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.
And skeptics are also saying that wind energy is an intermittent fuel that must always be backed up by a power source that can begin generating when the wind dies down, making it expensive to operate.