Solar Calculator

Q: What is the difference between grid-tied and off-grid solar?

A grid-tied system connects to your utility power grid. Extra energy you make goes to the grid, and you pull power from the grid at night. An off-grid system uses batteries to store power and is not connected to the grid at all. Grid-tied systems cost less and don't need batteries. Off-grid systems work for cabins, RVs, or places with no grid access.

Q: What system size do I need for my home?

Click the Estimate from my bill button after entering your monthly electric bill. The calculator divides your estimated yearly usage by your local solar resource to suggest a system size in kilowatts. A typical US home uses about 10,000 kWh per year, which usually needs a 6 to 9 kW system depending on location.

Solar Calculator

Updated Jul 16, 2026 By Jehan Wadia

Introduction

This free solar calculator helps you figure out how much energy a solar panel system can make for your home or business. It works for two types of setups: grid-tied solar systems that connect to your local power grid and off-grid solar systems that run on batteries alone.

In the grid-tied mode, you enter your monthly electric bill, your location, and a few details about your panels. The calculator then estimates your yearly energy output in kilowatt-hours, your cost savings, and your environmental impact. It also shows monthly production numbers, a step-by-step breakdown of the math, and key performance metrics like capacity factor and specific yield.

In the off-grid mode, you enter your daily power needs and battery specs. The tool tells you exactly how many solar panels and batteries you need, how to wire them, and gives you a visual diagram of your panel layout.

All results update instantly as you change your inputs. Whether you want to size a rooftop solar system, compare panel types, or plan a fully independent off-grid setup, this calculator gives you clear answers backed by real solar radiation data and industry-standard formulas.

How to Use Our Solar Calculator

Enter details about your location, electricity use, and solar setup below. The calculator will estimate your annual energy output, system size, battery needs, and environmental impact. Choose Grid-Tied Solar if your home or business is connected to the power grid, or Off-Grid Sizing if you need a standalone system with batteries.

Grid-Tied Solar Mode

Output Units: Pick US Customary or Metric to change how results like CO₂ and distance are shown.

Property Type: Select Residential for homes, Commercial for businesses, or Non-Profit for churches, schools, and similar buildings.

Average Monthly Electricity Bill: Type in the dollar amount you usually pay each month for electricity. This helps estimate how large your solar system should be. If you want to understand what your bill means in terms of energy consumption, our electricity cost calculator can help you break that down further.

Location Preset: Pick a city close to you from the dropdown list. This fills in your latitude and sky clearness automatically. Choose "Custom" if your city is not listed.

Latitude: Enter your location's latitude in degrees. This is filled in when you pick a location preset, but you can type your own value.

Longitude: Enter your location's longitude in degrees. This helps identify your solar resource area.

Local Sky Clearness: Choose how sunny your area typically is. Pick "Very Sunny" for desert climates and "Cloudy" for rainy or overcast regions.

System Size (DC kW): Enter the size of your solar panel system in kilowatts. Click Estimate from my bill to have the calculator suggest a size based on your electricity bill. For a more detailed look at individual panel sizing and specifications, you can also try our solar panel calculator.

Module Type: Pick the kind of solar panel. Standard is most common. Premium panels produce more power. Thin Film panels cost less but produce less.

Array Type: Choose how your panels are mounted. Roof Mount is the most common for homes. Tracking systems follow the sun and produce more energy. If you need to figure out how much roof space you have available, use our roof area calculator.

Tilt: Enter the angle of your panels in degrees. 0° is flat and 90° is vertical. Click Suggest Optimal Tilt & Azimuth to get the best angle for your latitude. If your panels are going on a pitched roof, our roof pitch calculator can help you determine the existing angle.

Azimuth: Enter the direction your panels face in degrees. 180° is due south, which is best for locations in the Northern Hemisphere.

System Losses: Enter the total percentage of energy lost to wiring, shading, dirt, and other factors. Click Break down losses to set each loss type on its own. Wiring losses in particular depend on cable length and gauge — our voltage drop calculator can help you size conductors to minimize those losses.

Soiling Loss: Enter the percentage of energy lost due to dirt, dust, and debris on your panels.

DC to AC Size Ratio: Enter the ratio of your panel wattage to your inverter wattage. A typical value is 1.10 to 1.25.

