Well, if you have ever been in highschool, you have probably run across a subject called "Physics".
And there you have been told that energy can neither be created nor destroyed: Law of conservation of energy.
So what is it they are all talking about, "source of energy", "energy crisis", "energy conservation" and so on - if you can neither create nor destroy it, how can there be sources and how shortages? How come that energy is conserved under all circumstances and we still constantly need more of it? What happens with the energy once we have used it if we are not annihilating it? Easy.
Let's look at another vital resource: Water.
Yes, it is different.
Yes, water can be "made" and "destroyed".
But in actual fact, this does not happen on a big scale.
So we are nearly right if we say: Water is neither created nor destroyed.
Still water can be in short supply, and I am not only talking about the earth's deserts here.
For instance: With all the people moving to the US West Coast, water supply has become an issue there.
Now let's ask the same question: What happens to the water once we have used it if we are not annihilating it? The answer is quite evident, what do you think? You drink something.
Even if it is a sugary softdrink of any kind, if it satisfies your thirst, it has to be basically water.
And then, where does it go after you drink it? Or think of laundry.
Fresh water enters the washing machine, cleans the wash, which then is tumbled dry.
And the water? May be you take a shower once in a while.
Clean water leaves the shower head,...
well you know the process.
Finally it goes down the drain.
Yes, you got it.
Some evaporates (sweating, drying wash), most remains liquid, but is degraded.
When we use water, we degrade it.
So after being used once, it cannot immediately be used again, not even the part we recuperate in liquid form.
It has to be processed one way or another.
Partly, mother nature takes care of it, lets the sun evaporate it and lets the atmosphere re-condense it to droplets which are clean - at least before they pass through polluted air.
We may need to help and do some of the re-processing in sewage plants.
Additionally we may have to purify the water after it has been "rain" or "river water".
And then we can use it again.
We are washing stuff with water.
Could we clean water with water? I don't know if this is done somewhere, but let's just assume it'd be possible: You have a bathtub full of dirty water.
You have found a way to transfer the dirt of the bathtub water to some other water.
Would only make sense if the cleaning water which has to receive the dirt is a smaller amount than the bathtubful of dirtwater which you are about to purify.
In the end you have less dirt water, but it is dirtier than the bathtub water was because the dirt is now more concentrated.
This does not sound like a way we would chose to reprocess "used" water, what do you think? Now: Energy? Similar - up to a certain point.
Just like water, we degrade energy once we use it.
And similar to evaporation, some of the energy we use does not end up in the final form we expect it to take on, but rather gets lost on the way converting into some other form.
But differently from water, we are very limited in our ways to reprocess energy.
We can only reprocess energy for another run through our machinery of needs, under condition that we degrade some energy.
It is like cleaning dirty water with water.
As the dirt has to remain somewhere, no matter how you transfer the dirt to the water-cleaning water, you will always end up with at least some dirty water.
Alongside with the cleaned water, you could at best end up with a smaller amount of dirtier water than you had before the treatment started.
The dirt is now more concentrated.
And that's precisely the situation: As a matter of principle, energy can only be "washed" with energy.
We have no other "sewage treatment".
In the case of water, we have a nice short word for the essence of degradation: Dirt.
Unfortunately, we only have a word derived from ancient Greek in the case of energy: Entropy.
Very sorry for that.
To make things even worse, this type of "dirt" even gets more in any kind of process, so you do not only have to "wash out" entropy from energy to prepare it for re-use, but the very "washing" process produces some more "dirt".
Heat-pumps are frequently used to "wash" energy.
They concentrate heat energy from a level of lower temperature to a level of higher temperature.
In our homes, we usually use them only for their cooling capacity in refrigerators and air conditioning appliances.
So what is the answer to our initial question "how come that energy is conserved under all circumstances and we still constantly need more of it"? The answer is: Because we degrade energy in the process of using it as it goes to a state with higher entropy.
Unlike water, energy cannot be reprocessed completely because we can only reduce entropy at one place when we increase it at another place, and we have even to accept that the overall entropy increases.
Still we should try and re-use as much energy as possible, because the entropy production we have to accept along the way is normally smaller than it is when we use "fresh" primary energy, and we are saving our energy resources.
Saving primary energy is the key to keeping fuel prices at bay.
So we could use heat-pumps not only in air-conditioners and refrigerators, but as well for heating purposes - and run them on renewable energy (wind, solar) as much as possible to cut down on our use of fossil fuels like oil, and to reduce pollution and global atmospheric warming in same time - all without sacrificing our way of life.