vvEPA United States Environmental Protection Agency United States Environmental Protection Agency August 2013 Renewable Energy Fact Sheet Viable Sources INTRODUCTION This fact sheet describes the use of auxiliary and supplemental powers sources (ASPSs), which can provide wastewater treatment plants (WWTPs) with a secondary power source in the case of a blackout or other problem resulting in a loss of power. Wastewater utilities can also use this power to supplement other sources of power on a continuous basis. In order to be effective, these ASPSs should provide the power necessary to run the WWTP efficiently and effectively, and also have a short start-up time if they are to be used in an emergency. Most WWTPs have electric power connections to at least two independent power substations, such that if power from one substation fails (i.e., due to a localized storm or the downing of a local power line), the WWTP could receive power from the other substation. However, if the entire grid fails (such as it did for much of the northeast and the Great Lakes states in August 2003), having power feeds from separate substations that are all connected to the same main grid will not meet the auxiliary power needs to keep many WWTPs operating during such a failure. Without an adequate reliable auxiliary power source, many WWTPs will discharge untreated sewage into the receiving waters. There are a number of different types of ASPSs that can provide reliable power to WWTPs on either a continuous or emergency basis. These include: • Internal Combustion Engine Driven Generators (diesel, natural gas, or bio-gas) • Microturbines • Fuel Cells • Solar Cells • Wind Turbines • Low Head Hydro Power • Wastewater Heat Recovery Some of these technologies can also be used by the wastewater utilities to supplement their commercial power sources. Technologies such as fuel cells, solar cells, wind turbines, and bio- gas driven generators can provide renewable energy on a continuous basis, while diesel or natural gas power generators have been used to reduce peak energy demands on a short-term basis. Planning for auxiliary power must take into account the expected flow rates at the WWTP during the time of the power failure in order to ensure that sufficient auxiliary power will be available to meet the normal operating needs of the WWTP. Planners should also consider other factors that could affect the amount of power required by the WWTP to remain operational, such as potential weather conditions (wet weather can increase stormwater flow to the WWTP in combined systems), collection system pump station operation, and whether drinking water is distributed during the power failure (this function requires increased pump capacity, and could be a factor for combined water/wastewater utilities). If the technology is planned to supplement commercial power, other considerations, such as continuous operating costs, energy market trends, and long-range fuel price projections, may need to be factored in. ------- In addition to general considerations related to evaluating auxiliary and supplemental power sources, there are also technology specific considerations that must be evaluated. These include: • Reliability: ASPSs must provide reliable auxiliary power under adverse conditions. ASPSs should be available for immediate service (i.e., warm up quickly) and be available for the time period for which they are needed without interruption. In some case, auxiliary power may be needed for extended periods of time (i.e., 48 hours or more), and sufficient fuel must be available for long-term operation. • Cost: ASPS technologies range widely in costs which will be a major factor in a utility's selection of the best options for providing auxiliary or supplemental power. Costs should be weighed against many other factors, including the expected life, annual maintenance, and reliability of the technology, as well as potential economic and environmental costs associated with an extended power failure at the POTW. • Appropriateness: ASPSs should have sufficient capacity to operate primary treatment and disinfection for all wastewater flows for at least 24 hours after a power interruption. For discharges to sensitive water bodies, capacity to operate additional unit processes (i.e., advanced treatment) may be required by state regulatory authorities. • Security: When possible, ASPSs should be located on-site, because it is easier for most wastewater utilities to protect on-site power supplies than it is to protect transmission lines and substations that feed the plant or remote pumping stations. • Environmental Factors: The goal of insuring an adequate auxiliary power supply is to protect human health and the environment i n the event of a power interruption. An auxiliary power supply should be adequate to prevent raw sewage from coming in contact with the public or discharging to sensitive receiving waters. However, spills or leaks from underground fuel tanks used to store fuel for ASPSs can create a risk to the ground water and the environment. In addition, some of the older gas or diesel engine driven generators produce air emissions that are harmful to public health. • Safety: One significant ob stacle to the installation of on-site electricity generation at WWTPs is the safety risk associated with the operation of such equipment. Operators must be trained to safely operate and maintain the equipment. There may also be concerns with fuel storage and handling. For example, large above-ground fuel or gas storage may pose a risk to public health from an accident or terrorist attack. INTERNAL COMBUSTION ENGINE DRIVEN GENERATORS Electric generators can be furnished with engines that can run on diesel fuel, natural gas, or