Inverter Efficiency: Enter the efficiency of your inverter as a percentage. Most modern inverters are between 95% and 98%.

Albedo: Enter how much light the ground near your panels reflects. Grass is about 0.2, concrete is about 0.3, and snow is about 0.8.

Ground Coverage Ratio: This field appears when you select a tracking array type. Enter the ratio of panel area to total ground area.

Bifacial Panels: Turn this on if your panels collect sunlight from both sides. Then enter the extra gain percentage, which is typically 5% to 12%.

Off-Grid Sizing Mode

Total DC Load: Enter the total wattage of all devices and equipment you plan to power. If you need to convert between amps and watts for your appliances, our amps to watts calculator or wattage calculator can help.

Hours Equipment Runs Per Day: Enter how many hours per day your equipment will run, from 0 to 24.

System Voltage: Pick the voltage for your battery bank. Common choices are 12V for small systems, 24V for mid-size, and 48V for larger setups. Understanding the relationship between voltage, current, and resistance is key — our Ohm's law calculator explains these fundamentals.

Days of Backup Power Required: Enter how many days you want your batteries to last without any sun. If you also want a fuel-powered backup, our generator sizing calculator can help you pick the right generator for your loads.

Battery Amp Rating: Enter the amp-hour (Ah) rating of one battery. This is usually printed on the battery label.

Region Preset: Pick the region closest to you. This fills in the peak sun hours value. Choose "Custom" to type your own.

Peak Sun Hours Per Day: Enter the average number of peak sun hours your location gets each day. This is set automatically when you pick a region.

Solar Panel Watt Rating: Enter the wattage of one solar panel you plan to use. The calculator will tell you how many panels you need in total.

Solar Panel Calculator: Grid-Tied & Off-Grid System Sizing

A solar panel system turns sunlight into electricity for your home or business. This solar calculator helps you figure out how much energy a solar system can produce and how many panels you need. It works for two types of setups: grid-tied and off-grid.

Grid-Tied Solar Systems

A grid-tied system stays connected to your local power grid. When your panels make more electricity than you use, the extra power goes back to the grid. When the sun is down, you pull power from the grid as normal. Most homes and businesses use this type of system because it costs less and does not need batteries.

The grid-tied side of this calculator estimates how many kilowatt-hours (kWh) your system will produce each year. It uses your location, roof angle, panel type, and system size to run the math. It also shows your capacity factor, specific yield, and performance ratio — three numbers that tell you how well your system performs. You can even see how much CO₂ your system offsets each year. To explore your household's broader environmental impact, try our carbon footprint calculator or ecological footprint calculator.

Off-Grid Solar Systems

An off-grid system is not connected to the power grid at all. It stores energy in batteries so you have power at night or on cloudy days. This setup is common for cabins, RVs, and remote buildings where grid power is not available.

The off-grid side of this calculator tells you exactly how many batteries and solar panels you need. You enter your daily power usage, pick your battery size, and choose how many backup days you want. The calculator then sizes your full system, including how to wire panels in series and parallel. When wiring your system, a wire size calculator can help you choose the right cable gauge to handle the current safely.

Key Terms to Know

Peak Sun Hours (PSH) is the number of hours per day that sunlight is strong enough for full panel output. A location with 5 peak sun hours gets strong, direct sunlight for about 5 hours a day. Sunnier areas like Arizona have more peak sun hours than cloudy areas like Seattle.

System losses are the small amounts of energy lost to things like dirty panels, wiring, shading, and inverter conversion. Every solar system has some loss. A typical total loss is around 14%, meaning your panels deliver about 86% of their rated power in real-world conditions. You can use our percentage calculator to quickly work out what any loss percentage means for your system's output.

Depth of Discharge (DoD) is how much of a battery's stored energy you actually use. Most lead-acid batteries should only be drained to 50% to last longer. This calculator uses a 50% DoD to protect battery life.

