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A home using 30 kWh per day (about 900 kWh per month) needs roughly 8.3 kW of solar at 4.5 peak sun hours, which is 21 panels of 400 W. In sunny regions with 6 sun hours it falls to 6.3 kW (16 panels); in cloudy climates with 3 sun hours it rises to 12.5 kW (32 panels).
Solar panel calculator
Estimates use the formulas explained in this guide. Plan a complete system with the all-in-one calculator →
The calculation
Array size (W) = 30,000 Wh ÷ (Peak sun hours × 0.80)
| Peak sun hours | Array size | 400 W panels | 450 W panels | Roof area (approx.) |
|---|---|---|---|---|
| 3.0 | 12.5 kW | 32 | 28 | 670 sq ft / 62 m² |
| 3.5 | 10.7 kW | 27 | 24 | 570 sq ft / 53 m² |
| 4.0 | 9.4 kW | 24 | 21 | 500 sq ft / 47 m² |
| 4.5 | 8.3 kW | 21 | 19 | 440 sq ft / 41 m² |
| 5.0 | 7.5 kW | 19 | 17 | 400 sq ft / 37 m² |
| 6.0 | 6.3 kW | 16 | 14 | 340 sq ft / 31 m² |
Roof area assumes about 21 sq ft (1.95 m²) per 400 W panel and excludes setbacks and walkways. See roof space for solar panels.
Grid-tied: the inverter
For a grid-tied 8.3 kW array, a string inverter of about 7 to 8 kW AC is typical; a DC-to-AC ratio of 1.1 to 1.25 is normal and loses very little energy. Microinverters or optimizers suit roofs with multiple orientations or shade. See microinverters vs string inverters.
Adding batteries
30 kWh per day is the whole house. Most grid-tied homes back up only what matters during outages:
| Backup goal | Battery size |
|---|---|
| Essentials (fridge, lights, internet, outlets) overnight | 10 – 13.5 kWh |
| Essentials + well pump + some cooking | 13.5 – 20 kWh |
| Whole home for one full day off-grid | about 35 kWh (30 kWh ÷ 0.85) |
See home battery backup size and is one Powerwall enough.
Fully off-grid at 30 kWh per day
Off-grid at this level is a large project:
- Solar sized for winter: at 2.5 winter sun hours, 30,000 ÷ 2 = 15 kW.
- Battery: about 35 kWh of LiFePO4 per day of autonomy, typically 70 kWh for two days.
- Inverter: 10 to 15 kW, often two or three units stacked for 120/240 V split phase. See split-phase off-grid inverters.
- Generator for long cloudy spells.
That is why off-grid homes usually start by cutting consumption.
Where 30 kWh per day usually goes
| Load | Typical daily share |
|---|---|
| Central AC or heat pump | 8 – 15 kWh (seasonal) |
| Electric water heater | 8 – 12 kWh |
| Clothes dryer | 2 – 3 kWh |
| Refrigerator + freezer | 2 – 3 kWh |
| Cooking | 1.5 – 3 kWh |
| Lighting, electronics, misc. | 3 – 5 kWh |
How to reduce the system size
- Heat pump water heater: can save 5 to 8 kWh per day versus a standard electric tank. See water heater on solar.
- Heat pump dryer or line drying: saves 1 to 3 kWh per load.
- Air sealing, insulation and a smart thermostat: cut heating and cooling by 10 to 30%.
- Replace an old fridge or second freezer.
Bringing usage from 30 to 22 kWh per day removes about 6 panels from a grid-tied design and about a quarter of the battery from an off-grid one.
Enter 30 kWh in the solar calculator and adjust sun hours to see your exact array, battery and inverter size.
Worked example: 30 kWh per day with net billing
A home in California uses 30 kWh per day under a net billing tariff where exported solar earns much less than imported power costs.
- Daytime use (9 am to 4 pm): about 9 kWh
- Evening and night use: about 21 kWh
Option 1, full-size array with no battery: 8.3 kW produces about 30 kWh per day, but 21 kWh is exported at a low rate and bought back at night at a high rate. Savings are limited.
Option 2, smaller array + battery: 6 kW (about 21.6 kWh per day) plus a 13.5 kWh battery. Daytime loads use solar directly, the battery stores about 12 kWh for the evening peak, and little is exported. More of each solar kWh offsets expensive imports.
Which is better depends on your tariff; under full retail net metering, option 1 usually wins.
Breaking 30 kWh into time of day
| Period | Typical share | Example loads |
|---|---|---|
| Morning (6 – 9 am) | 15% | Water heating, cooking, coffee |
| Daytime (9 am – 4 pm) | 30% | AC/heat pump, fridge, home office, laundry |
| Evening (4 – 10 pm) | 40% | Cooking, AC, lighting, TV, dishwasher |
| Night (10 pm – 6 am) | 15% | Fridge, AC/heating, standby loads |
Shifting laundry, dishwashers and water heating to midday increases direct solar use and reduces battery needs.
Equipment list for a grid-tied 30 kWh/day home (4.5 sun hours)
| Component | Typical choice |
|---|---|
| Panels | 21 × 400 W (8.4 kW) or 15 × 550 W (8.25 kW) |
| Inverter | 7.6 – 8 kW string or hybrid inverter, or microinverters |
| Battery (optional) | 10 – 15 kWh for backup or evening shifting |
| Monitoring | Inverter app with consumption monitoring (CT clamps) |
Common mistakes
- Treating 30 kWh/day as the battery size. Backup batteries usually cover essentials, not the whole home.
- Ignoring seasonal swings. Summer AC days may hit 45 kWh; spring days 20 kWh.
- Skipping efficiency upgrades that would shrink both the array and battery.
FAQ
How many solar panels for 30 kWh per day?
About 21 panels of 400 W at 4.5 peak sun hours; between 16 and 32 depending on your location.
How many batteries for 30 kWh per day?
About 35 kWh of LiFePO4 for one full day off-grid. For grid-tied backup, 10 to 20 kWh usually covers essentials. See how many batteries for solar.
Is a 10 kW system enough for 30 kWh per day?
At 3.75 peak sun hours or more, yes: 10 kW × 3.75 × 0.80 = 30 kWh per day.
How many kWh does a 10 kW solar system produce per day?
About 36 kWh at 4.5 peak sun hours (10 × 4.5 × 0.80), from about 28 kWh in cloudy climates to 44 kWh in very sunny ones.
Can a 5 kW system cover 30 kWh per day?
Only in very sunny places with more than 7.5 peak sun hours, which is rare. Most locations need 7 to 10 kW.
Related guides
- How Many Solar Panels Do I Need? (Step-by-Step Calculator Method)
- How Many Solar Panels Do I Need for 1,000 kWh Per Month?
- What Can a 1kW to 20kW Solar System Run? kWh per Day and Appliance List
- What Can a 3kW Solar System Run? kWh per Day, Appliances and Battery Backup
Sources and further reading
- U.S. EIA: How Much Electricity Does an American Home Use?: average household use, about 10,800 kWh a year.
- NREL PVWatts Calculator: solar output estimate for any address.
- European Commission JRC: PVGIS: free solar output and optimum-tilt tool for Europe and most of the world.
- U.S. Department of Energy: Solar PV System Design Basics: how panels, inverters, controllers and batteries fit together.