Explain why there is a surplus of solar energy at tropical latitudes and a deficit at the poles.

A diagram would be very useful for this answer. At the poles, the Sun's angle in the sky decreases, so the same amount of solar radiation is spread over a greater surface area. At tropical latitudes however, the sun is directly overhead so the sun's rays are concentrated on a smaller surface area. The curvature of the Earth also means that incoming solar energy must travel through a greater depth of atmosphere at higher latitudes than at the equator. This means that more solar energy is scattered and absorbed by clouds, gases, and atmospheric dust at the poles, so less insolation reaches the surface at these high latitudes than at the equator, where the sun's rays have less atmosphere to travel through. Albedo is another key factor. The ice coverage at the poles is highly reflective, so solar energy is reflected back into the atmosphere. At the tropics on the other hand, the dense green vegetation (e.g. the Amazon rainforest) is very dark and absorbs solar energy. The Earth's tilt (23.5 degrees) creates the seasons, and results in the poles having 24 hr darkness during the winter solstices, whereas the tropics receive insolation throughout the year. All of these factors together explain why there is a surplus of energy at tropical latitudes and a deficit at the poles. In the tropics more solar energy reaches the surface, and more is absorbed. At the poles however, less insolation reaches the surface, and less is absorbed.