Formulas used

Plane-of-Array Irradiance (Isotropic Tilt Model)

H_{POA} = H_b \, R_b \cos\gamma + H_d \frac{1+\cos\beta}{2} + GHI \cdot \rho \frac{1-\cos\beta}{2}

Annual AC Energy Output

E_{AC} = P_{dc} \times H_{POA} \times D

Combined Derate Factor

D = G_{array} \times M_{mod} \times B_{bifacial} \times (1 - L) \times \eta_{inv} \times C_{clip}

Capacity Factor

CF = \frac{E_{AC}}{P_{dc} \times 8760} \times 100\%

Off-Grid Corrected Daily Demand

E_c = P_{load} \times h \times 1.2

Off-Grid Required Battery Amp-Hours

Ah_{req} = \frac{\frac{E_c}{V_{sys}} \times d}{DoD}

Off-Grid Total Solar Panels Required

N_{panels} = \left\lceil \frac{E_c}{P_{panel} \times \frac{PSH}{1.55} \times N_{ser}} \right\rceil \times N_{ser}

Frequently asked questions

What is the difference between grid-tied and off-grid solar?

A grid-tied system connects to your utility power grid. Extra energy you make goes to the grid, and you pull power from the grid at night. An off-grid system uses batteries to store power and is not connected to the grid at all. Grid-tied systems cost less and don't need batteries. Off-grid systems work for cabins, RVs, or places with no grid access.

How accurate is this solar calculator?

This calculator uses NREL-style solar radiation models and industry-standard formulas. It gives a solid estimate, but real-world output can vary by about 7% in any given year due to weather changes. For the most precise numbers, a local solar installer can do a site survey that accounts for exact shading, roof condition, and local utility rules.

What system size do I need for my home?

Click the Estimate from my bill button after entering your monthly electric bill. The calculator divides your estimated yearly usage by your local solar resource to suggest a system size in kilowatts. A typical US home uses about 10,000 kWh per year, which usually needs a 6 to 9 kW system depending on location.

What does the clearness index mean?

The clearness index measures how much sunlight passes through the atmosphere to reach the ground. A value of 0.62 means very sunny, clear skies like a desert. A value of 0.40 means cloudy or coastal weather. Pick the option that best matches your area's typical weather.

What tilt angle should I set my panels to?

A good rule of thumb is to set your tilt angle equal to your latitude. Click the Suggest Optimal Tilt & Azimuth button and the calculator will set this for you. If your panels are on a roof, use the angle your roof already has.

Why is azimuth set to 180 degrees?

An azimuth of 180° means the panels face due south. In the Northern Hemisphere, south-facing panels get the most sunlight over the course of a day. If you live in the Southern Hemisphere, the calculator will suggest 0° (due north) when you click the optimize button.

What are system losses and why do they matter?

System losses are small amounts of energy lost to things like dirty panels, wiring resistance, shading, snow, and inverter conversion. The default value is 14.5%, which is typical. You can click Break down losses to adjust each category on its own. Lower losses mean more energy reaches your home.

What is the DC to AC size ratio?

This is the ratio of your total panel wattage (DC) to your inverter capacity (AC). A ratio of 1.2 means you have 20% more panel power than your inverter can handle at once. This is normal and helps the inverter run at full power more often during the day. Most installers use a ratio between 1.10 and 1.25.

What are bifacial solar panels?

Bifacial panels collect sunlight from both the front and the back side. Light that bounces off the ground or roof hits the back of the panel and makes extra electricity. The gain is usually 5% to 12% more output. Turn on the Bifacial Panels toggle if you plan to use this type of panel.

What is albedo and how does it affect my results?

Albedo is how much light the ground reflects back up toward your panels. A white roof or snow reflects a lot of light (0.6 to 0.8), while dark grass reflects very little (0.2). Higher albedo means slightly more energy hits your panels, especially at steeper tilt angles.

How does the off-grid calculator size my battery bank?

It multiplies your daily energy use by a 1.2 battery loss factor, then multiplies by the number of backup days you want. It divides that total by 50% depth of discharge to protect battery life. Finally, it calculates how many batteries you need in parallel for capacity and in series to match your system voltage.

Why is a 1.2 battery loss factor applied?

Batteries lose some energy during charging and discharging. The 1.2 factor adds 20% extra capacity to make sure you actually get the energy you need after these real-world losses. Without it, your battery bank would be slightly undersized.

What does 50% depth of discharge mean?

Depth of discharge (DoD) is how much of a battery's total energy you use before recharging. At 50% DoD, you only drain the battery halfway. This makes lead-acid batteries last much longer. The calculator uses 50% DoD as a safe default for all off-grid sizing.

What are peak sun hours?

