Hi, looking to have installed two powerwall 2 shortly. The batteries will be charged from my existing 7.2 KW solar system. From what I can gather the powerwall has a Round trip efficiency of 90%, which I interpret to mean when I discharge power, I lose 5%, so if I discharge 5 kwh from the battery my house or grid only gets 4.75 kwh (5 kwh x .95%). Likewise, if I charge the battery with 5 kwh from my solar system, the battery receives 5% less or 4.75 kwh. Is this correct?
I also understand from various Powerwall users the powerwall consumes power itself of around 400 – 500 watts a day referred to as overhead. The power loss is the result of the batteries naturally losing charge over time plus the cost of communication to the outside world by the powerewall and the cost of running the active cooling/heating system internal to the powerwall. At 500 watts a day per powerwall means if the batteries are not recharged for 27 days then both powerwalls will be dead (27,000 watts / 1000 watts = 27 days). Is the 400-500 watts per powerwall daily loss correct?
If the Round trip costs and overhead cost are in the ball park from above then in a month’s time maintaining the powerwalls with enough power to keep both powerwalls charged before running the house per month is equal to
31.5 kwh = (30 x 1,000 watts (overhead for two powerwalls) x 1.05 (one way trip)). Daily cost would be 1,000 watts x 1.05) = 1.05 kwh and yearly cost would be equal to 383.25 kwh (1.05kwh x 365). Want know the numbers to see if I need to add more solar panels.
Thanks for your thoughts.
I also understand from various Powerwall users the powerwall consumes power itself of around 400 – 500 watts a day referred to as overhead. The power loss is the result of the batteries naturally losing charge over time plus the cost of communication to the outside world by the powerewall and the cost of running the active cooling/heating system internal to the powerwall. At 500 watts a day per powerwall means if the batteries are not recharged for 27 days then both powerwalls will be dead (27,000 watts / 1000 watts = 27 days). Is the 400-500 watts per powerwall daily loss correct?
If the Round trip costs and overhead cost are in the ball park from above then in a month’s time maintaining the powerwalls with enough power to keep both powerwalls charged before running the house per month is equal to
31.5 kwh = (30 x 1,000 watts (overhead for two powerwalls) x 1.05 (one way trip)). Daily cost would be 1,000 watts x 1.05) = 1.05 kwh and yearly cost would be equal to 383.25 kwh (1.05kwh x 365). Want know the numbers to see if I need to add more solar panels.
Thanks for your thoughts.
