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Rooftop photovoltaic (PV) systems in combination with heat pumps are a key technology for decarbonisation of the residential sector. The main challenge of these systems is the temporal mismatch between the PV electricity supply and the heating demand of the building, resulting in a self-consumption ratio of only 30%. Cowa is developing a compact thermal storage solution that allows to store excess PV electricity produced during midday and to release this energy during periods of solar outage, thereby increasing the self-consumption ratio of the system.
Cowa's solution is based on capsules filled with Phase Change Materials (PCM). These materials offer a high energy density by utilizing a solid-liquid phase transition. The capsules are stacked into conventional heat pump water storages (buffer storages) to increase their storage capacity up to a factor of four. The extra storage capacity added by the COWA-Caps can boost the self-sufficiency of PV driven heat pump systems from 30% to 70%.
Thanks to the support of the Gebert Rüf foundation, Cowa has develop a long-lasting mass-producible encapsulation with optimized packing density and heat transfer characteristic.

The storage technology is based on from Cowa developed salt-water mixtures that offer an up to factor four higher energy density than water. The materials are non-toxic, non-flammable and recyclable. Furthermore, they do not lose capacity over time and are cost-effective. Based on these advantages, a much cheaper and more sustainable solution to increase photovoltaic self-consumption can be offered to the end-customers than electrical batteries. Finally, no change in the heat pump system configuration is required.

Several stable PCMs for heat pump applications and a unique, cost-effective encapsulation material with excellent long-term stability and diffusion barrier properties were developed. A real scale protype with a volume of 300l filled with the developed materials, has been produced and fully tested in summer 2021.
First storage systems could be sold and will be delivered as soon as the production line has been commissioned.
Jörg Worlitschek, Simon Maranda and Remo Waser founded the startup Cowa Thermal Solutions with the mission to boost renewables in buildings by compact thermal energy storages. Cowa has raised more than 1.4MCHF of non-dilutive funds, has won the Venture competition and was finalist in the De Vigier Preis and ZKP Pionierpreis in 2021. A seed round will be completed in early 2022 followed by a Swiss market expansion.

Waser, R.; Ghani, F.; Maranda, S.; O’Donovan, T. S.; Schuetz, P.; Zaglio, M.; Worlitschek, J. Fast and Experimentally Validated Model of a Latent Thermal Energy Storage Device for System Level Simulations. Appl. Energy 2018, 231, 116–126.
Residential-Scale Demonstrator for Seasonal Latent Thermal Energy Storage for Heating and Cooling Application with Optimized PV Self-Consumption. Waser, R.; Berger, M.; Maranda, S.; Worlitschek, J.; 2019, No. October.

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