You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Energy management for user’s thermal and power needs: A survey 
Chapter Title:  A.5. Hybrid renewable energy system 
1. Abstract of Cited Paper (BIB001):  Fast depleting fossil fuels and the growing awareness for environmental protection have led us to the energy crisis. Hence, efforts are being made by researchers to investigate new ways to extract energy from renewable sources. ‘Microgrids’ with Distributed Generators (DG) are being implemented with renewable energy systems. Optimization methods justify the cost of investment of a microgrid by enabling economic and reliable utilization of the resources. This paper strives to bring to light the concept of Hybrid Renewable Energy Systems (HRES) and state of art application of optimization tools and techniques to microgrids, integrating renewable energies. With an extensive literature survey on HRES, a framework of diverse objectives has been outlined for which optimization approaches were applied to empower the microgrid. A review of modelling and applications of renewable energy generation and storage sources is also presented. 
2. Abstract of Cited Paper (BIB002):  Abstract In this paper, a new methodology has been discussed on economical power management of a grid-connected CHP system which consists of a wind turbine, photovoltaic array, polymer exchange membrane fuel cell and an electrolyzer. Hence, the paper also attempts to present the thorough modeling of energy management of the hybrid system in the form of a nonlinear optimization problem; through which offline energy management is regarded to use the available options in order to determine the role of each generator in producing heat, power and hydrogen in the system under study. In addition to this, variable tariffs of daily exchange with local grid have been taken into account in different operation conditions so as to reach real utilization requirements. Based on these facts, choosing the most suitable model for each element of the hybrid system has been considered in regard to their dynamic behavior. The proposed hybrid system is to supply the electrical and thermal demands of renewable energy laboratory of Shahid Bahonar University of Kerman (SBUK). The economical energy management is comprehensively studied and surveyed in the form of various scenarios while the hybrid system is connected to the grid. 
3. Abstract of Cited Paper (BIB003):  Abstract Optimal operation of hybrid energy systems is a big challenge in power systems. Nowadays, in addition to the optimum performance of energy systems, their pollution issue has been a hot topic between researchers. In this paper, a multi-objective model is proposed for economic and environmental operation of a battery/fuel cell/photovoltaic (PV) hybrid energy system in the presence of demand response program (DRP). In the proposed paper, the first objective function is minimization of total cost of hybrid energy system. The second objective function is minimization of total CO 2 emission which is in conflict with the first objective function. So, a multi-objective optimization model is presented to model the hybrid system’s optimal and environmental performance problem with considering DRP. The proposed multi-objective model is solved by e-constraint method and then fuzzy satisfying technique is employed to select the best possible solution. Also, positive effects of DRP on the economic and environmental performance of hybrid system are analyzed. A mixed-integer linear program is used to simulate the proposed model and the obtained results are compared with weighted sum approach to show the effectiveness of proposed method.

Literature Review:
That of Hybrid Renewable Energy System (HRES) is a broad concept that refers to a group of RES, conventional distributed generation, and storage systems for load demand satisfaction BIB002 . The term HRES can indicate a few PV panels or a WT coupled with a battery, as well as a more complex system, as in BIB004 and  , where PVs, FCs, a back-up boiler, and both electrical and thermal storages are involved. In BIB001 , the proposed HRES includes only renewable sources, namely PV modules, a solar collector, a WT, and a biomass unit. Similarly, in BIB003 , the system is equipped with a small-scale hydrogen production-storage system, which includes an electrolyzer and a H 2 tank for a FC.