How Many Solar Panels Do I Need? 4 Step Solar Calculator Guide

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Most homeowners need 15 to 19 solar panels to meet their power needs. Understanding how many solar panels your home needs helps you evaluate solar quotes effectively so you can maximize your energy production and bill savings without sacrificing your budget. 

But how exactly do you calculate the right number of panels for your home? Our home solar experts put together a step-by-step solar calculator guide to help you answer the age-old question, “How many solar panels do I need?”.

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Solar system sizing guide: how many solar panels do you need?

Home Size	Estimated monthly electric bill	Number of solar panels needed	Estimated roof space needed	Estimated solar cost after incentives
1,000 sq. feet	$77	8	141 sq. feet	$6,537
1,500 sq. feet	$115	12	211 sq. feet	$9,806
2,000 sq. feet	$153	15	264 sq. feet	$13,075
2,500 sq. feet	$191	19	334 sq. feet	$16,343
3,000 sq. feet	$230	23	405 sq. feet	$19,612

Estimates assumed 146 monthly peak sun hours, 400-watt solar panels, and a $0.17/kWh electric rate.

How many solar panels you need varies with multiple factors, like where you live, the design of your roof, and energy consumption. To find out how much solar your specific home needs, use this solar calculator, which considers your personal energy usage and local rates to give you a personalized estimate.

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Step-by-step guide: how to calculate how many solar panels you need

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4 steps for calculating how many solar panels you need:

It's that easy! By using these four steps, you can estimate how many solar panels your home needs, so you'll be prepared when you talk to solar installers!

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Example: Calculating how many solar panels you need to power a home

Mr. Exampleson lives in sunny Florida and wants to install solar panels to lower his high electric bills so he can put that money toward retirement instead. He read his electricity bill and saw that he used 1,200 kWh of electricity last month, which cost him $168! 

He found that his home receives about 160 peak sun hours each month using the SolarReviews peak sun hour map. By dividing his energy usage and sun exposure, Mr. Exampleson figured out what size solar system is needed to cover all of his electric needs.

1,200 kWh ÷ 160 monthly peak sun hours = 7.5 kW

By researching, Mr. Exampleson discovered that the average solar panel usually has a power output rating of 400 watts, equal to 0.4 kW. Dividing the 7.5 kW solar panel system size from earlier by 0.4 kW per solar panel told him how many solar panels he needed.

7.5 kW system size ÷ 0.4 kW per panel = 19 solar panels

So, Mr. Exampleson can install 19 solar panels to lower his $168 in electric costs to $0!

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Factors that determine how many solar panels you need

Every home is unique, and so is every solar installation! Several factors influence the number of solar panels you need to install, including your electric bills, roof design, and the solar panels you choose.

Electric bills

The amount of electricity you use has the biggest impact on how many solar panels you need. If you use a lot of electricity, you’ll need a lot of solar panels!

Energy consumption can vary based on:

• The size of your family

• Your home’s energy efficiency

• The types of appliances you use

• The state you live in

The table below outlines how many solar panels you need based on different energy usage levels: 

Monthly energy consumption	Number of solar panels needed
800 kWh	14
1,000 kWh	17
1,200 kWh	21
1,400 kWh	24
1,600 kWh	27
1,800 kWh	31
2,000 kWh	34

Assumes 400 W panels

For example, a home with an electric stove, water heater, and clothes dryer will have a higher electricity bill than one with gas appliances. Your home’s electric consumption will be listed in kilowatt-hours (kWh) at the bottom of your electricity bill.

Sun exposure 

Solar panels rely on sunlight to generate electricity. Homes in sunnier places can install fewer solar panels to cover their electricity bills. For example, one 400-watt solar panel in Arizona can produce almost 90 kWh of electricity in one month. That same panel could only generate 36 kWh in Alaska. 

How much sunlight your home receives is measured in peak sun hours. The map below outlines how many peak sun hours each state receives in an average month.

Location	Daily Peak Sun Hours (PSH)	Monthly Peak Sun Hours	Average solar panel monthly energy production (kWh)
Alabama	4.5 – 5.4	150	60 kWh
Alaska	1.2 – 3	90	36 kWh
Arizona	7 – 8	222	88.8 kWh
Arkansas	4.5 – 5.4	132	52.8 kWh
California	5 – 7.5	192	76.8 kWh
Colorado	5 – 7	180	72 kWh
Connecticut	4.5 – 4.9	120	48 kWh
Delaware	4.5 – 4.9	135	54 kWh
Florida	5 – 5.9	162	64.8 kWh
Georgia	4.5 – 5.4	150	60 kWh
Hawaii	4 – 7.5	150	60 kWh
Idaho	4 – 6	150	60 kWh
Illinois	4.2 – 4.9	135	54 kWh
Indiana	4.0 – 4.4	120	48 kWh
Iowa	4.0 – 4.4	135	54 kWh
Kansas	5.0 – 6.4	165	66 kWh
Kentucky	4.0 – 4.9	135	54 kWh
Louisiana	4.5 – 5.4	150	60 kWh
Maine	4.0 – 4.4	120	48 kWh
Maryland	4.5 – 4.9	135	54 kWh
Massachusetts	4.5 – 4.9	135	54 kWh
Michigan	4.0 – 4.4	120	48 kWh
Minnesota	4.2 – 4.6	135	54 kWh
Mississippi	4.5 – 5.4	150	60 kWh
Missouri	4.5 – 5.4	135	54 kWh
Montana	4.5 – 5.4	135	54 kWh
Nebraska	5.0 – 5.9	150	60 kWh
Nevada	6 – 7.5	210	84 kWh
New Hampshire	4 – 4.5	120	48 kWh
New Jersey	4 – 4.5	135	54 kWh
New Mexico	6 – 7.5	210	84 kWh
New York	4 – 4.5	120	48 kWh
North Carolina	4.5 – 5.4	135	54 kWh
North Dakota	4.5 – 5.4	135	54 kWh
Ohio	4.0 – 4.4	120	48 kWh
Oklahoma	5.0 – 6.4	165	66 kWh
Oregon	3.5 – 6.4	150	60 kWh
Pennsylvania	4.0 – 4.9	120	48 kWh
Rhode Island	4.5 – 4.9	120	48 kWh
South Carolina	4.5 – 5.4	150	60 kWh
South Dakota	4.5 – 5.9	150	60 kWh
Tennessee	4.5 – 4.9	135	54 kWh
Texas	4.0 – 7.5	180	72 kWh
Utah	5.0 – 7.4	195	78 kWh
Vermont	4.0 – 4.4	120	48 kWh
Virginia	4.0 – 4.9	135	54 kWh
Washington	2.5 – 5	135	54 kWh
West Virginia	4.0 – 4.4	120	48 kWh
Wisconsin	4.0 – 4.9	135	54 kWh
Wyoming	4.5 – 6.4	165	66 kWh

