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Solar Panel Output and Wattage Explained (2024 Guide)

Author Image Written by Tamara Jude Updated 04/17/2024

Solar panel output is the amount of electricity a solar panel generates when exposed to sunlight. It’s measured in watts or kilowatt hours (kWh), and it directly affects how much you save on your energy bills. Higher output means more power for your home and a greater return on your solar investment.

Our guide covers everything you need to know about solar panel wattage, output, and efficiency—including how to tell if your panels are working efficiently.


How Do Solar Panels Work?

Solar panels absorb sunlight and transform it into electricity through a process known as the photovoltaic effect. They are made up of photovoltaic (PV) cells, also known as solar cells, that use light-sensitive semiconductor materials to generate an electrical current when exposed to sunlight. These individual cells are connected to create solar panels. Multiple solar panels can then be arranged into an array or system to generate more power.

A complete solar power system typically includes multiple components. At its core are the solar panels themselves and an inverter, which converts the direct current (DC) electricity they produce into usable alternating current (AC) electricity. Additional components may include controllers to regulate power flow, meters to monitor energy production, trackers to follow the sun’s movement, and solar battery storage.

Residential solar systems can power off-grid buildings, such as a remote hunting cabin, or they can be connected to the grid. A grid-tied system allows you to send extra electricity back into the grid and potentially earn credits from your utility company. You can also have a hybrid system that is connected to the grid but also includes solar batteries to store energy for later use.

For more information about how solar panels work, check out the video below. Heating and plumbing expert Richard Trethewey explains how a PV system uses sunlight to power your lights, appliances, and other electrical devices in your home:


Solar Panel Output Explained

As you research solar panels, you’ll see three key terms used to describe and compare how well different panels work. Although these terms are often used interchangeably, they do refer to slightly different metrics:

  • Output: Output is the total amount of electricity a panel generates over time, measured in kilowatt-hours (kWh). This varies based on weather conditions and other factors.
  • Wattage: Wattage is the maximum power a panel can produce under ideal conditions, measured in watts. Think of it as the panel’s potential output.
  • Efficiency: Efficiency refers to how much sunlight the panel converts into usable electricity, expressed as a percentage. A higher percentage means more power per square foot of panel.

When shopping for solar panels, look for a combination of high wattage and high efficiency. Lower-rated panels might seem cheaper initially, but you will need more panels and roof space to produce the same amount of energy—which could negate any savings. Aim for panels with efficiency ratings above 20%, if possible.

Solar panel wattage and efficiency ratings are based on their performance under standard test conditions (STC). This includes a cell temperature of 25° Celsius, solar irradiance of 1,000 watts per square meter, and air mass of 1.5. Different manufacturers test their panels under the same conditions to make it easier for customers to compare products.

You can estimate a solar panel’s output by multiplying its wattage by the average number of direct sunlight hours your home receives daily. However, we recommend consulting a qualified solar expert for the most accurate system design and savings calculations.


Factors That Determine Solar Panel Output

Real-world solar panel output depends on several variables, from weather conditions to panel specs. Here’s a look at the factors that affect your panels’ output:

Climate

Extreme temperatures—both hot and cold—can negatively impact solar panels. Fortunately, solar panels can function in a wide range of climates, so you should only see a slight dip in performance. Focus on optimizing panel placement for your specific location.

Efficiency Rating

Higher-efficiency panels generate more power per square foot. The efficiency rating refers to the amount of sunlight converted into electricity when the panel operates under ideal conditions.

Solar panel efficiency can range from less than 10% to more than 20%. As of 2024, the most efficient solar panels available on the market can achieve 20.9%–22.8% efficiency. SunPower provides home solar panels around this top efficiency ranking.

Roof Area and Exposure

The available roof area can limit the size of your solar array and, therefore, its total output. A larger, unobstructed roof means greater potential power generation.

Orientation and shading also matter. Ideally, your roof should face south for maximum sun exposure throughout the day (at least in the Northern Hemisphere). East or west-facing roofs will also work but may produce slightly less energy.

