Renewable Energy Resources (RES) play a critical role in electrical systems due to continuous demand increases. As a significant application of RES, modern electrical networks are very complex because of communication tools, smart meters, and real-time data processing. These smart tools and ongoing communication generate a high-speed tsunami of data that require novel methods for better performance and decision-making. Even though big data has become an important and useful method for facing the challenges of large volume data, it is a double-edged sword. It brings certain risks to the data as well as the ability of convenience to the network. As such, data involved in these electrical systems become major targets of attacks. As a result, cybersecurity becomes a critical issue. In this chapter, we first provide a brief introduction to using RES in power systems and big data. Then, different aspects of security are summarized in the same context while RES is specifically addressed. Next, we introduce big data and finally, a relation between big data and security aspect of using RES is discussed.