There is a bit of confusion here between force and energy. Gravity is not energy, it is a force. Energy is released when objects move nearer to each other, or slow down.
RickyB's explanation is good.
The water moved by the tides is very heavy, but very very small compared with the mass of the solar system. Some of the energy in the earth-moon-sun gravitational system is converted from their movement to movement of water. The earth, moon and sun all slow down a tiny bit each tide.
Eventually as RickyB says it does all add up. It is tides in the ocean and rock crusts which have stopped the moon rotating more than once a month, so it now turns the same side to the earth all the time. Likewise the earth used to rotate faster, giving more, shorter days in the year.