So... NRG Home $0.00 per kWh from 9PM to 6 AM. If I use 1500 kWh/month How long of using this + a power wall, until the power wall pays for it's self?! It's math time people! you know, that thing your teacher in 9th grade said would happen, and for the past 30 years... hasn't?! Well it's here now! 1500 kWh / 30 days = I need to suck down 50 kWh/day. So we will need a power wall of at least 50 kWh. Let's assume a 80% in efficiency, and 80% out? is that a good approx? So I need 63 kWhs of Power wall at 7kWh each = 9 power walls. 9 power walls at $3,000 each = $27,000 Hookup cost: $5,000 (estimate?) Total install cost = $32,000 Power cost now: $0.11 kWh Power costs at $0.00 (let's just pretend I can pull this off) and ignore power IN (charging) efficiency, since the cost is $0 I would need to consume 290,909 kWh for this system to pay for it's self. Or, roughly pay for it's self in: 193 months / 16 years. Or way after it doesn't work any more because it's been used daily for 16 years. So... yea, Math means... that ain't gonna happen.