This Is How Many Solar Panels You Need to Power Your House
This formula will tell you how many solar panels are needed to meet 100% of your home’s energy demand.
Jackie Lam is a contributor for CNET Money. A personal finance writer for over 8 years, she covers money management, insurance, investing, banking and personal stories. An AFC® accredited financial coach, she is passionate about helping freelance creatives design money systems on irregular income, gain greater awareness of their money narratives and overcome mental and emotional blocks. She is the 2022 recipient of Money Management International’s Financial Literacy and Education in Communities (FLEC) Award and a two-time Plutus Awards nominee for Best Freelancer in Personal Finance Media. She lives in Los Angeles where she spends her free time swimming, drumming and daydreaming about stickers.
- She is the 2022 recipient of Money Management International’s Financial Literacy and Education in Communities (FLEC) Award and a two-time Plutus Awards nominee for Best Freelancer in Personal Finance Media.
Taylor Freitas is a freelance writer and has contributed to publications including LA Weekly, Safety.com, and Hospitality Technology. She holds a B.A. in Print and Digital Journalism from the University of Southern California.
Chi Odogwu is a digital consultant, professor, and writer with over a decade of experience in finance and management consulting. He has a strong background in the private equity sector, having worked as a consultant at PwC and a research analyst at Renaissance Capital. Additionally, he has bylines in well-known publications, including Entrepreneur, Forbes, NextAdvisor, and CNET. He has also leveraged his writing talent to create educational email courses for his clients and ghostwritten op-eds published in top-tier publications such as Forbes, CoinDesk, CoinTelegraph, Insider, Decrypt, and Blockworks. In addition to his writing, education, and business pursuits, Chi hosts the top-rated Bulletproof Entrepreneur Podcast. Through this podcast, he engages in insightful conversations with talented individuals from various fields, allowing him to share a wealth of knowledge and inspiration with his listeners.
High inflation and the soaring costs of power bills can make powering your home with solar energy quite appealing. And if the allure of going green and saving money has you wanting to go solar, you’ll need to figure a few things before the installer swings by. For one, the number of solar panels to adequately meet your home energy needs.
A common misconception is to gauge how much bang for your buck you’re getting purely based on wattage, says Courtney Corda, co-founder of the California-based solar company Corda Solar. Knowing how many panels you need isn’t just about wattage, but the costs involved in installing, panel performance, location and your usage needs, Corda explains.
Here’s how to figure out how many panels can support your energy needs and what other factors can interfere in your production goals.
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How to calculate how many solar panels you will need
To get a realistic estimate of how many solar panels a home might need, we turned to Jake Edie, an adjunct professor at the University of Illinois Chicago. Edie provided us with a straightforward calculation method.
If you’re curious about how many solar panels your home might require, here’s how you can figure it out, Edie says. Let’s say your household uses 1,500 kWh of electricity each month. Here are the steps to calculate the solar panels you’ll need.
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Step 1. Review your monthly electric bill: It’s important to determine how many kilowatt-hours of electricity you consume monthly. In this example, this particular home uses 1,500 kWh every month.
Step 2. Convert monthly energy use to daily use: Given 1,500 kWh is consumed per month, to ascertain the daily usage, we need to divide this figure by the average number of days in a month, which is roughly 30.42 days (365 days divided by 12 months).
Hence, the average daily use = 1,500 kWh / 30.42, approximating 49.3 kWh daily.
Step 3. Determine peak sunlight hours: This factor varies based on location and climate. For this example, let’s assume that this home receives an average of about five peak sunlight hours per day.
To calculate the total daily energy production required, divide the daily energy consumption by the number of peak sunlight hours. This gives the amount of energy your solar panels need to produce per day.
Energy production required = 49.3 kWh per day / 5 hours, which equals 9.86 kW.
Step 4. Calculate the number of panels: Lastly, you’ll need to determine the wattage of the solar panels you plan to install. The average solar panel in the US is rated between 250 and 400 watts. For this example, we’ll assume the selected solar panel has a rating of 350 watts.
By dividing 350 by 1,000, we can convert this to kilowatts or kW. Therefore, 350 watts equals 0.35 kW.
To determine the required number of solar panels, we must divide the daily energy production needed by the solar panel’s power output.
Number of solar panels required = 9.86 kW / 0.35 kW per panel, which equals 28.17 panels.
This homeowner will need approximately 29 solar panels to generate enough electricity to match their current usage from the municipal electric company. While this calculation may seem straightforward, there are many factors that can affect the effectiveness of solar panels, such as shading, roof orientation, and seasonal variations in peak sunlight.
It is highly recommended that you seek the guidance of a professional solar installer who can assess your circumstances and provide a tailored solution to meet your needs.They should be certified from the North American Board of Certified Energy Practitioners, which is the solar industry standard. CNET also has a well-researched list of best solar companies.
