Alden turbine update

In 2007, an electric-power-research-institute (epri) report assessed waterpower potential and development needs in the US, and confirmed that an additional 10,000MW of conventional hydropower could be conservatively achieved by 2025 through research and development (R&D) support, economic incentives, and regulatory reform [1]. It was recognised that same year by the US Department of Interior that an estimated 2500MW of power capacity could be harnessed simply by incorporating hydropower plants in existing non-power federal dams, through the provision of low-carbon energy options that would not require the construction of new dams [2]. Any hydropower installation, however, must balance with one other vital factor: the effect of hydropower systems on local fish populations.

Fish passing through turbines are subjected to injury and mortality mechanisms that, ultimately, can negatively impact fish populations. Furthermore, on river systems with multiple dams, these impacts can be cumulative for those fish having to pass though multiple projects. Standard downstream passage structures require water to be spilled or bypassed around the units to provide safe passage flows for downstream migrants. However, spill and bypass also equate to loss of generating capacity for the project. The economic impact of lost generation is not trivial on large river systems like the mainstem Columbia River. This river system includes 14 dams in both Canada and the US and generation losses have been estimated at approximately 693MW of power capacity (potentially US$237M per year) due to spill required to safely pass juvenile salmon downstream [3].

In response to the opportunity to develop a solution that both harnesses the available power in our natural ecological systems and minimises damage to fish populations, Alden Research Laboratories (Alden) began the development of the Alden turbine in 1995. The Alden Turbine was designed to enable fish passage through an operating unit, an effort which would offset the need for alternative downstream fish bypasses and thus increase hydropower capacity. Its runner is comprised of only three longer-than-average blades designed to provide flow conditions that are optimal both for performance and for improved fish survival. The turbine has been developed in multiple phases, the earliest of which included a pilot-scale laboratory evaluation. This evaluation was performed at Alden for nearly 40,000 fish of varying species. The results indicated that when scaled to a full size turbine, survival would range from 97 to 100% – a significant improvement relative to existing turbine designs.

EPRI furthered the pilot scale efforts by completing laboratory studies that examined the relationship between turbine blade leading edge geometry and injury/survival after blade strike. The study combined computational fluid dynamics (CFD) simulations and laboratory experiments to analyse a semicircular (more blunt and gentle) leading edge profile to an elliptical (sharper) profile. Both the simulated and experimental studies examined the effects of blade thickness, fish length, fish orientation at impact, and fish biology (using trout as model bony fish and white sturgeon as model cartilaginous fish, and eels).

The laboratory results revealed that semicircular leading edge profiles increased the likelihood of post-strike survival for all fish types. CFD results indicated that the semicircular design initiated greater forces and moments near the leading edge just before impact, effectively pushing the fish away from the leading edge. Furthermore, this research indicated that cartilaginous fish and eels had a consistently higher survival rate under all test conditions when compared to bony fish. The results suggested that bony fish would have a survival rate of 90% or higher when fish length was approximately equal to or less than leading edge thickness. EPRI’s blade strike work significantly expanded the existing data on the effects of blade design on injury and mortality. Realising the opportunity to incorporate these findings into the Alden turbine design, EPRI funded improvements to the Alden turbine with a goal of producing a design that would be competitive with alternatives in the same operating range. This redesign effort included resizing the turbine’s scroll and runner, incorporating a semi-circular blade leading edge, and adding an initial draft tube into the system [4].

Engineering design

The Alden turbine is currently undergoing preliminary engineering design under a two-year grant from the Department of Energy to EPRI. This work is being conducted by EPRI, Voith Hydro and Alden. The goal of the additional development is to complete engineering efforts necessary to move the Alden turbine closer to commercial viability. This includes full system CFD analysis to provide baseline data for future modifications and physical model testing.

This current analysis is specifically documenting the turbine flow shear rate, pressure gradients, and minimum pressure, each of which can be harmful to fish when passing through a turbine. In addition to the baseline model, Voith also developed a similar CFD model for an improved design that incorporates alterations required for fabrication, assembly, installation, and structural integrity. This enhanced design also underwent modifications to improve flow shear rate, reduce pressure gradient magnitudes, and increase the minimum operating pressure of the system, resulting in reductions in efficiency losses in the new runner-draft section of the system as well as more uniform velocity with significantly reduced flow separation in the draft region.

