Construction costs, operating costs, maintenance costs, lifetime. Wind power and wave power and sun power might be free, but the thing you use to catch the power sure isn’t free.
True... there are those costs... but the operating and maintenance costs are generally significantly lower than alternatives....
I still say research into this is well worth the money... we’ve had more problems and far more cost in $$$ and lives in developing other sources of power.
BTW, the test was supposed to have helped determine potential cost reductions. I don’t think skimping on the bilge pump is a good idea... :P
As a side note, the cost of this prototype wasn’t much different than the cost of many automotive prototypes. Standard cost for a prototype car is generally placed at $500,000-1,000,000 or more. Yet they sell for $15,000-20,000 later.... In other words, using prototype costs doesn’t give us the best idea of what these things would cost IF they were put to use....