Easily scalable and with minimal ecological impact, the VETT is an ideal solution for generating power from low head streams, rivers, and tidal settings. It achieves a significant reduction to the cost of energy for low-head hydropower and does so with no environmental, visual or noise impact.
VETT can also operate in other low pressure sites, such as outfalls at existing high head dams, water treatment plants, wastewater outfalls and pressure reduction valves.
As power is a function of head and flow, generating significant power from low head locations requires large volumes of water. Conventional hydropower technologies have one downside in common: due to low available head pressures, they require large volumes of water which produce low rotational speeds therefore requiring gearboxes to efficiently drive generators. This results in very large, heavy, expensive equipment and civil infrastructure.
VETT addresses this issue by using venturi principles to achieve a pressure amplification for the turbine so that smaller, faster, no gearbox turbines can be deployed in low head hydro settings.
Read more about the VETT here from Innovate UK.
ACHIEVING PRESSURE AMPLIFICATION
With a VETT, a net 3.0 m water head across a weir can be amplified to 7.5 m.
How does it do this? The underlying principle is that when water is forced through a constriction - a venturi - the water speeds up and the pressure in the venturi will drop. A duct or secondary flow pipe is positioned so that the water flow ends in the low pressure area of the venturi. When a turbine is connected to that duct the pressure or head across that turbine is amplified.
Check out 'The 'shear' brilliance of low head hydropower' from the University of Oxford, who worked with VerdErg on the VETT's development.
Within a VETT the turbine discharges into a very low pressure region created by the venturi flow. As a result, the pressure differential across the turbine increases as the turbine not only experiences the site head pressure but also the considerably lower venturi pressure downstream of the turbine.
In a conventional VETT, 80 % of the water is used to create the low pressure in the venturi. This is shown as 'Venturi flow' in the above visual, and is the primary flow through the VETT. 20 % of the flow is used to drive the turbine at an amplified head - shown as 'Turbine flow' above. The Venturi flow and Turbine flow then combines and exits the VETT as the 'Total combined flow'.
This ratio can be amended for each site if more or less amplification is desirable.
This pressure amplification is how VETT captures and converts the abundant source of natural energy in water in an efficient, environmentally benign and cost effective way.
A key aspect of VETT's design philosophy is integration within its environment. VETT's structural, operational and installation specifications can accommodate for sensitive environmental parameters due to its design and configuration flexibility. As a result, VETT is able to achieve minimal environmental impact whilst maintaining its purpose as an economically viable solution to generate renewable hydropower.
VETT can easily be integrated into the existing water-course infrastructure. The unit can be located in the bank next to a weir or under the existing water level in a mill pond or lock structure.
The generator that is driven by the turbine is dry-encased and sits behind the turbine, also under water, negating the need for an above ground turbine house.
The control equipment of the VETT fits in a conventional road side kiosk which can be located near the hydro scheme in a location that doesn't disturb the landscape.
80% of the flow travels through the venturi part of a VETT unit which has no moving parts, allowing fish to migrate through the device. As fish will experience a sudden pressure drop extensive testing with live fish in an operating VETT was undertaken by expert parties Vis Advies in the Netherlands and Fishtek Consulting in the UK. This third party verified test data has classified VETT as “outstanding” for fish survivability with 100% of sensitive juvenile fish passing through the primary flow path safely.
These tests were done in constant communication with the Environment Agency and in 2017 the Environment Agency gave green light for VETTs to be installed .
Click here for Vis Advies' report on the successful VETT fish trials.
Fishtek Consulting presented the VETT trials at the 2018 IFM Renewable Energy & Fisheries conference, Wales. Click here for more information.
VETT scheme at Eaton Socon. The VETT turbine is located under the seating area of the pub.
Conventional river management techniques such as by-pass for flooding or for fish transit can be incorporated into the design.
VETT design for Dalston Hydro; Left: VETT intake with debris screen, VETT unit buried in embankment; Right: Existing fish pass
The fundamental advantage of VETT is the low cost of renewable energy production, driven by its low capital cost. In comparison to other low head hydropower technologies, VETT’s benefits are:
Small, high speed turbine
No gearbox required
Minimal fish screening - only 20% of flow passes through turbine
Small civil works
Very low visual impact
No impact on fish & aquatic ecosystems