Nick Rosen | |
Large domestic micro-hydro-turbine
Hydro turbines can be big

Intro to Small-Scale Hydro by Rory Bowen
There’s something completely relaxing about watching moving water flowing past you, on its journey to an unknown destination. Why not harness the power within the water? Because that running water contains energy. The key to making hydro-power work for you is to maximise the amount of energy you generate from the available water (you can buy the gadgets you need to harness your water power from )

Water (perhaps deposited by rain) at the top of a hill has potential energy. As it runs down a hill or a stream it turns to kinetic energy. Using a turbine, this can be turned into mechanical and ultimately electrical. Welcome to the world of hydro power.

Old principles, New outlook

Hydropower’s a mature technology which has harnessed the power of water for around two thousand years and played a major role in the development of Europe and North America. The beauty of hydropower. unlike some other renewables, is that the seasonal variation in flow generally matches the energy demands — i.e. the more rain there is, the more energy can be produced when it’s needed most — in winter.

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Today hydropower provides around 20 per cent of the world’s electricity and for 30 countries it is the main source of power. Projects creating such great amounts of electricity come at a cost, however. Environmental and social damage caused by large scale projects (over 5MW) have been well documented in recent years with the Three Gorges Project in China being the most high profile. Evacuation of large populations and flooding of forested areas are just some of the associated problems. Large dammed reservoirs silt up over the years, reducing the efficiency of the scheme every day and starving land downstream of nutrition. But it hasn’t always been this way.

Environmental concerns don’t mean that hydropower is dead in the water. Quite the opposite. Small can be beautiful – and powerful. The term Small-Scale Hydro (SSH) can apply to schemes ranging from the powering of a domestic home up to schemes creating a few hundred kilowatts and exporting the power to the Grid. The technology for SSH has been used increasingly in developing countries over recent years but has been sidelined in the UK through prohibitive cost and over-regulation. In fact SSH reached its peak in the 1920s and was the main source of electricity and mechanical power in many towns and villages all over the UK. The extension of the grid coupled with the rise of cheap oil and gas led to mills and turbines falling into disrepair. However, due to ever-rising fuel prices and concerns over climate change, interest in SSH is rising again.


Power produced at fairly constant rate compared to other renewables
Adaptable, simple robust technology cost effective
Can be very competitive on price
Low maintenance costs
No carbon emissions, little noise

Site specific
Power and expansion limitations
Weather dependent without reservoir
High costs upfront
Low level impact on watercourse

Horses for Water Courses

In the UK only about one per cent of electricity is produced from hydro and the potential for the extension of large-scale hydro is limited as most undeveloped suitable sites are in areas of natural beauty. But sites for small-scale hydro are plentiful and vary from mountainous regions with fast-flowing streams to wide rivers in lowland areas. In addition it’s estimated that there are as many as 20,000 historic SSH sites in the UK, lying dormant just waiting to be tapped again. The great advantage of such sites is the knowledge that flow is likely to be assured (as it has been used in the past) and it’s likely that you will be able to use some of the existing infrastructure, saving on installation costs and reducing environmental impact. In other areas SSH would require completely new construction but in remote areas, hydropower can be the most simple, reliable and affordable source of power.

How much water do I need?

The amount of power you get from a system depends entirely on two factors: the amount water flowing (flow) and the vertical distance over which it falls (head). Before taking the plunge and installing a system you need to work out your potential output and then, of course also need to determine whether your resource can meet demands directly or with the aid of battery storage. As with any stand-alone domestic energy system it’s easier in the first instance to reduce demand rather than increase supply, so make sure you are doing all you can to keep power requirements to a minimum, especially at peak use times in the day. If you are living totally off-grid, unless you have a relatively large and reliable output (10kW and above), the chances are you will be relying on some other form of energy, whether it be other renewables or a generator. And of course if you are connected to the grid you can always sell your excess power back to the grid, thereby balancing out your demand and supply over the day and throughout the year.

Most SSH plants are run-of-rivere schemes, with heads of only a few metres. Run-of-river schemes do not require a reservoir, they just use the water and return it to the watercourse downstream, extracting nothing but energy from the river water. The river will suffer a reduced flow between intake and the turbine and this aspect must be carefully considered to make sure adverse effects on the river are mitigated.

SSH is a mature technology that is adaptable and flexible to a variety of situations but siting remains the most important barrier to overcome. In fact your turbine can be located up to several kilometres from where you need the power through relatively modest cables without great transmission losses. The first thing to do is get a pre-feasibility study. For a domestic scheme these can be completed for around 100 and will tell you if your scheme is practical in terms of output and planning. A more detailed study may cost around 1000. In all cases some form of environmental assessment is essential to obtain planning permission so it’s advisable to work closely with the Environment Agency and your local planning authority too.

As stated at the beginning, the key to making hydropower work for you is to maximise the amount of energy you generate from the available water. It is possible to create a water store or reservoir which makes it easier to control the speed and amount of water that hits a turbine. The system should comprise a forebay tank, a penstock and a flow-shaping nozzle which lead to the turbine. But don’t let the jargon put you off. And this doesn’t need to be a major feat of engineering either. It can be done on a very small scale. As stated before most SSH schemes use a run-of-river approach, which will only involve a small amount of diverted flow. In fact there’s no bottom limit to the amount of power you can produce. PowerPal produce systems that don’t require any extraction of water at all, producing from 200W upwards, enough to charge batteries or provide lighting needs.

Such a system costs around 1400 for the turbine and the all important flow shaping components. From here costs can rise sharply as the size of the system (and output) rises. Additional pipework and installation costs can particularly prohibitive, so the closer you are to the source, the more cost efficient your system will be.

Two final advantages of hydropower over other renewables are that average rainfall is highly predictable and therefore output is reliable. Plus flow doesn’t fluctuate from minute to minute like the wind flow only changes gradually from day to day. In terms of reducing overall carbon emissions, hydropower can only expect to make a small contribution, but every bit counts. Plus you’ll get the satisfaction of watching that flowing water knowing what its doing for you.

Power produced at fairly constant rate compared to other renewables
Adaptable, simple robust technology cost effective

More information:

British Hydropower Association.

Grants in the UK.

Example Micro-hydro product site.

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