Sonnen batteries don't recharge from solar panels when the grid is down

Published on 05 Apr, 2019 by Michael Bishop

Categories: Home batteries

Sonnen offers a premier home energy-storage system, rivaling Tesla's Powerwall energy-storage system.

Most homes that get energy-storage systems aren't doing it for financial reasons (because the financials aren't good in most cases). They're doing it for peace of mind — they want a backup source of power if the electric grid goes down.

Sonnen energy storage system in a living room
Image source: Sonnen

Batteries and solar panels

Solar panels can take that independence to the next level. The solar panels can recharge the batteries during an especially long grid outage caused by a hurricane, wildfire, or possibly someday a cyberattack.

That's exactly how it works with the Tesla Powerwall. It'll recharge from on-site solar panels whether or not the electric grid is available. Tesla is even planning to offer an energy-storage system designed specifically for 100% off-grid use (for those in especially remote areas not served by the local utility, or those who are completely over dealing with their local utility).

Sonnen's "hybrid" energy storage system

At first glance, Sonnen seems to offer a better solution than Tesla for solar homes. Sonnen's "hybrid" battery backup system will take direct-current energy directly from the solar system, and convert it to grid-friendly (and home-friendly) alternating-current electricity. This avoids the added cost and complexity of a separate piece of equipment (the solar "inverter"). Tesla doesn't offer this — you'd have to buy a Powerwall-compatible inverter made by a different company.

The big catch with Sonnen's option is that if the grid goes down, it won't charge itself with the on-site solar panels. Instead, it'll provide backup power until it runs out of energy...and then you're out of luck like the rest of the neighborhood (meanwhile, your solar panels have become very expensive roof ornaments).

Frustrated homeowner during power outage


Sonnen or Tesla Powerwall?

Especially considering Sonnen's solar-specific "hybrid" option and their "it's time to declare your independence" tagline, I wonder why they didn't go the distance and support recharging from solar during grid outages. Outmatched by Tesla engineers?

If I had solar and was going to invest in an energy-storage system for backup power, a requirement would be: the battery backup must be recharged by my solar panels during a power outage. I'd choose the Tesla Powerwall.

Author: Michael Bishop

Michael's core purpose is to improve the customer experience around going solar. He primarily pursues this by writing articles and software at CutMyBill.