PORTLAND — A Maine tidal power company says its prototype underwater power system has aced its tests, paving the way for a commercial unit to be connected to the power grid by year’s end.

Ocean Renewable Power Co. says the prototype produced grid-compatible electricity and appeared to cause no harm to marine life. The company plans to install a larger unit off eastern Maine that’ll deliver power to the Bangor Hydro Electric Co. grid.

Another tidal power company, New York-based Verdant Power, plans this year to connect to the grid. Both require federal approval.

Both projects are relatively modest. Ocean Renewable’s 150-kilowatt unit will power up to 60 homes, for example. But Ocean Renewable President Chris Sauer says tidal power can become competitive with other renewable power sources within five years.