Other factors that affect how many solar panels you need
There are a variety of factors to take into consideration that will help you and an installer determine how many solar panels you need to power your home. Here is a breakdown:
Solar panel wattage
One big part of a solar panel’s performance is its wattage and will affect how many panels you need. The higher the wattage, the more power a panel can generate.
Most residential solar panels have ratings of 250 to 400 watts. The most efficient solar panels on the market are 370 to 445-watt models. The higher the wattage rating, the higher the output. In turn, the fewer panels you might need.
For example, you might buy a solar panel with a listed output of 440 watts. You’ll need to multiply the panel’s wattage by how many hours of sun you get every day to understand how much energy it will produce.
If you don’t have much space, you might want to invest in solar panels with higher efficiency and wattage ratings since they’re equipped to generate more energy per panel. But they’re also more expensive, so bear that in mind if the solar budget for your home is tight.
Output efficiency
If your roof has limited space for panels, you’re going to want to get the most performance per square inch of panel that you can, explains Corda.
Scientists and technical developers of solar panels have been working hard for decades to try to make each solar cell on the panel able to convert more of the sun’s light to electricity than before, or to make them more efficient, says Corda.
As she explains, currently, the most efficient panels on the market have anywhere from 18% to 22.8% efficiency, with most panels hovering around 20% efficiency. So the higher the efficiency, the fewer solar panels you might need.
In reality, a more efficient solar panel will require fewer panels overall for your home, assuming all other factors are equal.
Production ratios
A production ratio for solar panels helps you determine how much energy you can get from a panel. The production ratio, or performance ratio, is an important measure of the effectiveness and efficiency of a solar system. It compares the actual output of the system to the output it would produce under ideal conditions. This ratio takes into account factors that reduce output, such as temperature, dust, snow, shade, aging of the panels and inefficiencies in the inverter.
The performance ratio is expressed as a percentage, with a higher ratio indicating that the PV system is producing a greater percentage of its theoretical output. For example, a performance ratio of 80% means that the system is producing 80% of its rated output in real-world conditions. The higher the production ratios, the fewer panels you might need.
Panel size
There are three main sizes for solar panels: 60-cell, 72-cell and 96-cell. The 60- and 72-cell panels are more common for residential installations are generally about 3 by 5 feet, or 15 square feet.
Where you live and hours of sunlight
The more hours of sunlight your roof is exposed to, the fewer panels you’ll probably need to install. This is based on the direction, pitch and orientation of your roof, the weather and how much shade covers the roof. It also depends on the time of year and where you live.
In the winter [the solar panel] produces less than in the summer. So your energy production from solar will change throughout the year and then the usage within your home will change depending on what appliances are using electricity, says Justin Draplin, CEO of Eclipse Cottages, a sustainable home technology and development company.
So if you live in a really hot climate, then during the summer months, your electrical bill is going to be a lot higher to cool your home versus if you’re in a cold environment, your electrical bills are going to be a lot higher in the winter.
How much shade your roof gets always plays a factor in how many solar panels you’ll need for your home, Corda says. If your roof is covered by large oak trees or a chimney and gets a lot of shade, this will bump down solar panel output. In turn, you might need more panels to power your home. But if your roof doesn’t get much shade, your solar output will be higher for the same space.
Roof type and condition
The orientation, angle, shape and type of roof will affect the number of panels you can reasonably fit into a given area, explains Corda.
A home without a complicated roof structure, pitched at a 10 degree angle and south-facing is best for solar panels.
That would be an ideal roof for solar because you’ve got it tilted, it’s facing south, and the pitch of the roof is neither flat nor very steep, which is ideal for putting panels on there to capture as much energy from the sun as possible, says Corda. A house with a more complicated roof structure won’t be able to fit as many panels, she adds. For instance, Spanish tile-roofs are considered solar unfriendly and require special attachments.
Cost and budget
While powering your home on solar energy can save you money, it does require a serious investment upfront. The costs to power your home on solar and your budget will determine how many solar panels you can afford.
Currently, the average cost for a home solar panel system is around 3 per watt, according to data from the research firm Wood Mackenzie. Based on this figure, an 8-kilowatt sized system would be 24,000 before any tax breaks or incentives kick in.
Whether you are paying cash or financing, knowing what you can afford will play a factor in how many panels you add to your home.
Annual electricity usage
To know how many panels will meet your energy demand, you’ll need to know your annual energy usage. You can log onto your account online, review statements, you’ll see how many kilowatt hours of electricity you use. You’re going to want to look at your patterns over the course of a year.- if not the last couple of years, says Corda.
Once you have that number, you’ll know how much solar power you need to generate to cover your needs.
