Implications of hybrid decentralized energy systems composed of solar photovoltaics and combined cooling, heating and power systems within olarge urban regions

Abstract

Urban regions play a major role in the global economy and are responsible for a majority of the earth’s resource consumption. Water and energy are the two main growth limiting resources of an urban region and are highly interdependent. Increasing urbanization therefore means that there will be an increase in the demand for water, energy, and their associated infrastructure systems. Greater demand for water and energy also means that there will be an increase in the emissions generated to supply these resources to an urban region. In order for urban areas to become more sustainable, they must meet the resource demands of the population, provide resilient infrastructure to distribute these resources, and become more efficient in supplying these resources. Decentralized energy systems can improve the resiliency and efficiency of energy generation in an urban region while reducing the emissions generated. Combined cooling, heating and power (CCHP) systems are more efficient than conventional energy generation systems as they can simultaneously generate electricity, useful heat and cooling in the combustion process. The heat generated can be used to meet the heating demand, and with an absorption chiller, the cooling demand of a building. Adding solar photovoltaics to this system will further decrease the emissions and water consumption that result from the energy generation process. The objective of this work was to determine the efficacy of implementing CCHP systems, with and without solar photovoltaics, for five generic building types in the Atlanta metropolitan region, and the economic and environmental impacts of these systems under various loading strategies. CCHP systems were modeled using air-cooled microturbines and absorption chillers to match the thermal (heating, cooling, and hot water) load of the 5 building prototypes. The 5 prototypes consisted of 3 commercial and 2 residential buildings. The CCHP systems were modeled to operate under various thermal loading strategies to determine the best strategy to minimize costs, emissions, and water consumption for energy generation. The prototype buildings were then used to estimate the projected energy consumption of residential and commercial buildings in the 13-county Atlanta metropolitan region and determine the emissions and water for energy impact of conventional versus CCHP systems. Solar photovoltaics were then added to the CCHP system to determine the optimum PV area required for a given building and feed in tariff. These investigations found that operating microturbines to follow the thermal load of a given building results in the greatest reduction in CO2 emissions, and operating the turbine constantly to meet the maximum annual thermal demand results in the greatest NOx and water for energy reductions. A net metering policy will impact which operational strategy best reduces emissions, water for energy, and cost. When applied to the 13 county Atlanta Metropolitan region, CCHP systems can significantly reduce emissions and water for energy consumption. For all building types the economic feasibility of implementing solar photovoltaic systems with microturbines is dependent on the discount rate of the system, the cost of the solar-pv system, the feed in tariff rate assumed, and if various policies are implemented to provide benefits for the mitigation of CO2, NOx, and water consumption. This study can serve as a platform by which the implementation of other decentralized energy systems can be evaluated.