Calculator inputs
Example data table
Here is a sample load list and the kind of summary you can export.
| Appliance | Watts | Qty | Hours/day | Wh/day |
|---|---|---|---|---|
| LED Lights | 10 | 8 | 5 | 400 |
| Ceiling Fan | 60 | 2 | 8 | 960 |
| Laptop | 65 | 1 | 6 | 390 |
| Fridge (avg) | 120 | 1 | 10 | 1,200 |
| Total | 2,950 |
Formulas used
1) Daily energy per load
Wh/day = Watts × Quantity × Hours/day
Summing all rows gives total daily energy demand.
2) Adjusted daily energy
AC Wh / InverterEff + DC Wh
AdjustedWh = (… ) × (1 + MiscLoss)
DC share bypasses inverter; misc losses cover standby and aging.
3) PV array sizing
EffectiveSun = SunHours × Derate × ControllerEff
PV_W = AdjustedWh / EffectiveSun
PV_W *= (1 + SafetyMargin)
Panel count = ceil(PV_W / PanelRating).
4) Battery capacity
Ah = (AdjustedWh × AutonomyDays) / (Voltage × DoD × BatteryEff)
Ah *= (1 + SafetyMargin)
Choose a DoD suitable for longevity.
5) Inverter sizing
Continuous ≈ PeakRunningW × (1 + SafetyMargin)
Surge ≈ SurgeLoadsW × SurgeMultiplier
Select an inverter meeting both continuous and surge needs.
6) Controller current
I = (ArrayW / Voltage) × 1.25
Adds a conservative current factor for headroom.
How to use this calculator
- List every appliance, then enter watts, quantity, and daily hours.
- Mark loads with motors or compressors as Surge.
- Set system voltage, sun hours, and your desired backup days.
- Adjust derate, efficiencies, DoD, and margins for realism.
- Press Calculate to view sizing results above the form.
- Use Download CSV or PDF to save your estimate.
FAQs
1) What are “peak sun hours”?
They represent equivalent full-sun hours per day. Use a conservative monthly average for your location to avoid undersizing the array.
2) Why does the derate factor matter?
Real systems lose energy from heat, dust, wiring, mismatch, and aging. A derate factor converts panel nameplate power into realistic delivered energy.
3) How do I pick a good autonomy value?
Autonomy depends on your weather and how critical the loads are. Typical values are 1–3 days for cabins, and higher for mission‑critical setups.
4) Should I size for surge loads?
Yes for pumps, fridges, and tools. Startup current can be several times running power. Mark surge loads and set a realistic surge multiplier.
5) What DoD should I use for batteries?
Lower DoD extends battery life. Many lead‑acid banks use around 0.5. LiFePO₄ often supports around 0.8 while maintaining good cycle life.
6) Why split DC and AC energy?
DC loads bypass inverter losses. If most loads are AC, keep DC share near zero. If you run DC lighting or DC fans, increase it modestly.
7) Is the cost estimate accurate?
It is a rough bill-of-materials estimate using your entered unit costs. Taxes, shipping, installation labor, and brand differences can change totals significantly.