Development of a novel compact flat-plate solar collector integrated with thermal energy storage: experimental evaluation of the energy stored under outdoors conditions - M.K. Koukou,J.Konstantaras,G.Dogkas,K.Lymperis,V.N.Stathopoulos,M.Gr. Vrachopoulos,E.Douvi,Y.Caouris, P.Dimas (13th International Conference on Sustainable Energy & Environmental Protection, 13th – 16th September 2021, Vienna Austria, 2021)