A 'windmill' costs any amount. It pays for itself in x years. It falls apart in y years. If y>x then it is 'free', and indeed, 'makes money'. If y=2x, then we can have two, after y years. Two for the price of none. Other ratios give other times. We are in a far off fantasy fairyland, where Faraday existed, and maths holds true. We are on square 2, of the rice chessboard. Long before we reach square 64, everything is a 'windmill', and we have strayed into 'impractical'.
The letters page of any endearingly quaint 'newspaper' displays the sabre-wit of retired colonels, pointing out that sometimes the wind doesn't blow. Yet somewheres it always does. It may also be noticed that the 'Earth' is mostly sea, and that the sea moves - often as much as twice a day. This must remain a mystery to all contemporary Cnuts. There may be other such 'miracles'.
But can we really afford free energy? Financial experts, for a fee, will calculate the enormous inevitable 'subsidy' required. Energy experts, for a fee, will calculate the relatively greater cost, of free. And sado-masochistic Gaia martyrs, for Aztec lust over others, will preach we must pay. All as if the Sun were somehow metered, and Time cost money.
The cheaper the primary, the richer the world. Cheapest is free, which is infinite wealth. But of course the Sun is finite, and I only mean billions of years. With the economic causes of war, both domestic and 'neighbourly', removed, humans who like employment can have something socially useful to do, before the advent of 3D printed robots removes the idiocy of labour. Humans labour under delusion, and love's labours lost. Some have not even noticed they are 3D printed robots themselves.
Creationists of the non-Physics variety inform us that 'you can't get something from nothing'. Suitably chastised, we exercise caution in our conjecture:- Only if the Earth, Sun and moon existed, and I mean really, would all this be true.