HYDRO ENERGY

Waves Small-scale hydro (<1MW)

Introduction

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.

Evaluating a Hydro Site (Courtesy of the British Hydro-power association)

Non-Technical Hurdles

Before measuring the hydro potential of a site it is necessary to be aware of the non-technical hurdles that must be cleared before construction can start.

Land Ownership

You will need the permission of the landowner to build and have access to the powerhouse, intakes and discharge channels.

Environment Agency

All water courses of any size are controlled by the Environment Agency. To remove water from them (even though it may go back in) will almost certainly require their permission in the form of a licence. They are also responsible for fish protection and other environmental aspects of any riverside development.

It is essential to contact your local Environment Agency office at an early stage and discuss your proposed scheme. Whilst they have a duty to protect the environment from harmful development, EA officers are generally sympathetic to green energy schemes. They will also advise on the scope of any environmental assessment that may be needed.

Local Planning Authority & Ecological Designations

If you think your scheme may change the landscape in any way or it is in a National Park, then discussions with the local planning authority are recommended. For a site within a National Park, the National Park Authority is the relevant planning authority.

If the river is designated as an SAC or as an SSSI or another ecological designation, early contact with CCW, EN or SNH is advisable.

Physical Measurements Required

Three pieces of information are essential to evaluate the potential energy from a site.

1. The Head

This is the height the water falls through the hydro installation. The gross head is the difference between the upstream water level - where the water would enter a pipeline and the down stream level - where the water leaves the installation. The nett head is usually taken as the head across the turbine only and is the gross head less the losses due to pipeline friction, intake screen losses etc.

For the initial evaluation the gross head is measured.

2. Available Flow

This is the flow that can be directed through the turbine - it may not be the entire flow of the river since some water is usually left in the water course for environmental reasons.

3. The Duration of the Flow

The flow in most rivers varies with time. Hence a flow duration curve is required to estimate the amount of time that an installation can run during the year.

A guide to hydro basics and main issues can be found at http://www.british-hydro.org

Micro Hydro Scheme Further information

For further information on hydro-power information can be found on the following web-sites:

British Hydro-power association http://www.british-hydro.org

Assynt Hydro Assynt Crofter's Trust Case Study

Centre for Alternative Technology Hydro-power course www.cat.org.uk