Background: The technology of underground in-situ electric heating for oil shale extraction requires a large amount of electrical energy, which is one of the important factors restricting its further development. In this paper, a microgrid system is proposed, which combines renewable energy sources with conventional ones, to supply electricity for the underground in-situ electric heating installations of oil shale. Methods: The system takes the annual net present value as the evaluation index to determine the optimal solution considering the effects of oil shale electric heating well spacing, oil shale extraction area, and diesel price. Significant findings: The results showed that the spacing of electric heating wells plays a significant role in energy requirement, an increment of 271,195.00$ in the average annual costs is noted when 12 m of the spacing is considered instead of 10 m. Moreover, diesel fuel prices remarkably affect the annual costs, and increasing diesel price from 0.4 to 0.8 $ per liter causes an increase of 58.5% in the average annual costs. Furthermore, this situation increases the annual wasted electricity ratio by 2.96-folds. This study provides a useful reference for decision-makers to design the power supply scheme for underground in-situ electric heating of oil shale.