Peak sun hours (PSH) is the number of hours per day when sunlight is strong enough to equal full-power output from your panels. It is not the same as total daylight hours. Phoenix, AZ gets about 6 peak sun hours, while Seattle, WA gets about 3.5. The calculator uses this number to size your solar array.

Why are peak sun hours divided by 1.55?

The 1.55 weather derating factor accounts for cloudy days, rain, and seasonal changes that reduce actual sunlight below the average. Dividing by 1.55 makes the off-grid system large enough to keep your batteries charged even during bad weather stretches.

What is capacity factor?

Capacity factor is the percentage of a system's maximum possible output that it actually produces over a year. A 7 kW system could theoretically make 61,320 kWh in a year if it ran at full power 24/7. If it actually makes 10,700 kWh, its capacity factor is about 17.4%. Solar systems typically have capacity factors between 15% and 25%.

What is specific yield?

Specific yield is the total energy produced per kilowatt of installed panel capacity. It is measured in kWh per kWp per year. A specific yield of 1,500 means each kilowatt of panels produces 1,500 kWh in a year. Higher numbers mean your location and setup are more productive.

What is performance ratio?

Performance ratio (PR) compares your actual energy output to what the panels would produce if there were no losses at all. A PR of 80% means you keep 80% of the available solar energy after all losses. It helps you judge how well your system is designed regardless of location.

How is CO₂ offset calculated?

The calculator multiplies your annual energy output in kWh by 0.855 pounds of CO₂ per kWh. This is the average emission rate for the US power grid. The result shows how much CO₂ your solar system prevents from entering the atmosphere by replacing grid electricity.

Can I use this calculator for a commercial property?

Yes. Select Commercial under Property Type. The calculator works the same way for any size system. Commercial systems are often larger, so you may need to enter a higher monthly bill and bigger system size. The math and solar resource data apply equally to residential and commercial projects.

What does the panel array diagram show?

The diagram in the off-grid results shows how to wire your solar panels. Each column is a string of panels wired in series to match your system voltage. The strings are then wired in parallel to add up the current. This layout makes sure your array delivers the right voltage and power.

Should I pick 12V, 24V, or 48V for my off-grid system?

Use 12V for very small systems under 1,000 watts. Use 24V for mid-size systems between 1,000 and 3,000 watts. Use 48V for larger systems above 3,000 watts. Higher voltages reduce the current in your wires, which means less energy loss and thinner cables.

What module type should I choose?

Standard panels are monocrystalline and the most common choice. Premium panels have higher efficiency and a lower temperature coefficient, so they make more power in the same space. Thin Film panels cost less but also produce less energy per square foot. Most homeowners choose Standard or Premium.

Does this calculator account for shading?

Yes, but only as a percentage loss. The default shading loss is 3% under the loss breakdown. If your roof has heavy shading from trees or buildings, increase this number. For exact shading analysis, a solar installer can use specialized software with 3D modeling of your property.

What happens if I enter the wrong latitude?

The calculator uses latitude to estimate how much sunlight your location gets throughout the year. A wrong latitude will give you inaccurate energy estimates. Use a location preset from the dropdown or look up your latitude on any online map service to get the right value.

How many backup days should I plan for off-grid?

Most off-grid systems plan for 2 to 3 days of backup. This covers a typical stretch of cloudy weather. If you live in an area with long cloudy periods or harsh winters, consider 4 to 5 days. More backup days means more batteries and higher cost.

Why does the calculator round panel and battery counts up?

You cannot buy a fraction of a panel or battery. The calculator always rounds up so your system is never undersized. This means you may have slightly more capacity than the minimum required, which provides a small safety margin.

What is ground coverage ratio?

Ground coverage ratio (GCR) is the area of your panels divided by the total ground area they sit on. It only appears when you select a tracking array type. A lower GCR means more space between rows, which reduces shading between panels. A typical value is 0.3 to 0.5.

Can this calculator estimate my savings?

The calculator estimates your annual energy production, which you can multiply by your electricity rate to get approximate savings. For example, if your system produces 10,000 kWh and you pay $0.16 per kWh, your yearly savings would be about $1,600 before any credits or incentives.

Do the results update automatically?

Yes. Every time you change an input, the results recalculate instantly. You do not need to click the Calculate button unless you want to. This makes it easy to compare different system sizes, panel types, or locations quickly.

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