Technology

Archimedes Screw Turbines—ASTs. They move slowly. It isn’t about speed, but mass and balance.
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The technical balance is between efficiency, fish survivability and environmental protection

Archimedes Screw Turbines (ASTs) extract the potential energy from large blocks of moving water. The mass of the water turns the tilted turbine. The flow of that mass is controlled by hydraulically driven sluice gates. Water enters the AST at the top, and the significant weight of that water on the blades, or “flights”, rotates the turbine generating power. If they enter the turbine, fish are not damaged. There is plenty of space for large or small fish, debris and ice to pass through the machine.

Gearbox generator assembly

How ASTs work

A gearbox at the top of the screw connected to the generator produces standard three phase power for either the grid or direct users as state distribution laws allow.  The entire facility is linked to an electronic monitoring and control system that runs automatically, communicating to an operator whenever requested. Safety, shutdown and management protocols are strict and efficient.

Engineering choices

Selecting the AST:  Choosing the largest AST may maximize the power output by utilizing high volumes of water for short periods of flood, but this increases cost for a machine that will not be effective for most of the year.  At the other extreme, we can install a very small, less costly turbine that does not fully use the available flow of the waterway. Our goal is to find the right balance that is cost effective and operationally optimum, and can be permitted appropriately.

NEHC's expertise and experience enables us to find that balance among all of these elements, and to engineer the highest quality projects.  Each site offers a unique engineering situation. Deriving the best project by project solution where respect for environmental issues, selection of the appropriate generation capacity, and determining stable cost factors enable us to drive toward the best return on investment for all parties.

Archimedes Screw Turbines (ASTs) being lowered into place.
Archimedes Screw Turbines (ASTs) being lowered into place.

During the feasibility stage, two critical elements dictate the size of the AST: The drop in the water level from above the intake to below the discharge—roughly the height of the dam. A hydro-screw turbine runs most efficiently as a generator at a fixed slope range.  This coupled with the drop determines the length of the machine. The second element is the volume of water available to pass through the machine.

Engineer in underground sluiceway leading to Archimedes Screw Turbine (ASTs)
Engineer in underground sluiceway leading to Archimedes Screw Turbine (ASTs)

Local rainfall and the size of the river catchment upstream or canal system and volume determine this. Additionally, a key in the decision process is to protect both the aesthetics and environment of the site: An allowance is made for a significant water volume to by-pass the turbine and sustain the river habitat with continuing flow over dams, even in dry periods. At every site this is part of the calculus that drives balance.

Safety enhancements

NEHC’s systems are designed for entirely safe operation under all conditions. Water flow velocities at the intake are kept low ensuring safe recreational activities. The entire screw mechanism and all the flow channels are fenced and secured to ensure that no one can fall in to the turbine. Every aspect of the electronic monitoring and control system is designed to be ‘fail safe’ so that if a problem occurs the system will automatically shut down without the need for power or intervention. There are operational and safety sensors as well as river height sensors customized to each installation.

Safety gating at sluiceway entrance
Power house with signage

How things look

NEHC sites require a “power house.”  One of the first questions NEHC constituents want to know is, “What does it look like?” The answer parallels the engineering conversation:  Each site is unique and requires good selection and design sensibility. The goal is to create a facility that is a good complement to what is around it. It will be part of the local landscape for a relatively long period of time, so it is important. The power houses are tailored to the local community: wood clapboard, stone and brick facing along with more standard external materials are considered in the context of the project costs and the local environment.
The AST system is not in the middle of the dam, but on the side in every case, preserving the natural allure of seasonal water flow over each dam.

Fixing dams

Dams and canal systems need repair. Fish need to migrate. NEHC is careful to evaluate the quality of dams that are promising for power generation. In some cases, these requirements may be beyond the company’s ability to repair and then build an economically viable generating facility. At other sites, there may be excellent reason to pursue both repairs and improvements prior to developing generation. Each site requires feasibility study to determine the course of action.

Legacy dam with waterfall

Restoring North America’s original renewable energy resource.TM