Number of Solar Panels You Need (Energy – Sunlight – Consumption – Efficiency – Roof Space)

Getting off-grid by installing solar panels is an exciting prospect for many homeowners who want to reduce their energy costs and dependence on electrical supplies. Understanding how many solar panels you need is critical to ensure you meet your daily energy needs.

The average American home would require 20-25 solar panels to generate enough electricity per day to meet the power requirements. As this is just a general estimate, some additional considerations are required before confirming the number of solar panels required.

To understand how many panels you would need, the following need to be factored in:

  • The average daily power usage
  • The sunlight levels in your area
  • The size and efficiency of the solar panels
  • Number of solar panels you need
  • The available space on your roof

Now, let’s examine the process and calculations to determine how many solar panels you need to power your home!

How Much Energy Does Your Home Use Per Day?

Your first step in the process of understanding how many panels you would need is to know how much power your home uses every day. To do this is a relatively simple task, and you use your utility bills to calculate it.

How To Calculate Your Daily Power Consumption Using Your Utility Bill

Knowing your average daily, monthly, and annual energy usage is essential as this will determine how many solar panels would be needed to offset your usage. Here, your utility bill will give you all the information you need.

Find the line item that shows your kWh usage from the current or previous month, which will give your energy usage for that period. Ideally, you want the total annual energy usage to get an accurate monthly and then daily average.

You can calculate this by taking your monthly kWh usage and dividing it by 24 to get an average hourly usage. To get an annual usage, take that exact kWh figure and multiply it by 12 to give you a yearly usage.

See also: Calculate Solar Panel kWp & KWh (KWh Vs. KWp + Meanings)

What To Consider When Determining Existing Power Consumption

Before you look at solar panels, you need to consider a few aspects of your existing appliances, whether you have air conditioners or planning to add them in the future and how efficient your existing appliances are.

Let’s start with air conditioning. Aircon systems use vast amounts of power, so it would not be advisable to use your solar panels to run your air-con as it would leave minimal capacity for anything else.

This is why you may opt to have your panels only provide power to the home and keep your air-con running off the grid supply.

Check whether your major appliances have good energy ratings so they don’t take up most of the power generated from the panels. You also need to know whether you will be adding any other appliances in the future that could add to the load.

While this may seem like a lot of work, it will be worth the time invested in doing it properly to ensure you get the exact number of solar panels you need to run your home off the grid.

Use the following table to get an idea of the power you consume;

AppliancesStarting WattsRunning Watts
Central Aircon 10000 BTU45001500
Sump Pump21501050
Garage Door Opener2350875
Electric Fan Heater10002000
Internet Router515
Television 49” LED085
PlayStation 4585
Light Bulb LED09
Security System0500
Washing Machine21501150
Electric Kettle30001200
Electric Oven02150
Electric Stove 8-Element02100
Add Item With Highest Starting Watts To Total Running Watts450014463
Home appliance – starting power watts and running watts

How Much Electricity Does The Average US Home Use?

According to the US Energy Information Administration (EIA), the average US home uses around 10649 kWh per year, which is about 900 kWh per month, or around 30 kWh per day / 1,25 kWh per hour.

We will use these figures to determine the number of solar panels needed for the average home. Remember that you don’t get sunlight all the time, so when there is bad weather, the generating capacity of your panels is diminished.

It would be best to decide whether you want a total or partial energy usage offset if your panels deliver 100% of your required power or only 80% or 75%.

This is why it is wise to include a ‘buffer’ of 25% in the calculation to ensure that the number of solar panels you need will more than meet your daily and hourly requirements.

Now that we know the average, we can move to the next step of the calculation: the levels of sunlight you receive in your area.

Solar panels covering a roof of a house

Number of Solar Panels Based On Sunlight

Solar panels rely solely on the sunlight they receive to generate electricity for your home. However, depending on where you are in the US, the levels of sunlight vary.

So a home in Arizona or California would receive more average daily and annual sunlight than a home in Washington, which needs to be factored into the calculation.

The Renewable Resource Data Center provides information about the levels of sunlight for each state and major city across the USA.

A comparison, an average home in California would only need a 7 kW system to supply the total energy requirements. The available sunlight is more significant than in Massachusetts, where the same size home needs a 9 kW system.

Once you know the levels of peak sunlight you receive, we can move on to the next part of the calculation to establish how many solar panels you need for your home. We will estimate 5 hours of peak sunlight per day for this calculation.

How To Calculate How Much Power Your Panels Need To Produce Per Hour Of Sunlight

This calculation assumes that you want your solar panels to supply 100% of the required electricity to your home.

  • Take your hourly wattage in kWh and multiply by 1000 to get the unit to watts = 1250W per hour or 30 000W / 30kW per day.
  • Using 5 hours of sunlight means your solar panels need to generate 6000W or 6 kW of power in the available peak sunlight hours to achieve 30 kW per day.
  • If you were looking at 300W solar panels, you would need 20 of them to generate this power.

If you only wanted your solar panels to provide 80% of the power, you would take 80% of 30 kW, which is 24 kW per day, giving you 4,8 Kw per available peak hour of sunlight.

With 300W solar panels, this would be 16 would be required. However, it’s not as simple as other factors influencing solar panels’ production efficiency.

Solar panels on a house roof fitted vertical and horizontal 1

Calculate Solar Efficiency For your Solar Panels

This measures how much of the available sunlight can be used to create electricity. On average, the existing solar panels have an efficiency rating of 20%.

