This article reports on the implementation of a mathematical modeling activity about renewable energy. The activity was first implemented with twenty-four 10th grade students in a state high school in Turkey and lasted 2 lesson hours. Then, the revised version of the activity was implemented with four 10th grade students. Students built a mathematical model of the electricity consumption on a sailboat, and then decided which renewable energy source could be used on the boat using their models. The students experienced all stages of mathematical modeling: real life problem, mathematical problem, mathematical solution, and interpreting the solution. The students found a solution to the modeling problem by creating and interpreting tables, graphs, and functions, and by comparing the different graphs resulting from real life situations. Additionally, they increased awareness about renewable energy sources. The activity might provide an example application of mathematical modeling for mathematics educators.