This paper reports on the techno-economic assessment of a grid-connected solar thermal system used for electrical-energy saving in the residential sector. The technical characteristics of the solar thermal system, based on a line-focus parabolic-trough concentrator, are given and its useful electrical and thermal-energy production is estimated using a simulation program based on a Monte Carlo method for reading solar radiation data. The economic assessment is performed using the Life-Cycle Savings (LCS) method and the payback period (PBP) of the investment's initial capital cost is determined.