Augmenting Residential AC Electric Water Heating with Dedicated Direct-to-Element DC Solar Photovoltaic

Daniel Pfister, Arnold Johan Rix and Marthinus Johannes Booysen ()
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Daniel Pfister: Industrial Engineering, Stellenbosch University, Stellenbosch 7600, South Africa
Arnold Johan Rix: Electrical and Electronic Engineering, Stellenbosch University, Stellenbosch 7600, South Africa
Marthinus Johannes Booysen: Industrial Engineering, Stellenbosch University, Stellenbosch 7600, South Africa

Energies, 2025, vol. 18, issue 4, 1-16

Abstract: Residential water heating represents one of the most energy-intensive household applications, particularly in South Africa, where immersed resistive element heating dominates. Solar photovoltaic systems provide a promising solution for augmenting grid-based electrical water heaters, offering energy cost savings and environmental benefits. This study evaluates a novel approach to integrate solar photovoltaic directly into electrical water heater systems without using inverters. Using a combination of field experiments and simulation, four heating strategies were assessed, namely: “grid only”, “solar medium”, “solar heavy”, and “solar timer”. Metrics such as solar augmentation ratio, solar utilization, and cold event frequency were analyzed for different seasons using real-world and simulated water usage profiles. Results demonstrate significant grid energy reductions through solar augmentation, particularly in warmer seasons. However, the effectiveness of the strategies varies, with increased solar utilization often correlated with a higher frequency of cold events. A hybrid seasonal strategy is proposed to optimize energy savings while maintaining user comfort. This work highlights the potential of direct DC solar photovoltaic integration as a cost-effective and sustainable enhancement for residential water heating.

Keywords: electrical water heaters; photovoltaic; demand side management; renewable energy; residential water heating (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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