The debate between capacitors and batteries for storing electricity is a long one – the former can charge more quickly, store more energy and generally have a longer lifespan than batteries, but they don’t hold energy over time as well and, importantly, their voltage declines as they discharge. As a result, capacitors aren’t usually considered for long-term energy storage.
So I was surprised to see than a microgrid project for a small Maine island is using supercapacitors instead of batteries to store solar energy for the microgrid. They’re made by New York–based Kilowatt Labs, a power management company.
Story from ENSIA, a reporting project, is right here. It says they didn’t go with Li-ion batteries because they’re “not well suited for the island’s project for a number of reasons, including cost and anticipated lifetime.”
Otherwise the project seems like a pretty straightforward (but difficult to implement) as-clean-as-possible microgrid-for-island project.