An Introduction to Waterpower

Water power has been harnessed since the earliest civilizations for agricultural processing and latterly for the production of electricity. If you live in an old mill or have an upland stream flowing through your property, you probably have a site suitable to generate all or a significant proportion of your domestic power requirements.

If there is insufficient power to provide your needs electrically, then there is the additional possibility of using water power to drive a water source heat pump which will increase the power output by three times in the form of heat.

The main power requirements are in the winter months, so there should be little or no conflict with other river demands. Adequate provisions may have to be made for migratory fish, and if new works are to be constructed, care must be taken with regard to the effect on land drainage upstream of your intake. We recommend that our customers construct all schemes in an unobtrusive and environmentally sensitive manner, and where appropriate we will provide drawings of proven designs.

Available Power

The power available from a stream is determined by the head and flow of water on the particular site. This power is harnessed by constructing a dam or diverting the flow in such a way that all the fall occurs in one place. Where it is not practical to construct a channel, the water may be piped and the head of water is exploited as a high velocity jet driving an ‘Impulse Turbine’.

The power available is a function of the fall (head) and flow so building a large waterwheel on a low fall will only increase the cost and reduce the shaft speed but not increase the power.

Water wheels are limited to sites with a head of less than 10 meters. They are aesthetically pleasing and have good performance under low water conditions. Unfortunately, due to their size, they are both costly to build and install, largely because of the gearing required to increase the shaft speed, typically from 10 to 1500 rpm. The use of low speed generators does not help since it is the low speed end of the drive which is the expensive part.

Water turbines, on the other hand, are able to make use of a very wide range of head, from less than a metre to many hundreds of metres. To cover the full range of sites, it is necessary to make use of several different types of turbine. It is not that you cannot use one type of turbine for all sites but that each design has it economic and hydraulic area.

Types of waterpower site

Upland sites
Small streams typically employ a pipeline of 100 mm to 600 mm in diameter running downhill to the power plant which may have an operating head in excess of 20 metres. The pipeline could be as long as 1000 metres and still be economic, provided the gradient is steep enough, or most of the pipe run can utilize low cost materials. An impulse turbine having one or more jets is typical for this type of installation.

Low head sites
These use proportionately greater quantities of water frequently employ an open leat or channel to bring the water around the contour to a point where it can drop steeply down to the turbine or millhouse. Such sites with heads in excess of 10 metres can also use impulse turbines which can adapt well to varying water flows that occur between summer and winter.

For thousands of years waterpower has been harnessed for milling and pumping water but many good sites have fallen into disrepair as a result of competition from diesel and electric power Of over 70,000 mills in the UK, at the end of the 18th century, there are only a few hundred still working. Mills fall into several categories which will determine their suitability for redevelopment.

Mills with ponds
Seldom suitable for redevelopment for anything other than a few kilowatts because the water flow is obviously too little to sustain the mill on a continuous basis, and it is usually too expensive to install a wheel or turbine that can only be operated for a few hours a day.

In some cases the ponds were only needed in the summer months when the water flow was low and this can still be a useful system where the equipment to be driven requires a fixed power input. In such situations the plant operates until the water level is reduced by say 500mm, it is then stopped until the pond fills again.

Although it is not always very convenient, it is efficient, since the plant operates at full power when turned on. This system is suitable for heating, pumping and where there is an alternative source of power if it is required all the time.

Mills with leats or channels
These take their water from a water course along the side of a valley at a gradient that is usually less than one in five hundred. At a suitable point when enough fall can be achieved in one place.

If a turbine is installed to replace a waterwheel, it may be possible to increase the useful head by eliminating drops at mill pools, sluices and below the wheel. Since there was a mill there anyway there should be at least enough power for domestic purposes including heating. Improvements to the leat and head are usually possible but are very site specific and are made very much easier with mini excavators.

Mills on weirs
Weirs or lcations with short wide diversion channels present the most difficult challenge for the developer. The available head may only be a metre or so and the flow required to generate useful amounts of power will be several cubic metres of water per second.

The undershot waterwheels that were originally used at these sites are totally redundant on account of their high cost and low efficiency. The exact layout of the site becomes increasingly important with the lower falls, because access for excavators and to install the large items of equipment is more difficult.

Water falls ranging from one to three metres in height employ single or multiple high speed propeller turbines. Variable flow is achieved by automatically stopping and starting one or more of the turbines rather than using variable flow Kaplan turbines that are more expensive and less efficient.

Very low head and tidal causeway
These sites can be developed using modular bulb turbines. Propeller turbines, driving high pressure water pumps are arranged in a line across the river and the water is fed to another impulse turbine on the river bank. The lower efficiency is compensated for by lower maintenance costs and variable speed capability for the main turbines. Our largest units to date, have a runner diameter of 3.5 metres.

The range of project size

Applications range from power for remote monitoring equipment, telemetry or camp lighting, to small scale village electrification in remote rural areas. Our ‘Universal’ range of turbines has been designed to offer an alternative to diesel plants and to have much more flexibility in their installation than conventional waterpower equipment.

Larger projects over 100 kW for commercial power generation, need to be individually designed to make the best use of the power available Special projects have included very small units for battery charging, power recovery in industry and low-cost units for agricultural applications and water pumping.

Developing Countries
Simple robust technology is required to drive agricultural machinery; typically supplied bare shaft with mechanical governing. The machines are suitable for local manufacture.

Portable plants (5-15kW)
For rapid installation and relocation for disaster relief operations, survey camp power and recreation purposes.

Domestic power (5-25kW)
Supply for one house if heating is the main load, usually single phase. Sites include old mills and upland farms with or without grid connection.

Commercial power (15-100kW)
Usually three phase installations supplying small businesses, farms or estates. Can run in parallel with the grid and have accurate governing systems.

Grid connected plants (50-2500kW)
Specifically designed for commercial power connected to grid system. Designed to run fully automated with remote monitoring.

Training purposes
Models for training purposes either static for illustration only or as fully working desk top units, complete with pump tank and generator.

Special applications
Outside normal power and head range and are individually assessed. These include power recovery in desalination or industrial processes, aeration for fish farms, sub-sea power, fire fighting, mining, tidal and canal lock installations.

Power recovery
Turbines to replace head breaking valves or at the inlet to treatment works; for desalination plants using reverse osmosis; for compensation flows from reservoirs and the outfalls of sewage treatment facilities. In line power recovery on contaminated flows and raw sewage is also possible