Figure 1-15 Solar Energy in Summer and Winter At different times of the year, sunlight strikes the ground at different angles. As illustrated for northern mid-latitudes, we see that: (a) and (b) In winter, the sunlight is less concentrated, the days are short, and little heating of the ground takes place. This accounts for the low temperatures in winter. (c) and (d) In summer, sunlight is concentrated and the days are also longer, which further increases the heating.