Paving the Way to Smart Micro Energy Grid:Concepts,Design Principles,and Engineering Practices

The interconnection between initially independent energy infrastructures offers additional system flexibility and efficiency.The integration at distribution level simplifies the implementation of the integrated energy system functionalities.This paper proposes concepts and design principles of a smart micro energy grid(MEG)for accommodating micro-grids,distributed poly-generation systems,energy storage facilities,and associated energy distribution infrastructures.The energy management system is responsible for the smart operation of the MEG while supporting multiple criteria,such as safety,economy,and environmental protection.To realize the vision of the smart MEG,an engineering game theory based energy management system with self-approaching-optimum capability is investigated.Based on the proposed concepts,design principles,and energy management system,this paper presents a prototype of China’s first conceptual solar-based smart MEG,established in Qinghai University.

Liquid Air Energy Storage for Decentralized Micro Energy Networks with Combined Cooling,Heating,Hot Water and Power Supply

Liquid air energy storage(LAES)has been regarded as a large-scale electrical storage technology.In this paper,we first investigate the performance of the current LAES(termed as a baseline LAES)over a far wider range of charging pressure(1 to 21 MPa).Our analyses show that the baseline LAES could achieve an electrical round trip efficiency(e RTE)above 60%at a high charging pressure of 19 MPa.The baseline LAES,however,produces a large amount of excess heat particularly at low charging pressures with the maximum occurred at~1 MPa.Hence,the performance of the baseline LAES,especially at low charging pressures,is underestimated by only considering electrical energy in all the previous research.The performance of the baseline LAES with excess heat is then evaluated which gives a high e RTE even at lower charging pressures;the local maximum of 62%is achieved at~4 MPa.As a result of the above,a hybrid LAES system is proposed to provide cooling,heating,hot water and power.To evaluate the performance of the hybrid LAES system,three performance indicators are considered:nominal-electrical round trip efficiency(ne RTE),primary energy savings and avoided carbon dioxide emissions.Our results show that the hybrid LAES can achieve a high ne RTE between 52%and 76%,with the maximum at~5 MPa.For a given size of hybrid LAES(1 MW×8 h),the primary energy savings and avoided carbon dioxide emissions are up to 12.1 MWh and 2.3 ton,respectively.These new findings suggest,for the first time,that small-scale LAES systems could be best operated at lower charging pressures and the technologies have a great potential for applications in local decentralized micro energy networks.