The Tesla Powerwall is a 14 kWh static battery, using essentially the same technology as Tesla car batteries. It can charge and discharge at a rate of 5 kW. Therefore, if the sun is shining brightly, and our solar panels are capturing their full 10 kW capacity, it will take just under 2.5 hours to fill the Powerwall from completely empty to 100%.
We also use the Tesla app to set the Powerwall to charge between 00:30 and 04:30 every night, to take advantage of the 5p per kW electricity available with Octopus Go tariff
What typically happens is that the Powerwall will intelligently adjust its charge rate to the lowest possible required for the 4 hour Octopus Go cheap period and fill to 100% . It will then gradually discharge to meet the domestic electricity load throughout the day. It will be topped up by solar during the sunny part of the day. This will then generally ‘see it through’ the evening and night time requirement from the house so that our entire daily domestic consumption costs only 70p, by using the Powerwall to store 14 kWh of the Octopus Go cheap grid electricity, plus the solar ‘top up’, which costs 0p.
On summer days, there will be more solar energy stored in the Powerwall. This coupled with the shorter evenings, means that it will still be part full at 00:30, and so require less grid energy to reach 100% full by 04:30.