Besides recent use, factor in the future energy needs, Corda points out. For instance, do you anticipate purchasing an electric vehicle? Or do you plan on growing your family? Or are you and your spouse going to be working from home more? If so, then your energy needs will go up in the future years. On the flip side, if your teens will soon leave the nest to go to college, then you can expect your energy usage to taper off.
Your personal solar goals
Determining your personal solar goal is figuring out what you want to achieve with your solar panel addition. Living completely energy independent and off the grid would mean more solar panels. If you want to power your whole house, you have to really oversize it to make sure you have enough power in the winter, even though you’re going to be over producing in the summer, says Draplin.
Adding battery storage will also play a factor in how many panels you need. With solar battery storage, you can essentially bank energy and store it for later use when you’re producing excess energy.
If your goal is to lower your energy bill or reduce your carbon footprint, then maybe you won’t need as many panels, says Draplin.
Figuring out the number of solar panels you need is only part of the equation. Learn more about the benefits and costs of home solar from CNET:
Solar panel FAQs
Can I run my house on solar power only?
The simple answer is: Yes, you can power a house entirely on solar power. To meet your energy ends, you’ll want to factor in a handful of variables: the size, pitch and orientation of your roof, the size of panels you’d like to install, the amount of shade, output efficiency and wattage. Plus, you want to figure out current and future usage needs, and whether you want your entire home to be powered on solar energy or just part of it.
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Reviews and information on the best Solar panels, inverters and batteries from SMA, Fronius, SunPower, SolaX, Q Cells, Trina, Jinko, Selectronic, Tesla Powerwall, ABB. Plus hybrid inverters, battery sizing, Lithium-ion and lead-acid batteries, off-grid and on-grid power systems.
June 18, 2023 Jason Svarc
In the solar world, panel efficiency has traditionally been the factor most manufacturers strived to lead. However, a new battle emerged to develop the world’s most powerful solar panel, with many of the industry’s biggest players announcing larger format next-generation panels with power ratings well above 600W.
The race for the most powerful panel began in 2020 when Trina Solar revealed the first panel rated at 600W. Not long after, at the SNEC PV Power Expo in China, JinkoSolar unveiled a 610W version of the Tiger Pro panel. Around the same time, Trina Solar announced that a more powerful 660W panel was in development. Amazingly, close to 20 manufacturers at SNEC 2020 showcased panels rated over 600W, with the most powerful being the Jumbo 800W module from JA solar. However, this panel was enormous at 2.2m high and 1.75m wide and will most likely not become commercially available.
Despite the publicity around the many high-powered panels, many PV cell technologies enabling these higher power ratings are universal. Traditional commercial and residential panels have also increased in size and power, with 400W to 500W panels now standard. The considerable increase in power is primarily due to increases in efficiency thanks to many innovations, which we describe later in the article.
Designed for utility-scale systems
The main driver for developing larger, more powerful solar panels stems from the desire to decrease the cost of utility-scale solar farms and ultimately reduce electricity prices. Since larger panels require an equivalent amount of connections and labour compared to smaller panels, the installation cost per kW is reduced, resulting in lower overall cost and decreased LCOE. As explained below, the new high-powered panels are much larger than the ones used on residential rooftops. Those wishing to use ten 700W panels on their home rooftop to get an easy 7kW will be a little disappointed. At this stage, most high-powered panels will only be available for commercial and utility-scale systems, plus the extra-large size is not well suited and challenging to handle on most residential rooftops.
The solar industry has been slowly shifting towards larger, higher-wattage panels. The front runners in the race were traditionally Trina Solar, Jinko Solar, Canadian Solar, Risen Energy and JA Solar as these well-known companies were the first to launch ultra-power panels with ratings above 600W over the last two years. However, more recently, Jolywood, Huasun and the lesser-known company Akcome have moved forward with panels rated above 700W utilising more efficient N-type TOPCon or heterojunction (HJT) cell technology.
Interestingly, premium module manufacturers SunPower (now Maxeon) and REC are not racing to develop larger format high-power panels. Instead, they are focusing on supplying their traditional residential and commercial customer base with high-efficiency panels. That being said, Sunpower has revealed a larger 540W panel in the next-generation ‘Performance 5’ series.
