Considering going solar, but you’re not sure how many panels you’ll need to make it worthwhile? Many homeowners want to know how many panels they’ll need to buy as they budget for this home upgrade. 

While the average household needs around 15-20 solar panels to offset their energy needs, the amount you need will be impacted by your specific energy usage, roof size and orientation, home location, and more. Let’s dig into the details.

In this article: 

• How to Calculate How Many Solar Panels You Need 
• Factors That May Influence the Number of Solar Panels Needed
• Practical Considerations
• The Bottom Line About Solar Panel Needs
• Frequently Asked Questions

How to Calculate How Many Solar Panels You Need 

To calculate roughly how many solar panels you should install, you need to know specific details like how much energy you consume, the wattage of the solar panels you’re looking to buy, and even your area’s energy production ratio from solar power. (Production ratio is how much electricity a solar panel produces under the average sunlight and weather conditions in your region — in the U.S., production ratios can range from 0.9-1.6.)

Step-by-Step Calculation

1. Determine your annual energy usage in kilowatt-hours (kWh). You can total up your annual kWh by looking at past utility bills.
2. Find the production ratio in your state with a map like this one.
3. Consider the wattage of solar panels you want to purchase.

 

Your equation will look like this:

 

Annual Energy Usage (kWh) ÷ Production Ratio ÷ Solar Panel Wattage =

 Number of Solar Panels Needed

 

For example, let’s say that your home uses the American household average of 896 kWh per month. If we multiply that by 12 to get your annual usage, that number is 10,752 kWh. If you live right in the middle of the contiguous United States, your production ratio is 1.4. And maybe you’re looking at 350-watt solar panels. 

 

Your calculation would be:

 

10,752 kWh ÷ 1.4 ÷ 350 watts = ~22 solar panels

Online Calculators

You can use online calculators to estimate how many solar panels you may need, especially if you’re unsure of your annual energy usage or your state’s production ratio. This can simplify the process for you, but these online calculators can also have their limitations. They use general data that may not be accurate for your home’s specific solar needs and might give you an incorrect number.

 

We recommend consulting with a professional installer who will consider all of your home’s nuances, from details like tree cover and available roof space to your area’s climate quirks.

Factors That May Influence the Number of Solar Panels Needed

The number of panels you’ll need isn’t one-size-fits-all. Factors like the amount of electricity you use, the power output of the solar panels you buy, how much sun you get, and even your roof size can all impact how many panels you’ll need to invest in.

Energy Consumption

First, you need to understand how much electricity your home actually uses. 

 

Check your past few electric bills and see the kilowatt-hours consumed each month. This should give you a general sense of your regular electricity usage. According to the U.S. Energy Information Administration, the average household uses just under 900 kWh per month.

 

Habits like turning off lights when you leave a room, how often you use your air conditioning, and whether you have high-efficiency appliances all impact your electricity usage. The less electricity your home uses, the fewer solar panels you’ll need.

Solar Panel Wattage

How much electricity does a solar panel produce? Solar cells come in varying wattage levels, meaning one type or brand might have a different power rating than another. Many solar panels have a power output between 250-400 watts in ideal conditions. Since higher-wattage panels are able to produce more electricity than lower-wattage panels, you can install fewer panels if you opt for a high-wattage system.

 

If your area gets about four peak hours of sun per day, then 1 kW of solar panels would generate 4 kWh of energy in one day under ideal conditions. If you use 28 kWh of energy on a typical day, then 7 kWh of solar panels could meet your home’s needs. 

Climate and Sun Exposure

Another significant aspect to consider is your location’s general climate and weather conditions. Sunnier states can produce more solar energy, so homes that see regular sunshine would need to install fewer solar panels than homes in more overcast regions.

 

A region’s sunlight is measured in peak sun hours, which measure the intensity of sunlight under ideal conditions. One peak sun hour equals an hour of sunlight that reaches an average of 1,000 watts (1 kilowatt) of power per square meter. 

 

So while your solar panels may see seven hours of sunlight in a day, they’ll really only see maybe four or five peak sun hours. States in New England can get between three to five hours of peak sun hours per day, while states in the Southwest could see five to seven peak sun hours per day.

Roof Size and Angle

While solar cells can work in all weather conditions and climates, they do need quite a bit of open space and to be positioned at the proper angle. 

 

A solar panel system won’t work well in a shaded area with lots of tree cover. And your roof may seem large, but chimneys or skylights will limit the space you can cover with solar panels. A standard solar panel will measure around 3.25 feet by 5.5 feet, and you’ll need multiple panels as part of your overall solar panel system.

 

A solar system will also work best on a south-facing roof with a slope that corresponds to the latitude of where you live — many homes in the U.S. are positioned at a slope of 30-45 degrees.

