Use this free Solar Load Calculator to estimate the right solar system size for your home or office. Add your appliances, power consumption and daily usage hours to calculate total load, energy requirements, solar panel capacity, inverter size and battery backup needs.
SIZE YOUR SYSTEM
Solar Load Calculator
List what you run, get the panels, inverter and battery you need to run it.
Your appliances
0 items| Appliance | Watts | Qty | Hrs/day | Wh/day | Remove |
|---|
System parameters
Losses from wiring, charge controller & inverter conversion.
How long the battery should power your listed load with no sun.
Average full-strength sunlight your location gets daily.
Nominal system voltage of your battery bank.
Your recommended system
How the numbers are calculated
- Connected load (W) = Σ (watts × quantity) for every appliance.
- Daily energy (Wh/day) = Σ (watts × quantity × hours used).
- Solar array size (W) = daily energy ÷ (peak sun hours × system efficiency).
- Panel count = solar array size ÷ wattage per panel (330 W panels assumed), rounded up.
- Inverter size (W) = connected load × 1.25 safety margin, rounded to a standard size.
- Battery capacity (Ah) = (connected load × backup hours) ÷ (battery voltage × 0.8 usable depth of discharge).
Worked example
A home running 3 LED bulbs (10 W, 5 hrs), a fan (75 W, 8 hrs), and a fridge (150 W, 24 hrs) draws about 3,830 Wh/day. At 80% efficiency and 5 peak sun hours, that needs roughly a 960 W array (three 330 W panels), a ~590 W inverter, and, for 6 hours of backup on a 24V bank, about 144 Ah of usable battery.
How to use this calculator
- List your appliances. Add a row for every device you want the solar system to power — lights, fans, a fridge, a router, a TV, pumps, and so on. Use the label on the appliance itself or its manual for the wattage, since a printed sticker is far more reliable than a guess.
- Set realistic usage hours. Enter how many hours a day each appliance actually runs, not how many hours it’s plugged in. A fridge compressor cycles on and off, but for sizing purposes most people count it as running continuously.
- Set your system parameters. Adjust system efficiency, battery backup hours, peak sun hours for your area, and your battery bank voltage. These four numbers have a bigger effect on the final result than most people expect.
- Calculate and review. Tap “Calculate system size” to see your connected load, daily energy use, recommended array size, inverter rating, and battery capacity, along with a visual comparison of your consumption against your array’s output.
- Copy or print your results. Use the copy button to paste your numbers into a message to an installer, or print the page for your records.
Why correct sizing matters
An undersized solar system leaves you short on power exactly when you need it most — during long cloudy spells or extended outages, when the battery drains faster than the panels can refill it. An oversized system isn’t dangerous, but it wastes money on panels, batteries, and an inverter you didn’t need. Getting the numbers right the first time means fewer surprises, a shorter payback period, and equipment that’s rated for the load you’re actually putting on it rather than a rough guess. Inverters and batteries in particular are worth sizing carefully: an inverter that’s too small will trip or shut down under a heavy startup surge from a fridge or pump, while a battery bank that’s too small will shorten its own lifespan from being discharged too deeply, too often.
Tips for more accurate results
- Use the sticker, not a guess. Appliance wattage varies a lot between brands and models — always check the rating plate rather than assuming a “typical” figure.
- Account for startup surge. Motors, compressors, and pumps can draw two to three times their running wattage for a second or two at startup. Your inverter needs headroom for that spike, not just the steady-state load.
- Be conservative with sun hours. Peak sun hours change with season and weather. Sizing around your worst realistic month, rather than a sunny-day average, avoids winter shortfalls. Global Solar Atlas has free irradiance data for most locations if you want a more precise figure than a rough average.
- Only back up what you need. Batteries are the most expensive part of most systems. Sizing the battery for essential loads only, rather than everything on the appliance list, usually gives a far more affordable system.
- Leave a margin. Adding roughly 10–20% headroom on top of the calculated array and battery size helps absorb dust, panel aging, and days that fall short of your sun-hour estimate.
Frequently asked questions
Accuracy & trust
This calculator is built for quick, practical planning — not as a replacement for a site survey from a qualified installer. Here’s how the numbers are put together and what to keep in mind when using them:
- Calculations are based on standard electrical formulas for load, energy, and battery sizing.
- Recommendations reflect typical solar conditions in Pakistan, including average peak sun hours.
- Prices and system suggestions are updated regularly to stay in line with current equipment.
- Results are estimates and may vary based on location, weather, and equipment efficiency.
Related tools
Once you know your load and energy use, these calculators can help you take the next step in planning your system.
These link to solarpakistanguide.com — they’ll go live once each calculator page is published at that slug.
Related articles
A few guides worth reading alongside your results:
Estimates only. Confirm sizing with a licensed solar installer before purchasing equipment, especially for whole-home or safety-critical backup.