Using Battery Storage for Peak Shaving and Frequency Regulation: Joint Optimization for Superlinear Gains

We consider using a battery storage system simultaneously for peak shaving and frequency regulation through a joint optimization framework which captures battery degradation, operational constraints and uncertainties in customer load and regulation signals. Under this framework, using real data we show the electricity bill of users can be reduced by up to 15\%. Furthermore, we demonstrate that the saving from joint optimization is often larger than the sum of the optimal savings when the battery is used for the two individual applications. A simple threshold real-time algorithm is proposed and achieves this super-linear gain. Compared to prior works that focused on using battery storage systems for single applications, our results suggest that batteries can achieve much larger economic benefits than previously thought if they jointly provide multiple services.Comment: To Appear in IEEE Transaction on Power System

Application of a simplified thermal-electric model of a sodium-nickel chloride battery energy storage system to a real case residential prosumer

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, sodium-nickel chloride technology seems to be an interesting alternative to lead-acid and lithium-ion batteries. To accurately investigate the operation of the NaNiCl2 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

Plug and Play DC-DC Converters for Smart DC Nanogrids with Advanced Control Ancillary Services

This paper gives a general view of the control possibilities for dc-dc converters in dc nanogrids. A widely adopted control method is the droop control, which is able to achieve proportional load sharing among multiple sources and to stabilize the voltage of the dc distribution bus. Based on the droop control, several advanced control functions can be implemented. For example, power-based droop controllers allow dc-dc converters to operate with power flow control or droop control, whether the hosting nanogrid is operating connected to a strong upstream grid or it is operating autonomously (i.e., islanded). Converters can also be equipped with various supporting functions. Functions that are expected to play a crucial role in nanogrids that fully embrace the plug-and-play paradigm are those aiming at the monitoring and tuning of the key performance indices of the control loops. On-line stability monitoring tools respond to this need, by continuously providing estimates of the stability margins of the loops of interest; self- tuning can be eventually achieved on the basis of the obtained estimates. These control solutions can significantly enhance the operation and the plug-and-play feature of dc nanogrids, even with a variable number of hosted converters. Experimental results are reported to show the performance of the control approaches

Optimizing production efficiencies of hot water units using building energy simulations : trade-off between Legionella pneumophila contamination risk and energy efficiency

The energy needed for domestic hot water represents an important share in the total energy use of well-insulated and airtight buildings. One of the main reasons for this high energy demand is that hot water is produced at temperatures above 60°C to mitigate the risk of contaminating the hot water system with Legionella pneumophila. However, this elevated temperature is not necessary for most domestic hot water applications, and has a negative effect on the efficiency of hot water production units. A simulation model has been developed which proposes an alternative to this constant 60°C by predicting the Legionella pneumophila concentration dynamically throughout the hot water system. Based on this knowledge, a hot water controller is added to the simulation model that sets a lower hot water comfort temperature in combination with heat shocks. In this paper, the simulation model is used to estimate the energy saving potential in a case study building, at the level of the heat production system by reaching higher production efficiencies. Three different production units, namely an electric boiler, heat pump and solar collector have been investigated. The controller is expected to become an alternative for the current, energy intensive, high temperature tap water heating systems

Chance-Constrained ADMM Approach for Decentralized Control of Distributed Energy Resources

Distribution systems are undergoing a dramatic transition from a passive circuit that routinely disseminates electric power among downstream nodes to the system with distributed energy resources. The distributed energy resources come in a variety of technologies and typically include photovoltaic (PV) arrays, thermostatically controlled loads, energy storage units. Often these resources are interfaced with the system via inverters that can adjust active and reactive power injections, thus supporting the operational performance of the system. This paper designs a control policy for such inverters using the local power flow measurements. The control actuates active and reactive power injections of the inverter-based distributed energy resources. This strategy is then incorporated into a chance-constrained, decentralized optimal power flow formulation to maintain voltage levels and power flows within their limits and to mitigate the volatility of (PV) resources

Enabling Micro-level Demand-Side Grid Flexiblity in Resource Constrained Environments

The increased penetration of uncertain and variable renewable energy presents various resource and operational electric grid challenges. Micro-level (household and small commercial) demand-side grid flexibility could be a cost-effective strategy to integrate high penetrations of wind and solar energy, but literature and field deployments exploring the necessary information and communication technologies (ICTs) are scant. This paper presents an exploratory framework for enabling information driven grid flexibility through the Internet of Things (IoT), and a proof-of-concept wireless sensor gateway (FlexBox) to collect the necessary parameters for adequately monitoring and actuating the micro-level demand-side. In the summer of 2015, thirty sensor gateways were deployed in the city of Managua (Nicaragua) to develop a baseline for a near future small-scale demand response pilot implementation. FlexBox field data has begun shedding light on relationships between ambient temperature and load energy consumption, load and building envelope energy efficiency challenges, latency communication network challenges, and opportunities to engage existing demand-side user behavioral patterns. Information driven grid flexibility strategies present great opportunity to develop new technologies, system architectures, and implementation approaches that can easily scale across regions, incomes, and levels of development

A Risky Climate for Southern African Hydro

This in-depth study of the hydrological risks to hydropower dams on the Zambezi River gives an early warning about what Southern Africa could be facing as it contemplates plans for more large hydropower dams in a time of climate change.Currently, 13,000 megawatts of new large-dam hydro is proposed for the Zambezi and its tributaries. The report finds that existing and proposed hydropower dams are not being properly evaluated for the risks from natural hydrological variability (which is extremely high in the Zambezi), much less the risks posed by climate change.Overall, Africa's fourth-largest river will experience worse droughts and more extreme floods. Dams being proposed and built now will be negatively affected, yet energy planning in the basin is not taking serious steps to address these huge hydrological uncertainties. The result could be dams that are uneconomic, disruptive to the energy sector, and possibly even dangerous.The report recommends a series of steps to address the coming storm of hydrological changes, including changes to how dams are planned and operated