The solar altitude angle refers to the angle of the sun in comparison to the ground it is shining on. When the sun is higher in the sky the light shines more directly on the surface below it. Most days, this can be seen around noon as this is when the sun is directly facing a section of the globe.
As you move away from the equator, in latitude, the sun hits the earth at a more steep angle, causing solar radiation to be spread over a wider area. This lowers its intensity and the amount of solar radiation a panel could absorb. Closer to the equator the sun shines more directly, creating a year round warm climate. In the poles the opposite is true, with the sun barely glancing off of the surface and not leaving a great amount of heat and solar energy.
Solar panels rely on high amounts of solar radiation. In countries closer to the equator they can be very useful for harvesting this heat as an energy source. Closer to the poles, in countries like Chile and Norway the sun does not strike the surface, making solar panels ineffective, due to the extreme lack of solar energy for most of the year (except in Summer).