PW = Powerwall (can be for any version)
PW2 = Powerwall 2
PTO = Permission to Operate, usually required from utility to operate solar and/or battery backup
Note, as an energy forum, there are a lot of acronyms, but some of the most common ones are below:
AC = Alternating Current, most households and transmission lines use AC
DC = Direct Current, Solar panels produce DC and batteries store DC
W = Watt, the SI unit of power, equivalent to one joule per second
kW = Kilowatt, 1000 Watts
kWh = Kilowatt Hour, 1000 Watts used over an hour of time
MWh = Megawatt Hour, 1000 kWh. For reference, Tesla's PW2 US Warranty has an operating limit of 37.8 MWh for AC output based on a particular application of the PW2.
PV panel aka Module - a single physical solar panel.
"String" - a series of modules hook together in series. This boosts voltage but not amerage. A PV system can have multiple strings.
MC4 - Probably the most common type of quick connector to chain strings together. The Male is positive, the Female is negative. A simple inexpensive tool is what you should use to disconnect them. You can create custom cables with a crimping tool.
"Ballasted Racking" - These are Module mounts that sit directly on a flat roof or concrete. You use bricks to weigh them down. The amount of bricks is an engineering calculation based primarily on wind speed, angle, and module size. Do not guess at it.
"Ungrounded" - This is a system with two high voltage DC circuits. A positive line, and a negative line. Example - One line carries +400vdc the second carries -400vdc. These do NOT connect to the ground, you never see 400vdc. If you check the voltage, you will see 800vdc. If either line touches a real ground, the system will normally fault and go into rapid shutdown. This type of system DOES REQUIRE grounding everywhere. Frames, optimizers, conduit, racking, etc. Only the ±400vdc lines are isolated.
"Optimizers" - These can be called lots of various names, but what they do is apply a load to the module(s) to maximize output and communicate the main inverter. The module leads plug into the optimizers, then the optimizer has 2 ungrounded MC4 leads about 1-2 meters long. You daisy chain optimizers.
"Inverter" - The brains of the outfit. Do not skimp here. It not only takes the PV solar DC power and converts it to AC house power, but it checks system health, and acts as a safety device. Most newer ones are internet-aware. You can check everything, and even do Rapid Shutdown or Reboot from your cellphone or desktop.
'Rapid Shutdown' aka 2014 NEC 690.12 - All newer systems must be able to power down to under 30vdc in less than 30 seconds. The Rapid Shutdown must be marked. This RS should kick automatically if the inverter sees a ground fault. Remember Ungrounded? It needs total isolation.
Isolation Fault - Your inverter sees some current flow (under a million ohms?) between the DC strings and ground. It SHOULD go into Rapid Shutdown.