A new UK study has claimed there is currently “no economic benefit” from integrating electrical energy storage with solar PV systems in homes— and battery degradation could mean “significant” losses for homeowners.
According to the study by researchers at the universities of Warwick, Birmingham and the Centre of Excellence for Low Carbon and Fuel Cell Technologies, rooftop PV systems integrated with lithium-ion battery storage “are a promising route for the decarbonisation of the UK’s power sector”.
However, the study said when the cost of battery degradation is included, “the annual loss to the homeowner is significant— and the economic viability of solar home systems with electricity storage using lithium-ion batteries is totally diminished”.
For the study, a commercially-available 4kW solar system was installed in a three-bedroomed home in Leicestershire alongside a 2kWh battery with an 80% depth of discharge. A total of 45 3Ah 18650-type cells were used.
The annual electricity consumption of the house was 4,142kWh for 2016. Total electricity generated by the PV panels for the year was 3,691kWh and electricity exported to the grid was 2,771kWh. “Therefore, only 33% of the PV generated electricity was consumed within the home and 2,344kWh was exported,” the study said.
A comprehensive battery degradation model was developed for the study “based on long-term ageing data collected from more than 50 long-term degradation experiments on commercial lithium-ion batteries”. The model was validated with six “operationally diverse annual usage cycles”.
According to the study, the estimated battery degradation over five years indicated battery resistance almost doubled, while at the same time some 20% of the initial battery capacity was lost. The study said this would lead to a “tangible loss” in electricity generation from the solar panels, which in turn would hit export revenue.
This battery degradation could cost homeowners GBP400 ($517) in “effective profit” in the first year, the study claimed, with extra losses over the following four years of diminishing amounts before the system would require replacement.
The study said with battery storage, “the sum of utility savings and electricity export profits is GBP727 ($939), meaning the battery costs the home owner GBP1.00 ($1.29) per annum”.
For consumers, the financial benefits of lower utility costs and the potential of a financial return by providing grid services “is a strong incentive to invest in PV-battery systems”, the study said. However, the authors called for “a robust analysis of costs versus benefits” in assessing the potential future role of energy storage.
“Consumers should be aware of these ‘hidden’ costs, as it will have a material impact on how their batteries are most effectively used,” the authors added.
“Our results imply that providing ancillary services to the grid, with a lower depth of discharge, could lead to less battery degradation and extend the useful life of the device. To balance the full costs of battery ownership and operation will need more sophisticated control systems and a means of accumulating the split benefits of energy storage that would accrue to the grid, distribution network and suppliers.”
The study is online.
http://www.sciencedirect.com/science/article/pii/S030626191731190X