The role and benefits of solar water heating in the energy demands of low-income dwellings in Brazil

In Brazil the widespread use of electrical showerheads for providing hot water for domestic consumption contributes to a load curve that peaks in the early evening, imposing a considerable burden to generation, transmission, and distribution utilities. On average, over 73% of Brazilian households use these 3–8 kW electrical resistance showerheads. In some of the more temperate climate regions in the south of the country, where most of the Brazilian population is concentrated, electrical showers are present in over 90% of residential buildings. For the residential consumer, while these high-power heating devices are the least-cost investment alternative, they lead to high running energy costs. Furthermore, due to their very low load factor (typically below 2%), each of these high-power showerheads results in considerably low return on the high investment costs in terms of infrastructure for the electricity sector. Particularly in low-income dwellings, electrical showerheads represent by far the highest electrical loads, resulting in a considerable component in the monthly energy bill. On the other hand, Brazil is one of the sunniest countries in the world, and solar water heating technologies have demonstrated large financial benefits and short payback times. Due to their comparatively higher initial investment costs, however, domestic solar water heaters are used mostly in higher income residences. In this work we present the potential of a low-cost version of the typical domestic solar water heating system for low-income dwellings, where the electrical resistance, which is normally installed inside the hot water tank, is replaced by a variable power electrical showerhead. This design avoids the use of electrical power as auxiliary heating for the whole of the boiler volume, since only the water which passes through the showerhead might be heated by the electrical resistance. This system configuration is a commercially available low-cost solar water heater option. A case-study is presented for a statistically representative group of low-income dwellings with solar water heating systems in Florianópolis – Brazil. Our results show that the economies obtained are considerable, both in terms of energy consumption (kW h) and peak demand (kW) reduction. When compared with higher income typical users of solar water heating technologies, these economies represent a relatively higher benefit, both for the low-income population, as well as for the utilities involved. Our results also show that the avoided power costs, a benefit for the distribution utility company, might be more substantial than the avoided energy costs, a benefit for the end user. In the energy constrained on-peak hours period, the utility company might benefit from being able to sell this energy to other higher paying tariff consumers.