We run water down from a tank, onto a water turbine – which turns and generates power. Around 20kW.
But the pump to return the water only takes 5 W. So we can supply our house, and still sell around 10 kW to the grid. 30,000 UK pounds a year from the national grid.
We have used Academes' idea of mechanical advantage. We drive the turbine along a 1m lever we return the water with an effective radius of 2cm.
We have actually extracted the energy wasted by the Earth's gravitational field. So as we pump the water back, we consume 0.05% of the generated power.
And it was built in the 18th century – just without the return water pump. Once it is pointed out it is so obvious. Which is why perpetual motion fans have been fascinated by water turbines for 2 centuries.
I have a master's degree, and I inly thought of it after I saw a perpetual motion drawing.
We recycle the water, and take the free energy. The production of helium and oxygen gases as we do Molecular Nuclear Fusion on the water is largely unimportant.
The major cost is the turbine. Which will pay back in 2 weeks. Then no utility bill ever – the grid sends you money.