Open Access

ARTICLE

Heating the Future: Solar Hot Water Collectors for Energy-Efficient Homes in Sweden

Mehran Karimi¹, Hesamodin Heidarigoujani¹, Mehdi Jahangiri^1,*, Milad Torabi Anaraki², Daryosh Mohamadi Janaki³
1 Energy and Environment Research Center, ShK.C., Islamic Azad University, Shahrekord, Iran
2 Department of Civil Engineering, Ro.C., Islamic Azad University, Tehran, Iran
3 Faculty of Engineering, Shahrekord University, Shahrekord, Iran
* Corresponding Author: Mehdi Jahangiri. Email:
(This article belongs to the Special Issue: Solar and Thermal Energy Systems)

Energy Engineering https://doi.org/10.32604/ee.2025.070190

Received 10 July 2025; Accepted 03 November 2025; Published online 18 December 2025

Abstract

The technical, economic, and environmental performance of solar hot-water (SWH) systems for Swedish residential apartments—where approximately 80% of household energy is devoted to space heating and sanitary hot-water production—was assessed. Two collector types, flat plate (FP) and evacuated tube (ET), were simulated in TSOL Pro 5.5 for five major cities (Stockholm, Göteborg, Malmö, Uppsala, Linköping). Climatic data and cold-water temperatures were sourced from Meteonorm 7.1, and economic parameters were derived from recent national statistics and literature. All calculations explicitly accounted for heat losses from collectors, storage tanks, and internal and external piping systems, and established solar-fraction equations and NPV methodology were applied. Sensitivity analyses were conducted to determine optimal collector area and hot-water storage volume. Additionally, a Monte Carlo uncertainty analysis (10,000 iterations, ±10%) and break-even subsidy/carbon-credit assessments were performed. The discount rate for NPV calculations was set at 0% for capital interest with a 5% reinvestment return over a 25-year lifespan. The highest annual solar heat yield (8017.5 kWh) was obtained in Malmö with 32 m² of ET collectors, meeting 52.7% of total heating demand. Annual CO₂ emissions were avoided by FP and ET systems by approximately ~9.07 and ~10.55 tonnes, respectively. Economic analysis showed that no payback was achieved without government allowance; however, at a $0.05/m² allowance, positive NPV was exhibited at all stations. Lower levelized heat costs were delivered by FP systems, while ET systems demonstrated consistent superiority under climatic and economic variability according to the Monte Carlo analysis. Optimal design parameters were identified as 32 collectors and a 1680 L heating buffer tank, and Sankey diagrams highlighted collector losses as the dominant inefficiency. It was concluded that properly designed SWH systems, when supported by targeted subsidies, can significantly reduce fossil-fuel demand and CO₂ emissions in Swedish residential buildings. This work provides the first city-specific technical–economic–environmental dataset for Sweden, establishes a foundation for a national solar-heating atlas, and informs policymaking toward 100% renewable energy targets; beyond the baseline evaluation, explicit subsidy and carbon-price thresholds, quantified uncertainty ranges, and loss-flow visualizations are also provided, reinforcing the robustness and policy relevance of the findings.

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Keywords

Optical losses; heating losses; net present value; gas boiler; buffer tank

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