Combining solar thermal systems and a gas boiler for the production of domestic hot water is a rather widespread solution in Italy. It is a sustainable and economically beneficial choice, as it enables customers to make significant savings in their energy bills. Moreover, the existence of the gas boiler means that the customer is better equipped to deal with an emergency or an unusual requirement. For example, if an extraordinary amount of hot water is needed at night, a gas boiler can ensure its availability; in short, having both allows customers to feel secure and worry-free.