bio-gas. In many cases the engine can be provided with duel fuel capability. All of the engines currently being manufactured are required to meet Clean Air Act emissions requirements as stated in sections 89-90, Chapter 40 of the Code of Federal Regulations. Some states have additional requirements that restrict the use of some auxiliary or supplemental power sources. States are required to be as strict in environmental regulations as the federal government, but can be stricter if needed to meet local air quality restrictions (like emissions in California). While older engines can contribute to air pollution problems, today high-efficiency, low- emission engines are available for most generators. MICROTURBINES Microturbines are a new, innovative technology based on jet engines (more specifically the turbo charger equipment found in jet engines) that use rotational energy to generate power. Microturbines can run on bio-gas, natural gas, propane, diesel, kerosene, methane, and other fuel sources, making them suitable for a variety of applications. From an environmental standpoint, these new machines take up less space, have higher efficiencies, and generate lower emissions than reciprocating engines. If operated from a natural gas pipeline, no on-site gas storage is needed, thus reducing safety concerns. ------- Based on estimates by the Gas Research Institute and National Renewable Energy Laboratory, the total plant cost varies from about $2,600 per kilowatt (kW) for a 30 kW system to around $1,800 per kW for a 100 kW system. The 18.4 MGD Sheboygan Regional WWTP in Wisconsin has installed 10, 30 kW Capstone microturbines that provide an annual savings of close to $140,000. SOLAR CELLS Solar cells, also known as photovoltaic (PV) cells, convert sunlight directly into electricity. They are often assembled into flat plate systems that can be mounted on rooftops or other open areas. Solar cells require only sunlight (a renewable energy source) as fuel, and have no emissions. They generate electricity with no moving parts and require little maintenance, making them ideal for remote locations. However, solar cells are dependent on weather. If there is no sun there is no energy generated. If used as an auxiliary source of power, some type of storage system (i.e., batteries) must be provided. In 2007, the cost of implementing a solar power project was $8 per watt. Currently, solar power companies offer a "Power Purchase Agreement" model wherein the wastewater treatment plants do not have to incur expenditure on implementing a solar power project. The project costs are borne by the solar power company which would then sell the solar power to the wastewater treatment plant. An ideal example would be the City of Madera's WWTP in California. It has a solar installation that can produce 1.158 megawatts (MW) of electricity. This project would lower the WWTP's energy costs by $250,000 annually. FUEL CELLS A fuel cell is an electrochemical device similar to a battery. While both batteries and fuel cells generate power through an internal chemical reaction, a fuel cell differs from a battery in that it uses an external supply that continuously replenishes the reactants in the fuel supply of reactants. The fuel cell can supply power cell. A battery, on the other hand, has a fixed internal continuously as long as the reactants are replenished, while the battery can only generate limited power before it must be recharged or replaced. Most types of fuel cells can operate on a wide variety of fuels including hydrogen, digester gas, natural gas, propane, and landfill gas, diesel, or other combustible gas. In some cases such, as in a WWTP, methane (sludge gas) from anaerobic digesters can be reused in the fuel cell instead of flaring off the excess gas. Other advantages of fuel cells include few moving parts, modular design and negligible emission of pollutants. Palmdale Water Reclamation Facility in Los Angeles County, California, installed a 250 kW molten carbonate fuel cell at a cost of $1.9 million. The reduction in the energy expenditure for the facility was calculated to be $227,000 annually. WIND TURBINES Wind turbines convert wind into mechanical energy and electricity. A generator is equipped with fan blades and placed at the top of a tall tower. The tower must be tall in order to harness the wind at a greater velocity, free of turbulence caused by interference from ground obstacles such as trees, hills, and buildings. Generally, individual wind turbines are grouped into wind farms containing several turbines. The power generated from wind farms can be inexpensive when compared to other traditional power production methods. The cost to generate the electricity from wind farms decreases as the size of the farm increases. Wind turbines do not produce any harmful emissions nor do they require any fuel product for operation. However, wind turbines do require periodic maintenance, which can present a safety problem, since most turbines are mounted on tall towers. There is also concern about construction and other activities below each turbine, although the land can generally still be used for animal grazing or farming. Problems with birds flying into the turbine propellers have been reported, However, newer designs have reduced this problem. The costs of implementing a wind power project vary with the size of the project. The WWTP in Evansville, Indiana, installed a 100 kW wind turbine at a cost of $594,000, which translates to $5,940 per kW. The Jersey Atlantic Wind Farm owned by the Atlantic County Utilities Authority in Atlantic City, New Jersey, has an installed capacity of 7.5 MW and the cost per kW is $1,667. The Cost of wind generated at this facility is $0.076 per kilowatt hour (kWh) with