"but no matter how they are designed..."

For any form of energy to become a primary source of power, additional technology is required. It doesn’t matter if we are talking about sunlight from above or hydrocarbons buried deep in the earth,or tidal forces, converting an energy source into useful power always requires capital-intensive hardware designed, manufactured, and deployed using energy — unless it is built with pixie dust, hopes, and prayers. Right now we build our energy conversion machines using fossil fuels.