When considering a move to solar power, it’s essential to build the right system for your home’s energy needs. Selecting the correct number of solar panels will impact your energy production and long-term savings. Installing too few panels will underpower your home, while too many can result in an overpriced system. 

In this guide, we’ll explain how many solar panels to install and provide a formula to calculate your home’s panel needs. We’ll also explain other factors that leading solar companies consider when building a solar panel system.

 

 

---

 

How to Determine Your Solar Panel Needs

Consider three key factors to calculate your solar panel needs: annual energy use, roof size and angle, and solar panel size. We’ll review how each factor impacts your final panel calculation. 

Annual Energy Consumption

First, determine your annual energy consumption or the energy your home uses in a calendar year. This is measured in kilowatt-hours (kWh) and includes all devices and appliances that require a power source. Small and large appliances, including your refrigerator, HVAC unit, water heater, and lights, impact your average energy usage. Energy-efficient appliances and systems help reduce energy consumption and, thus, your need for more solar panels. 

In addition, your household’s size impacts your energy needs. According to the U.S. Energy Information Administration (EIA), the average household consumed 907 kWh of electricity monthly, or 10,884 kWh annually, in 2022.

Reputable solar installation companies will review your average electricity usage to determine the appropriate solar system size for your home. Review 12 months of monthly electric bills to determine your average annual use and find the sum of your typical consumption. Include your usage through a full calendar year to account for seasonal changes when heating and cooling bills are higher.  

Total Solar Panel Wattage

Top-quality solar panels provide the highest amount of power but are only the right choice for some homes. Since a solar panel system is built around your total electricity needs, your panels will match that necessary output. Panel wattage, or power rating, indicates how much electricity they produce in ideal conditions. Most solar panels emit between 250 to 450 watts (W) of power. The higher the panel’s wattage, the more power it generates. 

Opting for a high wattage will reduce the number of solar panels needed for your project. Homeowners may choose higher-wattage panels to cover up to 100% of their energy needs. If your energy needs are lower or you only want a partial conversion system, lower-wattage panels are a better choice. 

Production Ratio

Calculating a solar power system’s production ratio means determining its estimated power production over time versus the system size’s total wattage. Since the amount of sunlight your panels receive varies daily, this ratio is difficult to calculate accurately. However, you can get an idea by dividing the annual production estimate by the system’s size. 

We’ll use the example of a 10 kW system producing 15 kWh of electricity annually. This solar energy system has a production ratio of 1.5 (15 / 10 = 1.5). This scenario applies to homes located in areas with abundant days of sunlight, such as California. If you live in an area with frequent cloudy conditions, such as Connecticut, your ratio could drop to 1.2. In the United States, production ratios typically range from 1.3 to 1.6. 

 

---

 

How to Calculate the Number of Panels You Need

Now that we’ve covered the three contributing factors, we will apply these details to the formula used when planning a solar panel installation: number of panels = system size / production ratio / panel wattage.

Let’s revisit the previous average household stats and apply them to this formula.

• Household energy needs: The average U.S. household uses 10,884 kWh annually, which we’ll round up to 11,000 kWh.
• Production ratio: The average range is between 1.3 and 1.6, so we’ll calculate for both. 
• Panel wattage: A mid-range panel is 300 W.4

Here is our formula: 

• Number of panels = 11,000 kWh / 1.3 / 300 = 28.205 (28 panels needed)
• Number of panels = 11,000 kWh / 1.6 / 300 = 22.916 (23 panels needed)

Based on these calculations, the average home would need 23 to 28 300-watt panels to meet average household electricity consumption. 

Let’s try the same formula with higher-wattage solar panels:

• Number of panels = 11,000 kWh / 1.3 / 400 = 21.154 (21 panels needed)
• Number of panels = 11,000 kWh / 1.6 / 400 = 17.188 (17 panels needed)

Based on these updated calculations, the average home could use 17 to 21 400-watt panels to meet its energy needs effectively. Final calculations will vary based on your production ratio and average utility bill spending. 

Additional Calculation Tools

The National Renewable Energy Laboratory (NREL) provides the PVWatts tool to help homeowners estimate their energy production and solar panel costs. Once you enter your home address, the tool uses a satellite image of your roof. From there, you can adjust the number of panels, system size, and other factors to estimate how much energy your solar system will generate annually.  

