The impact of the use of CSDWHSs on the peak demand of a utility grid was determined for a group of low-income consumers. The energy consumption profiles of the groups are an average of the individual profiles; therefore they represent a variety of electric energy consumers.

The peak demand still remains, even with solar heating, but its use can reduce the peak by 60% on a monthly average basis of the hourly values. Using the power recorded in 5 minute interval averages, a reduction of 47% was achieved for the days where the highest values occurred. However, the obtained results were derived using only one month of data of a specific housing unit, therefore, results presented here are far from being conclusive. Data measurement will continue until one year is completed.

The estimated solar fraction for this period was 58%, but there is a high variability among the results for different families.

The ongoing research will take into account the determination of typical individual consumption profiles and the relative contribution of each profile on a group of low-income families. These consumption profiles will provide the basis for simulation of CSDHWSs conjugated to showerheads. The theoretical results will be validated against experimental data collected in the same housing unit. The validated results will be used to evaluate the impact of CSDHWSs on the peak demand of urban utility grids for other locations in Brazil.

An additional measure to further reduce peak demand on days of low solar irradiation may be electric preheating in the storage tank using weather forecast information. In this case, better thermal insulation of the storage tank as well as improved tank design may be necessary in order to maintain the stored water at acceptable temperature levels over long periods. The authors are presently investigating an algorithm that uses weather forecast information as input to predict the need of storage tank preheating.

Acknowledgements

The authors are indebted to CELESC for funding the present research, under contract FAPEU / P&D CELESC — ANEEL 032/435, and also to Caixa Economica Federal for authorizing the use of the housing unit for research purposes.

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