an annual energy cost saving is around $350,000. ------- LOW-HEAD HYDROPOWER The electric energy that is harnessed from the force of moving water is termed as hydroelectric power. The two types of systems used for this purpose are the run-of-the-river system and storage system. In either system, water is channeled through a pipeline to a turbine and the pressure at the end of the pipeline constitutes the net head. Hydroelectric power is renewable, clean, and the largest source of renewable energy in the United States. According to the U.S. Energy Information Administration, about 60% of the renewable energy produced in the United States in 2010 was from hydroelectric projects. Hydroelectric power systems that operate with a head or water level of less than 66 feet are termed low-head hydropower systems. In most cases, low- head hydropower systems are built as a run-of-the- river system, and the power generation is dependent on having perennial flow in the river. Loss of head due to build up of debris is also an issue. When implemented in a WWTP, the low- head hydro- power system will not encounter the same problems as a run-of-the-river system because of the constant supply of debris-free water. Figure 1 shows different types of turbines and their operating criteria. The power that can be potentially produced at a site is roughly given by the following equation: n ™ Head (feet) x Flow (cfs) v ,,. . Power (kW) = X efficiency 11.8 Where H is available head in feet; F is the flow in cubic feet per second (cfs); efficiency is overall system efficiency as a fraction; and 11.8 is a constant that converts the equation to kilowatts. By harnessing the potential energy of effluent water contained in a 4.5 mile long outfall, Point Loma Wastewater Treatment Plant of San Diego, California, is able to produce 1.35 MW of electricity. A hydroelectric turbine is operated by the effluent water before being discharged to the ocean. The head available from the plant to the outfall is 88.5 feet. The total cost of this project is $1.7 million, out of which $419,000 was provided by a California Energy Commission grant. Make Energy Systems Power Pal Canyon Hydro- Kaplan Hydro- e-kid Very Low Head Head (feet) 10 5 30-50 Varies 6.6-11 Flow (cfs) 2 5 100- 400 Varie s Varie s Power (kW) 1 1 Varies 2-200 486- 496 Figure 1: Types of Low-Head Hydropower Turbines WASTEWATER HEAT RECOVERY An estimated 350 billion kWh of energy stored in hot water is drained annually from households and most of it is recoverable. Using municipal wastewater as a heat source in the winter and as a heat sink in the summer, considerable savings in heating, ventilation, and air conditioning (HVAC) costs can be achieved. Wastewater heat recovery systems use a heat exchanger to transfer heat from the municipal wastewater to a conveyance medium, which is then pumped to individual buildings. Heat pumps located at these buildings then extract heat from the conveyance medium and deliver energy for space heating and cooling. The conveyance medium is sent back into the loop where it exchanges heat with the municipal wastewater again. The first project of this kind was announced jointly by the East Division Reclamation Plant, Renton, Washington, and The Boeing Company in 1992. Wastewater was pumped to one of Boeing's training facilities and used for space cooling purposes. The annual savings in energy costs, from this project was estimated to be $120,000. On a commercial scale, this system has been implemented at the Whistler Athletes' Village, British Columbia at a cost of $4.1 million. The incoming wastewater has an annual temperature range of 50° F to 64° F. The installed system is capable of generating ------- up to 11,000 megawatt hours (MWh) per year of heating energy for an occupied space of 85,000 square meters. Kent County, Delaware, is implementing this system to provide a heating and cooling solution for two buildings located at the Kent County Regional Wastewater Treatment Facility. Sustainability and flexibility are among the key benefits of implementing this system. REFERENCES 1. Renewable Energy Fact Sheet: Solar Cells, EPA 832-F-13-019, US EPA, Office of Wastewater Management, August 2013. 2. Renewable Energy Fact Sheet: Fuel Cells, EPA 832-F-13-014, US EPA, Office of Wastewater Management, August 2013... 3. Renewable Energy Fact Sheet: Wind Turbines, EPA 832-F-13-017, US EPA, Office of Wastewater Management, August 2013. 4. Renewable Energy Fact Sheet: Microturbines, EPA 832-F-13-012, US EPA, Office of Wastewater management, August 2013. 5. Small Hydro and Low-Head Hydro Power Technologies and Prospects, Congressional Research Service, March 2010. 6. Using Wastewater Energy to Heat an Olympic Village for the 2010 Winter Olympics and Beyond, Neil Godfrey, John Hart, William Vaughan and Wayne Wong, WEFTEC 2009. 7. Atlantic County Utilities Authority (ACUA). Atlantic City Wind Farm Project. (http://www. acua. com/alternative/ a_projects dsply.cfm?id=214 and http:/ /www. acua. com/file s/windfacts6o 7.pdf.) 8. Nova-Thermal Energy, LLC. http://www.novathermalenergy.com/index.html 9. Renewable Energy Fact Sheet: Low-head Hydropower for Wastewater (EPA 832-F-13- 018), Office of Wastewater Management, August 2013. Some of the information presented in this fact sheet was provided by the manufacturer or vendor and could not be verified by the EPA. The mention of trade names, specific vendors, or products does not represent an actual or presumed endorsement, preference, or acceptance by the EPA or federal government. Stated results, conclusions, usage, or practices do not necessarily represent the views or policies of the EPA. Environmental Protection Agency Office of Wastewater Management EPA 832-F-13-015 August 2013 ------- |