How many watts of solar can a Victron SmartSolar 100/20 take on a 12V battery?
The model name gives you two of the three numbers. "100" is the maximum PV open-circuit voltage in volts. "20" is the rated charge current in amps. The third number, the one people actually want, is on the datasheet: nominal PV power, which for the 100/20 is 290 W on a 12 V battery.
What "nominal" means here
Nominal PV power is the array size at which the controller can deliver its full 20 A into a 12 V battery. Connect more and the controller does not fail; Victron's own footnote says that if more PV power is connected, the controller will limit input power. Over-panelling is a legitimate way to get more harvest on cloudy days and early mornings, when the array is well below its rating anyway.
But the two electrical limits are not soft:
| Limit | 100/20 value | What happens if you exceed it |
|---|---|---|
| Nominal PV power, 12 V | 290 W | Output capped at 20 A; no harm |
| Nominal PV power, 24 V | 580 W | Same |
| Nominal PV power, 48 V | 1,160 W | Same |
| Max PV open-circuit voltage | 100 V | Controller damage |
| Max PV short-circuit current | 20 A | Controller damage; Victron's footnote is explicit |
How to check your array against the limits
Read two figures off each panel's label: open-circuit voltage (Voc) and short-circuit current (Isc).
- Panels in series: add the Voc figures; Isc stays that of one panel.
- Panels in parallel: add the Isc figures; Voc stays that of one panel.
Then apply cold-weather margin to the voltage. Voc rises as a panel gets colder, so an array that sits under 100 V on a summer afternoon can exceed it on a frosty morning. Leave real headroom on the voltage figure rather than running it to the line.
The current limit is the one that catches people who parallel several large panels. Adding up label Isc values and landing over 20 A means the array can push more current into the controller than it is built for, and that is the case the datasheet warns will cause damage.
One more requirement to start charging
The controller needs the PV voltage to exceed battery voltage plus 5 V before it starts, and to stay above battery voltage plus 1 V after that. A single 12 V-nominal panel does this comfortably on a 12 V bank; on a 24 V bank you need panels in series.
When to step up
If your array is going to sit well past 290 W on 12 V for most of the day, you are paying for panels whose output is clipped. The SmartSolar MPPT 100/30 and 100/50 share the 100 V limit with higher current ratings, and our controller pairing chart lists which size suits a given array. The SmartSolar 75/15 to 100/20 range is the right choice up to about 290 W of panel on 12 V, and it ships from Upland, California. Send us the panel labels and we will confirm the series and parallel arrangement before you buy.
What you need
Want the full walkthrough? Read the complete guide.