Solar Generator Sizing Calculator
Calculate the battery capacity, solar panel wattage, and system components needed for a complete solar generator. Size your solar backup system for off-grid living, emergency preparedness, or camping.
Appliance Loads
Backup Settings
How long you need backup power during the outage.
12V for small portable setups, 24V for mid-size, 48V for whole-home.
LiFePO4 recommended: safest, longest life, deepest discharge.
Auto-set by chemistry. LiFePO4: 80%, Lead-Acid: 50%.
Modern pure sine wave inverters: 90–95%. Use 90% for conservative sizing.
Extra capacity buffer for temperature, aging, and unexpected loads.
Total wattage of solar panels connected to charge controller.
Average daily peak sun hours for your location.
MPPT controllers: 95–98%. PWM controllers: 80–90%.
Backup System Results
Suggested Battery Configurations
Solar Recharge Estimate
Planning Notes
Common solar generator loads pre-loaded. Add your devices and enable solar recharge to size a complete system.
Mathematical Formulas
For indefinite off-grid operation, daily solar production must exceed daily consumption. Size panels for worst-case season.
Formulas & Worked Examples
Example 1: Camping Weekend Setup
Power a portable fridge, LED lights, and charge devices during a 3-day camping trip with 4 peak sun hours.
Given Values
- Portable Fridge: 60W
- LED Lights ×2: 20W total
- Phone + Camera Charging: 30W average
- Daily Use: 12 hours
Step 1: Daily consumption
= 1,320 Wh/day
Step 2: Battery (2 days autonomy, 24V LFP 80% DoD)
= 137.5 Ah → 24V 150Ah (3.6 kWh)
Step 3: Solar panels (4 peak sun hours, 95% controller)
= 347W → 400W of panels
Final Answer
400W of solar panels + 24V 150Ah LFP battery + 1,000W inverter for a comfortable camping weekend.
Camping loads are modest — a portable 400W panel array recharges the battery daily with margin.
Example 2: Emergency Home Backup (72h)
Keep fridge, freezer, Wi-Fi, and lights running for 3 days with daily solar recharge in winter (3 peak sun hours).
Given Values
- Fridge + Freezer: 270W combined
- Wi-Fi + Router: 12W
- LED Lights ×3: 30W
- Daily Use: 24 hours
Step 1: Daily consumption
= 7,488 Wh/day
Step 2: Battery (1 day autonomy, 48V LFP 80% DoD)
= 195 Ah → 48V 200Ah (9.6 kWh)
Step 3: Solar panels (3 winter sun hours, 95% eff)
= 2,627W → 2,800W of panels
Final Answer
2,800W of solar panels + 48V 200Ah LFP battery + 4,000W inverter for multi-day winter outage survival.
Winter solar requires significantly larger panel arrays — summer systems can be roughly half this size.
Example 3: Off-Grid Cabin (Full Time)
Power a small off-grid cabin with fridge, lights, well pump, and basic appliances year-round.
Given Values
- Fridge: 150W
- Well Pump: 750W (intermittent)
- Lights + Electronics: 100W
- Daily Use: 24 hours
Step 1: Average daily consumption
= 4,400 Wh/day average
Step 2: Battery (3 days autonomy, 48V LFP 80% DoD)
= 344 Ah → 48V 400Ah (19.2 kWh)
Step 3: Solar panels (5 peak sun hours, 95% eff)
= 926W → 1,000W of panels
Final Answer
1,000W of solar panels + 48V 400Ah LFP battery + 3,000W inverter for full-time off-grid cabin power.
Off-grid cabins need serious battery storage for cloudy day autonomy — 3+ days prevents dead batteries during storms.
Solar Generator Charging Flow
Energy flows from solar panels through the charge controller to the battery bank, then through the inverter to power AC loads.
