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Solar array
Solar + EV integration
EV charger amperage vs panel output tool
Which actually limits your charging speed, the charger or the array? Add your array size and voltage for a full table showing the real bottleneck at each charger level.
How it works
Three steps to finding your bottleneck
Step 1
Enter your array size and derate factor
Use your actual or planned array size, and a realistic derate factor rather than the panel's raw nameplate rating.
Step 2
Scan the comparison table for the crossover point
The table shows exactly where the bottleneck switches from charger to array as charger size increases.
Step 3
Decide if a bigger charger is worth it for grid charging too
Even if your array caps solar-only speed, a larger charger still helps when charging from the grid. Check the EV charger sizing calculator to confirm your panel supports the breaker size.
Understanding the charger vs array bottleneck
Two components, one speed limit
When charging directly from solar, the actual charging rate is always capped by whichever component supplies less power at that moment, either the charger's maximum rated output or the array's derated real-world output. Buying a bigger charger than your array can support does nothing for solar-only charging speed, since the array simply can't push more power than it produces no matter how large the charger's capacity is.
Why the crossover point matters for equipment decisions
Understanding exactly where your array's output equals a given charger size helps avoid overspending on charger capacity that solar alone can never use. A 6 kW array with a typical 0.80 derate factor produces about 4.8 kW, roughly equivalent to a 20-amp charger at 240 volts, meaning any charger rated above that level only shows its full speed advantage when charging from the grid instead, a similar concept to the inverter clipping output loss calculator.
There's still a good reason to size the charger larger
Many EV owners intentionally choose a charger rated well above their array's solar-only output, specifically so it can deliver full power during grid-assisted or grid-only charging sessions, like an unexpected need for a fast overnight top-up. In this framing, the array bottleneck only limits how fast solar-only sessions charge, not the charger's usefulness overall.
What the derate factor is actually capturing
The derate factor, a concept NREL's PVWatts calculator also relies on, rolls together inverter conversion loss, wiring resistance loss, dust and soiling on the panels, and temperature-related efficiency loss, all of which reduce real-world output below the array's nameplate DC rating. Using this derated figure, rather than the raw panel wattage sum, gives a far more realistic picture of where the true bottleneck actually sits.
Building on this result
Once you know your bottleneck, check the EV charger sizing calculator to confirm your electrical panel supports your chosen charger's breaker size, or the charger load vs panel clipping tool for a deeper look at how inverter clipping interacts with EV charging specifically. Consider running the DC to AC ratio calculator next.
Questions
Frequently asked
For a 6 kW array with a typical 0.80 derate, the crossover happens around 20 amps at 240 volts, since a 4.8 kW derated array output is roughly equal to a 20-amp charger's draw. Any charger rated higher than that is capped by the array, not by the charger itself.
No, once the array's derated output is smaller than the charger's rated power, increasing charger amperage further has no effect on solar-only charging speed. The extra charger capacity only matters when charging from the grid, which can supply full power regardless of array size.
The derate factor accounts for inverter loss, wiring loss, and other real-world inefficiencies, so a 6 kW array rarely outputs a true 6 kW even in ideal conditions. Using the derated figure rather than the nameplate array size gives a more accurate picture of where the real bottleneck sits.
Not necessarily. Many EV owners choose a charger sized larger than their array's solar-only output specifically so it can also deliver full power when charging from the grid, particularly for occasional fast top-ups. Sizing the charger to exactly match the array only makes sense if solar-only charging is the sole use case.
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