The energy-water nexus : energetic analysis of water and wastewater treatment, distribution and collection



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The water sector is responsible for a significant portion of energy use. Energy is required for water treatment, water distribution, wastewater collection and wastewater treatment. There is significant benefit to water utilities that can be gained by understanding how much energy, what type of energy, and at what time of day energy is being used. The Austin Water Utility (AWU) is a useful testbed for examining the energy use for each specific step of the process due to the availability of data and the fact that the majority of Texas (both in terms of population and land area) is serviced by a single electric grid. This research examines the type and quantity of energy used by AWU. From an electricity supply perspective, electric utilities work year round to ensure that there is enough electricity in their generation portfolios to meet the high loads that their customers demand, and to assure that the electric distribution grid is capable of providing the transmission requirements of that electricity. System peak demand is the largest amount of electricity consumed by a utility's customers at any given time. Therefore electric utilities, such as Austin Energy, create and market their energy efficiency programs to help reduce this peak and avoid the need to build new generation capacity which can be expensive. Because AWU is one of Austin Energy's largest customers, AWU's ability to shift its energy use from on-peak to mid-peak and off-peak time periods can contribute towards reducing the peak, and can help avoid the need for new generation capacity. This analysis finds that AWU can reduce its electricity demand during peak periods by making use of reservoir capacity, i.e. by filling its reservoirs prior to peak time and draining them during peak periods. This proposed pumping schedule could save AWU up to 29% of its monthly electricity costs under current Austin Energy time-of-use rate (as opposed to flat rate) structures at the specific pump station analyzed as part of this research. Together, state-wide water utilities provide even more opportunities for the interconnected Electric Reliability Council of Texas' (ERCOTs) grid that are also evaluated in this research.