# Solar Calculator Free solar panel calculator to calculate exactly how many solar panels you need, annual power generation, system costs, savings, and payback period for your home. Canonical page: https://invoicemama.com/calculators/solar-calculator This is a free browser calculator. Treat results as planning aids and confirm figures against your own measurements, codes, and professional judgment. ## How to use this solar calculator Enter annual electricity use, panel wattage, sun hours, and system assumptions to estimate array size, production, and ballpark savings. ### 1. Gather electricity usage Pull annual kilowatt-hours from your utility bill or estimate monthly usage and multiply by twelve so production targets match real consumption. ### 2. Enter panel and site details Choose module wattage that matches hardware you price, enter tilt and azimuth if prompted, and add peak sun hours or shading factors for your region. ### 3. Set efficiency and losses Adjust inverter efficiency, wire losses, and dust or mismatch derates so modeled output stays conservative compared with vendor quoting tools. ### 4. Interpret system size and production Read estimated DC capacity, AC energy yield, and offset percentage versus your load. Confirm roof space and electrical service limits before you finalize designs. ## Frequently asked questions ### How many solar panels do I need for my home? The number of panels depends on your electricity usage, panel wattage, and sun hours. A typical home uses 10,000-11,000 kWh per year and needs 20-30 panels (300-400W each). Use our calculator to get an exact number based on your specific situation. ### How do I calculate solar panel output? Solar panel output = Panel wattage x Peak sun hours x System efficiency. For example, a 400W panel with 5 peak sun hours and 80% efficiency produces: 400 x 5 x 0.80 = 1,600 Wh (1.6 kWh) per day. ### What are peak sun hours and how do they affect solar panels? Peak sun hours are the equivalent hours per day when solar irradiance averages 1,000 watts per square meter. Most locations get 3-7 peak sun hours daily. More peak sun hours mean more energy production and fewer panels needed. ### How much roof space do I need for solar panels? Each solar panel typically requires 17-20 square feet. A 6kW system (about 15-20 panels) needs roughly 300-400 square feet of usable roof space. South-facing roofs with minimal shade work best. ### What is solar panel efficiency and why does it matter? Efficiency measures how much sunlight a panel converts to electricity. Modern panels range from 15-22% efficient. Higher efficiency means more power from less space, important for smaller roofs or shaded areas. ### How long do solar panels last? Quality solar panels last 25-30 years with minimal degradation. Most manufacturers guarantee 80-90% output after 25 years. Inverters typically need replacement after 10-15 years, but panels keep producing for decades. ### Can I go completely off-grid with solar panels? Yes, but it requires battery storage and oversizing your system. Off-grid systems need 2-3x more panels than grid-tied systems to account for cloudy days and seasonal variations. Battery costs add significantly to the investment. ### How much money can I save with solar panels? Average savings range from $10,000-$30,000 over 20 years, depending on electricity rates and system size. With federal tax credits (currently 30%), payback periods are typically 6-10 years. Higher electricity rates mean faster payback. ### Do solar panels work on cloudy days? Yes, but at reduced capacity. Panels produce 10-25% of their rated output on cloudy days. This is why system sizing accounts for weather patterns and seasonal variations in your location. ### What is the difference between monocrystalline and polycrystalline panels? Monocrystalline panels are more efficient (18-22%) and space-efficient but cost more. Polycrystalline panels are slightly less efficient (15-17%) and more affordable. For most homes, monocrystalline panels offer better long-term value. ### How do I maintain solar panels? Solar panels need minimal maintainence. Rain usually cleans them naturally. In dusty areas, hosing them down 2-4 times per year maintains efficiency. Annual professional inspections ensure optimal performance and catch issues early. ### Will solar panels increase my home value? Studies show solar panels increase home value by 3-4% on average. A $20,000 solar system typically adds $15,000-$20,000 to resale value. Buyers appreciate lower utility bills and environmental benefits. ## Solar Installers: Get Paid Faster with Professional Invoicing Invoice Mama helps solar contractors create professional estimates and invoices in seconds. Turn your solar calculations into polished proposals that win jobs and get you paid faster. - [Create your first invoice free](https://app.invoicemama.com/sign-up) --- Invoice Mama is invoicing software for contractors, freelancers, and small businesses. It is not a tax, legal, or accounting firm. For current pricing, use the live pricing page. **More:** [Home](https://invoicemama.com/) - [Pricing](https://invoicemama.com/pricing) - [Guides](https://invoicemama.com/guides) - [Tools](https://invoicemama.com/tools) - [Calculators hub](https://invoicemama.com/calculators)