Solar Generator Panel + Battery Combo Guide
| System Size | Battery (LFP) | Solar Panels | Daily Production | Best For | Winter Adequate? |
|---|---|---|---|---|---|
| Small Portable | 24V 50Ah (1.2 kWh) | 200W | 800–1,000 Wh | Phones, lights, small fridge | Summer only |
| Camping Standard | 24V 100Ah (2.4 kWh) | 400W | 1,600–2,000 Wh | Fridge, lights, devices | Yes (mild climate) |
| Weekend Backup | 24V 200Ah (4.8 kWh) | 600W | 2,400–3,000 Wh | Fridge + freezer + Wi-Fi | Yes |
| Home Emergency | 48V 200Ah (9.6 kWh) | 1,200W | 4,800–6,000 Wh | Essential home loads | Yes |
| Whole-Home | 48V 400Ah (19.2 kWh) | 2,400W | 9,600–12,000 Wh | Full household backup | Yes |
| Off-Grid Cabin | 48V 600Ah (28.8 kWh) | 3,600W | 14,400–18,000 Wh | Full-time off-grid living | Yes |
Winter production assumes 3 peak sun hours. Summer production at 5–6 peak sun hours is roughly 60–100% higher.
Frequently Asked Questions
How many solar panels do I need for a solar generator?
For a system running 1,500Wh/day, you need approximately 400–500W of solar panels at 4 peak sun hours. In winter (2–3 peak sun hours), you'd need 700–800W to maintain the same daily recharge.
What battery size for a solar generator?
Size the battery for 1–2 days of autonomy. If daily consumption is 2,000Wh, a 4,000Wh (4 kWh) battery bank provides 2 days of backup without any solar recharge. Use LiFePO4 for 80–100% usable capacity.
Can a solar generator power a house?
A properly sized solar generator (5–15 kWh battery, 1–3 kW solar) can power essential household loads indefinitely. Running everything (AC, oven, dryer) requires a 20+ kWh system with 5–10 kW of solar panels.
How long does a solar generator take to charge?
Charge time depends on panel wattage and sun exposure. A 400W panel system in 5 peak sun hours generates ~2,000Wh. A 2,000Wh battery charges from empty to full in about 5 hours of peak sun. Most systems take 4–8 hours.
What Is Solar Generator Sizing?
Why This Calculation Matters
→ Solar generators require matching three components: battery capacity, solar panel wattage, and inverter size. Mismatched components waste money or fail to power your loads.
→ Battery capacity determines overnight runtime — how many hours you can run loads when the sun isn't shining.
→ Solar panel wattage determines recharge speed — how quickly the battery replenishes during daylight hours.
→ Peak sun hours vary dramatically by location and season: 4–6 hours in summer, 2–3 hours in winter. System sizing must account for worst-case conditions.
→ A properly sized solar generator can provide indefinite backup power during extended outages — unlike fuel-limited gas generators.
Practical Applications
Off-Grid Cabin Power
Size a complete solar generator system for remote cabins, tiny homes, or off-grid living where grid connection isn't available.
Emergency Whole-Home Backup
Design a solar backup system that recharges daily from sunlight, providing indefinite power during multi-day grid outages.
Camping & Overlanding
Size portable solar panels and battery storage for extended camping trips, van life, or overlanding adventures.
Construction & Remote Sites
Power tools, lighting, and equipment at job sites without grid access using solar-charged battery systems.
Common Mistakes to Avoid
✗ Using peak sun hours from summer to size for year-round operation — winter sun hours (2–3h) are 50% lower than summer (4–6h), requiring larger panel arrays.
✗ Oversizing battery without matching solar panel wattage — a large battery without sufficient panels never recharges during daylight hours.
✗ Ignoring charge controller efficiency losses — PWM controllers lose 10–20% versus MPPT, directly reducing daily solar production.
✗ Assuming solar panels produce rated wattage continuously — real output depends on sun angle, temperature, shading, and panel orientation.
✗ Not accounting for battery DoD limits — a 4,000Wh battery at 80% DoD provides only 3,200Wh usable, not the full rated capacity.
✗ Using household consumption (10–30 kWh/day) to size a portable solar system — this requires impractically large panel arrays (3–10 kW).
✗ Ignoring inverter standby consumption — many inverters draw 5–15W continuously, adding 120–360Wh/day to your daily consumption.
✗ Forgetting that cloudy days reduce solar production by 50–80% — system design must account for worst-case weather conditions.
Why Trust These Calculations?
This calculator uses standard solar engineering formulas. All calculations assume MPPT charge controllers and standard panel efficiency. Actual performance varies by location, weather, and equipment quality.
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