Efficiency of the different electric generators :

Hydraulic : 90%
Tidal : 88%
Gasified wood : 88%
Wood : 70%
Ethanol E85 : 46%
Solar : 40%
Diesel : 39%
Wind : 38%
Nuclear : 38%
Ethanol E10 : 38%
Coal : 37%
Petrol : 37%
Natural gas : 35%
Geo thermal : 35%
Fuel : 30%
Waste : 21%
Thermal solar : 12%

And the wind doesn't always blow, it's not daylight all the day. The gas, the coal, the nuclear, the diesel require : extraction, transport, refining, enrichment, stocking, buyring; the cost is exorbitant.

Whereas, the sea is always here, the waves, the stream, the low and high waters are always here.

So, it seems that the tidal engines would be the best choice to replace the old coal and nuclear power plants.