Most current hydroelectric projects use a large hydraulic head to power turbines to generate electricity. The hydraulic head either occurs naturally, such as a waterfall, or is created by constructing a dam in a river valley, creating a reservoir. Using a controlled release of water from the reservoir drives the turbines. The costs and environmental impacts of constructing a dam can make traditional hydroelectric projects unpopular in some countries. From 2010 onwards new innovative ecologically friendly technologies have evolved and have become economically viable. An overview of these techniques can be found on multiple databases.
Old technologies mostly involve Kaplan turbines which have the following characteristics:
- High efficiency
- Need for large infrastructure in natural environment
- Low operational expenditures
- Long lifetime
- The cavitation, pressure differences and (high rpm) rotating and stationary blades damage and kill certain migrating fish species.
- all machinery is below the waterlevel (submarine)
- Low LCOE (Levelised Costs of Energy)
The new waterframework directive and national legislation make it almost impossible to use these technologies in Western Europe.
New innovative technologies such as modified drag, bulb and Darrieus devices have the following characteristics:
- medium efficiency
- no need for invasive infrastructure
- low operational expenditures
- long lifetime
- very low pressure differences and low rpm and will not harm or kill migrating fish species
- machinery partly of fully above water level
- Low LCOE (Levelised Costs of Energy)
Within low head hydropower you have a couple of standard situations:
Low head small hydropower: Low head small hydropower can be produced from rivers and estuaries. Suitable locations include weirs, streams, locks, rivers and wastewater outfalls. Weirs are common in rivers across Europe, as well as rivers that are canalized or have groynes. Generating significant power from low head locations using conventional technologies typically requires large volumes of water. Due to the low rotational speeds produced, gearboxes are required to efficiently drive generators, which can result in large and expensive equipment and civil infrastructure.
Low head tidal energy: Europe is the frontrunner for tidal energy, there are a couple of low-head tidal energy projects in Europe. This technology is still in development it is expected that first projects will be economically viable by 2025.
Low head pumped seawater storage: Curently at very low TRL levels but in the coming decade these technology could become part of the energy system
Another potentially promising type of low head hydro power is dynamic tidal power, a novel and unapplied method to extract power from tidal movements. Although a dam-like structure is required, no area is enclosed, and therefore most of the benefits of ‘damless hydro’ are retained, while providing for vast amounts of power generation.
Weirs and groynes have a positive effect on transport and water levels and are used for water management of rivers during floods and low water periods. Most of weirs and groynes are therefore required for water management. But weirs and groynes also have negative effects on sediment transport and can create river bottom erosion that will have an effect on the waterlevels in the surrounding areas. With new innovative technologies with devices that can increase sediment transport, do not kill fish (<0,1%), produce economical viable energy (12ct/kwh) about 100.000 MW can be installed in Europe close to the location where the energy is needed without harming the environment and highly predictable and therefor an alternative for wind and solar.
However, low-head units are necessarily much smaller in capacity than conventional large hydro turbines, requiring many more to be built for a given annual energy production.
Construction a dam / weir for low head hydropower may have harmful environmental effects. For example, the damming of a river may “block the movement both of fish upstream to spawn, this can be prevented by installing fish ladders or the installation of newer technologies.
Where large sites aren’t cleared “the vegetation overwhelmed by the rising water decays to form methane – a far worse greenhouse gas than carbon dioxide”, particularly in the tropics. Low head dams and weirs do not produce harmful methane. Groynes but also weirs prevent the transport of silt (sediment) downstream to fertilize fields” and to move sediment towards the oceans.
The Very Low Head (VLH) turbine is a recent turbine technology developed in Europe for low head sites in the 1.4 – 4.2 m range. The VLH turbine is primarily targeted for installation at existing hydraulic structures to provide a low impact, low cost, yet highly efficient solution. Over 35 VLH turbines have been successfully installed in Europe and the first VLH deployment for North America is underway at Wasdell Falls in Ontario, Canada. Deployment opportunities abound in Canada with an estimated 80,000 existing structures within North America for possible low-head hydro development. There are several new considerations and challenges for the deployment of the VLH turbine technology in Canada in adapting to the hydraulic, environmental, electrical and social requirements. Several studies were completed to determine suitable approaches and design modifications to mitigate risk and confirm turbine performance. Diverse types of existing weirs and spillways pose certain hydraulic design challenges. Physical and numerical modelling of the VLH deployment alternatives provided for performance optimization. For this application, studies characterizing the influence of upstream obstacles using water tunnel model testing as well as full-scale prototype flow dynamics testing were completed. A Cold Climate Adaptation Package (CCA) was developed to allow year-round turbine operation in ice covered rivers. The CCA package facilitates turbine extraction and accommodates ice forces, frazil ice, ad-freezing and cold temperatures that are not present at the European sites. The Permanent Magnet Generator (PMG) presents some unique challenges in meeting Canadian utility interconnection requirements. Specific attention to the frequency driver control and protection requirements resulted in a driver design with greater over-voltage capability for the PMG as well as other key attributes. Environmental studies in Europe included fish friendliness testing comprised of multiple in-river live passage tests for a wide variety of fish species. Latest test results indicate fish passage survivability close to 100%. Further fish studies are planned in Canada later this year. Successful deployment must meet societal requirements to gain community acceptance and public approval. Aesthetics considerations include low noise, disguised control buildings and vigilant turbine integration into the low profile existing structures. The resulting design was selected for deployment at existing historic National Park waterway structures. The integration of all of these design elements permits the successful deployment of the VLH turbine in Canada.