Most approaches for providing incentives for resource sharing on energy-constrained mobile devices rely on some kind of payments, secured by means of public key cryptography. Checking the validity of such payments creates substantial energy overhead itself. We evaluate the energy overhead of an incentive system based on hash coins. Therefor we created a prototype of a hash coin based incentive system in a wireless ad hoc network and conducted extensive energy measurements. The results are compared to solutions based on public key cryptography. Using the knowledge about the energy consumption of these approaches helps us to chose the best suited incentive system and reasonable system parameters for an incentive system in a wireless ad hoc network.