Solar Load Calculator
Add common appliance and equipment loads to estimate daily watt-hours, adjusted kWh, running watt demand, and surge capacity before sizing a solar system.
Enter system values
Estimate daily energy use, running watts, and surge demand before sizing panels, batteries, and inverter.
Results update locally in your browser. Raw inputs/results are not stored, logged, placed in URLs, or sent to analytics.
Solar planning sanity check
Use these rows to check assumptions before buying panels, batteries, inverter, controller, or cable.
Educational estimate only. Verify electrical code, permits, equipment manuals, fuse/breaker sizing, and qualified installation requirements before using results in a real system.
What this means
Plan around about 3.74 kWh/day after margin, with roughly 1125 W running and 1600 W surge capacity.
| Load | Watts | Hours/day | Daily energy |
|---|---|---|---|
| Fridge / always-on load | 70 W | 24 | 1680 Wh |
| Lights | 40 W | 5 | 200 Wh |
| Laptop / office load | 65 W | 6 | 390 Wh |
| Pump / motor load | 800 W | 0.5 | 400 Wh |
| Miscellaneous loads | 150 W | 3 | 450 Wh |
- Watts
- 70 W
- Hours/day
- 24
- Daily energy
- 1680 Wh
- Watts
- 40 W
- Hours/day
- 5
- Daily energy
- 200 Wh
- Watts
- 65 W
- Hours/day
- 6
- Daily energy
- 390 Wh
- Watts
- 800 W
- Hours/day
- 0.5
- Daily energy
- 400 Wh
- Watts
- 150 W
- Hours/day
- 3
- Daily energy
- 450 Wh
Copy / print
Copy or print this local-only worksheet. Values are not stored by CalcShelf.
Watch-outs
- Nameplate watts and real duty cycles can differ.
- Motor starts and compressors may need much higher surge power.
- Use a plug-in meter for critical loads before buying equipment.
Safety boundary
Load estimates drive every other solar number. Measure critical loads when possible. Treat these outputs as planning estimates, not installation instructions.
Displayed numbers are rounded to 2 decimal places where helpful.
Use the Solar Load Calculator for the right job
Use this first when you are asking “how much solar do I need?” because panel, battery, inverter, and generator math all start with the load.
Good for
- Off-grid cabin load estimates
- RV, van, or small backup-power planning
- Checking whether motor or compressor surge will drive inverter size
How to use it
- Enter realistic watts and hours for each load group.
- Add a safety margin for cold weather, cloudy days, or unknown usage.
- Use the adjusted daily kWh in the panel count and battery bank calculators.
What changes the result
- Nameplate watts versus measured watts
- Duty cycle for fridges, pumps, fans, and compressors
- The largest starting surge load
- Seasonal or cloudy-weather margin
Next calculators to check
Solar Panel Count Calculator
Convert daily kWh into panel quantity.
Solar Battery Bank Size Calculator
Turn daily kWh into storage capacity.
Solar Inverter Size Calculator
Use running and surge watts to size inverter output.
FAQ
How do I calculate solar load?
List each appliance or load, multiply watts by hours used per day, then add the watt-hours together. Add margin before using the result to size panels or batteries.
Should I use running watts or surge watts for solar sizing?
Use daily watt-hours for panels and batteries. Use running watts plus surge watts when sizing the inverter and checking motor-start loads.
Does CalcShelf save my solar load numbers?
No. The calculator runs in your browser. CalcShelf does not save raw inputs or results, put them in the URL, or send them to analytics.
Safety and accuracy notes
Solar and battery systems can involve high DC current, fire risk, permit requirements, electrical code, roof loading, wind loading, temperature derating, fusing, disconnects, and manufacturer limits. Use this as an educational planning estimate only, then verify real designs with qualified sources and equipment manuals.
Get a better answer from the Solar Load Calculator
- Start with the example values to see how the tool behaves.
- Swap in your own numbers, even if they are rough first-pass estimates.
- Change one input at a time so you can see what actually moves the result.
What the result means
The result is a planning number for one part of a solar system: load, panels, strings, wire, battery, inverter, controller, mounting, backup, or payback.
How to use it
Use it to compare scenarios before buying hardware, then cross-check the adjacent calculators so one component is not sized in isolation.
What can change it
Solar estimates can move quickly with sun hours, shading, temperature, battery limits, voltage drop, surge loads, roof constraints, utility rules, and code requirements.
Good for
Plan a solar or backup-power system before buying equipment.
Check next
Compare your result with Solar Panel Count Calculator, Solar Battery Bank Size Calculator, Solar Inverter Size Calculator when you want more context.
Best habit
Run a conservative case and an optimistic case. The gap between them is often more useful than a single answer.
Common uses
- Plan a solar or backup-power system before buying equipment.
- Check one sizing layer with local-only browser math.
- Pair with adjacent solar calculators for a full system sanity check.
Common questions
Is the Solar Load Calculator private?
Yes. CalcShelf calculators run without an account, do not save calculator entries, and do not put raw inputs into shareable URLs or analytics events.
How accurate is the Solar Load Calculator?
It is a solar planning worksheet. Sun hours, shading, derating, temperature, fusing, wire ratings, battery limits, permits, and equipment manuals can change the final design.
What should I check after using the Solar Load Calculator?
Verify electrical code, fusing, wire ampacity, voltage drop, battery and inverter limits, roof constraints, permits, and manufacturer manuals.
Which calculator should I try next?
Use the related calculators below to cross-check the same decision from another angle before you act.
Method behind the estimate
Solar calculators use load, energy, voltage-drop, battery-capacity, inverter, controller, roof-fit, and payback formulas with bounded user-entered assumptions.
Why the detail matters
Treat the output as a planning worksheet. Electrical code, permits, fusing, disconnects, temperature derating, battery chemistry, roof structure, and manufacturer limits can change the real design.
Privacy guardrail
Your calculator values are for you. CalcShelf does not require an account, save calculator entries, put your numbers into shareable URLs, or use raw inputs as analytics events.
Copy or print safely
Use any copy, print, or worksheet controls as local handoff tools for your own notes, supplier calls, lender questions, or implementation checklist. They are there to help you explain the result to a human.
Before acting
Treat the result as a decision draft, not a verdict. Recheck the source numbers, run a downside case, and verify the real-world rule, quote, label, or spec that controls the final answer.
Last reviewed: May 11, 2026. See methodology and editorial policy for formulas, assumptions, rounding, review approach, and limitations. Before buying or installing solar equipment, confirm electrical code, permits, fusing, wire ratings, battery limits, roof constraints, and equipment manuals.