A homeowner who planned on installing two Tesla Powerwall 3 units with expansions alongside only 4.2 kilowatts of solar drew immediate skepticism. 

Here's what to know

The homeowner posted their plan to Reddit's r/TeslaSolar community before receiving an onslaught of comments criticizing it.

In a Reddit thread, the homeowner asked how a 4.2 kW solar array would connect across two Powerwall 3 systems tied to separate 200-amp panels, writing, "how is solar split between the two PW3s?"

But instead of staying focused on the original poster's wiring question, much of the discussion turned to whether the overall setup made sense, with several commenters saying the plan leaned far too heavily on batteries for the amount of solar involved.

The top comment read, "54kWh of storage for a 4.2kW array?" Another Reddit user wrote, "It's a mistake to do what you're trying to do. > 80,000 residential installs talking." A third commenter wrote, "You need more panels," and another simply added, "The math ain't mathin."

One commenter even joked, "Is there supposed to be a 1 in front of that 4.2kw maybe?" An especially pointed comment read, "Your solar array is a rounding error to your storage."

The OP later updated the forum, saying that their area gets 12-16 outages a year, with interruptions lasting from about five minutes to as long as four to five hours.

And even with a small solar array, a large battery bank can still help during blackouts. But if the batteries are too big for the attached solar system, they may end up recharging largely from the grid, which can reduce the system's usefulness for cutting electric bills.

What can be done?

System goals usually drive how installers size both the batteries and the solar array. For lower electric bills, installers should be able to show how much solar production will offset usage and how quickly batteries can recharge each day.

When outages are the main concern, backing up only essential circuits can often cut costs while still covering refrigeration, internet, lights, and medical devices.

Battery storage can keep a home running when the grid fails. It can also save money when paired with enough solar or time-of-use utility rates, since homeowners can shift when they use electricity instead of buying it at the most expensive times.

For homeowners considering a similar project, comparing options through EnergySage can help clarify whether a system is designed mainly for backup power, monthly bill savings, or both. EnergySage has teamed up with the electrification brand Qmerit to guarantee you get the best price on home battery storage solutions. 

For people who want backup power without committing to a full-scale installation, Pila offers another option, with plug-and-play batteries priced at a fraction of what a whole-home backup system would cost.

Where can I learn more?

For another look at how Tesla Powerwalls are being used and priced, these stories go beyond this unusual Reddit setup. 

• In California, a homeowner saw his Tesla Powerwall earn $600 in a virtual power plant.

• Tesla confirmed several game-changing details about Powerwall 3, including a possible standout new feature.

• Tesla's home energy division surpassed half a million Powerwall installations as battery adoption kept growing.

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