Most Powerful Solar Panels
List of the most powerful panels currently in production or soon to be released with a maximum panel size of 2.4m high x 1.35m wide. Availability and release dates may vary for different regions.
| Akcome | iPower 7 | 730 W | 210mm | N-Type HJT Bifacial | 23.5 % | Q3 2023 |
| Huasun | Himalaya G12 | 715 W | 210mm | N-Type HJT Bifacial | 23.0 % | Q1 2023 |
| Risen Energy | Titan | 710 W | 210mm | N-Type Bifacial | 22.5% | Q1 2023 |
| Jolywood | JW-HD132N | 700 W | 210mm | N-Type TOPCon | 22.5 % | Q2 2022 |
| Trina Solar | Vertex N | 690 W | 210mm | N-Type TOPCon | 22.2 % | Q2 2023 |
| TW Solar | 210TNC | 690 W | 210mm | N-Type TOPCon Bifacial | 22.2 % | Q2 2023 |
| EGING PV | Aurora Pro | 685 W | 210mm | N-Type TOPCon | 22.0 % | Q2 2023 |
| Canadian Solar | HiKu7 | 675 W | 210mm | P-Type PERC | 21.7 % | Q2 2022 |
| Astronergy | Astro 6 | 670 W | 210mm | P-Type PERC | 21.6 % | Q1 2022 |
| Yingli Solar | Mono GG | 670 W | 210mm | P-Type PERC | 21.6 % | Q1 2022 |
| Suntech | Ultra X Plus | 670 W | 210mm | P-Type PERC | 21.6 % | Q1 2022 |
| Seraphim | S5 Bifacial | 670 W | 210mm | P-Type PERC | 21.6 % | Q1 2022 |
| Talesun | BiPRO | 670 W | 210mm | P-Type PERC | 21.6 % | Q1 2022 |
| AE Solar | Aurora | 665 W | 210mm | P-Type PERC | 21.4 % | Q2 2022 |
| Jinko Solar | Tiger Pro NEO | 620 W | 182mm | N-Type TOPCon | 22.3 % | Q3 2021 |
| AIKO | Hole Series | 625 W | 182mm | N-Type Back Contact | 23.7 % | Q3 2023 |
| JA Solar | Deep Blue 4.0X | 625 W | 182mm | N-Type TOPCon Bifacial | 22.4 % | Q2 2023 |
HC = Half-cut cells, MBB = Multi busbars. Maximum panel size = 2.4m high x 1.35m wide.
Larger panel sizes
In the past, most increases in power came from efficiency gains due to advances in solar PV cell technology. While that is partly a driver behind the massive jump in panel wattage, the main factor is the new larger cell and panel sizes being developed together with a higher number of cells per panel. These new cell formats and configurations mean the panels have become physically larger in size. Generally, these large-format panels are best suited for utility-scale solar farms or large commercial installations.
Traditionally, solar panels were available in two main sizes. the standard format 60 cell panels (roughly 1.65m high x 1m wide) used for residential rooftops, and the larger format 72 cell commercial size panels (roughly 2m high x 1m wide). Then half-cut cell panels emerged in roughly the same size but with double the amount of half-size cells at 120 cells and 144 cells. Besides the standard sizes, a few premium manufacturers, such as SunPower and Panasonic, produce unique 96 and 104-cell panels.
The industry-standard panel size for much of the last decade was built around the 156mm x 156mm or 6-inch square cell format. However, the new panel sizes emerging are up to 2.4m long and 1.3m wide and built around the larger 180 and 210mm wafer cell sizes. This is a size increase of 20% to 30% compared to the traditional 2.0m x 1.0m 72-cell panels, which naturally corresponds to a considerable boost in power.
Larger cell sizes
To decrease manufacturing costs and gain efficiency, most manufacturers moved away from the standard 156mm (6”) square cell wafer size in 2020 in favour of larger wafer sizes. While there are a variety of cell sizes under development, a few sizes have emerged as the new industry standard; these include 166mm, 182mm and 210mm. Many of the leading manufacturers, including Jinko, Longi and Canadian, aligned with the 182mm format. Trina Solar is pushing the larger 210mm wafer size, while Longi, the world’s largest mono silicon wafer manufacturer, uses 166mm and 182mm sizes, depending on the application.
To remain competitive, many smaller volume manufacturers may need to align with one of the new wafer sizes to utilise common wafer and equipment suppliers. For a complete history and insight into wafer and PV cell sizing standards, this detailed article from PV Tech examines the various wafer and ingot sizes, technology changes, and manufacturing trends around current and future PV cells.
Along with the different cell sizes, there is a myriad of new panel configurations built around the many cell combinations. The three most popular which have emerged are 66-cell (half-cut 132), 78-cell (half-cut 156), and 84-cell (half-cut 168) panels. The extra-large 210mm cells are also well suited to unique cell dividing formats such as 1/3 cut cells; where the square wafer is divided into three segments rather than the common half-cut or half-size cell.
High-efficiency cells
To achieve these impressive power ratings, panels and cells have not just increased in size, but cell efficiency has improved substantially using numerous new technologies (listed below) along with more advanced rear-side passivation techniques like TOPCon.