Suppose you have a panel with a 14% efficiency rating vs. a 21% efficiency rating. The higher rating will produce 50% more power with the available sunlight than the lower-rated panel. As a rule, higher efficiency rated panels are more expensive but worth the extra investment.

Chinese manufacturers like Trina Solar, Canadian Power, and LongGi produce panels with higher efficiency at lower costs per W than US manufacturers like LG, Panasonic, and SunPower.

What Factors Influence Solar Panel Efficiency?

A few different elements contribute to the efficiency of solar panels.

  • The material used to build the panel, whether monocrystalline or polycrystalline construction
  • Positioning and angle – Solar panels should be mounted facing north and optimally angled based on geographical location and solar angle to receive the most sunlight.
  • Reflective quality – some materials reflect more light than others, so a material with lower reflective properties is more efficient.
  • Wiring – how well the wiring is organized and the quality thereof within the panel also affects the efficiency.
  • Busbars – the structures that capture and transfer the electricity will affect the panel’s efficiency.
  • Location climate – Less electricity would be produced with snow or more cloudy conditions with rain vs. clear sunny conditions.
  • Temperature – With higher temperatures, the efficiency and electricity output will decline, so you need panels designed to be efficient in warmer environments if you live in a warm area.

While this is a lot to consider, most reputable solar installers will have this information readily available for your area. They will advise on the type, size, and quantity of the panels you need.

Mono and Poly Solar Panels Two house with different solar panels

Which Are More Efficient Panels – Monocrystalline Or Polycrystalline?

When it comes to construction, solar panels are either monocrystalline or polycrystalline, which refers to the material the panel is made of.

Monocrystalline panels are made from a single source of silicon and, as such, are more efficient due to their uniformity. In contrast, polycrystalline panels are made from various silicon crystals melted together.

In addition, the top 5 most efficient solar panels available are all monocrystalline panels.

How Much Roof Space Would You Need For Your Solar Panels?

The average US home would require between 20 and 25 solar panels to meet the energy needs daily and since these have to go on your roof, knowing how much space you have and how much you need is essential.

Another essential element is the space available on your roof to install solar panels. Based on your property size and the relative roof space available, you may be able to utilize more panels at a lower wattage if you have the space.

If you don’t have a lot of roof space, fewer higher-wattage panels would be required to cover the power generation requirements.

You would need first to know the available square footage of your roof and match that to the wattage and size of the panels that would deliver the power you need to run your home. The average solar panel size for residential installation is about 17,55 sq ft.

So if you have available roof space of 2000 sq feet, then you could install 113 solar panels, and if each of those were 300W, this would give you 33,9 kW, which is massive.

For a 9 kW system, you’d only need 30 X 300W solar panels totaling about 526 square feet. If you were using 250W panels, you would need 36 panels, which would take up 631 sq feet.

Solar panels on a house with a metal roof

How Many Panels Would I Need Based On System Size?

Now that we have determined all the various factors around solar panels and calculated the system size you would need, let’s end with a look at how many solar panels you would need based on system size.

The table below shows how many 320W solar panels would be needed for each average system size.

No. of PanelsSystem SizeAnnual Electricity Output
134 kW6400 kWh
196 kW9600 kWh
258 kW12 800 kWh
3210 kW16 000 kWh
3812 kW19 200 kWh
4414 kW22 400 kWh
Number of solar panels and the energy output

As a ballpark figure, you can see how many solar panels you would need for your home based on the system size, so your first order of business is to know your electricity consumption and then proceed through the rest of the calculations.

Number of Solar Panels Based On Your Property Size

The table below indicates the number of panels required based on property size.

Home Size in SQ FTProjected Energy required per annumEstimated No. Of Solar Panels
10004,71 kWh /year15
20009,42 kWh / year29
250011,775 kWh / year37
300014,130 kWh / year44
The number of solar panel needed for size of home

Number of Panels Based On Weight and Supporting Roof

Most solar panels weigh about 40 lbs and in most cases, installing them on a pitched roof only adds about 2,8 lbs per square foot, and for flat roofs, that number is about 5 lbs per square foot.

Aside from the space, another critical consideration is whether your roof can handle the weight of the installation. Solar panels are not light by any means, and the design and construction of your roof influence the number of panels you can install.

At this point, it becomes a question of wattage VS weight as if you add too many panels and your roof can’t support the weight, it will eventually collapse, which is NOT something you ever want to deal with.

Adding 20 solar panels would increase the weight by around 800lbs, spread over the roof space and across the roof frame.

Solar panels mounted on a flat roof

When Would You Need Roof Support For Solar Panels?

Most homes won’t struggle with the extra weight, but if you live in an area where you have to contend with the weight of snow on your roof, you may need additional roof support structures for your solar panels.

If your roof is old or has any failures or weak points, you may require supporting structures for the solar panels.

A reputable solar installer would first inspect the roof to ensure that the existing superstructure can deal with the added weight and consider the impact of rain, sleet, or snow on the roof weight.

They would advise whether any supporting structures need to be added to your installation to support the weight of the panels.

Also, solar panels are becoming lighter and more efficient as the research and development of this technology improves bodes well for current and future installations.


Photo of author
Elliot has 20+ years of experience in renewable technology, from conservation to efficient living. His passion is to help others achieve independent off-grid living.

SolVoltaics is an affiliate and an Amazon Associate, we earn from qualifying purchases - at no extra cost to you.