Techno-economic and environmental analysis of second-life batteries compared to new in revenue-stacking network-constrained solar PV farm

Abstract

Introduction: a mathematical model has been developed to investigate the use of second-life electric vehicle batteries to expand a solar photovoltaic (PV) farm’s generation capacity beyond its grid export limit. While second-life batteries are lower-cost than new, they must be replaced more frequently. And while they displace the embodied emissions of manufacturing new batteries, their lower efficiency causes more energy conversion losses. A quantification of the environmental and financial net benefits of second-life batteries was sought.

Methods: the modelled system trades electricity on the day-ahead market during the hours 07:00-23:00, and provides a frequency regulation service 23:00-07:00. Linear programming is used to schedule electricity export and battery charge/discharge to maximise day-ahead revenue, given forecasts of PV generation and electricity prices, leaving enough charge stored each evening to fulfil its frequency regulation obligation. The Net Present Value (NPV) and carbon emissions savings are calculated for second-life batteries compared to new batteries.

Results: figure 1 shows the export/charge schedule for an example day with a new battery. Figure 2 shows how the schedule adapts itself for a second-life battery. The whole-life (25-year) NPV and emissions savings in each case do not differ significantly relative to the model uncertainties.

No existing work studies in as much detail the relationship between financial and environmental benefits of a revenue-stacking PV-and-battery farm using second-life batteries. This is important because financial and environmental objectives must be aligned if decarbonisation of electricity networks is to be achieved. As the case for second-life batteries is marginal, further study is needed before advocating or ruling out the concept.

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Identifiers

ORCID for Susan Isaya Sun: orcid.org/0000-0003-1976-269X

ORCID for Mahdi Kiaee: orcid.org/0000-0002-4169-7188

ORCID for Andrew Chipperfield: orcid.org/0000-0002-3026-9890

ORCID for Richard Wills: orcid.org/0000-0002-4805-7589

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