- MBB. Multi-busbars
- PERC/PERC. Passivated emitter rear cell
- Heterojunction (HJT)
- TOPCon. Tunnel-Oxide Passivating Contact
- N-type silicon cells
- High-density cells. Reducing inter-cell gaps
Manufacturers are exploring ways to increase power and cell efficiency by spending big on research and development. N-type silicon wafers are one of the best ways to boost efficiency but have traditionally been more costly. However, the price gap between P-type and N-type silicon is reducing as the economies of scale lower the cost of manufacturing the high-performance N-type silicon wafers used as the basis for more efficient HJT and TOPcon cells. In the future, Perovskite cell technology is expected to become stable and viable, allowing manufacturers to create next-generation tandem cells with power levels up to 800W.
MBB. Multi-busbars
Of the many cell improvements, the most common technology used to increase efficiency has been multi-busbars (MBB). Traditional ribbon busbars (5BB or 6BB) are being rapidly phased out in favour of nine or more thin wire busbars (9BB). Some manufacturers, such as REC have even moved to 16 micro-wire busbars in the new Alpha panel series. Wider cells also mean more busbars can fit across the cell surface with 10 or 12 busbars cells also becoming more common.
Bifacial panels featuring MBB are also growing in popularity due to the increased power output by utilising the rear side of the panel to achieve up to 20% or more power (roughly 80W extra). However, bifacial panels are generally only beneficial over light coloured surfaces such as light sandy or rocky ground used in large MW scale solar farms located in more arid areas.
High-density Cells
To further boost panel efficiency and increase power, manufacturers such as Trina Solar have introduced techniques to eliminate the vertical inter-cell gap between cells. Removing the typical 2-3mm vertical gaps and squeezing the cells together results in more panel surface area being available to absorb sunlight and generate power. Manufacturers have developed a number of techniques to minimise or eliminate the gap with the most common being to simply reduce the cell spacing from around 2.0mm to 0.5mm. The reason for this gap was due to traditional larger ribbon busbars requiring 2.0mm to bend and interconnect the front and rear of each cell. However, the transition to using much smaller wire busbars enabled the gap to be reduced significantly.
LONGi Solar is another manufacturer that managed to reduce the inter-cell gap down to 0.6mm by using what the company describes as a “Smart soldering” method using integrated segmented ribbons. This new technology uses a unique triangular busbar design across the front surface of the cell, with a very thin flattened section that bends and runs behind the cell to form the interconnection.
TR. Tiling Ribbon technology
Jinko Solar, currently the world’s largest panel manufacturer, developed what the company refers to as Tiling Ribbon or TR cells. Tiling Ribbon cell technology is the elimination of the inter-cell gap by slightly overlapping the cells creating more cell surface area. This in turn boosts panel efficiency and power output. The tiling ribbon technology also dramatically reduces the amount of solder required through using inter-cell compression joining methods rather than soldering. Shingled cell panels, such as those used in the Sunpower Performance series, uses a similar technology where overlapping thin cell strips can be configured into larger format high-power panels.
Several other leading manufacturers such as Q Cells have taken a similar approach to boost efficiency by completely eliminating the inter-cell gap. However, most manufacturers have taken the more common approach and reduced the inter-cell clearance as much as possible leaving a very small 0.5mm gap; this effectively removes the gap without having to develop new cell interconnection techniques.
N-Type TOPCon silicon cells
Cells built on an N-type silicon substrate offer improved performance over the more common P-type silicon due to a greater tolerance to impurities which increases overall efficiency. In addition, N-type cells have a lower temperature coefficient compared to both mono and multi P-type cells. N-type cells also have a much lower rate of LID or light-induced degradation and do not generally suffer from LeTID (light and elevated temperature induced degradation) which is a common problem with P-type cells.
TOPCon or Tunnel Oxide Passivated Contact refers to a specialised rear side cell passivation technique that helps reduce the internal recombination losses in the cell and boosts cell efficiency. The process has been available for several years but is now becoming the new industry standard as manufacturers strive to increase efficiency and performance.
How Many Solar Panels Do You Need: Panel Size and Output Factors
How many solar panels does the average house need? How many solar panels do I need for a 3-bedroom house? How many solar panels do I need for a 2000 sq. ft. home? These are all common questions for an aspiring solar homeowner. Determining how many solar panels you’ll need for your home requires first knowing what your goals are.
Do you want to minimize your carbon footprint? Maximize the return on your investment? Save as much money as possible?
Most people want to save money while minimizing their environmental impact.
To calculate how many solar panels you need, you need to know:
- Your average energy requirements
- Your current energy use in watts
- The climate and amount of sunlight in your area
- The efficiency of the solar panels you’re considering
- The physical size of the solar panels you’re considering
One simple way of answering the “How many solar panels do I need” question is to consult a professional solar installer, who can give you a free home solar evaluation.
How much solar power will you need?
