Energy is a vital input for social and economic development. As a result of the generalization of agricultural, industrial and domestic activities the demand for energy has increased remarkably, especially in emergent countries. This has meant rapid grower in the level of greenhouse gas emissions and the increase in fuel prices, which are the main driving forces behind efforts to utilize renewable energy sources more effectively and develop the research of heat storage systems. The objective of this paper is to investigate the possibility of using a continuous solid medium, composed mainly of an unsaturated sandy soil, which is the case in many desert areas in the world, where the solar energy is abundant, for long or short term like Underground Thermal Energy Storage System (UTESS) using a simple configuration and local means of low cost. Despite all attempts made by researchers and the continuous progress brought about, UTESS are still dependent mainly on the geological nature of the soil and they require enormous means for their construction in some cases with non usual cooling and heating systems. As a matter of fact, solar heat is characterized by its intermittency, in order to overcome this disadvantage, similar techniques can be useful to store thermal energy for later use. A mathematical model based on the heat conduction equation in two dimensional cylindrical coordinates is adopted to describe the heat transfer between a buried pipe and the storage medium (soil). Using a new analytical approach, a steady state solution of this model is presented, which consists of an exact solution composed of the sum of two functions. The approach is then used to determine the overall heat coefficient, the amount of heat stored, the amount of heat recovered and the heat storage efficiency. Some original conclusions and suggestions are given.
efficiency, exact solution, heat conduction, underground heat storage
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