How many solar panels can I fit on my roof? How many solar panels do I need for a 4-bedroom house? How many solar panels do I need for a 2000 sq ft home? All of these are typical concerns for a prospective solar homeowner and may have crossed your mind as well. But you need not worry; this article is sure to clear all your doubts and questions regarding how many solar panels you need, so keep reading!

How Many Solar Panels Do I Need –Main Factors to Consider

When it comes to calculating how many solar panels one needs, there are quite many factors that the person must consider before coming to a definitive conclusion. Furthermore, you must also decide what your primary objective behind going solar is.

Do you only wish to reduce your carbon footprint as much as possible? Do you want to become partially self-sufficient for your energy needs? Or do you want to eliminate your reliance on your utility completely are some of the questions you will have to ask yourself?

In this article, we will be focusing on a homeowner intending to install a solar panel system capable enough to accommodate their entire energy needs so as to eliminate their reliance on their utility for energy.

In order to calculate how many solar panels you need, you need to have the following information:

  • How much energy do you use on average
  • The physical size of the solar panels you’re considering
  • What is the climate like in your area, and how many hours of the sun do you get
  • The efficiency of the solar panels you’re considering

How Much Energy Does Your Home Consume on a Monthly or Yearly Basis?

In order to gain insight into how much energy is consumed in your home, you should take a look at your monthly utility bill. Your bill will, in most cases, be able to provide you with the current months as well as the past months’ and annual figures of your energy consumption based on historical data.

Knowing that your energy consumption fluctuates considerably from Month to Month as the seasons change, it would not be wise to calculate the size of your solar panel system based on the energy consumption value of any one month. Instead, your yearly consumption figures will give you the best average value for how big a system you should install and how many solar panels you need.

If the energy consumption for the past year is not stated on your utility bill, you should contact your utility and ask them to provide you with a copy of the past year’s bills or provide you with the figures. Once you have your annual consumption, divide it by 12 (since there are 12 months in a year) to get a monthly average value for your energy consumption.

The values of energy consumption are given in Kilowatt Hours or kWh. If you’re curious, a kilowatt-hour is a unit of energy that entails the amount of electrical power you have consumed multiplied by the duration for which the power was used. In the rare case that your bill does not provide you with your monthly energy usage in kWh, look for the initial and final meter readings and deduct them.

To make further calculations easier, it would be better to convert the average monthly consumption to a daily average by dividing the value by 30 (since there are mostly 30 days in a month).

A small home in a moderately cool area might consume 200 kWh per month, whereas a larger residence in the south, where air conditioners make up the majority of residential energy consumption, maybe use 2,000 kWh or over per month.

An average American home uses about 10,715 kWh of electricity per year. When we divide this by 12 to get the monthly usage, we get an average monthly consumption of around 893 kWh.

It’s vital to keep in mind that solar panels don’t run at full capacity 24 hours a day. Weather conditions, for instance, can potentially diminish the efficiency of your system. For this reason, experts advise adding a 25% margin to your average daily energy needs to ensure you can create as much clean energy as you require.

How Many Hours of Sunlight Can You Expect in Your Area?

The amount of electricity your home solar system will produce is primarily influenced by how many peak sunlight hours you get in your state.

For a better perspective, suppose you reside in Nevada; you will have more peak sunlight hours compared to if you were located in a less sunny state such as Kentucky. This would mean that you’d be able to generate more solar energy than a Kentucky resident having the same size of the system as you do. That isn’t to say that a Kentucky household should not go solar; it just means that a homeowner in Kentucky would require more solar panels to satisfy their energy needs.

A peak sun hour is a period of time during the day in which the irradiation of the sun provides an average of 1000W of power per square meter (roughly 10.5 feet). To look at it another way, 1000 W/m2 of sunlight every hour is one peak solar hour.

Additionally, the number of daily or monthly peak sun hours also entails how much kWh of solar energy 1 kilowatt (kW) of solar panels will produce in one day in your area. So, if your state gets 5 peak sunlight hours per day, 1 kW of solar will generate 5 kWh of energy each day.

What Affects Solar Panel Output Efficiency?

Solar panels aren’t all the same. As such, the solar panels you choose for your system will have a huge impact on the number of solar panels you require as well as their maintenance and longevity. PV solar panels come in a range of wattage capacities from roughly 150 to 400 watts per panel, depending on the cell technology, efficiency, and panel size.

You may be surprised to learn that there are three primary PV solar panel types which are Polycrystalline, Monocrystalline, and Thin-film. Monocrystalline offer the highest efficiency (15% to 20%) among the three but are also the most expensive.

In addition, some modern solar panels have also been introduced that have little to no gridlines allowing them to harness more radiation from the sun. These panels also claim to be less susceptible to delamination compared to traditional solar cells and are more efficient. Furthermore, higher-end panels are also built to be more durable and resistant to rusting and cracking. All these factors play a major role in deciding the number of solar panels you might need for your property.

