Last Updated: June 17, 2026
What Size Solar Generator Do I Need? Getting It Right.
The right size solar generator isn't the most powerful one — it's the one matched to your actual loads. Most homeowners get this wrong because they skip the load calculation. A refrigerator needs 150 watts running but 1,000 watts to start. A well pump needs 750 watts running but 3,000 to start. Buy for the surge, not the steady state, and you'll have a system that works when you need it.
You spent real money on a solar generator. The next storm hit. You plugged in the well pump. Nothing happened. Or the system ran for six hours and died. Or the battery bank couldn't handle the startup surge and tripped the inverter. You're not alone. Undersized systems are the most common and most expensive mistake in home backup power. This guide exists so you don't make it.
- Refrigerator: 100–300W running | 600–1,200W surge
- Chest freezer: 100–250W running | 500–1,000W surge
- Well pump: 750–2,500W running | 2–5× surge at startup
- CPAP machine: 30–90W running | minimal surge
- FEMA minimum self-sufficiency: 72 hours (Ready.gov)
Most People Start With the Wrong Question
Most buyers start by asking: "What's the best solar generator?"
That's not the first question.
The first question is: "What am I trying to keep running?"
Every home is different. Some homeowners only need phones, internet, and a refrigerator. Others need well pumps, chest freezers, medical equipment, and home office equipment.
The answer determines the size of system you need.
Get this wrong and you'll own an expensive paperweight.
As I explain in the dependency article: the outage isn't the problem. The dependency is. Map your dependencies first. Then size the system that covers them.
Step 1 — Identify Your Critical Loads
Before you buy anything, list the systems your family cannot live without for 72 hours.
For most rural homeowners, that list looks like this:
| Appliance | Running Watts | Surge Watts |
|---|---|---|
| Refrigerator | 100–300W | 600–1,200W |
| Chest freezer | 100–250W | 500–1,000W |
| Well pump (½ HP) | 750W | 2,000–3,000W |
| Well pump (1 HP) | 1,500W | 4,500–6,000W |
| CPAP machine | 30–90W | Minimal |
| Internet router | 10–25W | Minimal |
| LED lighting | 5–15W per bulb | Minimal |
| Phone charging | 5–20W | Minimal |
| Sump pump | 800–1,200W | 2,000–3,600W |
The well pump column is where most people get surprised. A 1 HP well pump drawing 1,500 watts running requires 4,500–6,000 watts at startup. That surge demand determines your minimum inverter size — not the running load.
Start with the solar basics guide if you're not familiar with how inverters, batteries, and panels work together. Understanding the components makes the sizing math much clearer.
Step 2 — Running Watts vs Surge Watts
Every appliance has two power requirements.
Running watts — the electricity needed during normal operation.
Surge watts — the temporary spike required during startup.
This distinction is the most common sizing mistake in home backup power.
A refrigerator may only use 150 watts running. But it briefly requires 1,000 watts to start the compressor. If your solar generator's inverter can't deliver 1,000 watts at startup, the refrigerator won't start — even with a full battery.
The rule: size your inverter for the largest surge load, not the largest running load.
If your well pump surges to 4,500 watts, you need a pure sine wave inverter rated for at least 5,000 watts. No exceptions.
— Wattson | US Solar Institute Trained | Over a decade off-grid
Step 3 — Calculate Daily Energy Use
Now calculate how much energy your critical loads consume in a day.
Example household — basic resilience:
| Appliance | Watts | Hours/Day | Daily Wh |
|---|---|---|---|
| Refrigerator | 150W | 8 hrs | 1,200 Wh |
| Internet router | 15W | 24 hrs | 360 Wh |
| LED lighting (4 bulbs) | 40W | 5 hrs | 200 Wh |
| Phone charging | 15W | 3 hrs | 45 Wh |
| Total | 1,805 Wh |
A system with 2,000 Wh of usable battery storage covers this load for one day.
Example household — full resilience:
| Appliance | Watts | Hours/Day | Daily Wh |
|---|---|---|---|
| Refrigerator | 150W | 8 hrs | 1,200 Wh |
| Chest freezer | 150W | 8 hrs | 1,200 Wh |
| Well pump | 750W | 2 hrs | 1,500 Wh |
| CPAP machine | 60W | 8 hrs | 480 Wh |
| Internet router | 15W | 24 hrs | 360 Wh |
| LED lighting | 60W | 5 hrs | 300 Wh |
| Total | 5,040 Wh |
This household needs at least 5,000 Wh of usable battery capacity per day — plus a buffer for cloudy days and unexpected loads.
