I wouldn’t patent it first. It’s too big. The money to be made off this thing depends on being first to get it into production and start selling units. People will bust, ignore, circumvent or otherwise bypass your patent if everyone’s starting from the same place. Patent it just before you start shipping, and count on your head start more than on your lawyers.
You’ll need investors, and a manufacturing plant with a LOT of spare capacity up and ready, before you let on how it works. (Which you’ll have to do, to patent it.) So you need a public demonstration that maintains your secret, and for safety’s sake, your anonymity as well.
So. A few classified ads appear that a certain brewha has invented a free energy device, and on April 1st he will begin to boil the sea with a constant 100kW at such-and-such a location. For a month. The device will be a sealed “black box” which will destroy itself if tampered with or stolen. The guys supervising the demo do not how the thing works, and do not know the identity of brewha or how to contact him.
A truck appears on a pier. A sealed metal box in the back, about a cubic yard in volume, is suspended in the air from a frame by woven flat strops. Two arc-welder cables snake into the water, where they connect to an industrial heating element. A screen of chickenwire in the sea prevents anyone or anything approaching the hot water zone.
The sea boils. And boils. And boils. Local press turn up, and national press looking for silly April 1st stories. Engineers turn up, and examine the box. No obvious inlets or outlets, no noise. A clamp meter confirms 200 amperes in the cables, at 500 volts.
People wonder how the trick is done. The best bet is a sealed fuel cell. A week goes by. The sea still boils. By now, the thing has put out as much energy as burning 2800lb of gasoline at 100% efficiency. It is not a sealed fuel cell.
People look more closely. Is power being sent in through the strops? Is induction being used? Geiger counters are brought into play, as are infra-red cameras. Smoke is used to see if the box has hidden intakes and exhausts. People check for microwave beams. The four guys on rotating watch who are looking after the thing tell all they know, which is not a lot. They were contacted and paid anonymously. PIs and intellignence services are put into action. Governments wonder whether to seize the box and see if the bomb disposal people can get into it without blowing it. The bomb disposal people advise them that a really carefully booby-trapped device is a very poor bet.
A month goes by. The guys supervising the demo pack it up and drive it away to a pick-up site, where a helicopter removes it to whereabouts unknown.
At this point, you shouldn’t have too much trouble attracting investors. Choose wisely and be VERY careful!
Course, if it IS a hoax, you could still make a fair bit of money that month on the markets…