Roof orientation

South-facing roofs with an angle of 30 to 45 degrees are ideal for maximum solar energy production. Solar panels can still be installed if your roof faces another direction, but you might need a few extra panels to generate how much power you need.

Solar panels used

Not all solar panels are the same, so the ones you choose will impact how many you need to install. A solar panel’s output has the biggest impact on how much energy it produces. An average 400-watt monocrystalline solar panel will produce 2 kWh of energy per day. Solar panels with higher efficiency ratings will generally have higher wattages and are best for homes with limited roof space. The table below outlines how much energy different types of solar panels produce per month:

Panel wattage	Panels needed for average electric usage
250 watts	26
300 watts	22
350 watts	19
400 watts	17
450 watts	15

Assumes 137 monthly peak sun hours. 

Home size

Although the square footage of your home isn’t the most accurate way to calculate how many solar panels you need, it can give you a general idea as you start your solar journey. The table below shows how many solar panels different-sized homes need on average:

Square footage	Number of 400 W solar panels needed
1,000	8
1,500	12
2,000	16
2,500	20
3,000	24

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4 things that can limit how many solar panels you can install

Sometimes, you won’t be able to install all of the solar panels you need. Here are a few limiting factors that impact the number of solar panels that you can get.

1. Roof size and design

A typical 7.6 kW solar installation has an area of about 334 square feet, about 20% of the space of an average residential roof. If you have space constraints, consider high-efficiency panels that can produce more electricity in less space. 

Solar panels can’t be installed where there are obstructions on your roof, like vents, chimneys, or skylights, ultimately limiting how many solar panels you can install.

The following table outlines how much roof space is needed for different amounts of solar panels:

Number of panels	System size	Minimum roof space required
10	4 kW	177 square feet
15	6 kW	265 square feet
20	8 kW	353 square feet
25	10 kW	442 square feet
30	12 kW	530 square feet

Assumes 400 W panels

2. Shading

Shading can be an obstacle when installing solar panels. While trimming trees or bushes can help reduce shading, things like neighboring houses are harder to manage. If shading is unavoidable, you won’t be able to install solar panels on certain areas of your roof. However, you could install more solar panels elsewhere if its more suitable. 

3. Utility restrictions

Every utility company bills solar customers differently, impacting the number of solar panels you should install. Some utilities don’t provide full credit for excess solar power produced beyond your monthly energy consumption, meaning you’ll want to install fewer panels to avoid overpaying for a larger system. 

Many utilities also have system size limits based on energy usage, so people don’t over-install solar panels just to get extra bill savings. Most utility companies allow installations to cover up to 120% of a home’s annual energy usage, but the exact restrictions depend on the utility.

4. Personal budgets and cost

Solar panels can deliver substantial electric bill savings, but they come with a significant price tag. Solar panels cost about $3.03 per watt installed, or about $14,000 after the federal solar tax credit is considered. That's not pocket change!

If the price is too high, you can install fewer solar panels you install to better fit your budget.

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How many solar panels do I need to go off-grid?

Going completely off the grid with solar panels requires you to install enough solar to cover all of your energy usage, plus a big enough battery system to power your home after the sun goes down. Off-grid solar systems are not connected to the grid at all, so it’s even more important that your solar and battery systems are properly sized. 

For a monthly energy usage of 1,000 kWh, you would need at least 17 solar panels and three solar batteries to go off-grid. 

Monthly energy usage	Solar panels needed	Solar batteries needed	Total system cost after tax credit
500 kWh	9	2	$22,611
1,000 kWh	17	3	$34,373
1,500 kWh	26	5	$53,066
2,000 kWh	34	6	$66,718

Assumes 400-watt solar panels and 13.5 kWh lithium-ion batteries.

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7 questions to ask yourself to calculate how many solar panels you need

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Can solar panels run an entire house?

Yes, solar panels can power your entire house, but it might not be in the way you think.

For most home solar arrays, solar panels only run your house during the day, and any excess solar energy produced is sent to the utility grid in exchange for electric bill credits through a process called net metering. Those credits are then used to cover all or a portion of the costs of electricity you use from the grid when your solar panels don’t produce energy, like at night.

If you want to run your house entirely on solar power, install a solar battery that will store excess electricity generated during the day for you to use later rather than sending it to the grid for bill credits. Battery storage is required for off-grid solar systems, as they don’t have the utility to fall back on. 

Usually, a solar installer will install enough solar panels to generate your daily electricity usage during daylight hours, so you have credits to offset your electricity costs later. Solar companies use advanced software to provide accurate quotes that include the exact number of solar panels to meet your energy needs.