Limited in the sense of being renewable and non-renewable. We don't have to worry about renewing the wind or water currents or the fuel garnered from plants because they are practically a stable fixture of our environment or else easily renewed by planting. But the petro chemical on which we are presently dependent isn't that way.
BTW
I'm not just inventing terminology or giving a personal opinion, I took an elective course in environmental science and renewability-and non-renewability of resources was a basic concept of the curriculum.
Your course was all propaganda. Every energy source has
costs involved and side effects. If you SHADE the earth
with massive solar farms, just imagine the environmental
destruction you could cause. Evaporation rates, ground
cooling, wind patterns, you might influence weather with
enough solar panels.
Wind farms? Same problem.
Water power? The downside is well known.
The "non-renewable" resources will last forever
as the price on them increases and we switch
to more expensive energy sources.
"Renewable" resources also have limits on
how much we can suck from the environment
and the space to gather the weak-slow energy
back into fast usable energy.
The number of dams we can build is limited.
The number of solar panels we can erect and afford is limited.
The number of acres with steady winds is limited.
Locally wind farms are built on higher terrain in
an area with steady wind. In town, our wind mills
sit still and silent, quit often.
And windmills don't last forever anyway.
Likely your course ignored all the limitations
of renewables.
