DC-coupled solar (connected directly to Powerwall 3) is strongly preferred over AC-coupled solar for the following reasons:
Less equipment required for
DC-coupled solar, resulting in reduced system cost
Increased efficiency for DC-coupled solar
In some scenarios, it is difficult or not feasible to avoid systems with AC-coupled
solar. Most commonly, this occurs when Powerwall 3 is installed on a system with
existing AC-coupled solar. As shown below, solar can be installed alongside Powerwall 3 solar, or with Powerwall 3 as storage only.
Note
Powerwall 3 can also be used without any
solar on the site.
Figure 1. Powerwall 3 with AC and DC Coupled
SolarFigure 2. Powerwall 3 with AC Coupled Solar (Storage
Only)
PV to Powerwall Ratio
For systems with AC-coupled solar only, a maximum of AC per Powerwall is allowed in
the backup circuit (the smaller of AC inverter rating or DC system size1).
Note
When Powerwall 3 is installed with Expansion unit(s), a maximum of 10 kW AC is allowed in
the backup circuit. This means that a system with (1) Powerwall 3 and up to (3) Expansion units can have up to 10 kW
AC-coupled solar in the backup circuit, and a system with (2) Powerwall 3 units and up to (3) Expansion units can have up to 17.68
kW AC-coupled solar in the
backup circuit (the increased ratio only applies to the Powerwall 3 unit with Expansion unit(s) connected).
1The PV to Powerwall ratio was put
in place to protect the Powerwall system from excessive PV power . is used because it is a common solar
inverter size,
allowing more PV systems to be fully backed up without needing to be split apart,
and inverters don’t always produce their maximum power. This ratio does not prevent
all issues; Powerwall’s maximum charge rate is 5
kW under ideal conditions (notably
operating temperature). If there is more than 5
kW of excess PV per Powerwall, the
system will frequency shift to try to reduce PV power, and may have to shut PV
production down completely.
Note
The AC-coupled PV to Powerwall
ratio and the maximum DC solar system sizing are independent of each other. See
Powerwall 3 DC System Sizing for
information about sizing the Powerwall 3 DC system.
Note
When
using Tesla Solar Inverters, the number of inverters is not impacted by the PV to
Powerwall ratio (the maximum number of Tesla Solar Inverters in the backup circuit
is 200A, or 5 Solar Inverters).
CAUTION
Exceeding the PV to
Powerwall ratio may result in high fault current , which creates a serious risk of damage to Powerwall and/or the
customer's home loads. If a Powerwall is damaged by high fault current due to excess
PV during an outage, it will be out of warranty.
Options to avoid exceeding the ratio:
Increase number of Powerwalls
on site
Utilize Tesla Brand Solar Device for all PV on
site to avoid PV to Powerwall ratio
Split PV Inverter Point of
Interconnection, In / Out of the A Powerwall 3 site can
have a maximum of three Tesla Remote Energy
Meters: one
connected via RS-485 and up to two connected via Wi-Fi. (confirm with local AHJ that this practice
is accepted)
Downsize PV to meet
ratio
Shed part of the PV system
using grid dependent relays/contactors
Powerwall Qty
Maximum continuous output of solar array (kW)
Examples
Explanation
1
7.68
10 kW DC solar on 7.68 kW AC inverter
Allows solar over 7.68 kW DC because the output will be capped to
7.68 kW AC by the (overdriven) inverter. The Powerwall will not see
more than 7.68 kW solar.
7.68 kW DC solar on 10 kW AC inverter
While the inverter is capable of 10 kW AC, the 7.68 kW DC solar
array will not produce more than 7.68 kW AC solar.
2
15.36
20 kW DC solar on (2) 7.68 kW AC inverters
Allows solar over 15.36 kW DC because the total output will be
capped to 15.36 kW AC by the (overdriven) inverters.
15.36 kW DC solar split between (1) 6 kW AC inverter and (1) 10
kW AC inverter
The 16 kW AC combined output of the inverters can exceed 15.36 kW
because the 15.36 kW DC solar array will not produce more than 15.36
kW AC solar. Note that the solar does not need to be evenly split in
the ratio; instead, consider the total output.
Note
The 7.68 kW PV to Powerwall ratio can be applied to
any Powerwall unit in the system, including Powerwall+ or Powerwall 3. For example, a 7.68 kW third party solar inverter can be backed
up with a single Powerwall+ or Powerwall 3, as the ratio rule does not
apply to the solar inverter portion of the Powerwall+ or Powerwall 3.