A California homeowner thought they had finally solved an expensive energy issue — only to find their battery charging from the grid while their panels were still producing power.
The result, they said, was a one-day swing that turned a money-saving setup into an $8.50 headache.
Here's what to know
According to Reddit, the latest issue began once the battery dropped to 35%.
Despite ongoing solar production, the system began importing power, drawing 21 kWh from the grid at roughly $0.40 per kilowatt-hour.
The homeowner said this came after they had already corrected a different problem that had been exporting battery power during peak-rate periods even though PG&E was paying only $0.03 per kilowatt-hour.
After that earlier change, sunny-day grid use had fallen to about 0.4 kWh.
At those prices, 21 kWh bought from the grid works out to roughly $8.40 to $8.50, while exporting 21 kWh at $0.03 per kilowatt-hour would bring in only about 63 cents.
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The homeowner said Enphase support attributed the behavior to his microinverters communicating with a controller a few houses away.
One commenter replied, "Yes it's possible, they use power line comms, and that is rated to around 300'."
More background
This kind of issue can quietly chip away at the financial benefits of rooftop solar and battery storage. A setup meant to lower utility bills can end up doing the opposite if export settings, battery profiles, or installer commissioning are wrong.
Commenters said crosstalk between neighboring systems can happen, especially when homes share a utility transformer, and noted that installers usually work with support to filter each site's equipment so the systems stay separate.
Multiple users said the problem most likely pointed to an installation or provisioning mistake rather than a flaw in the panels or battery hardware.
The homeowner later said support's explanation matched what commenters described about power-line communication. They added that support told them the microinverters may have continued supplying power even after communication failed, which could have caused the controller to count that output as grid usage.
What can be done?
If a whole-home system is not the right fit, Pila offers plug-and-play batteries priced at a fraction of the cost of a whole-home backup system.
As for the OP, they wanted more reassurance the fix would last: "In my case, the support person, who btw handled my frustration really well, claimed to have made 'adjustments' to the configuration that should avoid this in the future. I didn't get any more detail than that, which makes me wary that it is a robust solution."
"Something seems odd about this situation," a commenter agreed.
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