Pressure Control Hydroelectric Facility Maerkle Reservoir

City of Carlsbad, 
California

Pressure Control Hydroelectric Facility Maerkle Reservoir

Service Type: 
Project Highlights: 
  • Includes feasibility study, design, and construction phase services.
  • Utilizes higher pressure from San Diego Aqueduct to generate power.
  • Consists of paralleling an existing pressure reducing station to install hydroelectric turbines and generate electricity from the pressure reduction.
  • Feasibility study identified appropriate design head and flow for the turbine, generated list of turbine alternatives, evaluated alternatives in an economic analysis over 20 years, and recommended one alternative.
  • Recommended alternative consists of one 6.75 cfs, 135 kW turbine and one 3.6 cfs, 68 kW turbine installed in parallel, which together have the potential to generate 985,000 kWhrs per year based on historic flow rates.
  • Design will include preparation of Small Conduit Exemption application.

The Carlsbad Municipal Water District (CMWD) receives a portion of its water from the San Diego County Water Authority (SDCWA) Tri-Agency Pipeline Connection No. 3 (TAP3). The pressure in the TAP3 is relatively high compared to the pressure needed to fill the Maerkle Reservoir and Dam. Currently, CMWD reduces the pressure of TAP3 from 178 psi to approximately 20 psi through a pressure-reducing station. The stored energy that is in the high-pressure water is wasted when the pressure is reduced with pressure-reducing valves. CMWD hired Carollo to design a Pressure Control Hydroelectric Facility (PCHF) to recover this wasted energy by installing the PCHF in parallel with the pressure-reducing station.

CMWD is considering the installation of the PCHF to help it meet two goals: to reduce the amount of electricity it purchases from San Diego Gas and Electric (SDG&E), and to reduce its carbon footprint by recovering this valuable renewable energy.

Based on the current technology of small hydroelectric generators, this application presents a good opportunity for energy recovery. There are several types of turbines used to generate electricity based on flow and available pressure head. The PCHF is a high-head, low-flow application. The different types of turbine generators range from low-cost, lower-efficiency to high-cost, higher-efficiency systems. Selection of the most long-term, cost-effective system is key to the success of this project.

The project included a feasibility study, design, and construction services for the hydroelectric facility. The feasibility study included identifying the appropriate design head and flow for the turbine based on historic flow and pressure, generating a list of turbine alternatives, evaluating the alternatives in an economic analysis over 20 years, and recommending an alternative. The feasibility study also included preliminary design including building size, location, and piping connections and determination of available electric utility rate tariffs.

The design of the hydroelectric facility includes building, piping, valves, electrical, and related equipment. Deliverables will include drawings and specifications. The project also includes completion of a Federal Energy Regulatory Commission (FERC) Conduit Exemption application, which will allow the facility to generate power.