Anyone starting with solar and battery power wants a simple path to reliable backups. This printable backup sizing worksheet  focuses on critical loads first, helping you map what matters most and size your system with real numbers, not guesswork.

Why start with critical loads

In any backup plan, focus first on devices you rely on daily. You can run a small system longer if you minimize nonessential loads.

What you’ll map

On the worksheet, you’ll list devices, note running wattage, and estimate how many hours they run each day. Then convert to daily energy (Wh/day) and compare to the inverter and battery you’re considering.

How to fill it out

• List essential devices (fridge, lights, water pump, CPAP or medical devices, Wi‑Fi, phone chargers).
• Find each device’s running wattage (label, manual, or use a watt meter).
• Estimate daily runtime in hours for a typical day.
• Calculate energy per device: watts × hours = Wh per day.
• Sum all devices to get total daily energy.
• Choose an inverter rated above the peak load and size the battery to safely supply the daily energy with a healthy DoD (depth of discharge) buffer.

Sample scenario

In a small RV, common essentials might include:

• Refrigerator: 60–70 W, runs ~12 h/day → 720–840 Wh
• LED lighting: 10 W per light, 4 lights, ~4 h/day → 40 Wh
• Water pump: 60 W, 0.5 h/day → 30 Wh
• Phone chargers: 10 W, 2 h/day → 20 Wh

Estimated total: about 820–930 Wh/day. For a practical setup, plan for a 1000–1200 Wh/day capacity and an inverter of 1000–1500 W with a battery bank around 100–200 Ah at 12 V (or equivalent in 24–48 V). Depth-of-discharge limits and efficiency losses should be included in your final decision.

Printable worksheet tips

• Use a simple grid you can print and fill by hand or in a spreadsheet that sums watts, hours, and Wh/day automatically.
• Save a copy for future adjustments as your needs change.