Feasibility of residential solar air-conditioning in Australia, including space heating and hot water

Abstract

In Australia residential air-conditioning has been claimed as one of the main drivers for peak electricity demand problems in the years from 2007 until 2012. Expensive network infrastructure upgrades have been required to maintain legislated reliability of electricity supply. This electricity grid augmentation has translated to increased cost of electricity for residences by around 70% until 2012 and 100% until 2014. This thesis investigates the potential for residential solar cooling to ease stress on the electricity grid while providing electricity cost savings to consumers and reductions in greenhouse gas emissions using a modeling approach. The modeling examines residential solar cooling performance in seven different climates in Australia, reviewing solar electric as well as solar thermal cooling options. Space heating and domestic hot water are included throughout this work. It strongly contributes to the cost-effectiveness of solar thermal systems and colder climates benefit most. The solar collector array for electricity and heat is sized to a cooling and heating solar fraction of 60%. In the first part of this work reference models are established to represent a residential building typical for each climate. In these models, the building is cooled and heated by a reverse cycle air-conditioner and domestic hot water is provided by a hot water system with an electric heating element. The first investigation involves addition of photovoltaic modules to offset grid electricity consumption of the reverse cycle air conditioner. In this configuration, the electricity grid acts as an energy supply buffer to supplement fluctuations in solar energy. The photovoltaic driven system design is very simple and proved to be the most cost-effective one. This investigation was extended to include options for electricity storage and a diesel electricity back up rather than the grid. The next investigation involved modeling a solar thermal system consisting of a single effect absorption chiller and an evacuated tube solar collector, following European examples. Initially, a sensitivity study was performed to better understand the model behavior and to size components correctly. The cooling system is scaled in a unique way to match the cooling load of each climate and to normalize energy consumption and cost. The absorption chiller uses gas as its backup energy source. The thermal solar cooling system model is extended by inclusion of options for a latent storage and a sensible chilled water storage tank. The results of the solar thermal system simulations are rather disheartening for the case of residential solar cooling using absorption chillers. Unless domestic hot water and space heating are included in the calculations, the levelized cost of space cooling and heating is too high to be acceptable when comparing it to the solar electric option. Including cold storage increases this cost even more, but additional greenhouse gases can be saved due to lower auxiliary gas consumption. The analysis would be expected to be different for large scale solar cooling installations, where absorption chillers can operate under base load conditions backed up by conventional chillers with good part load performance. Show more