Analysis of Energy, Economic and Environmental Performance of Solar Water Heaters for Domestic Hot Water Supply in Northern European Climate

Abstract

A significant portion of energy expense of a residential household goes toward the provision of domestic hot water (DHW) ~19%. The use of solar thermal water heating provides a local way to offset this energy requirement with a renewable resource. Solar thermal water heating systems are commonly used in hot climates from Southern Europe to the Equator however in the past they were seen as not so economically viable in colder climates. The solar collector that is readily available on the market for DHW generation is the standard flat plate collector (SFPC), but they are not attractive for use in higher latitudes due to low operating temperature and high heat loss. Although convection suppression has been identified as a method to improve the performance of flat plate collector it has not yet achieved mainstream commercialisation. In this work we attempt to show that the conventional flat plate collector still has potential in higher latitude when modified to suppress convection heat loss. The modified FPC that is particularly of focus in this work is the one with honeycomb transparent insulation (MFPC). We compare the performance of SFPC and MFPC in colder climate considering different auxiliary heating options such as electricity, gas, and oil, at their recent energy prices. Using TRNSYS software, we modelled the annual energy generated by these collectors using a typical domestic load case and found that SFPC produced 1446.60 kWh/year while MFPC produced 1993.50 kWh/year. For a typical household with a daily hot water consumption of 200 L, SFPC requires 3858.69 kWh/year of auxiliary energy while MFPC requires 3458.24 kWh/year. The economic analysis shows that the MFPC with electrical heating is the highly viable option with a Net Present Value (NPV) of € 5078.95. The CO2 emission reduction from the SFPC and MFPC with electrical auxiliary heating are 39.54 kgCO2/year and 79.58 kgCO2/year, respectively, compared to conventional electrical immersion heaters.