Run the Numbers for Your Home
The Solar Calculator tells you panel count, battery bank size, inverter capacity, and cost range based on your actual loads. Five minutes. Real numbers.
GET THE FREE SOLAR CALCULATOR →✅ US Solar Institute Trained · Over a decade off-grid · No inventory to move
Step 4 — Plan for the Real Emergency
Most homeowners size for ideal conditions.
Emergencies are not ideal.
Cloud cover reduces solar charging. Multi-day outages increase total consumption. Unexpected loads appear. Temperatures drop and appliances run harder.
The U.S. Department of Energy reports that average outage duration has increased significantly as extreme weather events intensify. (Source: DOE Electric Power Annual 2024)
The buffer rule: Add 25–50% to your calculated daily energy need.
If your loads total 5,000 Wh per day, size your battery bank for 6,500–7,500 Wh usable capacity.
Size your solar array to recharge that bank in 4–6 peak sun hours.
This is exactly what the system design guide walks through — full sizing methodology with worked examples.
Small, Medium, Large — Which System Fits
Small Backup (500–2,000 Wh)
Best for: Phones, laptops, router, LED lights, CPAP machine
Does not cover: Refrigerator, freezer, well pump
Who it's for: Apartment dwellers, short-term outages, communications priority
Medium Backup (2,000–5,000 Wh)
Best for: Refrigerator, freezer, communications, medical equipment
Does not cover: Well pump, air conditioning, extended outages
Who it's for: Suburban homeowners, 2–3 day outage resilience
Large Backup (5,000–15,000 Wh)
Best for: Well pump, multiple appliances, home office, extended outages
Covers: Most rural homestead critical loads for 1–3 days
Who it's for: Rural homeowners, well-dependent properties, families with medical equipment
Whole Home Backup (15,000–40,000+ Wh)
Best for: Large homes, air conditioning, multiple critical circuits, 7+ day autonomy
Who it's for: Full off-grid or grid-optional homeowners
The cost and ROI guide breaks down what each tier actually costs with real numbers and honest payback timelines.
— Wattson | US Solar Institute Trained | Over a decade off-grid
The Most Expensive Mistake
The biggest mistake isn't buying too much system.
It's buying too little.
An undersized system creates a false sense of security. It works right up until the moment you need it. Then you discover the problem during the outage — the worst possible time to learn.
I made a similar mistake early on. The system looked fine on paper. It failed when the loads hit. Not because the equipment was bad. Because the sizing was wrong.
That's why I flew to Florida and trained at the US Solar Institute. Not because solar is complicated. Because getting the math wrong costs more than getting the education right.
If you want to understand how to avoid the contractor and sizing traps that cost most homeowners thousands, start with the solar basics guide.
Calculate My System Size
Enter your critical loads. Get panel count, battery bank size, and inverter capacity. No guesswork. No contractor needed to get the first number.
CALCULATE MY SYSTEM SIZE →Final Thought
The best solar generator isn't the most expensive one.
It's the one matched to your actual loads — sized for the worst day you'll face, not the average day you hope for.
Get the math right first.
List the critical loads. Find the surge watts. Calculate daily energy. Add the buffer.
Everything else becomes much easier.
The Solar Calculator does this math in five minutes. Use it before you spend a dollar.
— Wattson | US Solar Institute Trained | Over a decade off-grid
The rancher in East Texas who watched his well pump fail during the ice storm knows this feeling. The father in Tennessee who lost a chest freezer full of deer meat knows it too. The veteran who built his forever home and assumed the grid would cooperate — he learned the hard way. You don't need to. Map your loads. Size your system. Build what actually protects your family.
- Solar Basics — Start Here — understand the system before you size it
- System Design Guide — full sizing methodology with worked examples
- Cost and ROI Guide — what each system tier actually costs
- Water Systems Guide — well pump power requirements in detail
- Emergency Preparedness Guide — the full resilience system
- The Outage Wasn't the Problem — why dependency mapping comes first
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