My understanding is that the seasonal variation in temperature, amongst many other things, is a reflection of the Earth's tilt. Simply put, at the equator, sun rays fall "straight down" (100% vertical), and all of their energy hits the surface of the Earth. At different latitudes, these rays begin to have a horizontal component, so only the vertical portion (cosine of angle of incidence, I believe) hits the surface. I assume this generalization also applies to solar panels: sun rays falling on the panel completely vertically will have more energy than those falling at an agle. What would happen if you tilted your solar panel to match the sun ray's angle of incidence? Would it be just as effective in the middle of winter in Wisconsin (assuming no snow was on it) as in the summer in Ecuador? Perhaps solar panels just don't work in the cold, even if high energy sun rays are falling upon it.