It’s a bright summer day and solar photovoltaic systems across the country are generating lots of electricity. Some of this meets on-site demand, some is stored in charge batteries for use later in the day, whilst the rest is exported to the grid. These increasingly complex interactions between generation, demand and storage make forecasting and balancing the electricity system more challenging for National Grid Electricity System Operator (ESO).
One of the core responsibilities of the ESO is to keep the lights on by balancing supply and demand of electricity in real time – accurate forecasting and planning are critical to making this possible. However, increasing electricity generation from distributed, variable sources is making this more difficult, with storage that is embedded in the distribution networks playing more of a role. Installed capacity of storage is set to keep growing, driven by a combination of falling battery prices and expanding market opportunities.
Analysis carried out by the Carbon Trust revealed that national electricity demand could increase or decrease by up to 3.5GW due to uncoordinated operation of embedded storage. This is equivalent to 1.9 million UK homes unexpectedly and simultaneously switching on their kettles.
To the ESO, most distributed generation (like solar) and embedded storage assets are completely invisible, which makes it difficult to predict what impact they are having on transmission system demand. Recent work by Electralink carried out with Western Power Distribution (WPD) estimated that over 15,000 households connected to WPD’s network had Electric Vehicle (EV) charging points or PV panels installed, which were previously not known about, highlighting the potential materiality of these ‘invisible systems’.
Importance of understanding impacts of embedded storage
The Carbon Trust has been working with National Grid ESO to better understand the impact that embedded energy storage could have on transmission system demand and, consequently, on transmission system operation. The Network Innovation Allowance (NIA) funded project, System Impacts of Embedded Storage (SIES), focused on understanding and modelling different use cases to explore ways in which distribution network connected storage might operate and evaluate its potential impact on the transmission system out to 2030. The objective was to understand the behaviour of storage assets under different use cases, and to develop a structured method to analyse these behaviours over time and assess their materiality on the ESO.
The SIES project focused on exploring three main questions:
How will embedded storage be used in the future?
Twelve distinct use cases of how embedded storage might be used over the next 10 years were developed. These ranged from established operations such as providing ancillary services, to more nascent ones like renewable co-location and EV charging support. Scenarios tied to National Grid's Future Energy Scenarios (FES) were used to estimate the capacity of each use case deployed by 2030.
Table: SIES use cases investigated
How will these storage units behave?
Simulating storage behaviour is complex. It is driven by a multitude of regional and national market signals to maximise revenue and may be influenced by secondary purposes such as the need to provide resilience to a site during power outages. For example, storage co-located with a solar PV system on a business premises will look to charge when demand is low and supply is high, and then discharge when there is low or no solar PV output to reduce electricity imported from the grid. In this example, the battery will need to know solar PV output, demand profiles, the solar PV export tariff and the import tariff to work out the right time to charge and discharge to deliver savings to the customer. To determine these behaviours, the Carbon Trust used Plexos market simulation software to model the distinct charge and discharge characteristics of each use case.
How will this affect system operation and how material will this effect be?
Using Plexos data, an Excel-based tool was developed to calculate key metrics, which captured the impact of storage behaviour on transmission system demand. These included changes in peak demand, changes in minimum demand and the rate of change in demand. These metrics helped to evaluate the impact of storage across different future scenarios. Some of the key emerging findings are:
- A rise in EVs and corresponding use of storage to support vehicle charging, along with Vehicle to Grid (V2G) services could materially change transmission system demand and were revealed to have the biggest impact on system demand of all the use cases analysed.
- Wholesale price volatility is likely to be a key driver in storage charging and discharging times. The impact of this on transmission system demand is an increase in the rate of change in demand; more frequent sudden changes in demand resulting from wholesale price changes.
- Storage makes daily peaks and minimum demand points more volatile such that peaks could reduce and minimum demand could increase in certain scenarios. The changes to daily minimum demand were seen to be more significant due to storage.
What lies ahead?
The SIES project provides a basis for understanding how the integration of new technologies like electricity storage could change the way in which the electricity system might behave in the future. The project demonstrated the potential materiality of these changes and their impact on balancing the electricity system, highlighting the need for new transmission demand forecasting tools to better predict and manage these changes. National Grid ESO are currently assessing the outcomes of the project and are looking to integrate the Excel-based SIES tool into existing processes to aid with system planning.
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