Example Data Table
| Home Type |
Daily Use |
Peak Sun |
Panel Size |
Offset |
Battery Backup |
| Small home |
10 kWh |
4.5 hours |
450 W |
80% |
0.5 day |
| Average home |
18 kWh |
5 hours |
550 W |
90% |
1 day |
| Large home |
32 kWh |
5.5 hours |
600 W |
100% |
2 days |
Formula Used
Solar daily target = Daily kWh × Solar offset
Loss factor = 1 − System losses ÷ 100
Required array kW = Solar daily target ÷ Peak sun hours ÷ Loss factor
Panel count = Required array watts ÷ Panel watts, rounded up
Daily output = Actual array kW × Peak sun hours × Loss factor
Inverter size = Actual array kW ÷ DC to AC ratio
Nominal battery kWh = Daily kWh × Critical load × Backup days ÷ Depth of discharge
Battery Ah = Nominal battery kWh × 1000 ÷ Battery voltage
System cost = Actual array kW × 1000 × Installed cost per watt
Annual savings = Usable annual production × Electricity rate
How To Use This Calculator
Enter your average daily energy use from your electricity bill.
Add local peak sun hours for your roof location.
Choose the percent of electricity you want solar to cover.
Enter panel size, roof area, loss estimate, and inverter settings.
Add battery, cost, rate, and analysis values for deeper planning.
Press the calculate button. Review the result above the form.
Use CSV or PDF buttons to save the result.
Home Solar Planning Guide
Why accurate sizing matters
A home solar system should match real energy use. A small array may disappoint. A large array may waste roof space and budget. Good sizing starts with daily kilowatt hours. It also needs peak sun hours, panel rating, losses, and backup goals. These values show how much direct current capacity you need.
Understanding daily load
Daily load is the base of the calculation. You can read it from a utility bill. Divide monthly use by the number of billing days. Then decide the solar offset. A full offset aims to cover nearly all annual use. A smaller offset can reduce cost. It can also fit tighter roofs.
Panel and roof planning
Panel count depends on array size and panel wattage. Higher watt panels reduce the number of modules. Roof area still matters. Each panel needs usable space. It also needs safe access around edges. The calculator checks the planned roof requirement. It flags when the design may not fit.
Battery and inverter choices
Battery size depends on backup days, critical load, and depth of discharge. Critical load means the circuits you want during an outage. It may include lights, fans, internet, refrigerator, and basic outlets. Depth of discharge protects battery life. A higher allowed discharge needs less nominal capacity. Battery amp hours help compare low voltage battery banks.
Cost and savings view
Solar cost is estimated from installed cost per watt. Annual savings use expected usable production and power price. Long term savings also include rate escalation and panel degradation. Payback is a simple guide. It is not a financing quote. It does not include taxes, rebates, interconnection fees, export limits, shading, or seasonal tariff rules.
Better input habits
Use conservative assumptions for losses. Include inverter loss, wiring loss, dust, temperature, mismatch, and shading. Local peak sun hours should come from a nearby solar map. Check several months, not only summer. Compare the result with installer proposals. The final design should be reviewed by a qualified solar professional.
Safety and rules
Keep safety rules in mind. Roof strength, breaker limits, wire size, grounding, and disconnect placement are important. Permits may be required. Net metering rules can change project value. Review before purchase. They affect value.
FAQs
1. What is peak sun hour?
A peak sun hour equals one hour of sunlight at strong solar intensity. It helps convert panel size into daily energy production.
2. Why are system losses included?
Solar systems lose energy through heat, wiring, inverter conversion, dust, mismatch, and shading. Losses make the estimate more realistic.
3. How do I find daily kWh use?
Check your electricity bill. Divide monthly kWh by the number of billing days. Use a yearly average for better planning.
4. What does solar offset mean?
Solar offset is the portion of your electricity use covered by solar production. A 100% offset aims to match annual use.
5. Why is panel count rounded up?
You cannot install part of a panel. The calculator rounds panel count upward to meet the required solar array size.
6. What is depth of discharge?
Depth of discharge is the usable share of a battery. Limiting discharge can improve battery life and reduce stress.
7. Is the payback result exact?
No. Payback is an estimate. It may change with rebates, financing, export rates, maintenance, taxes, and installation conditions.
8. Should an installer review this result?
Yes. A qualified installer should check roof structure, electrical limits, permits, shading, equipment choice, and local code rules.