I sense you have a misunderstanding of how DC energy is transferred from source to load which is hindering your ability to understand how AC energy is transferred.
The picture many people have in their heads is that the power source somehow gives energy to electrons. The electrons then flow down a wire carrying this energy and then somehow release the energy when the electrons flow through the load. I would bet that your mental picture of electricity is something like this. And if that is close to how you view electricity, then the question of how an AC energy source transfers energy is perplexing. Afterall, electrons aren't flowing back and forth 50 or 60 times a second from the lightbulb in your kitchen all the way the way back to the generator at the power plant. We know electrons move much, much slower than that (they move on the order of a meter an hour, depending on a number of factors like current, size of the conductor, etc.). And given that there are transformers in between your kitchen light and the generator, it makes even less sense, since they are 2 different electrical circuits that have different electrons in them. The wires aren't even connected.
But this is not how it works. Energy isn't carried from source to load via electrons. Energy doesn't even flow down the wires. Instead, electrical energy travels from the electrical source to the electrical load via an electromagnetic (EM) field in the space surrounding the source, wires, and load.
Look at the picture below of a DC circuit consisting of a battery, some wire and a resistor. The green arrows represent the magnetic field that arises due to current flow. The red arrows represent the electric field due to the voltage source. The blue arrows represent the energy flux density, or the Poynting vector, which is the cross product of the electric and magnetic fields. The Poynting vector can be thought of as the rate of energy transfer per area.
Notice the flow of energy is from the battery to the resistor. Also notice that the energy flows into the resistor not from the wire but through the space surrounding the wires.
If you replace the DC source with an AC source, you should be able to convince your self - by looking at the electric and magnetic fields - that the Poynting vector still points from source to load even though the current is switching directions. Because the Poynting vector is a cross product of the two fields, its direction stays the same even as the fields are changing.
There have been some questions in the comments about the scientific validity of what I've said above. How electromagnetic energy travels in circuits has been known for some time ... since at least the late 1800's. The Poynting vector, named after John Henry Poynting who explained this theory in a paper in 1884, entitled On the Transfer of Energy in the Electromagnetic Field. The paper is pretty readable and explains the theory pretty well. He explains:
Formerly a current was regarded as something travelling along a
conductor, attention being chiefly directed to the conductor, and the
energy which appeared at any part of the circuit, if considered at
all, was supposed to be conveyed thither through the conductor by the
current. But the existence of induced currents and of electromagnetic
actions at a distance from a primary circuit from which they draw
their energy has led us, under the guidance of Faraday and Maxwell, to
look upon the medium surrounding the conductor as playing a very
important part in the development of the phenomena. If we believe in
the continuity of the motion of energy, that is, if we believe that
when it disappears at one point and reappears at another it must have
passed through the intervening space, we are forced to conclude that
the surrounding medium contains at least a part of the energy, and
that it is capable of transferring it from point to point.
He goes on to say:
Starting with Maxwell's theory, we are naturally led to consider the problem: How does the energy about an electric current pass from point to point — that is, by what paths and according to what law does it travel from the part of the circuit where it is first recognisable as electric and magnetic to the parts where it is changed into heat or other forms?
The aim of this paper is to prove that there is a general law for the
transfer of energy, according to which it moves at any point
perpendicularly to the plane containing the lines of electric force
and magnetic force, and that the amount crossing unit of area per
second of this plane is equal to the product of the intensities of the
two forces, multiplied by the sine of the angle between them, divided
by \$4\pi\$, while the direction of flow of energy is that in which a
right-handed screw would move if turned round from the positive
direction of the electromotive to the positive direction of the
He then goes on to show how energy enters and heats up a wire:
It seems then that none of the energy of a current travels along the
wire, but that it comes in from the non-conducting medium surrounding
the wire, that as soon as it enters it begins to be transformed into
heat, the amount crossing successive layers of the wire decreasing
till by the time the centre is reached, where there is no magnetic
force, and therefore no energy passing, it has all been transformed
into heat. A conduction-current then may be said to consist of this
inward flow of energy with its accompanying magnetic and electromotive
forces, and the transformation of the energy into heat within the
Richard Feynman also talks about this in his lectures on physics. After an explanation of this phenomenon, Feynman derives how a charging capacitor gets its energy, then says:
But it tells us a peculiar thing: that when we are charging a
capacitor, the energy is not coming down the wires; it is coming in
through the edges of the gap.
Feynman then, like Poynting, explains how energy enters a wire:
As another example, we ask what happens in a piece of resistance wire
when it is carrying a current. Since the wire has resistance, there is
an electric field along it, driving the current. Because there is a
potential drop along the wire, there is also an electric field just
outside the wire, parallel to the surface. There is,
in addition, a magnetic field which goes around the wire because of
the current. The E and B are at right angles; therefore there is a
Poynting vector directed radially inward, as shown in the figure.
There is a flow of energy into the wire all around. It is, of course,
equal to the energy being lost in the wire in the form of heat. So our
“crazy” theory says that the electrons are getting their energy to
generate heat because of the energy flowing into the wire from the
field outside. Intuition would seem to tell us that the electrons get
their energy from being pushed along the wire, so the energy should be
flowing down (or up) along the wire. But the theory says that the
electrons are really being pushed by an electric field, which has come
from some charges very far away, and that the electrons get their
energy for generating heat from these fields. The energy somehow flows
from the distant charges into a wide area of space and then inward to