"I learned the hard way what happens when you get solar wrong. Melted batteries. Almost burned down my house. Now I'm here to make sure you get it right the first time—no guessing, no contractor BS, just real numbers."
⚠️ TARIFF ALERT: Equipment prices jumping 25-40% in 2025. Calculate your needs NOW before the supply chain tightens.
🦍 Why I Built This Calculator (And Why You Can Trust It)
It was 2011. My electric bills went from $80/month to $850/month in six months — brand new house, energy-efficient appliances, no changes. The power company's explanation? "That's what your meter says."
I was done feeding the beast. Time to go solar.
So I hired an electrician with 20 years of experience, figuring he knew his stuff. Dead wrong. He undersized everything. Recommended a 4 kW, 12V system that blew up every time I plugged in a water kettle.
Within a year, the batteries literally melted. Almost caught the whole system on fire.
But I wasn't done yet! I convinced my partner we needed to learn this ourselves. We flew to Florida, spent three weeks getting officially trained at the US Solar Institute — the same training that state-licensed installers go through. Came back home and built a proper 16 kW, 48V system that actually works.
Since then, we've helped over 5,000 patriot families size and build their own systems. I built this calculator so you don't have to learn the hard way like I did — whether it's an oversized contractor rip-off or an undersized disaster waiting to blow up.
This tool uses the EXACT formulas professional installers use — the same math they taught us in certification classes in Florida. Add your devices, get your real numbers, and size your system based on what you actually need.
I don't make a dime from this calculator. I just want you to get it right the first time. — Wattson
Calculate Your Real Power Needs
"You can't fight the system if your lights blink out every time a cloud sneezes. Add your gear below and I'll show you how much power you really need to live off the leash."
Start with your everyday tools: fridge, lights, pump, screens. If it eats watts, it goes on this list. But don't forget to add gear you may not use every day—like power tools and shop equipment. When we get to the actual components recommendation, we'll point you toward a system that can grow as your power needs grow.
🏠 Appliances
💡 Electronics & Lighting
🔨 Power Tools
🔧 Shop & Hand Tools
⚕️ Medical Equipment
Wattson's Tip
When in doubt, round UP on watts and hours. The grid will fail at the worst possible time. Better to have a little extra power than a little extra regret.
Your Daily Energy Appetite
Total Daily Energy
0.0
kWh/day
Wattson's Safety Buffer (+30%)
0.0
kWh/day
Recommended Array Size
0.0
kW
Add your devices above and I'll tell you what you need to stay powered when the grid goes dark.
📧 Email Me These Results
Get your personalized power calculations + access to our FREE Solar Estimator tool (normally $197). No BS, just real numbers you can use to plan your system.
🔒 Zero spam. Your email stays private. Used only to send your results.
Join 5,000+ patriots who've already calculated their path to energy independence.
Wattson's Recommended Setup
☀️ Solar Array
🔋 Battery Bank
⚡ System Voltage & Inverter
"Print this out and hand it to your installer—or use it to fact-check the next 'expert' who walks onto your land."
🔗 Ready to Build Your System? Start Here:
📚 Complete Beginner's Guide
New to off-grid solar? Start with our comprehensive beginner's guide covering everything from basic concepts to complete system design.
This calculator uses industry-standard formulas with a 30% safety buffer, accounting for system efficiency losses (80%), winter conditions, and real-world performance degradation. It's the same method US Solar Institute-certified installers use, but without the profit-padding oversizing. Your results will be within 5-10% of professional assessments.
What size solar system do I need for a small cabin?
Most small cabins need 2-4 kW of solar panels with 6-10 kWh battery storage, depending on your specific appliances and usage patterns. Use the calculator above to input your actual devices for a personalized recommendation. Don't let contractors sell you a 12 kW system when you only need 3 kW.
Can I use this calculator for RV or van life?
Absolutely. This calculator works for any off-grid application: cabins, tiny homes, RVs, vans, boats, or full homesteads. Just input your devices and get recommendations sized for your lifestyle. RV systems typically range from 800W-2000W of solar with 3-6 kWh of battery storage.
Why does this calculator add a 30% safety buffer?
The 30% buffer accounts for real-world conditions contractors conveniently ignore: winter sun angles reducing output by 40-50%, aging panels losing 10-15% efficiency over 10 years, cloudy days producing 10-25% of rated capacity, and system losses from wiring, inverter efficiency, and battery charging inefficiency. This buffer keeps your lights on when theory meets reality.
Should I hire a professional or DIY my off-grid system?
DIY saves $15,000-$40,000 on a typical 5-8 kW system, but requires electrical knowledge and proper permitting. Use this calculator to get your real numbers, then decide: hire a professional for complex installations (grid-tied, whole-home backup) or DIY for simpler off-grid setups. Either way, knowing your true power needs prevents getting oversold by 200-300%.
What's included in the recommended battery bank size?
The battery recommendation provides 2 days of autonomy at 80% depth of discharge (DOD), which means you can survive two consecutive cloudy days without solar input. This is the sweet spot between safety and cost. Lithium batteries handle 80% DOD easily; lead-acid should only use 50% DOD, requiring larger banks.
🤖 Get Jurisdiction-Specific Advice
Access our FREE OffGridPowerHub GPT Assistant for personalized guidance on permits, regulations, and location-specific requirements. Enter your zip code and get instant answers to questions like "Do I need a permit?" and "What are my local building codes?"