To determine your home’s average energy requirements, look at past utility bills. You can calculate how many solar panels you need by multiplying your household’s hourly energy requirement by the peak sunlight hours for your area and dividing that by a panel’s wattage. Use a low-wattage (150 W) and high-wattage (370 W) example to establish a range (ex: 17-42 panels to generate 11,000 kWh/year). Note that the size of your roof and how much sunlight your roof gets are factors as well.
If you work with an experienced solar installer, they will handle all these calculations for you. If you’re searching for a calculator to figure out “how many solar panels do I need?”, look no further. You can use SunPower Design Studio to estimate your own system size, monthly savings, and the actual appearance of a solar array on your own roof. This interactive tool provides a solar estimate in just a few seconds and can be done on your own or on a call with SunPower (800) 786-7693.
How many watts do you currently use?
Look at your electricity bill for average usage. Look for “Kilowatt Hours (or kWh) Used” or something similar, and then note the length of time represented (usually 30 days). If your bill doesn’t show kilowatt hours used, look for beginning and ending meter readings and subtract the previous reading from the most recent one.
You want daily and hourly usage for our calculations, so if your bill doesn’t show a daily average, just divide the monthly or annual average by 30 or 365 days, respectively, and then divide again by 24 to determine your hourly average electricity usage. Your answer will be in kW. (And just in case you’re wondering, a kilowatt-hour is how much power you are using at any given time multiplied by the total time the power is being used.)
A small home in a temperate climate might use something like 200 kWh per month, and a larger home in the south where air conditioners account for the largest portion of home energy usage might use 2,000 kWh or more. The average U.S. home uses about 900 kWh per month. So that’s 30 kWh per day or 1.25 kWh per hour.
Your average daily energy usage is your target daily average to calculate your solar needs. That’s the number of kilowatt-hours you need your solar system to produce if you want to cover most if not all of your electricity needs.
It’s important to note that solar panels don’t operate at maximum efficiency 24 hours a day. (See Solar 101: How Does Solar Energy Work?). Weather conditions, for example, can temporarily reduce your system’s efficiency. Therefore, experts recommend adding a 25 percent “cushion” to your target daily average to ensure you can generate all the clean energy you need.
How many hours of sunlight can you expect in your area?
The peak sunlight hours for your particular location will have a direct impact on the energy you can expect your home solar system to produce. For example, if you live in Phoenix you can expect to have a greater number of peak sunlight hours than if you lived in Seattle. That doesn’t mean a Seattle homeowner can’t go solar; it just means the homeowner would need more panels.
The Renewable Resource Data Center provides sunlight information by state and for major cities.
Now multiply your hourly usage (see question No. 1) by 1,000 to convert your hourly power generation need to watts. Divide your average hourly wattage requirement by the number of daily peak sunlight hours for your area. This gives you the amount of energy your panels need to produce every hour. So the average U.S. home (900 kWh/month) in an area that gets five peak sunlight hours per day would need 6,000 watts.
What affects solar panel output efficiency?
Here’s where solar panel quality makes a difference. Not all solar panels are alike. Photovoltaic (PV) solar panels (most commonly used in residential installations) come in wattages ranging from about 150 watts to 370 watts per panel, depending on the panel size and efficiency (how well a panel is able to convert sunlight into energy), and on the cell technology.
For example, solar cells with no grid lines on the front (like SunPower ® Maxeon ® cells) absorb more sunlight than conventional cells and do not suffer from issues such as delamination (peeling). The construction of our cells makes them stronger and more resistant to cracking or corrosion. And a microinverter on each panel can optimize power conversion at the source, in contrast to one large inverter mounted on the side of the house.
Because of these wide variations in quality and efficiency, it’s difficult to generalize about which solar panels are right for you or how many you’ll need for your home. The main takeaway is that the more efficient the panels are, the more wattage they can produce, and the fewer you will need on your roof to get the same energy output. Conventional solar panels usually produce about 250 watts per panel, with varying levels of efficiency. In contrast, SunPower panels are known to be the most efficient solar panels on the market.
To figure out how many solar panels you need, divide your home’s hourly wattage requirement (see question No. 3) by the solar panels’ wattage to calculate the total number of panels you need.
So the average U.S. home in Dallas, Texas, would need about 25 conventional (250 W) solar panels or 17 SunPower (370 W) panels.
What is the effect of solar panel size?
If you have a small or unusually shaped roof, solar panel size and numbers are important considerations. With a large usable roof area, perhaps you can sacrifice some efficiency and buy larger panels (at a lower cost per panel) to get to your target energy output. But if your usable roof area is limited, or if it’s partially shaded, being able to use fewer smaller high-efficiency panels may be the best way to make the most possible power over the long term, ultimately saving you more money.
