| Small hydro
VETT-in-a-Box is an adaptation of the company’s
proven VETT technology, which underpins its larger run-of-river and tidal products. A VETT-in-a-Box unit would typically be 5-30kW whereas the larger Standard VETT targets everything above 30kW up to 1MW with flow rates from 2000 l/sec and above (all at low head). VerdErg’s vision and the purpose behind the VETT- in-a-Box development is for every community, no matter how remote, to have access to clean, affordable and predictable off- or on-grid power without harming the local environment. Micro-utilities have the potential to revolutionise urban development worldwide, especially in remote regions or those afflicted by aging national grid infrastructure. 11GW of the global low-head hydropower market is however underutilised, a significant section, because existing turbine solutions cannot provide cost- effective power from 1-4m drops. Many community scale projects are therefore left undeveloped. The problem VerdErg is addressing is that with projects
that are very small, civil costs remain unproportionally high. An installation method is required to reduce or nearly eliminate these costs from a project. A fundamental difference of VETT-in-a-Box therefore is the move away from an open tank design to have all the M&E equipment placed into a pressurised chamber instead, which is fed by a pipe rather than an open channel. This allows for a design that is compact, transportable, can be mass produced and off-site manufactured and especially reduces excavation on site.
Technology
At the heart of VETT-in-a-Box is the VETT technology. Proven and in operation in the UK, VETT is designed to increase the pressure differential across a standard axial flow propeller turbine. Rather than providing the turbine with a large volume of water at low pressure, VETT amplifies the pressure and provides the turbine with a lower volume of water but under increased pressure. To achieve this, 65-80% of the flow passes through a constriction in a Glass Reinforced Plastic (GRP) pipe, the venturi, where according to Bernoulli’s theorem the pressure drops as the flow velocity increases. The remaining 20-35% of the flow passes through a turbine, discharging into the area of low pressure created within the venturi. The two flow streams mix within the venturi and pass through a diffuser which
Above left: Axial propeller turbine installed at Eaton Socon, UK Above right: VETT pipe, made from GRP, lifted into position at Eaton Socon, UK Right: Turbine with draft tube, extending into venturi pipe, Eaton Socon, UK Below right: Intake with debris screen in front of listed Rivermill, Eaton Socon, UK
decelerates the flow, recovering the static pressure. By discharging the turbine into the area of low pressure the head or pressure across it is amplified, increasing for example, a 2m head into a 5m head. As a result, turbines get up to 83% smaller and up to 15x faster, do not require a gearbox and become dramatically more affordable.
By passing up to 80% of the water through a venturi with no moving parts the risk for blade strike is significantly reduced. The turbine itself can be screened and as it only needs to be designed for 20% of the flow, it is comparably small and manageable.
Advantages The greatest advantage of VETT-in-a-Box is its ability
to harness meaningful power from 1-4m head drops at affordable costs.
Equipment manufacturing costs (turbine, generator,
controls) with this approach are dramatically reduced, also due to the use of standardised, off-the-shelf components. VerdErg is not a manufacturer; the equipment for a project using a VETT system is sourced from the existing industry supply chain, who supply the turbines based on the changed operating conditions (less flow, higher pressure) from the use of a VETT system. This means VETT-in-a-Box can be mass produced, important as it removes obstacles often faced by hydropower installations due to long project lead-times and unpredictability due to site-specific requirements.
In addition, VETT-in-a-Box has reduced installation cost and increased flexibility because the whole system is designed with ease of transportation in mind. The compact design gives the ability for temporary setup, making VETT-in-a-Box a practical solution for supplying electricity for disaster relief responses. f
www.waterpowermagazine.com | April 2022 | 19
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