10-20 kWh capacity minimum (ideal would be at least 2 times thesize of the tesla battery), Also depends on where you are located ,how much driving per day you do . number of hours of sunshine (usable sunshine) per day you get. The 2100w solar system is too small to keep up with the charging. 2100 x 5hours max production is just 10 kW a 21000w system is 105 kW
- How large would the intermediary battery need to be?
- What voltage should a system like this run on?
- Do I need any other parts other than solar controller, battery, inverter?
- Is there any off the shelf system that could handle this, either partially or completely (and that is not outrageously overpowered or expensive!)
How often you want to charge the car ? The assumption is that you would charge during the day for a solar charge system to work. But if you up the size of the battery bank to 160 kWh storage capacity and only use 20 kW per day that gives you 7-8 charges you could use the car during the day charge it at night.
51.2-51.8v 16s LiFePO⁴ 14s NMC, any of the 3.6-3.8v nominal lithium cells. these voltages work with most 48v lead acid based inverters
There are inverters that take higher voltages.
A bms is required for all lithium based ESS
Tesla powerwall, LG RESU, There are many most have a high price. DIY for large systems one of the best resources around for DIY powerwalls is Second Life Storage & Solar
later floyd