Polyethylene glycol (PEG) is one the most promising organic phase change materials (PCMs) due to good latent heat thermal energy storage (LHTES) characteristics. However, leakage issue in melting state and low thermal conductivity restrict its further real applications. In order to eliminate these disadvantages as well as increasing its incorporation ratio, polyethylene glycol (PEG600) was impregnated with raw diatomite (RD)/carbon nanotubes(CNTs) pre-composites. Without exhibiting melt leakage, PEG was successfully confined as 42.8, 44.5 and 51.7 wt% in the novel shape-stabilized composite phase change materials (S-SCPCMs) including 0.57, 1.70 and 2.50 wt% CNTs while it was absorbed by RD as 41.0 wt%. The chemical and morphological characterizations of the produced S-SCPCMs were made by FT-IR and SEM techniques. The DSC analysis showed that the S-SCPCMs had melting temperatures in the range of about 7-8 degrees C and latent heat capacity between 53.8 and 62.9 J/g. Moreover, compared to the RD/PEG composite, the thermal conductivities of RD/CNTs/PEG composites were enhanced between 73% and 93% as well as the latent heat capacity of them was increased in the range of 5-31%. The melting times and total heating times of the S-SCPCMs were drastically shortened depending on the improvement in thermal conductivity of them. Thermal cycling test and TGA results demonstrated that the S-SCPCMs had commendable long-term chemical stability, LHTES reliability and thermal durability. Consequently, the loading of CNTs to RD/PEG composite provided beneficial outcomes such as increasing impregnation ratio with no liquid leakage, reducing heat storing/releasing periods depending on enhanced thermal conductivity, without damaging chemical stability and thermal durability. In view of these advantageous properties, the S-SCPCMs can be incorporated with ordinary structural elements to generate various building sections with solar energy harvesting/releasing capability. Such combinations can be also evaluated for passive solar cooling purposes in radiant floor heating systems, insulation and ceiling panels or walls depending on the climatic circumstances. (C) 2018 Elsevier B.V. All rights reserved.