Because geothermal produces consistent, base-load power--it doesn't depend on the wind blowing or the sun shining--utilities will pay up to three times more for geothermal electricity than for electricity from an intermittentsource, like wind.
Tidal turbines can be installed closer to shore than wave energy equipment, and thanks to the regularity of the tides, tidal power offers a more stable renewable energy source than, say, intermittent wind or solar.