Here's a description of exactly what's going on in detail, the simplicity of the solution is beautiful.
To explain the Heins effect firstly we should take a look at how electricity is generated using copper wire and magnets, like it's generated in wind turbines, car alternators, bicycle dynamos and the like.
In a standard generator configuration you have a disc that has magnets embedded in it, and you have a set of coils positioned in a circle underneath the disc in such a way that when the disc is rotated, the magnets pass over the coils with the centers of the magnets over the centers of the coils when they are in the same position.
When the magnet passes over the coil, electric potential is induced in the copper. Science has labels and can tell you how the electrons move etc but noone knows why this happens, just as noone knows why magnets attract and repel. Yes science will explain about 'domain alignment' but all they are doing is describing their observations. The full nature of electricity and magnetism isn't yet understood.
So we just have to accept that when we have something like copper or aluminium that can conduct electricity, and that conductor is in the presence of a magnetic field, when one of them is moving, electricity appears in the metal. We could rotate the copper coils or the magnets, as long as they are moving or changing with respect to one another, and they are in close proximity, electricity will be induced.
Now for some detail, let's examine a single magnet on our rotor in it's circular journey toward, passing over and then moving away from a copper coil.
Our magnet has it's North face pointing up and it's South face pointing down, toward the top of the coil of copper wire.
As this South pole starts to move across the copper coil, the electric potential induced in the copper coil gives rise to a magnetic field in the coil, the South pole of which is at the top of the coil (underneath the magnet). Since we have a South pole magnet above the South pole of a coil then they naturally repel each other, it's the force that is turning the rotor that overcomes this, that force being produced by gas, coal or whatever, keeps the rotor turning.
When the magnet is directly over the coil (the center of the magnet and the center of the coil are aligned) there is no attracting or repelling force, it's a kind of neutral zone.
When the magnet is moving out of the coil, the top of the coil becomes the North pole, which wants to naturally attract the South pole face of the magnet.
So on the way in, the coil wants to repel the magnet and stop it's incoming movement, and on the way out the coil wants to attract the magnet and stop it moving out.
The magnetic field that's induced in the coil is therefore called the counter electro-motive force (CEMF) because it is counter to, or in opposition of, the pole of the magnet that induced it. In America this is often called Back EMF, or BEMF.
This behaviour is known as Lenz's Law, which says that :
The direction of the current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field.
Now, this opposing magnetic field takes a certain amount of time to be created, or to 'rise', the proper physical term is the rise-time of the inductor (an inductor is just a coil of conducting wire such as copper or aluminium), how long it takes for the opposing magnetic field to be created.
Inductance is a measure of the ability of a coil to produce electricity, different coils have different inductance values, they can have more turns of wire, which increases inductance, or less turns of wire, which decreases it. Other factors such as the shape of the coil also effect the inductance value.
Inductance is measured in Henrys (named after Joseph Henry, the American scientist who discovered induction at roughly the same time as Michael Faraday in Britain) and is denoted by the letter L.
The formula to calculate the rise-time of an inductor is :
T = L/R
Where T is the time it takes for the opposing field to rise in seconds, L is our inductance in Henrys and R is the resistance of the coil in Ohms. If you don't know then resistance is a measure of how hard it is for electricity to flow through a conductor, thinner wires have higher resistance, thicker wires have less so allow more electricity to flow).
So if we have a coil with a resistance of 200 Ohms and an inductance of 2 Henrys then :
T = L/R
T = 2/200
T = 0.01
So in this case it would take 0.01 seconds, or 10 milliseconds (ms) for the opposing field to rise.
But what if we increased our inductance, say we increased it to 3 Henrys :
T = L/R
T = 3/200
T = 0.015
So in this case, with our increased inductance, the formula tells us that the rise time has now increased to 15ms, we have delayed it a little.
What if we increase just the resistance in our first case (thinner wire or just longer wire) to, say 300 :
T = L/R
T = 3/200
T = 0.005
Now we have 5ms for the rise-time.
So we can see that as our inductance value increases, the time it takes for the opposing magnetic field to rise also increases. We can delay the rise-time or accelerate it.
So why is this interesting, how can we exploit this behaviour ?
What if we could construct a coil that delayed the rise-time enough so that the opposing magnetic field (or CEMF) rose too late to oppose our incoming magnet? It would also rise too late to attract our outgoing magnet. Anything that helps our rotor spin more easily means cheaper electricity generation.
Of course it's not all just about the coil, it's about the speed the magnets are travelling at (remember they are embedded into a rotating disc), if we have the rotor spinning at a certain speed and a coil (inductor) that delays the rise-time for a certain period of time, we can construct a generator that delays the rise-time just enough so that, when the magnet is incoming, the opposing magnetic field rises just when the magnet's center is nearing the coils center (but before it's at top dead center (TDC), so we still have 2 South poles and aren't in the neutral zone yet), this means that the South pole of the coil doesn't push away at the incoming magnet, but helps the magnet on it's way to TDC. It also means that we delay the rise of the North pole in the coil when the magnet has passed TDC and is on the way out, so the North pole of the coil doesn't get a chance to pull the magnet in when it's on the way out of the coil.
In short, we've used Lenz's Law to negate it's undesirable effects and more than that, to actually accelerate the movement of the magnet.
Now that we are getting this free acceleration, we need less power to drive the rotor, so our input current goes down, and our magnet is experiencing no drag, so the rotor turns faster.