SolarToolsHow This Tool Works
Choosing the right EV charger power for your solar system is the difference between free solar charging and expensive grid charging. A 11.5 kW Level 2 charger on a 5 kW solar system means 60% of your charge comes from the grid. A 3.6 kW Level 2 charger on the same solar system means 80%+ comes from the sun. Smaller isn't always worse — when paired with solar, matching charger power to panel output maximizes solar self-consumption.
This calculator shows you exactly how much of each charge comes from solar vs grid, based on your solar system size, time of charging, and charger power level. It also recommends the optimal charger size for your solar setup. Most homeowners with 6-9 kW solar systems do best with a 7.2 kW (32A) Level 2 charger — the sweet spot for solar matching.
Smart chargers (Wallbox, Zappi, Enphase) can dynamically modulate power to match live solar output — your charger ramps up at noon and down at dusk. If you have one of these, set the charger to max power (11.5 kW) and let the charger match solar. If you have a "dumb" Level 2 charger, manual sizing matters more — use this calculator to pick the right power level.
- Solar system size — total panel capacity in kW DC. 20 × 400W panels = 8.0 kW.
- Peak sun hours — daily full-sun equivalent hours. The calculator assumes you charge during sun hours.
- Home daytime load — what your home is consuming while the EV charges. Fridge + standby: 300-500W. AC running: 1,500-3,000W.
- EV battery size — total battery capacity in kWh.
- Current/target % — daily charging typically 40% → 80% (preserves battery life vs charging to 100%).
- Charger power — Level 1 (1.4 kW, standard outlet), Level 2 (3.6/7.2/9.6/11.5 kW, 240V circuit).
- Charger efficiency — AC to DC conversion. Level 2: 90-94%. Level 1: 85-90%.
The calculator assumes you charge during sun hours (midday). If you charge at night, all energy comes from the grid regardless of solar — pair with a home battery or use a smart charger that schedules daytime charging.
When to Use This Calculator
The solar matching principle
Solar produces power in real-time — you can't store it without a battery. When your EV charges during sun hours, it absorbs whatever your panels produce beyond your home's baseload. If your charger draws more than solar surplus, the grid fills the gap. Smaller charger = smaller gap = more solar share. Bigger charger = faster charge but more grid draw.
Example: 8 kW solar system, 400W home baseload. Solar surplus during peak: 7.6 kW. A 7.2 kW charger matches almost perfectly (95% solar share). An 11.5 kW charger would draw 11.5 kW — 7.6 from solar, 3.9 from grid (66% solar share). For most homes, 7.2 kW is the solar-matching sweet spot.
Level 1 vs Level 2 — when each wins
Level 1 (1.4 kW, standard 120V outlet) wins when: you drive under 30 km/day (overnight Level 1 fully recharges), you have no 240V circuit (apartment, rental), or you want minimum install cost ($0 if outlet exists). Level 1 adds about 5-6 km of range per hour — plenty for most daily driving.
Level 2 (7.2 kW) wins when: you drive 50+ km/day, you have a 240V circuit (dryer outlet, EV circuit), or you have solar and want to charge during midday peaks (5 hours of Level 2 = 35 kWh = 200+ km of range). Most homeowners should get Level 2 — the install pays back in 1-2 years vs Level 1's slower charge times forcing public charging.
Smart chargers: the solar cheat code
Smart chargers (Wallbox Pulsar Plus, Zappi, Enphase, Tesla Wall Connector with solar match) dynamically adjust charging power to match live solar output. At noon with full sun: charger ramps to 11.5 kW. At 4pm with weakening sun: charger drops to 4 kW. At night: charger pauses (or runs at minimum if needed). This eliminates the charger-sizing dilemma — set max power and let the charger optimize. Premium: $200-500 more than dumb chargers, but pays back in 2-3 years via higher solar share.
Why charging during the day matters
Night charging (cheapest grid rate in many TOU plans) means 100% grid electricity — your solar exported all day with no benefit (or low net metering credit). Day charging (when solar produces) means 50-95% solar electricity — your panels directly power your car. The economics flip when you have solar: day charging wins, even if grid TOU rates are higher during the day. With a smart charger, set "solar-only mode" and the charger waits for sunny hours automatically.
Should you oversize your charger?
If you have a smart charger that matches solar, get the biggest charger (11.5 kW) — it costs only $100-200 more than 7.2 kW and gives you faster charging when grid is needed (winter, cloudy days, road trip prep). If you have a dumb charger, size to match your solar surplus (typically 7.2 kW for 6-9 kW solar, 9.6 kW for 10-12 kW solar). Avoid 11.5 kW dumb chargers unless you have 12+ kW solar — you'll pull mostly from grid.
Frequently Asked Questions
Match charger power to solar surplus. 3-5 kW solar: Level 1 (1.4 kW) or Level 2 (3.6 kW). 6-9 kW solar: Level 2 (7.2 kW) — ideal match. 10-12 kW solar: Level 2 (9.6 kW). 12+ kW solar: Level 2 (11.5 kW). With a smart charger (Wallbox, Zappi), always get 11.5 kW — it'll auto-match solar output.
Yes, but inefficiently. Level 1 (1.4 kW) is so slow that even small solar systems easily cover it — but you'll only add 5-6 km of range per hour. For 30+ km/day driving, Level 1 may not fully recharge overnight. Best for plug-in hybrids and very low-mileage EV drivers.
Yes, strongly recommended. Smart chargers (Wallbox, Zappi, Enphase, Tesla Wall Connector) dynamically match charging power to live solar output — maximizing solar share to 80-95%. Premium cost of $200-500 pays back in 2-3 years via higher solar self-consumption. Without a smart charger, you must manually size the charger to match solar.
Depends on charger size vs solar surplus and time of charging. With a 7.2 kW charger on 8 kW solar, charging midday: 80-95% solar. With an 11.5 kW charger on 8 kW solar: 60-70% solar. Night charging: 0% solar (100% grid). Use the calculator above for your specific setup.
Day wins, decisively. Day charging lets you absorb your own solar production directly — 50-95% solar share. Night charging is 100% grid (your solar exported all day with low net metering credit). The only exception: if your utility offers super-off-peak night rates below your solar LCOE (rare). With a smart charger, schedule 'solar-only' mode and the charger handles it automatically.
Depends on charger power and battery state. Level 1 (1.4 kW): 20-30 hours for full charge (best overnight top-up). Level 2 (7.2 kW): 6-10 hours for full charge, 2-3 hours for daily top-up (40-80%). Level 2 (11.5 kW): 4-6 hours for full charge, 1-2 hours for daily top-up. Most EV drivers need 2-3 hours of Level 2 charging per day for typical driving.
Further Reading
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