Electric water heaters are better at storing energy than a Tesla Powerwall

"storing excess wind and solar as heat... 30GWh equivalent 2 million Powerwalls... smart” heat pumps and electric resistance systems in homes across Australia. During off-peak hours, these water heaters can essentially store renewable energy in the form of heat and help balance electricity supply as renewable energy availability fluctuates... widespread adoption of electric-powered water heaters would not only lower emissions, but also save customers some $4 billion (USD) in energy bills"

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