power plants have caused controversy more recently however and tend to divide environmentalists. Huge hydro dams can cause havoc with local ecosystems and have negative effects on communities – particularly for nearby agriculture. The disturbances to migrating fish, erosion of river beds and drying of land can have profound consequences on the local environment. At Good Energy, we tend to stay clear of large scale hydro electric for these reasons, and focus instead on small scale Hydro power. Good Energy works with nearly 40 small scale independent hydro electric generators to supply our customers with electricity. Small scale hydro does not present the same environmental concerns, and can provide a reliable, plentiful source of renewable energy.

So how does hydroelectric power work?

Hydro power can be captured wherever a flow of water falls from a higher level to a lower level.  This may occur where a stream runs down a hillside, or a river passes over a waterfall or man-made weir, or where a reservoir discharges water back into the main river.  As the water moves towards sea level as a result of gravity, its kinetic energy is consolidated.

Hydro electricity is created from falling water. The water is channeled and its gravitational force can be used to spin turbines that generate electricity. The further the water falls, the more energy it can generate. Humans have used hydro power for centuries and many of the micro hydro electricity projects being installed today use the existing infrastructure of a Victorian mill, such as the original weirs and mill races for example and adapt it for electricity production. This is common practice because building, new infrastructure is often too expensive to make micro hydro electric projects viable.

The vertical fall of the water, known as the “head”, is essential for hydro electricity generation; fast-flowing water on its own does not contain sufficient energy for useful hydro power production except on a very large scale, such as offshore marine currents.  Hence two quantities are required: a Flow Rate of water Q, and a Head H. It is generally better to have more head than more flow, since this keeps the equipment smaller.

The Gross Head (H) is the maximum available vertical fall in the water, from the upstream level to the downstream level.  The actual head seen by a hydro electric turbine will be slightly less than the gross head due to losses incurred when transferring the water into and away from the machine.  This reduced head is known as the Net Head.

Sites where the gross head is less than 10 m would normally be classed as “low head”.  From 10-50 m would typically be called “medium head”.  Above 50 m would be classed as “high head”.

The Flow Rate (Q) in the river, is the volume of water passing per second, measured in m3/sec.  For small schemes, the flow rate may also be expressed in litres/second where 1000 litres/sec is equal to 1 m3/sec.

Energy is an amount of work done, or the ability to do work, measured in Joules.  Electricity is a form of energy, but is generally expressed in its own units of kilowatt-hours (kWh) where 1 kWh = 3,600,000 Joules and is the electricity supplied by 1 kW working for 1 hour.

Power is the energy converted per second, i.e. the rate of work being done, measured in watts (where 1 watt = 1 Joule/sec. and 1 kilowatt = 1000 watts).

Hydro electric-turbines convert water pressure into mechanical shaft power, which can be used to drive an electricity generator, or other machinery. The hydro power available is proportional to the product of head and flow rate. The general formula for any hydro electric  system’s power output is:

P = h r g Q H

Where:

The best hydro electric turbines can have hydraulic efficiencies of over 90% (higher than all other prime movers), although this will reduce with size.  Micro-hydro power systems (<100kW) tend to be 60 to 80% efficient.

If we take 70% as a typical water-to-wire efficiency for the whole system, then the above equation simplifies to:

P (kW) = 7 x Q (m3/s) x H (m)

(Source BHA)

Most hydro electric stations have dams  built at specific points on rivers that have a large dropping point. The dams flood the area behind the dam and allow water to be directed in large volumes through turbines. Being able to control the volume of water flowing through the turbines with the dam is one of hydro electricity’s strong points as it allows energy to react to the demand – at peak demand the reservoir will let full volumes of water through, and at low demand the volume can be restricted. There are some huge hydro electric plants around the world generating vast amounts of clean energy, consistently. The advantages of hydro electric power are clear – once they are built the plants need no fuel, and produce no emissions. Built in the right places, hydro power beats all other electricity generating technologies with a pay-back ratio of 300 (energy produced/energy to produce) – this is ten times better than coal-fired power stations.

Drawbacks of Hydro Electric power

Unfortunately, hydro electricity isn’t without its critics, even within environmental circles. Despite being a low carbon way of generating electricity, the plants can have unacceptable consequences on local eco systems and communities. Dams that are built to house hydro electric plants can flood the river upstream. This can have hazardous effects on wildlife and communities that surround the area. Farmland, for example, can be ruined by the flooding. The disruption caused to fish stocks has resulted in some hydro power stations being shut down, despite efforts by the plants with the likes of fish ladders. Fish migrating upstream cannot get to their spawning grounds, and those swimming downstream are harmed when swimming through the turbines. The knock-on effects of dwindling fish stocks can be severe.

Small scale hydro electric stations

Small scale hydro electricity does not suffer from the same criticisms. Most of the “micro-hydro” projects that Good Energy work with, for example, have no dams and are “run of the river” generators. The visual and environmental impacts are  minimal. Small scale hydro electric plants can produce anything between 1MW and 30MW of electricity, and can be a perfect constant energy source for a small community. We support these projects with our power purchase agreements (PPAs), and in the case of our HomeGen customers, we even pay them for the electricity the use themselves. This reward scheme helps our customers to generate their own renewable energy. Take a look at some of the projects we work with here. If you are interested in becoming a small scale hydro generator please visit our site www.generateyourown.co.uk to find out more.

Don’t have a river nearby?

We still think we can help. Switching your home or business from your standard electricity supplier to Good Energy means that all the electricity you use will be supporting independent renewables around the UK, including small scale hydro electric power. We are the UK’s only 100% renewable electricity supplier and fight for renewable energy every day.

Switching to Good Energy is the first step in supporting hydro electric power.