Solar Sustainability: A Going Off-Grid Case Study

September 2023

Baker Dewey

When SPAN sent one of our customers a video of a family going off grid for 48 hours, they saw this as a challenge they wanted to take part in. Our customer decided to put their system to the ultimate test, and in their words, “rough it “ for the two days.

About The System

The system is a 23.36 kW system with an estimated production capacity of 31,026 kWh located in South Carolina. There are 64 REC REC365AA Black panels that are connected to two SolarEdge Single Phase Inverters. Along with the PV solar system, the Kelly’s also invested in two Tesla Powerwalls and a SPAN Panel.

Off Grid Performance

This system was not built to function continuously off grid, but the combination of two inverters, two Powerwalls, and the SPAN panel made living off grid a temporary possibility. Once the power was turned off at the main disconnect, the customer’s family continued to use appliances in the home as if they were connected to the grid. At this time, both Powerwalls were charged at 100%. 

Initial Findings

Our customer took a close look at his system with the SPAN app to keep track of the system off the grid. Some of the first things they noticed were: 

• Solar production stopped since the Powerwalls were at 100% charge
• The Tesla Gateway turned off inverters
• Solar production turned on once the Powerwalls dropped to 85%
• Solar production stops once the Powerwalls are charged to 98% 

Our customer learned that each Powerwall is capable of using and storing 5kW of continuous power. So two Powerwalls plus the solar production equates to 17kW system capacity  for the home since the grid isn’t there to offset extra energy produced. This means the home can use 17kW while solar production is on and 10kW when solar production is off.

Challenges and Solutions

Running this system off grid was made possible thanks to load sharing with the SPAN panel and the Powerwalls, but there were still some challenges to keep life off grid going. Main challenges for going offgrid include power management and energy usage. Some challenges this customer faced include:

• Challenge: The customer’s family over-pulled from the Powerwalls (over 10kW continuous power) while making dinner, running both A/C units, and the microwave.

• Solution: One of the A/C units was moved to non-essential in the SPAN app, then the other was moved for bedtime. 

• Challenge: Both Powerwalls weren’t charging when the system was disconnected from the grid. The inverters were sending too much power, so the Gateway shut off both inverters to prevent overpowering the Powerwalls.

• Solution: Only one inverter was used so there wasn’t too much power being sent to the Powerwalls. Heavy electrical loads were also engaged to prevent overpowering the Powerwalls. 

Conclusion

Eight days, nine hours, and 22 minutes later, our customer reconnected their system to the grid. Our customer never intended on continuing this challenge for over eight days, but figuring out how to use the SPAN panel with the Powerwalls to manage off grid power usage encouraged our customer to tough it out even on cloudy days. The biggest challenge our customer faced was maintaining solar production without sending too much power to the Powerwalls. By moving appliances to ‘non-essential’, using heavy electrical loads, and shutting off one inverter, our customer was able to maintain power while charging both Powerwalls. In total, the SPAN app showed the home was powered by 59% solar and 41% Powerwalls. Even though this customer’s system wasn’t installed for offgrid life, our customer was pleased to find that the system was able to support off grid life in the event of an outage.