Impact of compact solar domestic hot-water systems on
the peak demand of a utility grid in Brazil

Samuel L. Abreu1, Juan Pablo de L. C. Salazar1, Sergio Colle1
1LABSOLAR — Solar Energy Laboratory / Federal University of Santa Catarina —
Florianopolis — SC — Brazil
Wilson Reguse2

2Centrais Eletricas de Santa Catarina — CELESC (Santa Catarina state utility)
samuel@emc. ufsc. br, phone +55 4 8 331 9379, fax + 55 4 8 3317615

Introduction

A particular characteristic of the electric energy consumption in Brazil is the widespread use of electric showerheads and the resulting peak demand between 18h and 21 h. Over 90% of the residences in Brazil have electric showerheads. Studies have shown that electric showerheads represent approximately 23% of a household’s energy consumption and this fraction increases to around 35% of the total demand during the peak hours for low-income consumers (Prado and Gongalves, 1998). Electric showerheads are very cheap, usual prices lie under US$30 in Brazil, have a nominal power between 4kW and 8kW and are very efficient in terms of energy conversion. All these aspects contribute to the large scale use of electric showerheads for water heating among low-income consumers. Furthermore, showering is the only use of hot-water by this class of consumers in Brazil. Therefore, Compact Domestic Solar Hot-Water Systems — CDSHWS, cheaper and easy to install when compared to conventional solar hot-water systems, may be an economically attractive alternative to supply large scale hot-water usage, with the benefit of reducing the peak demand on the utility grid.

Utilities in Brazil are obliged by regulation laws to supply electric energy to low — income consumers. However, the associated costs of energy generation and distributions are heavily affected by the power of the electric showerheads, making investments in almost all cases economically unviable. Januzzi and Schipper (1991) estimate that the marginal expansion costs lie around US$ 1,500.00 per kilowatt. (falta ref para inserir). This scenario leads to the conclusion that the utility can account for the large scale installation of CSDHWS in its investment policy. In other words, the utility can share the cost of the solar heaters, which lies around US$ 300,00, with low — income electricity consumers.

In a previous work, Salazar et al. (2003) optimized seven parameters of a CSDHWS using peak demand and total cost as constraints. The optimized parameters were: collector aperture area, storage tank volume, heater power, electric showerhead power, set-point temperature of the storage tank, mixing valve temperature and collector slope. The chosen optimization procedure was successful, but the lack of information on hot-water consumption profiles is a limitation on the reliability of the predictions.

Colle et al. (2003) carried out the economical optimization of the CSDHWS storage tank insulation thickness. The optimization showed that life cycle cost savings are sensitive to insulation costs, when preheating of the storage tank during the morning early hours is required in order to avoid the expected peak demand. This optimization concern should be taken into account, in order to minimize the cost of CSDHWSs.

To study the effects of CSDHWSs on the peak demand, ninety low-income consumers from a housing unit were chosen to have their showerhead electric energy consumption monitored. Sixty consumers were equipped with CSDHWSs, while the remaining consumers served as a reference case. The electric energy
consumption of the showerheads was continuously measured, providing the profiles from which the results of this paper are derived.