We provide this calculator for Czech customers. The return on investment value strongly depends on local legal and tariff regulations. These values vary from country to country and still evolve as the PV-branch evolves. We are unable to provide a generous ROI-calculator for all. WATTrouter devices considerably increase the self-consumption ratio and decrease the energy flows through main electricity meter in both directions. According to your local regulations and the informations on this web site you should be able to consider whether WATTrouter devices are the best choice for you.