Energy Efficiency Program
The Energy Efficiency Program is representative of the Public Utilities Department's ongoing commitment to protect the environment by preserving our natural resources, reducing power consumption, using renewable energy sources, seeking cheaper sources of power and serving the needs of all our customers. The energy savings made by the Public Utilities Department directly benefit the residents of San Diego by helping to maintain lower sewer rates while providing renewable electric energy to the region.
The volume of wastewater conveyed and treated in the City's wastewater facilities on a daily basis requires a great deal of electrical and thermal power. Electricity is needed to run pumps, lights, computers, mechanical valves and machinery. Thermal energy, usually generated by electrical power or by burning natural gas, provides heat and cooling necessary for both buildings and the wastewater treatment process.
Point Loma Wastewater Treatment Plant
Eight digesters at the Point Loma Wastewater Treatment Plant use heat and bacteria to break down the organic solids removed from wastewater, much as our stomachs digest food. One of the by-products of this biological process is methane gas. Methane, a colorless, odorless flammable hydrocarbon gas, is found almost anywhere that organic solids decompose in the absence of oxygen - in mines, marshes, landfills and digester tanks.
This methane gas is collected from the digesters and is piped to the on-site Gas Utilization Facility (GUF). The methane fuels two continuously running generators that can each produce up to 2235 kilowatts of electricity (a total of approximately 4.5 megawatts). Using new technology under a grant from the California Energy Commission, a diesel powered generator is now able to also burn methane and produce an additional 1220 kilowatts (1.2 megawatts) as a peaking generator.
Using the methane produced on site, the wastewater treatment plant has not only become energy self sufficient, the facility is also able to sell excess power it generates to the local energy grid. Because the heat produced by the engines is used in turn to heat the plant's digesters, the GUF is termed a cogeneration system. Utilizing one source of fuel (methane), it produces two forms of energy, electricity and heat.
Other On-Site Power Generation Systems
Even before the dramatic increase in electrical rates in 2000, the Wastewater Branch had made a commitment to reduce power consumption, conserve natural resources and pass along savings to ratepayers. Another example of this commitment is the on-site generation of green power at our Metro Biosolids Center (MBC) and the North City Water Reclamation Plant (NCWRP).
Methane is a by-product produced in the digesters at the Metro Biosolids Center, and in the adjacent Miramar Landfill. When the facility was being built in the mid-1990s, a private company was contracted to build a cogeneration facility at MBC and a gas collection system in the landfill. Methane produced by the MBC on-site digesters and from the adjacent landfill is converted to electricity which is used to run the facility. Thermal energy produced by the generators is used to heat the MBC, and through a process called absorption chilling, to also air-condition the plant. (MBC received the San Diego's Taxpayers' Association Fiscal Watchdog Award in 1998 for its innovative privatization of the cogeneration system and the installation of the landfill gas collection system).
The success of cogeneration at MBC led to the building of a similar facility at the North City Water Reclamation Plant (NCWRP), using methane piped underground two miles from the Miramar Landfill.
On average, the MBC can produce 6,400 kilowatts through cogeneration and uses about 30 percent of that for its operations. On average, NCWRP produces approximately 3,800 kilowatts and uses more than 75 percent of that for its operations. Excess power produced is sold to the electrical grid by the private company for use by San Diego area electric customers.
Stage III Power Alerts - Emergency Power Generation
During Stage III Power Alerts, the Public Utilities Department uses a remote control system that can turn on backup generators at eight of its pump stations, the Department's Central Operations & Management Center (COMC) in Kearny Mesa and the Point Loma Wastewater Treatment Plant. As a result, more than two megawatts of power can be made available for use by the local electric grid during periods of critical power levels.
When a Stage II Alert begins to move toward a Stage III level, a radio signal will be sent by San Diego Gas & Electric to COMC. Our computer control system will then automatically start up the generators to power the eight pump stations and COMC, effectively taking a total of 1 megawatt of power used off the grid. In addition, the generator at Point Loma will be able to provide an additional 1.2 megawatts of electricity to the grid. The new system (COMC Control of Emergency Generators or CCEG), funded by a $486,000 grant from the California Energy Commission, went on line in January 2001.
The two backup generators at the Point Loma Plant have been converted from straight diesel engines to dual fueling, allowing them to be run with a methane/diesel mixture.
Hydro Electric Power
The Point Loma Wastewater Treatment Plant is located on a bluff above the Pacific Ocean. The treated wastewater or effluent is discharged into the ocean through a 4.5 mile ocean outfall after a 90-foot drop from the plant to the ocean outfall. A 1,350 kilowatt hydroelectric plant captures the energy of the treated wastewater as it flows down the outfall connection. The power plant, partially funded by a grant from the California Energy Commission, can produce an additional 1.35 megawatts for sale to the San Diego electric grid, enough power to supply energy to 1,300 homes.
MOC III Photovoltaics
The Public Utilities Department is headquartered in a facility complex of eight buildings in Kearny Mesa. One of these buildings, MOC III, is being used for a first-of-its-kind solar power system pilot using a novel, lightweight mounting system and semiconductor material in the panels. These solar panels, mounted on the building's roof, will convert sunlight to electricity and provide the building's energy needs. The project is partially funded by a San Diego Regional Office's California Public Utilities grant. The system came on line in late summer 2003.