Due to the enormous variations in the efficiency and quality of solar panels, determining which solar panels are ideal for you or how many you’ll need for your home can be challenging. The point of the matter is that the more efficient the panels are, the more solar energy they will generate and the fewer panels you’ll need to provide the same amount of electricity.

The Physical Size of the Solar Panels You’re Using

It is clear that the size of your roof plays a decisive role in determining the number of solar panels you can install. But did you know that your roof space can also play a part in deciding which type of solar panels you can use?

The size and quantity of solar panels are crucial factors if you have a tiny or irregularly shaped roof. With an expansive usable roof area, you have the option to purchase a large number of big, low-efficiency panels in order to save some cost, all the while meeting your target energy output. However, if your usable roof space is tight or partially unusable, using fewer high-efficiency panels that are small in size might be your only viable option for generating enough power to meet your home’s energy requirements.

Solar panels for residential properties usually measure in at 5.4 feet by 3.25 feet or 65 inches by 39 inches, with some variation across manufacturers. For ages, these measurements have remained mostly the same, yet the efficiency and power output of that same footprint has improved substantially.

How Many Solar Panels Do I Need – Step-By-Step Calculation

Now that you know what factors you need to consider when designing your solar panel system let’s go through an example that will help you better understand how to implement these factors into your planning.

It is important to note, however, that the values used in this example are an average for the entire United States. Therefore, when calculating the number of solar panels for your property, be sure to use values of your own state and property.

Step #1: Determine Your Monthly Energy Consumption

This value will be different for each household in each state so be sure to calculate your average daily consumption correctly using your past utility bills and not pick up a value from the internet. As stated before, the average energy consumption of an American home is 10,715 kWh for a year. Dividing this value by 365 to calculate the average daily consumption gives us approximately 30 kWh.

Average daily consumption: 30 kWh

Step #2: Find Out How Many Peak Hours of Sun Your Area Receives

Figuring out the number of peak sun hours in your area is one of the most challenging parts of the entire calculation because a majority of people do not even have a clue as to what this means, let alone knowing what the value is for their area state.

However, the term “peak sun hours” has been explained above in the “How Many Hours of Sunlight Can You Expect in Your Area?” subsection, so go through it once again if you’re still unclear about it.

For this part, you can use the average number of peak sun hours in your state or city instead of trying to calculate a specific value for your home, which would be incredibly challenging for a layperson.

For this example, let us suppose that you are a resident of the state of Florida, which receives average peak sun hours of 4.

Peak sun hours: 4

Step #3: Calculate the Size of Your Solar Panel System

To calculate the size of the system, we need to divide the average daily consumption by the average number of daily peak sun hours in your state. We will also multiply the fraction by 1000 to convert kilowatts to watts.

In addition, we must also include the efficiency factor in the calculation, which factors in the energy losses during the conversion of solar energy to electrical energy. For this problem, let us take the efficiency factor to be 1.15. However, your solar installer will be able to guide you better about what should be the value for your case.


Size of the system: 8,625W

Step #4: Calculate the Number of Solar Panels You Need

According to the calculation above, your home will need an 8.7kW system. Divide the size of your system by the wattage of the panels you intend to use to get the number of panels you’ll need.

If the number is a decimal, always round up. This means that if you use 400W panels, you’ll need 22 solar panels.

It’s worth noting that the solar panel wattage options available don’t quite match up to an 8.7kW installation. Assuming you’re employing 400W panels, an 8,800W system is your next best alternative.

Frequently Asked Questions (FAQs)

How Many Solar Panels Do I Need for a 4-Bedroom House?

An average American 4-bedroom home needs a 7.8kW system which would mean 20 400-watt panels.

How Many Solar Panels Do I Need for a 2000 Sq Ft Home?

On average, a 2000 sq ft home would need a 4kW system which means 10 400-watt panels. As the wattage of panels decreases, the number of panels used must increase.

How Many Solar Panels Are Needed to Power an Average House?

An average home would need around 20 to 24 340-watt solar panels.

How Many Solar Panels Can I Fit on My Roof?

According to calculations, if a homeowner with an average-sized roof utilized each square foot of their roof space, they could fit in nearly 97 solar panels.

How Many Solar Panels Do I Need for 1000kWh Per month?

A home that has an energy usage of 1000kWh per month would need around 27 300-watt solar panels.


The knowledge provided in this article answers a very common question that homeowners have which is, “How many solar panels do I need?” However, it is recommended to get the assistance of a professional solar installer when designing your own personal system, as the information in the article, while helpful, does not factor in any specific state.

The team at Firefly Solar is ready to answer your questions and give you a no-obligation price quote. Feel free to call us at 864-252-7858 or book a consultation online. And we’ll get in touch within 24 hours.