There is a TL:DR version below. Fluffy story version:
The law that entropy always increases holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation. Sir Arthur Stanley Eddington, The Nature of the Physical World (1915), chapter 4
Well, son, Eddington was wrong about the Chandrasekhar Limit and thus about what cases ought to collapse in deepest humiliation. Someone did it! They made a working engine based on a technological equivalent of Maxwell's daemon.
You ought to see it! It's the darndest thing, on the one hand it must be the most fascinating device known to man, infinite energy, a gift from God himself, but on the other hand, the dullest, most unremarkable metal box around even before you go through what I did.
It has to be entirely sealed to work, and the only item of any interest at all is the electrical inverter on the front, and the signature purple light that Maxwell Corp puts on the front when it's turned on. There's no speed control and only the faintest of hums emanates from it.
The one I saw was about 1 cubic metre, a simple steel box, but it produces 1 kW of electricity, and will do until the world ends. I stayed in that room with it for 4 years, son. Your uncle and I never let that damned box out of our sight for 4 whole years. We lifted it on a forklift. It's the real deal.
After the 4 years, the Maxwell Corp chief engineer finally signed us up. He let us see the inside, what no one else has ever seen, nor ever will, as the seal tamper detection and self destruction unit is unbeatable. There's nothing nuclear and most of the space is empty. It scales up linearly, apparently; if you build one that takes up 20 cubes, it produces 20 kW, and costs $20 times as much. The lifespan's thought to be a century, with Maxwell Corp providing a service contract that you pay for up front.
Now, boy, you and I are different. I never could make a buck. But those big demonstration units that they have downtown, that are written off as a hoax: They aren't. In a few years, every man and his dog are going to want Maxwell Corp shares. Right now only a few crazies like your uncle and I want them. The only question I have is this:
Son, can they make a dollar? I know how much they cost to build. At what price do they stop selling as a real power source and become a curiosity?
PS Let's assume long term real interest rates of 5%.
1 m3 metal box; produces 1 kW of electricity for a century with perfect reliability. Hums faintly.
Produced and maintained by a monopoly company that keeps its secret jealously. Non reverse engineerable. Lump sum payment up front. Proven that it's not a scam.
Scales linearly in both cost and output.
Long term interest rates of 5%.
At what price do they stop selling as a real power source and become a curiosity?