AC-Coupled Solar System Sizing

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
  • Low energy management during a grid outage
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.
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Note
Powerwall 3 can also be used without any solar on the site.
Figure 1. Powerwall 3 with AC and DC Coupled Solar
Figure 2. Powerwall 3 with AC Coupled Solar (Storage Only)

For systems with AC-coupled solar only, a maximum of 7.6 kW AC per Powerwall is allowed in the backup circuit (the smaller of AC inverter rating or DC system size1).

1The 7.6 kW PV to Powerwall ratio was put in place to protect the Powerwall system from excessive PV power during a grid outage. 7.6 kWis used because it allows to cover as much installations as possible while being compliant to the local regulation, 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.

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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.
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CAUTION
Exceeding the PV to Powerwall ratio may result in high fault current during a grid outage, 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:

  1. Increase number of Powerwalls on site
  2. Utilize Powerwall 3 for all PV on site to avoid PV to Powerwall ratio
  3. Split PV Inverter Point of Interconnection, In / Out of backup (confirm with local electrical regulator that this practice is accepted)
  4. Downsize PV to meet ratio
  5. Shed part of the PV system using grid dependent relays/contactors