How one Sol-Ark home cut its peak monthly bill from $597 to $121.

An Atlanta home had solar and a big battery — and was still paying $500–600 a month every summer. The problem wasn't the hardware. It was when the battery charged. Here's what changed.

The home

A residential solar install in metro Atlanta: a Sol-Ark 15K system (two inverters, paralleled), an 80 kWh battery bank, on Georgia Power's Overnight Advantage time-of-use rate plan. Plenty of panels, plenty of storage. On paper, a home that should barely have a power bill.

The problem: charging on the clock, not the rate

Time-of-use plans price electricity by when you use it. The gap is enormous:

That's a ~13× difference. The winning move is obvious: fill the battery overnight when power is nearly free, then run the house off the battery through the expensive afternoon. But the inverter's built-in scheduler is static — it charges to the same fixed percentage every single night, no matter what tomorrow looks like.

So the home did the worst of both worlds: on sunny days it over-charged (paying to top off a battery the sun would've filled), and on cloudy days it under-charged and drained into the peak rate by mid-afternoon. Nobody wants to log in every night, read a weather forecast, and re-tune their inverter by hand — so nobody does. The result was $500–600 summer bills on a system that should've crushed them.

What changed

ChargeSmart automates the nightly re-tune:

• Every evening it pulls tomorrow's solar forecast and the home's learned usage pattern.
• It computes the minimum overnight charge that covers tomorrow's gap between what the house will use and what the sun will make.
• It's deliberately cost-asymmetric: because a shortfall costs the peak rate (13× the overnight rate), it leans toward charging a little extra on cloudy days rather than ever leaving the home short.
• It writes that target straight to the inverter during the cheap window — automatically, every night. The owner does nothing, and can see the reasoning and override any time.

The results

Every monthly Georgia Power bill for this home, Dec 2022 → Jun 2026. The step-down is unmistakable — and it holds across seasons, not just one lucky month.

Real billing data, one home. Amounts are the monthly auto-draft from Georgia Power.

The peak monthly bill went from $597 to $121. Annual spend fell from about $4,250 (2023) to $2,600 (2025) — and the biggest drops are exactly in the high-AC summer months, where the rate arbitrage matters most.

Why it works

Nothing exotic — just doing the obvious thing correctly, every night. The hardware was always capable of beating a time-of-use plan; what was missing was a brain that knew how much to charge for tomorrow specifically. Charge against the rate, not the clock.