What do we mean by "natural resources"?  The term natural resources has undergone changes in meaning over time.  In the past, natural resources (the term) were considered to be sources of useful commodities (physical substances, such as food, grains, and metals; products; goods for sale; articles of commerce - such as trees, fish, oil, natural gas, and coal).  In a limited  sense, the term natural resources is still used in this way.  More recently, however, the concept of natural resources has been expanded to include the total natural environment  - the entire surface layer of the planet (including whole ecosystems).  Human activities can have an affect on these natural resources.

So, utilizing the definitions above, we would not be considering the Sun as a natural resource, even though it is a resource supplied by nature.  Or should we?  Solar energy from the Sun can be collected, bought and sold as a commodity, and it can be collected on the surface layer of the planet.  But, solar energy is a product of the reactions within the Sun.  It is not the Sun.  The Sun is made up of gases, and it is the source of our light and heat.  Solar energy comes from thermonuclear reactions within the center of the Sun, and a portion of that energy comes to Earth in the form of sunlight which heats the earth.  We have no control over the Sun.   We cannot buy it, sell it or exploit it.  The Sun is not a commodity.  The Sun, itself, is not a resource that we can manage - or mismanage (fortunately).  We can manage or mismanage our forests, our fresh water sources, our fish stocks, our ecosystems.  We can manage or mismanage our non-renewables, such as fossil fuels and minerals.

The sun is 4.5 billion years old.  Astronomers believe that the Sun will be a continuing source of energy for Earth at least another 5 billion years.  If we continue in the current rate of global population increase and continue in the exploitation, mismanagement and pollution of our natural resources which we have control over, we (the human species) may not even be around to watch the sun become a 

Astronomers predict that in approximately 5,000,000,000 years the outer regions of the Sun will expand and cause Earth's temperature to become too hot for life to exist.  The Sun will then be called a Red Giant.  Then the Sun will use up its thermonuclear energy and shrink to about the size of the Earth.  During this time it may throw off nova explosions of huge amounts of gases, as it becomes what is termed a

Then after billions of years of losing all its heat and energy as a White Dwarf, it will become a 

And the surrounding planets will be dark and cold.

Good reasons for our space exploration and development programs, don't you think?