As part of this engineering effort, a physical scale model of the Alden Turbine is being tested at Voith to assess actual performance before installation in the field. It is being tested for efficiency, power, cavitation inception, cavitation breakdown, axial thrust, and steady radial thrust as a function of model gate opening and at head ranges appropriate for typical projects feasible for this design. Voith will also assess the system for runaway speed, wicket gate torque, and pressure variation in the spiral case and draft tube.

In addition to the engineering design work currently underway, EPRI is soliciting the industry for potential demonstration sites for the first turbine installation. One potential demonstration site has been identified at Brookfield Renewable Power’s School Street Hydroelectric Project on the Mohawk River in New York State. In a landmark settlement agreement between a dam owner and interveners in the federal licensing of project in the US, state and federal resource agencies responsible for the management and protection of fishery resources agreed to the installation of an Alden turbine as a means to pass fish downstream. In addition to the School Street Project, EPRI is seeking an additional demonstration site at an existing or new hydropower development. The additional demonstration site will complement the tentatively planned installation and testing of an Alden turbine at School Street.

The EPRI Demonstration Site Programme solicited the US hydropower industry for applications to host a demonstration of the Alden Turbine. A project solicitation list of utilities, vendors, and agencies was created from FERC, EPRI, and Alden sources. Notifications were sent via e-mail to approximately 500 industry contacts to alert interested parties to the initiation of this project. Interested applicants submitted project information via a web-based application form. The application period closed on 1 August 2010.

Alden received a total of 23 applications from 14 utilities. EPRI has completed an evaluation of all applicants and has created a numeric ranking of the submitted sites. The ranking criteria included primary factors (ie, head, flow, and fish species of concern) and secondary factors (ie, whether or not the project currently bypasses flow, relative construction logistics, willingness to commit resources, etc.) with numeric values assigned to responses. Three sites, two in the US and one in Europe, have been selected for further evaluation.

The tasks scheduled for the last quarter of 2010 include conducting site visits to the three candidate sites. Site visits will provide Alden and EPRI staff an opportunity to discuss specific project benefits and issues related to the addition of power generation using the Alden turbine. During the same trip, Alden engineers will collect and verify existing site and civil works information and take necessary measurements needed for the feasibility study. A key component of this visit will be to conceptualise the layout of the turbine, intake/penstock, and to consider possible construction methods.

The three sites will then be evaluated based upon: applicant commitment; sizing and general layout of turbine and water conveyance; predictions of fish survival; appraisal level cost estimates; energy analysis and return on investment; installation schedule; and permitting requirements. EPRI will then create a final numeric ranking of the three sites based upon the collected information and select a final site in the first quarter of 2011.

Problems

The major problem facing further development of hydropower in the US and around the world is impacts to migrating fish. Protecting migrating fish has been the number one industry R&D need identified in numerous workshops held since the 1990s, including the recently held 2008 EPRI workshop. In the US, considerable untapped hydropower resources exist, estimated at 60,000MW. However, its development is hindered by potential impacts to fish.

EPRI’s analyses have concluded that by 2020, it will be technically feasible to begin reducing CO2 emissions from the US electricity sector while accommodating continued growth in the demand for power. Expansion of conventional hydropower is an important component of this projection.

As electricity demand increases concurrently with the emphasis on generating power renewably, it will be critical to capture the full extent of the hydropower available to respond responsibly. The value of the Alden turbine in this response is that it offers utilities a means to maximise water use for generation without sacrificing the equally important aquatic resources of the river. The R&D efforts outlined above highlight a comprehensive method for bringing an important renewable energy technology closer to market. The completion of an Alden turbine demonstration in the field will be a sound building block in advancing this technology to commercial status.

Norman F. Perkins is a Senior Civil Engineer and Project Manager at Alden Research Laboratory, 30 Shrewsbury Street, Holden, MA 01520, US. Dr. Douglas Dixon is a Senior Project Manager in the EPRI Environmental Sector, 3420 Hillview Avenue, Palo Alto, California 94304, US