 

---

 

Factors That Impact How Many Solar Panels You Need

Below, we discuss key factors to consider when determining the number of solar panels to install on your home’s roof. 

Amount of Sunlight

The amount of sunlight your roof receives plays a major role in your photovoltaic (PV) panel production. Panels that receive unrestricted, direct sunlight convert more energy. Although panels could receive up to seven hours of sunlight daily, most areas in the United States average between three and five peak hours. 

Installing residential solar panels in areas with consistent shade results in poor solar panel output and limits the power available to your home. Overcasting from nearby trees or other obstructions will reduce your energy production. Solar installers will install panels based on contact with direct sunlight.

Available Roof Space

Depending on the type of solar panels chosen, you may need ample roof space. Installers must work around chimneys, skylights, and shaded areas to accommodate solar panels. You’ll need higher-efficiency panels to compensate for these restrictions if you have limited space. These panels generate more energy, reducing the number of panels needed for your project. With ample roof space, you could opt for less efficient, more affordable solar panels. These panels generate lower energy, requiring more panels on your roof. 

Solar Panel Cost

According to the Solar Energy Industries Association’s 2022 U.S. Solar Market Insight report, the average cost of a solar system was $25,000 before incentives. However, final costs vary based on your local solar market, system size, and solar panel type. Choosing the best solar panels will yield the most energy production and savings, plus they require less roof space. However, you’ll pay more in upfront costs. Less efficient solar panels carry a lower price point but require more panels to generate ample power. 

Homeowners can use the federal solar tax credit to offset installation costs. You receive up to 30% back as a credit to apply toward your federal tax liability. Additional state credits, rebates, and incentives are available but vary in each state. Check the Database of State Incentives for Renewables & Efficiency (DSIRE) for available incentives in your area. 

Solar Panel Efficiency

Solar panel efficiency refers to the amount of sunlight a solar panel can convert to usable electricity. These ratings, expressed as percentages, represent how well the panels make this conversion. The higher the rating, the better the panel generates usable energy. For example, if a solar panel has an efficiency rating of 22%, it absorbs and converts 22% of the sunlight that hits its surface. The most efficient solar panels today range between 16% to 20%. Panels with ratings of 20% or above are considered high efficiency.

How much solar power your panels generate depends on your roof’s location, panel composition, and design. Although investing in efficient panels requires a higher upfront cost, you’ll generate more electricity and see long-term savings on your energy bills. In addition, efficient solar systems often generate more power than needed. You can pair a solar battery with your system to store this extra energy when panels are inoperable or during blackouts.

Solar Panel Size

Solar panels come in different sizes to suit your roof’s design. Solar cells affect how much power is produced by a solar array. The more cells within the structure, the higher the potential power production. 

A standard residential 60-cell solar panel is 39 inches by 66 inches (3.25 feet by 5.5 feet). Professional solar installers will measure your roof and choose your solar panel size based on available space and home energy needs. Larger panels could contain up to 72 solar cells and will increase your total project costs.

Solar Panel Type

The three most common types of solar panels are monocrystalline, polycrystalline, and thin-film panels. Each panel type has different benefits, power outputs, and costs. Here’s an overview of each panel option. 

• Monocrystalline: These high-efficiency panels offer the best power production and highest efficiency with ratings between 15 to 20% or higher. They carry the highest price tag, but your solar project would require fewer panels due to better performance. Monocrystalline panels work well on homes with limited roof space.
• Polycrystalline: This panel option offers 13% to 16% efficiency ratings and starts at a lower price point. These panels work well on homes with ample roof space. Because they have a lower energy production than monocrystalline options, you’ll need more panels for your solar system. 
• Thin-film: Offering the least efficiency and power production, thin-film panels work best for smaller home projects such as a garage or shed. Thin-film panels are the most affordable but offer efficiency ratings as low as 7%. 

 

---

 

Our Recommendation

While the formula shared in this article can give you an idea of your solar panel needs, it won’t be completely accurate. Additional factors, including your energy needs, home design, local climate, surroundings, and budget, will affect your solar system design. A solar installer will take measurements of your roof and give a more accurate estimate of how many panels you need. We recommend requesting quotes from at least three installers to find the best system. 

---

Read more: Our Methodology