Connect PV Strings to MPU

Required Tools

PPE
- Cut resistant gloves
- Safety Glasses (ANSI Z87 rated)
Tape measure
9/16” socket
Drill and/or socket wrench
Small Philips and flat drivers
Wire strippers and cutters
MC4 extension cables
Multimeter
12VDC source & 2-pin jump connector
Grounding hardware (split bolts, ground rod clamps)
Zip ties
Hex key set

Step 1: Plan PV Stringing

Each PV string must be made up of the same type of solar panel
Note
This rule is always true for Tesla Solar Inverter and Powerwall 3, and should be assumed true for commercial solar inverters unless those inverter specifications explicitly state otherwise.
Consider the inverter specifications:
- Tesla Solar Inverter and Powerwall 3 both have a nominal input voltage of 450 VDC with a DC input voltage range of 60 - 550 VDC
- String voltage should be calculated so that it does not exceed 550 VDC, but should preferably not exceed 500 VDC
- String Calculation Example 1:
  - This panel has an Open Circuit Voltage (V_OC) of 48.5 VDC
  - Maximum number of panels per string = 450 VDC
  - 450 VDC / 48.5 VDC = 9.27 panels per string
  - 10 panels per string provides a string voltage of 485 VDC, which is less than 500 VDC, and is therefore acceptable
- String Calculation Example 2:
  - This panel has an Open Circuit Voltage (V_OC) of 37.6 VDC
  - Maximum number of panels per string = 450 VDC
  - 450 VDC / 37.6 VDC = 11.96 panels per string
  - 12 panels per string provides a string voltage of 451.2 VDC, which is less than 500 VDC, and is therefore acceptable
Plan the solar panel layout for the available area
- Identify 500 ft² of dry, flat land that will ideally not be subjected to flooding
- For optimal racking usage, arrange panels in a 5 x 6 panel array (other configurations will use more ground mounts)
- Be aware of traffic patterns near where the solar panels will be arranged, and prepare the area as needed with barriers/cones

Step 2: Lay Out Solar Racking and Panels

Note

See the UNIRAC Install Manual (download RM10 EVO Install Manual from Product Support Documents) for complete racking installation instructions.

Don't overtighten the racking equipment
CAUTION
Overtightening racking equipment may lead to cracked panels.
For a 5 x 6 panel array, 42 bays and 144 clips/bolts are required
Note
Bolts and clips are not needed for the front or rear-most rows

Step 3: Connect Solar Panels in String

Connect the solar panels for the designated string in series, connecting the male MC4 connector of one panel to the female MC4 connector of the next panel.
Connect either end of the string to the inverter.

CAUTION

Do not connect the MC4 connectors at either end of the string directly to each other. This will result in permanent damage to the PV array.

Important notes on connecting solar panels:

Older SMA inverters only have one MPPT, and all strings must have the same number of panels and be of the same type
Inspect connectors as panels are being set to ensure they are secure and in good condition
Use MC4 extension cables for longer home runs if needed
Measure the open-circuit voltage of each string
- Open circuit voltage should be approximately V_OC * # of panels (e.g. 45V * 10 = 450V)
Ground the PV array
Connect the racking/frames of the array to a local earth electrode or to an earth terminal block in MPU breaker panel

Step 4: Ground the MPU

If a local ground grid is available, utilize 10 AWG ground wire to ground the MPU to the local ground grid
If a local ground grid is not available, ground the MPU using a grounding rod per local requirements (typically driving an 8 ft ground rod into soil)
Connect the earth terminal block of the MPU breaker panel to an earth electrode or terminal block in breaker panel on site

Step 5: Connect Strings to Solar Inverter

Warning

Never make or break PV connections under load. Always confirm the solar inverter / Powerwall 3 is powered OFF and is not connected to AC power, and there is no voltage on the PV inputs before connecting / disconnecting wiring.

Confirm the inverter is powered OFF:
- For Tesla Solar Inverter, confirm the Solar Inverter breaker is open (OFF).
- For Powerwall 3, confirm the switch on the left side of the unit is OFF, then confirm the Powerwall 3 breaker is open (OFF).
- For older third party solar inverters, confirm the DC disconnect is open (OFF), then confirm the inverter breaker is open (OFF).
Label each string by either placing bands of tape of the string (1 band of tape = String 1), or by placing number tape on the string
Connect the strings to the inverter:
- For Tesla Solar Inverter, connect each string's conductors to the appropriate positive and negative terminals (e.g. connect String 1 to MPPT 1+ and 1-):
  Note
  Where the DC input current exceeds an MPPT rating of 13 A, jumpers can be used to allow a single MPPT to intake strings with a total DC input current of up to 26 A. 4-inch MPPT paralleling jumpers are included in the Solar Inverter accessory bag. See the Tesla Solar Inverter installation manual for more information.
- For Powerwall 3, connect each string's conductors to the appropriate positive and negative terminals (e.g. connect String 1 to MPPT 1+ and 1-), noting that the order of the PV conductors depends on the Powerwall 3 variant:
  Note
  Where the DC input current exceeds an MPPT rating of 13 A, jumpers can be used to allow a single MPPT to intake strings with a total DC input current of up to 26 A. Jumpers are included in the Powerwall 3 accessory bag. See the Powerwall 3 installation manual for more information.
  Note
  When the Powerwall 3 product label lists 15 A I_MP, jumpers can be used to parallel MPPT to double the total PV input current capacity to 30 A.
- For other third party inverters, connect the PV strings per the manufacturer's instructions.

Turn the MPU ON

For MPU variant 1 with an SMA inverter, turn the DC disconnect ON. The inverter screen and LEDs should turn on when DC power is provided.
Turn all Powerwall breakers ON, then turn the Powerwall switches ON.