The use of renewable energy sources is increasing due to national and international regulations. Such energy sources are less predictable than most of the classical energy production systems, like coal and nuclear power plants. This causes a challenge for balancing the electricity system. A possibility to meet this challenge is to use the flexibility in electricity demand for balancing with unpredictable electricity supply. In this paper, we introduce a model for flexibility in electricity demand and supply and give some examples of flexibility models for existing devices. In addition, we describe the business advantages for using flexibility and some pricing mechanisms that provide financial incentives for using flexibility by the consumer and the balance responsible party in the grid.