This article presents an approach for the participation of datacenters and supercomputing facilities in smart electricity markets. This is a relevant problem in modern smart grid systems to implement demand response strategies for a better use of resources to guarantee energy efficiency. The proposed approach includes a datacenter model based on empirical information to determine the power consumption of CPU-intensive and memory-intensive tasks. A negotiation approach between the datacenter and its tenants and a heuristic planning method for energy reduction optimization are proposed. The experimental evaluation is performed over realistic problem instances modeling the operation of the National Supercomputing Center in Uruguay. The obtained results indicate that the proposed approach is effective to provide appropriate demand response actions according to monetary incentives. Accurate results are reported for realistic problem instances and different types of clients.