Practical Considerations

Even after calculating the number of solar panels you may need, other factors must be considered before scheduling your installation. How much will it cost? How many solar panels do you need if your family expands? Can you get any financial incentives for installing solar? 

 

Keep these questions in mind as you look at your solar options.

Budget Constraints

While using solar power for your home can help save on electricity bills, there are the upfront costs to think about. Solar panels and installation can range in price from $2.40 to $3.60 per watt. 

 

So if you need a 7 kW solar system to power 28 kWh of daily electricity use, you could be looking at total installation costs of $16,800 to $25,200.

 

You should also factor in the cost of regular maintenance over time, which will increase your solar panel system’s lifespan and preserve its efficiency. Panel cleaning can cost around $10-$20 per panel, and solar panels are designed to last for 20-30 years. So make sure you save up for that annual maintenance over several decades.

Future Energy Needs

Your home probably won’t use the same amount of energy year in and year out. Perhaps your family will expand, or you’ll build a new addition to your house. No matter what, you should think about the potential for increased energy consumption over time. 

 

While you may not need extra kilowatts of solar power now, you may need it sometime in the future. It could be beneficial to install an extra panel just in case, or leave room for additional panels in the coming years.

Local Regulations and Incentives

Typically, solar installers need permits from their local governments before installing rooftop panels. Afterward, the local government will have an inspector ensure the new system follows the proper electrical and safety codes before they approve it to connect to the power grid. Permitting fees will vary depending on your jurisdiction.

 

On the other hand, your local government may offer incentives or rebates to help lower solar installation costs. Many states offer property tax exemptions to keep homeowners from paying more based on the increased property values that come with solar. Other states also offer sales tax exemptions on solar systems, and even a few offer exemptions on both taxes.

 

There’s also the federal solar tax credit, which gives back 30% of the cost of installing a solar panel system when you file a claim on your federal income taxes. And lastly, look into rebates from your utility company that may reduce the up-front cost of a solar installation.

The Bottom Line About Solar Panel Needs

In the end, the best way to determine how many solar panels your home needs is by speaking with installers who know your area. They can talk with you about your home’s specific power needs, suggest a proper wattage level for your solar panels, and make informed recommendations based on your region’s climate conditions.

 

Professional solar installers can also sit down and talk with you about any budgetary concerns and point you in the direction of available rebates or incentives that can help offset those costs.

Frequently Asked Questions 

How do I calculate how many solar panels I need for my house? 

You need three details: your annual energy usage in kilowatt-hours, the solar production ratio in your state, and the wattage of your desired solar panels. You’ll divide your energy usage by the production ratio, then divide that by the wattage.

 

Annual Energy Usage (kWh) ÷ Production Ratio ÷ Solar Panel Wattage = 

Number of Solar Panels Needed

How many solar panels do you need for different home sizes? 

Home Size	Average Annual Energy Consumption	Estimated Number of Panels
1,000 sq ft	4,710 kWh	8-12
1,500 sq ft	7,596 kWh	14-17
2,000 sq ft	10,512 kWh	16-25
2,500 sq ft	12,025 kWh	20-30
3,000 sq ft	14,175 kWh	24-30

 

While home size doesn’t automatically dictate how many solar panels you need, it can give you a general idea. You still need to factor in details like how many hours of peak sunlight you get and the wattage of the solar panel system.

How many solar panels do I need based on my energy usage?

That depends on how many peak sunlight hours your home gets in a day and the wattage level of the solar panels you want to use. If your home gets about four peak sun hours in an average day, then 1 kW of solar panels would generate 4 kWh of energy in one day under ideal conditions. If your energy usage is around 28 kWh in a typical day, then you’d need at least a 7 kW solar panel system. And if your solar panels are 350 watts each, then that’s 20 panels you’d need.

Can solar panels power my entire house? 

Yes, it’s possible to have your entire house powered by solar energy.  To power your home at night or on low-sunlight days, you’d also need backup solar batteries to store the solar power you’d collected during the daytime. Solar systems that allow you to go completely off-grid tend to be larger than average and more expensive.

Do I need solar batteries? 

You definitely need solar batteries if you want to store and use the solar power you’ve collected during peak sunlight hours. This can help you keep your home running at night, during low-sunlight days, or through power outages.

Are solar panels good for the environment? 

Solar energy doesn’t produce greenhouse gasses or other air pollution — that’s just Solar 101. By reducing our reliance on polluting power sources like fossil fuels, we can work to slow continuing climate change. The production process for sourcing materials for solar panels can be environmentally intensive, however, so make sure you research the types of panels you’re getting, how their materials are sourced, and whether they can be recycled when they reach the end of their life.

Can solar panels run my house during a power outage?

Solar panels can’t power your home during an outage, but if you keep backup solar batteries, you can continue to run your house that way if you’ve lost power.