With power outages on the rise, increasing electricity costs and environmental concerns, residential solar power is fast becoming an attractive option. However, installation can quickly get pricey. Before you start, youll need to calculate how many solar panels are necessary to power your home.
Installing solar panels on your roof can cost anywhere from $15,000 to $50,000, but the 30% federal tax credit, incentives like state and municipal tax credits and tax exemptions can help bring down that cost significantly.
It’s not just about wattage; installation costs, panel performance, location and usage needs also matter. While a professional installer can handle the calculations, this guide will help you estimate your solar panel needs and understand the factors that influence them.
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With climate change accelerating and electricity prices rising, more homeowners are looking to solar power to meet a portion of their energy needs. If you want about 25% of your home’s electricity to come from solar, this guide will walk you through how to make it happen.
Why Go Partially Solar?
There are a few key reasons why homeowners may opt for having solar meet only 25% of their energy use rather than their full demand:
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Cost Savings Installing a full solar system to cover 100% of your home’s energy use can be expensive Going for 25% solar can help reduce the upfront investment while still lowering electric bills
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Limited Roof Space If your roof cannot accommodate enough solar panels to meet all your energy needs partial solar allows you to produce what you can.
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Future Expansion Some homeowners start with 25% solar with plans to add more panels down the road as budgets allow
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Net Metering Limits: Utilities limit the amount of excess solar energy you can sell back to the grid. Partial solar works within those constraints.
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Storm Resiliency: When grid power is down after storms, partial solar can provide backup electricity for critical loads.
No matter the reason, if your goal is for solar to meet 25% of your home’s electricity demand, the steps below will help you get there.
Calculate Your Annual Electricity Usage
The first step is figuring out how much electricity your home uses each year, measured in kilowatt-hours (kWh). Check your last 12 months of electric bills and total up your usage.
The Department of Energy says the average home uses about 10,791 kWh annually. But your actual usage could be higher or lower based on the size of your home, appliances, number of occupants, and local climate.
Once you’ve got your annual usage totaled, multiply it by 0.25 to determine how many kWh 25% of your demand would be.
For example, if your home uses 15,000 kWh per year, 25% of that is 3,750 kWh.
Choose an Appropriate System Size
Next, determine the right solar system size to produce 25% of your electricity. The size is measured in kilowatts (kW).
As a rule of thumb, you’ll need about 20-30 square feet of solar panels per kW of capacity. So for a 5 kW system, you’d need 100-150 square feet of roof space.
Work with a qualified solar installer to evaluate your specific electricity needs, roof size, and panel options to choose the ideal system size.
For the 15,000 kWh home above, a 3-4 kW system would likely cover the 3,750 kWh 25% portion.
Understand Solar Panel Options
There are a few key specs to understand when it comes to solar panels:
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Efficiency: More efficient panels convert more sunlight into energy. Look for at least 18% efficiency.
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Wattage: A solar panel’s power rating (300W, 400W etc). Higher is better.
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Type: Monocrystalline silicon panels are the most efficient and long-lasting.
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Size: Standard panels are about 65″ x 39″. Compact panels are available for small roofs.
Discuss panel options with your installer to choose products optimized for your goals and roof. Top brands include SunPower, LG, Panasonic, and REC.
Carefully Evaluate Roof Size and Orientation
To accommodate solar panels, you’ll need adequate south-facing roof space free from excessive shading. Areas that receive full sun from mid-morning to mid-afternoon are best.
Trees or other buildings that shade your roof can significantly limit solar production. Your installer will assess shading and space constraints to plan the optimal system design and panel locations.
For homes with limited suitable roof space, ground-mount systems are an option albeit at a higher cost.
Understand Local Permitting and Incentives
Most areas require permits to install solar, which your installer will take care of. But it helps to research the local permitting process and costs, which can vary significantly by municipality.
Also be sure to utilize all available federal, state, and local solar incentives and rebates to reduce costs. The federal solar tax credit is 26% for systems installed in 2025. Additional incentives can potentially cover 25-50%+ of your system cost.
Consider Battery Storage
Adding a home battery like the Tesla Powerwall allows you to store excess solar energy for use at night. This also provides backup power when the grid is down.
For 25% solar systems, a battery may be less essential. But it can optimize use of the solar power generated while also providing emergency resilience. Evaluate costs and benefits with your installer.
Focus on Energy Efficiency First
Before going solar, be sure to optimize energy efficiency. This will reduce the system size needed. Prioritize upgrades like air sealing, insulation, ENERGY STAR appliances, and LED lighting. Your utility may offer free energy audits and efficiency rebates.
The less power you use overall, the fewer solar panels you’ll require to meet 25% of your electricity needs. Energy efficiency is the perfect first step.
Final System Design and Installation
Once you’ve evaluated all the factors above, your solar installer will provide a final system recommendation tailored to your goals.
The proposal will include details on the exact number of panels, inverter specs, projected production, monitoring capabilities, and more. They’ll also pull all required permits and coordinate inspection and interconnection.
