Financial and environmental life cycle assessment of domestic PV-battery systems

Abstract

How green is a home battery? With the rapid development of lithium-ion batteries in portable electronics and electric vehicles, they quickly found a use in the home, storing excess electricity generated by solar PV panels. Some literature estimates suggest that this is not beneficial to the environment, considering the energy lost in charging and discharging, and the embodied emissions of battery manufacture. But when the time-varying nature of grid CO2 emissions intensity is accounted for, possibilities are opened up for scheduling battery operation more intelligently. Furthermore, second-life electric vehicle batteries are being researched as a potentially inexpensive, low-CO2 source of batteries compared to manufacturing anew.

This project comprises the development of a model that takes real measured PV and load data as input, and calculates the time-series operation of the battery, accounting for the impacts of degradation on both its lifetime and short-term performance. A novel Emissions Arbitrage Algorithm was developed for scheduling the battery operation. Additionally, a novel method of predicting the evolution of second-life battery price decades into the future was developed to account for second-life battery replacement costs over the system lifetime.

It was found that for a grid-connected urban home, a PV-only system strikes the best balance between financial and environmental sustainability. While adding a new battery running the standard Greedy algorithm becomes more profitable by 2030, this option tends to reduce the environmental benefit. And while a second-life battery is significantly better for the environment than a new one in terms of metals depletion, freshwater ecotoxicity, freshwater eutrophication, human toxicity, water depletion and ozone depletion, it cannot beat a PV-only system except in terms of CO2 emissions and fossil fuel depletion, and requires the Emissions Arbitrage Algorithm to do so.

Contrary to much of the literature on second-life battery usage, the financial net costs are similar to or greater than using new batteries. No configuration could be found that simultaneously maximised both financial and environmental sustainability. This does not preclude its existence, especially in other contexts and applications, and with more work on designing market structures that incentivise environmental sustainability. This work also highlights the need for improvements in material selection and recycling of PV, batteries and power electronics, especially to mitigate the impacts of metals depletion

More information

Identifiers

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

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

Catalogue record

Export record