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Off-Grid Power Calculator
"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."
🦍 Why I Built This Off-Grid Power Calculator
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. Figured 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.
We flew to Florida. Spent three weeks getting officially trained at the US Solar Institute. Same training that state-licensed installers go through. Came back home and built a proper 16 kW, 48V system that actually works.
I built this off-grid power calculator so you do not have to learn the hard way. Whether it is an oversized contractor rip-off or an undersized disaster waiting to blow up.
This tool uses the EXACT formulas professional installers use. Add your devices. Get your real numbers. Size your system based on what you actually need.
I do not make a dime from this off-grid power calculator. I just want you to get it right the first time. — Wattson
Calculate Your Real Power Needs
"You cannot fight the system if your lights blink out every time a cloud sneezes. Add your gear below and I will 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. Do not 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 will 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 will tell you what you need to stay powered when the grid goes dark.
🔗 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.
Read the Full Guide →⚙️ Component Selection Guide
Ready to buy equipment? Learn which inverters, charge controllers, and panels deliver the best value without contractor markup.
Choose Your Components →🔧 Installation Guide
Step-by-step instructions for installing your off-grid solar system safely and correctly.
Start Installing →💰 Cost & ROI Guide
Calculate your payback period, compare DIY vs contractor pricing, and see the real cost of staying on the grid.
Analyze Your Costs →Frequently Asked Questions
How accurate is this off-grid power calculator?
This off-grid power calculator uses industry-standard formulas with a 30% safety buffer. It accounts for system efficiency losses (80%), winter conditions, and real-world performance degradation. 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. Depends on your specific appliances and usage patterns. Use this off-grid power calculator to input your actual devices for a personalized recommendation. Do not let contractors sell you a 12 kW system when you only need 3 kW.
Can I use this off-grid power calculator for RV or van life?
Absolutely. This off-grid power calculator works for any 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 off-grid power 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. Requires electrical knowledge and proper permitting. Use this off-grid power 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 is included in the recommended battery bank size?
The battery recommendation provides 2 days of autonomy at 80% depth of discharge (DOD). 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 Location-Specific Guidance
Access our FREE OffGridPowerHub GPT Assistant for personalized guidance on permits, regulations, and location-specific requirements. Enter your zip code and get instant answers.
Access Free GPT Tool →Used by homesteaders and preppers to navigate the permit maze without hiring expensive consultants.