No, not quite. There are running cost. But they are a fraction of the costs of just using gas, electric or oil. A small amount of electricity is used to run the system but all of the energy used to heat your water is free.
Where's The Free Energy From?
The free energy used to heat your water is extracted from everthing that comes into conatc with the panel. Air, sunlight, rain even snow!
How Does It Work?
In the same way as your freezer. If you took some slightly soft ice cream, which would be around -5࠷ and put it in your freezer; your freezer will extract heat from that until its temperature was down to -18࠷. That extracted enrgy is sent out of the back of your freezer as heat.
With a thermodynamic panel, the energy is extracted from environment around the panel and sent to your hot water system to heat the water.
Just Hot Water?
No, Thermodynamic panels are modular and can be used for to provide energy for hot water, hot water and heating or even to heat indoor or outdoor swimming pools, with the potential to save thousands of pounds per year in energy costs.