The vast potential of ocean energies is of increasing interest. Harnessing marine currents driven by the tidal cycle have triggered the development of various power conversion systems. However, the comparably high levelized cost of electricity is still the main hindrance for a faster market penetration. The paper describes a novel strategy to decrease the cost: A number of small prefabricated turbines of low complexity form an arbitrary scalable array of turbines; a modular design of the key unit "turbine" allows an easy adaption to the tidal current velocity profile at a particular site; hydraulically optimized turbine blades ensure maximum annual energy production and minimum immersion depth. Results of the design efforts are a 4 m and a 6.3 m diameter horizontal axis free flow turbine with an identical drive train for a rated electrical power of 70 kW. Four turbines have been tested on a 30 m x 26 m trimaran placed for several months near the Falls of Lora in Scotland. The power yield fully confirmed the prediction. As an example, the annual electric energy production from such a turbine, placed in the Minas Passage area of the Bay of Fundy in Canada - an ideal site of harnessing tidal currents, is forecasted as 230 MWh. (C) 2019 Elsevier Ltd. All rights reserved.