Solar panel dimensions
Typical residential solar panel dimensions today are about 65 inches by 39 inches, or 5.4 feet by 3.25 feet, with some variation among manufacturers. SunPower panels are 61.3 inches by 41.2 inches.
These dimensions have remained more or less unchanged for decades, but the efficiency and output from that same footprint have changed dramatically for the better. In addition, SunPower designs entire systems to have virtually no gaps between panels and uses invisible framing and mounting hardware to keep the rooftop footprint as tight, efficient, and attractive as possible.
How much do solar panels weigh?
If you’re planning on installing a rooftop solar system, understanding the weight of your solar panels is another key factor to consider. Knowing a solar panel’s weight is the best way to be certain that your roof can support a full installation.
While panel weights vary from brand to brand, most panels weigh about 40 pounds.
SunPower panels are the lightest of all major brands. with some of our panels weighing as little as 33 pounds. For comparison, at the top end of the range, some conventional panels weigh as much as 50 pounds.
Summary: How many panels do you need?
Knowing the answers to the above questions will give you an idea of the ideal number of panels for your electricity generation needs — or at least a realistic range. Next, a professional installer needs to assess your roof architecture, angle to the sun, and other factors to see if and how you’d be able to physically arrange the right number of panels on your roof to achieve your daily energy production goals.
You should also consider net metering as you’re considering how much money you’ll save and make from your solar system. Net metering is how your utility company credits you for producing excess solar energy when the sun is shining and then lets you draw from those credits when you’re using a conventional power grid at night if you don’t store your excess solar energy in a battery storage system.
To get started, check out our solar power calculator, which can help you figure out how much you might save going solar.
Interested in high-efficiency solar panels for your home? Contact SunPower for more information.
- . Based on datasheet review of websites of top 20 manufacturers per IHS, as of April 2021.
- . Energy Sage, July 2021, https://news.energysage.com/average-solar-panel-size-weight/
Solar Panel Output: How Much Power Does a Solar Panel Produce?
Emma Stenhouse is a marine scientist, educator, and writer with more than 16 years of experience. She holds an M.S. in Marine Science from the University of Plymouth.
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On average, solar panels designed for domestic use produce 250-400 watts, enough to power a household appliance like a refrigerator for an hour. To work out how much electricity a solar panel can produce in one day, you’ll need to multiply the wattage by the hours of sunlight.
The higher the wattage of each panel, the more electricity produced. By combining individual panels into a solar system, you can easily generate enough power to run your entire home.
In 2020, the average American home used 10,715 kilowatt-hours (kWh), or 893 kWh per month. If you want a solar system to power your entire home year-round, you’ll need to install a system that can supply all of these energy needs.
The actual output of each individual solar panel will also depend on a range of factors including your location, local weather conditions, plus the angle and direction that the panels have been installed.
What Are Watts and Kilowatts?
To understand how much electricity a solar panel can produce, we first need to get comfortable with some units of power and energy.
If you’ve been reading about solar panels, you’ll have noticed some specific units being mentioned: watt (W) and kilowatt (kW), plus watt-hours (Wh) and kilowatt-hours (kWh). Watt and kilowatt are units of power, and indicate how much power a solar panel can provide; 1,000 watts (W) = 1 kilowatt (kW).
Watt-hour and kilowatt-hour are units of energy, and are used to show how much work (by work we mean running a light or an air conditioning unit) can be completed in one hour; 1,000 watt-hours (Wh) = 1 kilowatt-hour (kWh).
How Is Solar Panel Output Calculated?
The maximum or peak amount of electricity that can be produced by a solar panel is defined by its wattage. Remember this is measured under standard test conditions (STC) of 77 degrees F, 1 kW of solar radiation per square meter, and no wind. You’ll rarely find these conditions in nature, so expect your solar panel’s output to be a little less than this peak rating provided by the manufacturer.
Once you know the wattage of your solar panel, you can use the following calculation to work out how much electricity your solar panel can produce in one day:
Solar panels watts x average hours of sunlight = daily watt-hours
This calculation relies on you knowing (or being able to estimate) the number of sunlight hours your panel receives. You can either estimate this or use a solar calculator like the National Renewable Energy Lab’s solar resource maps. Let’s look at some examples:
Your solar panel has a rating of 250 watts, and your home receives six hours of sunshine per day. Multiply 250 x 6, and we can calculate that this panel can produce 1,500 Wh, or 1.5 kWh of electricity per day.
On a cloudy day, solar panels will only generate between 10% and 25% of their normal output. For the same 250-watt panel with six hours of cloudy weather, you may only get 0.15-0.37 kWh of electricity per day.
Upgrade to a 400-watt panel, and with the same amount of sunshine, you would now get 2,400 Wh, or 2.4 kWh of electricity per day. On a cloudy day, the electricity generated may only be 0.24-0.6 kWh per day.
