1. Watts
Watts describe how much power the load uses while running. A light, refrigerator, pump, tool, heater, and EV charger all use very different watts.
Solar kit sizing
Kit Sizing Basics Start With Watts, Time, and Truth
A solar kit should not be sized from hope, advertising, or a box label. It should be sized from the real load, how long that load must run, whether it has startup surge, how much solar can be produced, and what the battery, inverter, wiring, permits, and inspection path can safely support.
The sizing question
What Are You Actually Trying to Power?
Kit sizing begins with a load list. Without the load list, panel count and battery size are guesses.
A homeowner may say, “I need a solar kit.” A better starting sentence is: “I need to run this refrigerator, these lights, this internet router, this well pump, this garage door, or this EV charger for this many hours.”
Once the load is clear, the kit can be built around real numbers: watts, amps, volts, surge, runtime, battery capacity, solar production, inverter output, wiring, and code requirements.
Core sizing ideas
The Six Numbers That Matter First
These are not the only numbers in a real design, but they are the first numbers that keep the conversation honest.
2. Volts
Voltage matters for equipment selection, wiring, breakers, inverter output, pump compatibility, and whether the load belongs on backup at all.
3. Amps
Amps affect conductor size, breaker size, service capacity, charger planning, pump circuits, and whether electrical upgrades may be needed.
4. Surge
Motors, compressors, pumps, refrigerators, freezers, garage doors, and tools may need extra startup power for a short moment.
5. Runtime
Runtime turns power into energy. A 500-watt load for one hour is a very different battery problem than a 500-watt load for twelve hours.
6. Recharge
Solar production, weather, shade, roof direction, season, battery charging, and utility interaction decide how the system recovers after use.
Sizing Is Not a Substitute for Design
Back-of-napkin sizing can help a property owner ask better questions, but it is not the final design. Real solar and battery systems require equipment specifications, code review, wiring calculations, disconnects, grounding, labels, permits, utility approval where applicable, and inspection.
SunKits.com is educational. Solar kits, battery backup, pumps, EV charging, and hybrid inverter systems require proper design, licensed installation, and code compliance.
Read the Safety Page
Common mistake
Confusing Power With Energy
Power is how hard the load pulls. Energy is how much it uses over time.
A high-power load that runs briefly may use less total energy than a smaller load that runs all day. A pump can create a large startup demand but may only run a short time. A refrigerator may draw less power while running but cycle throughout the day and night.
Battery sizing needs both ideas: how much power must be delivered now, and how much energy must be delivered over time.
Sizing language
Plain-English Solar Kit Terms
These words show up in almost every kit conversation.
Watt
Instant power. A load drawing more watts is pulling harder from the inverter, battery, solar system, or grid.
Kilowatt-Hour
Energy over time. A 1,000-watt load running for one hour uses one kilowatt-hour.
Surge
Short startup demand. Motors and compressors may need a burst of power before settling down.
Runtime
How long the system should run the load. Runtime is where battery capacity gets real.
Simple math
The Basic Runtime Conversation
The rough idea is simple: load size multiplied by time creates energy demand.
A 100-watt load running for ten hours uses about 1,000 watt-hours, or 1 kWh. A 1,000-watt load running for ten hours uses about 10 kWh. Real designs add losses, inverter behavior, battery limits, temperature, reserve capacity, surge, manufacturer instructions, and safety factors.
The purpose of this simple math is not to create a final design. It is to prevent fantasy sizing.
Quick Sizing Pattern
- List each load.
- Write down running watts.
- Estimate hours per day or outage hours.
- Check startup surge for motors and compressors.
- Add realistic simultaneous loads.
- Compare the result to inverter output and battery capacity.
- Add design review, code review, and permit requirements.
Planning path
How to Size a Kit Conversation
Name the Job
Bill reduction, backup, pump power, EV charging, pool runtime, workshop power, ranch loads, and critical loads are different sizing problems.
List the Loads
Include every load that matters. Do not forget hidden loads, controls, chargers, pumps, refrigeration, and future equipment.
Read Nameplates
Equipment labels can reveal voltage, amps, watts, horsepower, breaker size, and manufacturer requirements.
Estimate Runtime
Decide how many hours each load should run and whether it runs during the day, at night, during peak rates, or during outage.
Check Surge
Motors, pumps, compressors, garage doors, refrigerators, freezers, and tools may need more startup power than their running watts suggest.
Match Equipment
The inverter, batteries, panels, wire, breakers, disconnects, and permit drawings should be selected after the load reality is clear.
What Sizing Can Clarify
A good sizing conversation turns fuzzy expectations into reviewable facts.
- Which loads are essential
- Which loads are battery killers
- How long the battery might need to run
- Whether pump or motor surge is a major issue
- Whether EV charging changes the electrical service plan
- Whether the project is simple, moderate, or serious
What Sizing Should Not Pretend
Rough sizing is not engineering. It should make the project smarter, not bypass the professionals.
- Do not use rough math as permit drawings.
- Do not ignore manufacturer instructions.
- Do not ignore wire sizing, voltage drop, and breaker rules.
- Do not include every heavy load on battery backup casually.
- Do not promise runtime without understanding actual usage.
- Do not install solar or batteries without qualified design and inspection.
Manga lesson
Load Monster Hates Math
Load Monster wants everyone to guess. Sunny Kitto wants to buy more panels. Solar Sensei brings a clipboard, reads the nameplates, and ruins the monster’s day.
Solar Sensei Says:
“Watts tell you how hard. Hours tell you how long. Surge tells you how rude the load will be when it wakes up.”
See Manga Episodes
Next step
Use Sizing to Ask Better Questions
Start with the load list, then review runtime, surge, battery capacity, inverter output, solar recharge, site conditions, and the permit path.