Application of a Simplified Thermal-Electric Model of a Sodium-Nickel Chloride Battery Energy Storage System to a Real Case Residential Prosumer

Fabio Bignucolo, Massimiliano Coppo, Giorgio Crugnola, Andrea Savio
2017 Energies  
Recently, power system customers have changed the way they interact with public networks, playing a more and more active role. End-users first installed local small-size generating units, and now they are being equipped with storage devices to increase the self-consumption rate. By suitably managing local resources, the provision of ancillary services and aggregations among several end-users are expected evolutions in the near future. In the upcoming market of household-sized storage devices,
more » ... storage devices, sodium-nickel chloride technology seems to be an interesting alternative to lead-acid and lithium-ion batteries. To accurately investigate the operation of the NaNiCl 2 battery system at the residential level, a suitable thermoelectric model has been developed by the authors, starting from the results of laboratory tests. The behavior of the battery internal temperature has been characterized. Then, the designed model has been used to evaluate the economic profitability in installing a storage system in the case that end-users are already equipped with a photovoltaic unit. To obtain realistic results, real field measurements of customer consumption and solar radiation have been considered. A concrete interest in adopting the sodium-nickel chloride technology at the residential level is confirmed, taking into account the achievable benefits in terms of economic income, back-up supply, and increased indifference to the evolution of the electricity market. the unit income obtainable by injecting energy into the grid. Since a large reduction of net-metering advantages is expected in the near future, the maximization of the self-consumption rate of the generated energy is a key point to increase the economic potential of PV. In Reference [3], storage units coupled with PV systems are analyzed in terms of profitability to make PV economically attractive even in the absence of regulatory support, taking into account the different components of costs and revenues. Electrochemical battery energy storage systems (BESSes) are a promising solution for the maximization of customers' self-consumption, since they are nowadays available on the market for residential use, and their cost is expected to significantly decrease thanks to the spread of several technologies integrating storage devices (e.g., electric vehicles). The aim of today's batteries, i.e., the self-consumption of the PV production, is achieved through the energy-on-demand function. In fact, if no communication systems with the distribution system operator (DSO) are available, different strategies to combine local generators and storage devices have been addressed. For instance, in Reference [4], a control strategy is presented for a residential BESS able to maximize the self-consumption and to minimize the curtailment losses caused by feed-in thresholds without need of generation/load forecasts. Results show that the increase of self-consumption is desirable from a network management perspective, given the reduction in the curtailment losses. Furthermore, the authors point out that the aggregation of several local units is preferable in comparison with district storage. In Reference [5], a comparison among a few battery discharge strategies for a grid connected building is presented, focusing on the self-consumption maximization, the time-shift function based on the predicted load, and the economic income. Neural networks are employed to set the sizing equations of the storage units, then the proposed discharge algorithms aim either at pursuing a network global optimum or the maximum user income. Analogously, in Reference [6], the authors described the design of a lithium-ion storage system to increase the matching between generation and consumption in a residential zero-energy building, resulting in a reduction of the power exchange with the grid by more than 75% and a decrease in the energy bill of 87%. Nevertheless, several smart pricing models have been investigated. It seems to be an opportunity for DSOs to involve active end-users (integrating local generation and BESSes) in the electric system management, e.g., in the network power flow reduction [7, 8] or in the voltage regulation [9]. In Reference [7], active demand is coupled with storage, improving the self-consumption in order to study the relation between annual energy flows and the storage size. Regarding innovation in the energy market, an alternative pricing strategy is proposed to incentivize the energy independency of end-users from the grid in Reference [8], whereas a network controller based on local price signals is presented in Reference [9]. Many research works are based on the demand-side management (DSM) approach, in which customers are economically remunerated for adjusting two-way power flow at their point of delivery (PoD), either in terms of absorption or injection, to contribute to congestion reduction when the distribution network is under stress. In References [10,11], some of the most common DSM approaches available in literature are surveyed to compare individual vs. cooperative management, deterministic vs. stochastic methods, and day-ahead vs. real-time operation. In Reference [12] , an optimized home energy management system facilitating the RESes exploitation and the participation to DSM activities is implemented considering an optimized scheduling of the home appliances according with a varying energy price. The simultaneous optimization of both electric and gas distribution networks through DSM is investigated in Reference [13], showing a reduction of the energy bill by 20%. Generally, the DSM is achieved through both the optimized management of storage units (with scheduling procedures and real-time corrections [14] ) and the classification of loads depending on their supply priority [15] . In Reference [14], the energy production, including the BESS management, is scheduled one day ahead, following which a real-time control scheme tracks the expected profile to minimize the power curtailment. A fast-balancing service for the power system is obtained through the management of controllable loads (either passive or active) in Reference [15] . The end-user satisfaction (i.e., the reduction of the inconvenience due to the scheduled loads operation) Energies 2017, 10, 1497 3 of 29 is additionally considered in the DSM scheme proposed in Reference [16], elaborating an optimal compromise between user-budget and satisfaction, whereas these factors are used in a multi-objective optimization in Reference [17] to reduce the energy exchange with the grid and, eventually, the bill cost. At the same time, a further income can be obtained by allowing distributed resources to participate to the ancillary services market, such as the network voltage regulation and the containment of voltage unbalances. In Reference [18] , a study about the optimal sizing, siting, and managing of storage units is presented to investigate their impact on the ancillary services provision. A voltage unbalance mitigation strategy is proposed for three-phase inverters in Reference [19], aiming at the compensation of negative and zero sequence voltage components in LV systems, whereas the same approach is extended to RESes connected to medium voltage (MV) networks in Reference [20] . The exploitation of BESSes has been proposed for power quality improvement. Control schemes for reducing the harmonic distortion, both referring to a single customer equipped with a PV plant [21] and aggregating the storage contributions in a smart community [22] , are discussed in the literature. The use of RESes in the dynamic grid support is highlighted in Reference [23] according to the most recent standard requirements, whereas the BESS role in stand-alone systems with wind generation is investigated in Reference [24] . Storage units are included in the management strategy of an islanded network in Reference [25] . Nevertheless, the increasing diffusion of storage systems, although compliant with European standards and national grid codes (e.g., [26, 27] ), may lead to safety issues. In the case of faults, portions of the LV network may be maintained energized by dispersed generators and BESSes, since their stabilizing contributions mask voltage and frequency perturbations, resulting in the failure of present passive anti-islanding protections [28, 29] . An increased attention on storage systems has been recorded in the last couple of years. New norms and standards currently regulate the procedures/rules for installing and operating BESSes, both in LV distribution systems [26, 27] and in MV networks (e.g., [30, 31] ). The main drivers of this possible market evolution are linked to:
doi:10.3390/en10101497 fatcat:dgxvf3g6ifdurcmgaprapg5gma