What's the difference between W and kW?
Watts (W) and kilowatts (kW) both measure power — the rate at which energy is being used or produced at any instant. One kilowatt equals exactly 1,000 watts. A 100W solar panel running at full output is producing 0.1 kW.
The kilowatt scale is more practical once you're sizing whole systems: a typical off-grid cabin might need 2–5 kW of solar capacity, while a single LED bulb runs at 0.01 kW (10W). Both numbers describe the same physical thing — just at different magnitudes.
Wh vs kWh — energy, not power
Watt-hours (Wh) and kilowatt-hours (kWh) measure energy— power accumulated over time. Your utility bill is in kWh. A 100Ah battery at 12V stores 1,200 Wh (1.2 kWh). Run a 100W load for 5 hours and you've consumed 500 Wh (0.5 kWh).
The formula is simple: Wh = W × hours. Convert to kilowatt-hours by dividing by 1,000. This is why the unit converter above asks for hours when you're converting between power (W/kW) and energy (Wh/kWh) — you need that time dimension.
What about mAh?
Milliamp-hours (mAh) appear on phone batteries, power banks, and small lithium cells. The catch: mAh tells you nothing without knowing the voltage. A 10,000 mAh power bank at 3.7V stores 37 Wh. That same 10,000 mAh at 12V would be 120 Wh — a completely different amount of energy. Always convert mAh to Wh using the actual cell voltage.
How the load calculator works
The Load Calculator tab adds up your daily energy consumption (watts × hours for each appliance), then sizes three components:
- Solar panels — daily Wh × 1.25 safety factor ÷ (peak sun hours × 0.80 system efficiency). The 1.25 factor accounts for real-world panel degradation and wiring losses.
- Battery storage — daily Wh × autonomy days ÷ depth of discharge. LiFePO₄ batteries can safely use 90% of rated capacity; AGM is limited to 50% to protect cycle life.
- Inverter — peak appliance wattage × 2 to handle motor surge loads at startup. This is a conservative estimate; check your specific appliances for surge ratings.
Common conversions at a glance
| From | To | Formula | Example |
|---|---|---|---|
| W | kW | ÷ 1,000 | 500W → 0.5 kW |
| kW | W | × 1,000 | 2 kW → 2,000W |
| Wh | kWh | ÷ 1,000 | 1,500 Wh → 1.5 kWh |
| W | Wh | × hours | 100W × 5h → 500 Wh |
| Wh | mAh | × 1,000 ÷ V | 120 Wh at 12V → 10,000 mAh |
| mAh | Wh | × V ÷ 1,000 | 10,000 mAh at 12V → 120 Wh |