A reputable local company that has been vetted through the EnergySage Solar Marketplace is your best bet for seamless system design and installation.
Enjoy Lower Electric Bills and a Smaller Carbon Footprint
With an appropriately-sized solar array in place, you’ll quickly notice the benefits of your investment. On sunny days, your meter will spin backwards as excess energy is exported to the grid. And your utility bills will drop as solar meets about 25% of your total electricity consumption.
Going partially solar provides an ideal balance of cost savings, energy resilience, and environmental stewardship. With the right planning and preparation, 25% solar is a powerful step toward energy independence and sustainability.
How to calculate how many solar panels you will need
You can use this formula to calculate how many solar panels youll need. But first, youll need to know:
- Your homes monthly energy consumption
- The wattage of the panels you plan to install
- The amount of peak sunlight hours your home receives per day
Jake Edie, an adjunct professor at the University of Illinois Chicago suggests taking the following steps:
Step 1. Review your monthly electric bill: Its important to determine how many kilowatt-hours of electricity you consume monthly. As an example, we will use 1,500 kWh every month.
Step 2. Convert monthly energy use to daily use: Given 1,500 kWh is consumed per month, to ascertain the daily usage, we need to divide this figure by the average number of days in a month, which is roughly 30.42 days (365 days divided by 12 months).
Hence, the average daily use = 1,500 kWh / 30.42, approximating 49.3 kWh daily.
Step 3. Determine peak sunlight hours: This factor varies based on location and climate. For this example, lets assume that this home receives an average of about 5 peak sunlight hours per day.
To calculate the total daily energy production required, divide the daily energy consumption by the number of peak sunlight hours. This gives the amount of energy your solar panels need to produce per day.
Energy production required = 49.3 kWh per day / 5 hours, which equals 9.86 kW.
Step 4. Calculate the number of panels: Lastly, youll need to determine the wattage of the solar panels you plan to install. The average solar panel efficiency in the US is rated between 250 and 400 watts. For this example, well use a rating of 350 watts.
By dividing 350 by 1,000, we can convert this to kilowatts or kW. Therefore, 350 watts equals 0.35 kW.
Step 5. Determine the required number of solar panels: Divide the daily energy production needed by the solar panels power output.
Number of solar panels needed = 9.86 kW / 0.35 kW per panel, which equals 28.17 panels.
This hypothetical homeowner will need approximately 29 solar panels to generate enough electricity to match their current usage from the electric company. While this calculation may seem straightforward, there are many factors that can affect the effectiveness of solar panels, such as shading, roof orientation and seasonal variations in peak sunlight.
We highly recommend that you seek the guidance of a professional solar installer who can assess your circumstances and provide a tailored solution to meet your needs.They should be certified from the North American Board of Certified Energy Practitioners, which is the solar industry standard. CNET also has a well-researched list of best solar companies.
Factors that affect how many solar panels you will need
The number of solar panels youll need depends on a variety of factors and is going to vary drastically by household. A few factors affecting the amount of panels youll need are:
- Wattage per panel
- Panel efficiency
- How much energy your solar panels are producing
- Your households energy consumption
- Size of the panel
- How many hours of peak sunlight you receive
- The condition and shading of your roof
- Your own personal energy goals and needs
How Many Solar Panels Do You Need? Follow This Easy Breakdown!
FAQ
How much solar is needed to power a home?
Can a house run 100% on solar?
How many solar panels for 25 kWh per day?
Why are solar panels only 25% efficient?
How many solar panels do you need to power a house?
The goal for any solar project should be 100% electricity offset and maximum savings — not necessarily to cram as many panels on a roof as possible. So, the number of panels you need to power a house varies based on three main factors: In this article, we’ll show you how to manually calculate how many panels you’ll need to power your home.
Should you choose solar energy for your home?
Before starting the process of powering your home with solar energy, homeowners should investigate their energy use and consider potential efficiency upgrades. Homeowners should be well aware of their total electricity usage, and consider low-cost and easy-to-implement efficiency measures before choosing solar.
How many solar panels does a tiny home need?
A typical tiny home needs around 15 solar panels to power it completely. However, most tiny homes can only fit a few solar panels on the roof. To compensate for the lack of roof space, you can install a ground-mounted solar array with solar panels lined up adjacent to the house.
Do solar panels increase the value of your home?
Installing solar panels can increase the value of a home by an average of $15,000. Not only can they significantly reduce greenhouse gas emissions, but this addition is becoming more common, with enough solar panels installed across Texas to power over 350,000 homes.
How much does it cost to run a house with solar?
You can run your house using entirely solar energy, but it is a significant investment. Solar panels cost $2.86/W on average, and the total cost of an installation averages $20,000 for a 10 kW system (after accounting for the 30 percent federal solar tax credit).
Can you use 100% green energy in your home?
You can use 100% green energy in your home without the challenges of solar panel installation and at rates as affordable as regular electricity companies, according to Chariot Energy. However, it can take the average U.S. homeowner nearly 8 years to break even on solar panel installations.
