But Australian company Lavo has built a rather spunky (if chunky) cabinet that can sit on the side of your house and store your excess energy as hydrogen.
The Lavo Green Energy Storage System measures 1,680 x 1,240 x 400 mm (66 x 49 x 15.7 inches) and weighs a meaty 324 kg (714 lb), making it very unlikely to be pocketed by a thief. You connect it to your solar inverter (it has to be a hybrid one) and the mains water (through a purification unit), and sit back as it uses excess energy to electrolyze the water, releasing oxygen and storing the hydrogen in a patented metal hydride "sponge" at a pressure of 30 bar, or 435 psi.
It stores some 40 kilowatt-hours worth of energy, three times as much as Tesla's current Powerwall 2 and enough to run an average home for two days. And when that energy is needed, it uses a fuel cell to deliver energy into the home, adding a small 5-kWh lithium buffer battery for instantaneous response. There's Wi-Fi connectivity, and a phone app for monitoring and control, and businesses with higher power needs can run several in parallel to form an "intelligent virtual power plant."
At AU$34,750 (US$26,900), it costs more than what you'd pay for three Powerwalls in Australia, but not by a huge amount, and that price is set to drop to AU$29,450 (US$22,800) in the last quarter of 2022, by which point Lavo says it'll be available internationally.