The investigation of the reliability, effectiveness, and impactdof Distributed Energy Resources (DERs) on smart grid ap- plications (demand-response, real time price, etc.) requires an integrated evaluation framework. In this paper, we design an integrated simulation platform and demonstrate its use via investigating the impact of DERs on smart grid applica- tions (demand-response and energy market) under various adverse conditions, along with network architectures. Using the standard IEEE bus system, we systematically evaluate the integration of DERs and the performance impact on de- mand response and energy markets with respect to system management, uncertainties and different network architec- tures. Our experimental results demonstrate the ability of designed co-simulation tool to evaluate the performance of DERs and system management and networking techniques. Our results are comprehensive, providing a concise represen- tation of DER performance for the design and implementa- tion of real smart grid system.