Hydro-Electric, Wave & Tidal
Key FactsThe principle components of a micro-hydro scheme is a suitable river, with a dam or weir that diverts part of the river down a power canal to a collection area known as a forebay. From the forebay, the water is directed through a penstock or drive pipe, to the control valve and into the turbine. The water then flows through the tailrace and back into the river. Using this scheme, the environmental impact is minimised, and affects only that part of the river that is denied the redirected water flow (3).
Potential power can be calculated as Q × h × g, where Q = flow in litres/second, h = head height in metres, and g = gravity. The head height is the difference in altitude between the firebay outlet and control valve. In a well designed system, losses due to friction should be less than 5%.
The dam or weir is designed to allow water through such that the river always maintains a safe, minimum level. The water is diverted into a settling area to prevent sediment travelling along the power canal, into the penstock and ulimately into the control valve and turbine. The control valves should be a butterfly or gate valve, as water needs to be shut off slowly to avoid the "water hammer" effect.
Types of impulse turbines include pelton (4) wheels with a single or multiple jets, turgo turbines (5) which are the next size up from Pelton wheels, and crossflow or banki turbines that are suitable for low head height systems and are easily made.
Types of reaction turbines (all of which are fully submerged in water) include Francis turbines, Kaplan and Propeller turbines. Kaplan-types (6) can adjust their pitch according to the flow rate.
Despite Britain having the natural marine advantages of over 11,000 miles of coastline and some of the highest tidal ranges in the World, wave and tidal renewables are only just developing where they can be deployed commercially (7). UK estimates for wave power are at least 50 TWh per year, and for tidal power are put at 34 TWh per year (8). Tidal power has the great advantage of being highly predictable compared with some other forms of renewable energy.