This is an appropriate question in view of earth day! One of the great and very important movements that started in earnest in the mid-1900's is the nature conservation movement. People began to realize that the world in which we live has been exploited for generations. The waterways and land has been polluted for the sake of profit and gain. And industries did not consider the long-term effects of exploiting the earth in this way. Consider the fact that many bodies of water are still polluted. Think of what this does to the life in the water and even our food supply. Some places are so filled with air-pollution that people have to wear masks before they go out. Finally, the green movement is the logical conclusion of all of this.
I believe the definition you're referring to is that of conservation, a movement that started in the late 1800s, largely with the help of a naturalist named John Muir. He advised President Teddy Roosevelt to set aside some land for national parks and is the father of our modern park system.
Later, in the 1960s, a modern movement began to look at ceaning up pollution in air and waterways. The "Green" movement we know today is just the latest version of the conservationism they started a long time ago, and is no standard scientific practice, and is taught widely in the public schools.
Preservation or conservation of land, water, and air generally refers to the maintenance of quality of these natural resources and prevention of environmental pollution. Preservation of water may have the additional meaning of reducing wastage of water available for domestic use, industrial use, and agricultural irrigation. In case of preservation of land may also refer to erosion of soil or to reduction of green cover of forests.
However, I have not come across the any concept like preservation of sun.