SGVWC conducted an initial feasibility assessment of the potential project between June and August 2011 (see Figure 2 for project timeline) and identified three alternative locations within SGVWC systems: F13, F14 (Sandhill), and F19. Initial assessment showed that location F14 in Sandhill Water Treatment Plant (managed by FWC) to be the most economically feasible site due to its large pressure differential (breaking 120 – 150 psi to 10 psi). There was also negligible change in the flow rate in this particular pipeline during 24/7 operation (4 – 13 cfs, but generally stays around 10 cfs).
Based on these conditions, two types of turbines were proposed: Pump-as-Turbine (PAT) and Francis turbine. For Francis turbine, flow can be varied to accommodate supply or demand variations but at the expense of reduced efficiency and power generation. A Francis turbine also becomes unstable below 40 percent of full flow and does not operate well at less than 40 percent of full electrical load. Thus, it was determined that installation of two Pump-as-Turbines (PAT) would be most suitable for the site. The twin PATs operate in both sequence and parallel, enabling the system to process flows ranging from 4 cfs to 13 cfs with a system nameplate rating of 310 kW.
The feasibility assessment determined if the project was feasible from an economic, environmental, technical and regulatory perspective. This preliminarily assessment took approximately 3 months to finish and determined that the initial project cost was approximately $1,400,000, would generate approximately 1,000,000 kilowatt hours annually and would have a sub 10-year payback.
It is also important to note that these estimation were made based on the assumption that the IEUA’s water uptake capacity was 5000 acre-feet/year which would be taken over a period of approximately seven to nine months, depending on hydrology and water demand. After conducting the feasibility assessment, FWC proceeded to complete 100% design in March 2013, and finally received the permission to operate in November 2013. It took approximately 2 years to complete the project, as depicted by Figure 2 below.
Figure 2. The timeline of the project starting from feasibility assessment to operation startup