VoltStorage (HAX 09) has raised $6.4M in funding to further develop its vanadium redox-flow technology for home energy storage — a non-explosive alternative to lithium-ion batteries that doesn’t use scarce rare earth metals. The Munich-based startup has developed a stationary battery about the size of a small fridge to store solar energy and power a house for 20 years.

While lithium-ion batteries are still the most popular power source for mobile phones, laptops, and cars, they require materials in short supply like lithium and cobalt, mined at environmental and ethical costs. In contrast, vanadium redox-flow batteries offer more longevity, safety, and affordability—a strong alternative for stationary home energy storage use.

“Millions of houses now have solar panels on the roof, so it makes sense to have a battery that can really make use of the energy these generate,” VoltStorage co-founder and CTO Michael Peither told Sifted.