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In a significant step towards more affordable and efficient Solar Energy utilization, researchers at the Technical University of Madrid have pioneered a hybrid energy storage system that integrates Lithium-Ion Batteries with power-to-heat-to-power thermal batteries (PHPS). Their innovative approach promises to cut energy costs by 7% and increase the self-consumption of solar power in buildings by up to 20%.

The team tackled the limitations of conventional solar power storage systems, which often rely heavily on lithium-ion batteries. While effective for short bursts of high power, the high capital cost of Li-ion batteries hinders scalability and limits the amount of self-generated solar energy that can be directly used. To address this, the researchers incorporated PHPS units into their system. These thermal batteries offer a cost-effective alternative for large-scale energy storage by converting electricity into heat, storing it efficiently, and then converting it back to power when needed.

A key advantage of the PHPS system lies in its ability to repurpose the waste heat generated during the energy conversion process for building heating, adding another layer of efficiency and cost savings.

To evaluate the performance of their hybrid LP system, the researchers created a detailed model of a fully electrified building in Madrid using simulation tools like PVSyst and EnergyPlus. This comprehensive model incorporated photovoltaic (PV) panels, lithium-ion batteries, PHPS units, heat pumps, and low-temperature energy storage (LTES). They then compared this hybrid setup against a more traditional L system that solely utilized PV and lithium-ion batteries.

The simulation results revealed the significant benefits of the hybrid approach. When coupled with a heat pump, the LP system achieved a levelized cost of energy (LCOE) of $86 (EUR 76) per megawatt-hour, a notable 7% reduction compared to the $87 (EUR 77)/MWh cost of the lithium-only system. This cost advantage widened further when electric heaters were considered, with the hybrid system reaching $166 (EUR 147) per megawatt-hour versus $169 (EUR 149) per megawatt-hour for the conventional setup.

Beyond cost savings, the hybrid configuration demonstrated a substantial improvement in PV self-consumption – the proportion of solar energy generated that is directly used within the building rather than being exported to the grid. With a heat pump, the PV self-consumption rate reached 68.3% in the hybrid system, compared to 68.1% in the lithium-only version. The difference became even more pronounced when electric heaters were used, with self-consumption soaring to 79.5% in the hybrid setup, a significant leap from the 68.6% achieved by the conventional system.

The researchers highlighted the complementary nature of the two Battery Technologies. Lithium-ion batteries excel in providing high power for short durations, making them ideal for managing evening peak loads. In contrast, PHPS systems are better suited for delivering a steady base-load power over extended periods. This synergy allows for a more flexible and efficient overall energy management strategy.

The findings, published in the journal Applied Energy, underscore the potential of rethinking energy storage management in solar-powered buildings.