For reference, the average American home uses about 29 kWh per day. Install a solar power system with 20 panels of 250 watts each, and in the same six hours of sunshine, your system will generate 30 kWh, which is just enough to power the average home for one day.
Variables Affecting Solar Panel Output
In addition to the amount of sunlight received per day, there are other factors that affect the output of your solar panel or system.
Dirt
Anything that builds up on the surface of your solar panel can affect the output. This can include dust, leaves, snow, or bird droppings. A clean solar panel can be 6.5% more efficient than a dirty and dusty panel.
Roof Direction and Angle
Solar panels are most efficient when directed in a south-east to south-west direction, at an angle of 30-45 degrees. Systems at other directions and angles can still work, but your outputs will be decreased.
Shade
Solar panels are very sensitive to shade, including trees, or a building next door. Minimal shading in the morning or evening is fine, but significant shading throughout the middle part of the day will significantly impact the amount of electricity a panel can produce.
Location
The amount of sunshine and Cloud cover will affect the amount of energy a solar panel can produce.
Time of year
Solar panels can produce electricity year-round, even on overcast days. Through summer, the days are longer which generates more output, but shorter days in winter mean your output will be lower over these months.
Age
As solar panels age, their efficiency decreases at around 0.5% each year. The life cycle of the system is approximately 25 years before performance has decreased to the point a new system is needed.
Temperature
The efficiency of solar panels is usually measured at 77 F, and temperatures above this can end up decreasing their efficiency. Solar panels can work well in cold weather, and can still generate power in snowy conditions, too.
How Much Electricity Does My Home Need?
One solar panel on its own isn’t going to create enough electricity to power your entire home, but a solar panel system can. To work out what size system you need, you’ll need to complete some basic calculations that we’ve covered in our article How Many Solar Panels Do You Need?
To fully power an average home using 11,000 kWh per year, a typical solar power system will need between 21-24 panels of 320 watts each. The exact number and wattage of panels, as well as the output they can produce, will depend on where you live and the setup of your specific system.
Types of Solar Panels and Output
There are three main types of solar panels used for domestic systems:
- Monocrystalline. These are the most popular type of panel, made with pure silicon. They have an efficiency of 24.4%, with a moderate cost and a long lifespan.
- Polycrystalline. These are made of silicon crystals that have been melted together. They have an efficiency of 19.9%, a low cost and a moderate lifespan.
- Thin-film. Made with a variety of materials including small amounts of silicon, thin-film panels have an efficiency of 18.9%, with a high cost and a shorter lifespan.
The output of each type of panel will vary depending on the individual manufacturer, but will always be stated as a power rating in watts. The higher the watts, the higher the output. You may also see a kilowatt peak rating, which is the maximum power the panel can produce under the standard test conditions mentioned earlier.
Cost vs. Value
The solar market is very cost competitive, but some brands will offer you a more efficient system for a slightly higher investment. These systems will generate more electricity over the life of the system, so in the long run, they will create more value with consistent increased output.
Remember to look into federal tax credits and other incentives designed to reduce the cost of solar panel installation.
Given your house gets about six hours of daily sunshine, a standard 250-watt solar panel would produce 1.5 kWh of energy in a day.
You would need about 20 250-watt solar panels to generate the amount of energy the average American home uses in a day.
You can increase solar panel efficiency by cleaning the dirt off your panels regularly, pruning any trees that could be shading the panels, optimizing the panels’ angle (ideally to a 30- to 45-degree angle facing south), or installing an automatic solar tracker that rotates the panel to keep it aligned with the sun.
- How Many Solar Panels Do I Need for My Home? EnergySage.
- How Much Electricity Does an American Home Use? U.S. Energy Information Administration, 2020.
- Do Solar Panels Work at Night or on Cloudy Days? EnergySage.
- Hussain, Athar, et al. An Experimental Study on Effect of Dust on Power Loss in Solar Photovoltaic Module. Renewables: Wind, Water, and Solar, vol. 4, no. 9, 2017., doi:10.1186/s40807-017-0043-y
- Solar Panel Performance: How Much Does Roof Orientation and Angle Matter? EnergySage.
- Jordan, Dirk and Sarah Kurtz. Overview of Field Experience—Degradation Rates and Lifetime. National Renewable Energy Laboratory, 2015.
- Mow, Benjamin. STAT FAQs Part 2: Lifetime of PV Panels. National Renewable Energy Laboratory, 2018.
- How Hot Do Solar Panels Get? Effect of Temperature on Solar Panel Performance. EnergySage.
- Belyakov, Nikolay. Chapter Seventeen—Solar Energy. Sustainable Power Generation: Current Status, Future Challenges, and Perspectives. 2019, pp. 417-438., doi:10.1016/B978-0-12-817012-0.00031-1