Optimal integrated energy storage solutions for the electrification of heat and transport at a domestic level

Abstract

The increase in renewable electricity generation, and the electrification of heat and transport are key elements for a successful energy transition to mitigate global warming impacts. However, they bring important challenges for the electricity network, such as i) increasing the overall demand of electricity, ii) changing the structure of energy flows within the networks, and iii) by increasing uncertainty of supply, caused by intermittent and unpredictable energy sources (e.g., wind and solar). Energy storage technologies can help address these challenges, by managing flows of electricity within the network, therefore adding flexibility between production and demand. A thorough review of the literature indicates that the most promising solution consists in behind-the-meter (BtM) integrated battery energy storage systems: smaller-scale batteries, connected directly at the demand level.

The choice of control method for the fleet of BtM batteries completely determines the impact on the grid. Although rich, the literature on this topic presents the following shortcomings: i) the scope is usually very narrow, typically restrained to a single dwelling, or to only optimising the system’s economics for the owner, regardless of the potential grid impacts; ii) most existing control methods are based on non-linear mathematical optimisations which make unrealistic assumptions, e.g., requiring a perfect forecast, or very high computational resources; iii) heat pumps (HPs) and electric vehicles (EVs) are very often considered as solutions to another existing problem (e.g., to reduce photovoltaic exports), but the risks of their own unmanaged implementation, and the mitigation role of residential storage are not addressed.

The research presented in this thesis assesses the role of residential integrated battery storage systems to provide grid support for the integration of distributed intermittent renewable generation, and the electrification of heat and transport. Algorithms are developed in order to operate the batteries based on existing and improved control methods, such as selfconsumption maximisation, taking advantage of cheaper night tariffs, or using the batteries’ state of charge as a reference. Moreover, a coordinated control method is developed, which allows cooperation between batteries to further improve the network’s operation. Performance indicators are defined and used to assess each control method regarding the achieved reduction in peaks, losses, overall demand, and reverse power flows. The control methods are implemented in a real-world low-voltage grid to analyse and compare their performance. Further, their impact on the reduction of the threat caused by HPs and EVs on the network is assessed. Finally, the economic viability is assessed for both customers and aggregator, for all of the different scenarios.

In this thesis, the importance of the control strategy choice is demonstrated, with the emphasise that current usual methods are suboptimal. Most BtM batteries are used in a self-consumption mode for photovoltaic installations, which can be detrimental to the grid. The other allowed to maintain the self-consumption feature, while reducing peaks and losses. We also show that although unmanaged EVs and HPs cause a serious risk on the network, smarter battery operation methods can bring indicators back to safe values, for example by reducing peaks by half, with only a 50% uptake. The viability of residential batteries is mostly conditioned by expensive initial costs, however, transferring a fraction of this investment to the aggregator, and applying incentivising tariffs was shown to allow profitability for customers. With a regular flat tariff, it was required for capacity costs to be lower than £200/kWh to ensure viability, while costs up to £600/kWh could be reached with tariffs incentivising peak-shaving. Finally, the revenues generated via energy arbitrage were enough to allow economic viability for the aggregator, when considering EVs and HPs. Including grid services could make it even easier for the aggregator to subsidise the installation of BtM batteries. Yet, regulatory measures should also be put in place in addition to business opportunities, particularly for unsupervised EV charging, which yielded good economic results, while being highly detrimental for the grid.

Date of Award	Nov 2021
Original language	English
Supervisor	Caterina Brandoni (Supervisor) & Aggelos Zacharopoulos (Supervisor)