Adding panels stops buying you a faster recharge at a limit your batteries set, and the manufacturer publishes the number. Victron’s gel and AGM datasheet, read today, says the charge current “should preferably not exceed 0,2 C (20A for a 100Ah battery).”
That scales with the bank. A 200Ah AGM bank caps at 40 amps. A 400Ah bank caps at 80.
What that is in watts
At a bulk and absorption voltage in the mid 14s, 40 amps is roughly 570 watts going into the battery. A 400Ah bank at 80 amps is roughly 1,150 watts.
Now the part that catches people: an array does not deliver its nameplate. Panel temperature, angle, wiring loss and sun angle all take a cut, and on a fixed roof at midday in real weather a working assumption of 70 to 80 percent is not unreasonable. That is our estimate, not a Victron figure, so treat it as a planning number. On that basis a 200Ah bank hits its ceiling somewhere around 700 to 800 watts of nameplate solar. Past that, extra panels are not raising the peak. Run your own numbers through the solar calculator with your actual loads before you buy anything.
Why the ceiling exists
The datasheet says it in one sentence: “The temperature of a battery will increase by more than 10°C if the charge current exceeds 0,2 C. Therefore temperature compensation is required if the charge current exceeds 0,2 C.”
On the ordinary three step charge curve it is blunter still. The datasheet lists as a disadvantage that “during the bulk phase the current is kept at a constant and often high level, even after the gassing voltage (14,34V for a 12V battery) has been exceeded. This can lead to excessive gas pressure in the battery. Some gas will escape through the safety valves, reducing service life.”
Gas that leaves a sealed battery does not come back. That is capacity you paid for, walking out of the case. And a hot battery needs a lower voltage setpoint on top of all this, which we covered here.
What the ceiling does not limit
It caps peak amps into the bank. It does not cap how much energy you collect in a day. A bigger array reaches the ceiling earlier in the morning, holds it through thin cloud, and holds it later into the afternoon, and that is genuinely what shortens a charge day in October or under trees. So panels above the ceiling are still worth money. They are just worth it for a wider window, not a higher peak, and that is not how they get sold.
The honest limits of the figure
This is Victron’s number for Victron gel and AGM batteries. Other manufacturers publish their own and they are not identical, so read the datasheet for the battery you actually own before you size a charge controller to 0.2C. The wording is “preferably not exceed,” not a hard cutoff, and the datasheet’s own remedy above the line is temperature compensation rather than a prohibition. None of it transfers to lithium.
One more thing worth pairing with it: the amp-hour number on the label is measured at the 20 hour rate, so the bank you are charging is smaller in practice than the sticker suggests. We worked that out here, and our battery sizing guide puts both halves together. Everything quoted above was read from the datasheet on August 25, 2026.