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> We need energy storage in the terawatts... we are close to half a megawatt.

Does she mean megawatt-hours? Or the rate at which energy can be transferred into their tanks? Power = energy / time, and watts are a unit of power, not energy.

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If I had to guess she's talking in terms of each individual tank/unit set-up. So, one tank has a capacity or power rating of 500kW (capacity in the sense of the way a utility refers to size/ability of generating units). This link[1] possibly covers some of the confusing terminology here, and why it is that way.

EDIT: Scrolling to the bottom of their homepage[2] explains it, their system components are independent of each other.

[1] https://gigaom.com/2012/01/04/how-to-compare-energy-storage-...

[2] http://www.lightsail.com/

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