Assessment of Integrated Solar-Based Residential Energy Systems with Seasonal Thermal Storage

Abstract

The transition to low-carbon energy systems requires the electrification of residential heating using renewable electricity. However, renewable electricity generation, of which solar electricity forms an important share, and residential heat demand are strongly mismatched across the seasons. This thesis critically evaluates and further develops the Solar Storage in Diverse Climates (SOLSTICE) modelling framework into SOLSTICE V2, an accessible and transparent hourly Excel-based model for the early-stage assessment of residential energy systems. The model is intended to enable users such as policymakers and planners to compare system configurations and explore energy-system behaviour without requiring advanced simulation software or specialised modelling expertise. SOLSTICE V2 combines photovoltaic or photovoltaic-thermal collectors, heat pumps, electrical battery storage, and high-temperature aquifer thermal energy storage. The existing component representations were assessed and adapted where necessary, with particular attention given to plane-of-array irradiance, duty-specific heat-pump operation, electrical battery losses, photovoltaic-thermal and heat-pump coupling, and the physical representation of useful heat stored in the aquifer. The resulting framework uses hourly weather, demand, and electricity-price data to simulate energy flows and compare system configurations under different climatic conditions.

The results show that converting excess summer solar electricity into directly usable winter heat can achieve electrical self-sufficiency above 90%. For the Berlin reference case, adding high-temperature aquifer thermal energy storage to the photovoltaic and electrical battery configuration reduced annual grid import from 2024 kWh to 450 kWh per household. Replacing photovoltaic modules with photovoltaic-thermal collectors further improved system performance because the higher heat-source temperature significantly increased heat-pump performance. In Berlin, the investigated system used approximately 25 m² of solar collectors per household and a shared effective hot-well volume of 230,000 m³ for 1000 households. Under the higher solar irradiation and lower heating demand of Madrid, comparable performance was achieved with approximately 13 m² of solar collectors per household and an effective hot-well volume of 100,000 m³. The results demonstrate the complementary roles of short-term electrical storage and seasonal thermal storage, as well as the importance of climate-specific system sizing.