Even partial shading from trees, chimneys, or nearby buildings can significantly decrease solar panel output. When evaluating your roof, carefully consider potential sources of shading throughout the day and across different seasons.

Type of Panel

There are three main types of solar panels. Each offers certain benefits and drawbacks, but we recommend most homeowners choose monocrystalline solar panels. Below is a breakdown of each solar panel type. 

Monocrystalline panels are the most efficient. Each of their cells is a single crystal of high-purity silicon, which allows electronics to flow with less resistance. This design helps monocrystalline panels achieve the highest kilowatt-hour (kWh) output per square foot.

Polycrystalline panels have intermediate efficiency ratings. Their solar cells use multiple silicon crystals instead of a single piece, which creates more boundaries for electrons to cross. This design reduces panel efficiency but is generally less complex and expensive to produce. The price gap between mono and poly panels has narrowed in recent years, though.

Traditionally, thin-film panels have been the least efficient. However, technological advancements have significantly improved their performance. This type of solar panel uses a layer of photovoltaic material, without crystalline structure, applied on a rigid or flexible substrate.


How Many Solar Panels Are Needed To Power a Home?

The number of solar panels a home needs depends on sunshine, electricity consumption, and panel wattage. For an accurate calculation, you should contact a professional solar installation company.

You can estimate the number of solar panels needed using the information in the dropdown tabs below:

Your energy consumption represents the total annual electricity your home consumes, measured in kWhs. This includes electricity usage from all sources within your home, such as appliances, air conditioning units, lights, and water heaters.

According to the U.S. Energy Information Administration (EIA), the average American household uses about 10,500 kWh of electricity per year.

A panel’s wattage is the amount of electricity the solar panel produces under standard test conditions. Wattage is the most significant factor determining the best solar panels for your project. The higher the wattage, the fewer panels you’ll need.

Wattage varies by manufacturer and product, and most residential solar panels range between 250 and 400 watts of power.

The production ratio of a solar panel system refers to its estimated energy output over time (measured in kWh) compared to its actual system size (measured in W). Though you might assume it’s a 1:1 ratio, various complex factors come into play, such as the amount of sunlight the home receives and the level of shading it experiences.

For example, a 10-kilowatt (kW) system generating 14 kWh of electricity annually would have a production ratio of 1.4 (14/10 = 1.4). This example applies to a sunny state like California, where there’s abundant sunlight throughout the year. However, for homes in a state like New York, where cloud cover and frequent rain are more common, the production ratio may decrease to around 1.2.

Determining this ratio can be complicated, so it’s best to seek professional assistance to understand the factors affecting power production.


How To Know if Your Solar Panels Are Working Efficiently

Regularly monitoring your solar panel system is key to ensuring peak efficiency and catching potential issues early. Here are the best ways to check your system’s performance:

  • Active monitoring: Most newer solar panel systems allow you to track your system’s energy production and even receive alerts in real time. Be sure to ask your installer about these solar monitoring systems before purchasing. 
  • Review energy bills: Compare your energy bills from the same time of year before and after installing solar panels. A significant decrease in cost suggests your panels are working as intended.
  • Perform a visual inspection: Check your solar panels regularly for physical damage, cracks, or accumulated dirt and debris. Dirty panels won’t work as efficiently as clean ones.
  • Schedule a professional inspection: Schedule periodic inspections by a certified solar technician. They can thoroughly assess your solar panel system, including electrical connections, wiring, and overall performance.

Our Conclusion

Solar panel output depends on factors like panel type, climate, roof conditions, and system design. To maximize your investment, it’s essential to monitor your system’s performance regularly and consult with a qualified solar installer. They can help you select the right panels, optimize placement, and ensure your system consistently produces enough clean, cost-effective energy to meet your needs.

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FAQ About Solar Panel Output

How much power does a 400W solar panel produce?

A 400-watt solar panel can produce 400 watts of power under standard test conditions (STC). However, a 400W panel will rarely produce exactly 400 watts in real-world conditions. Its actual output depends on panel efficiency, temperature, shading, obstructions, and sunlight intensity, which varies by location, weather, and time of day,

How many solar panels do I need for a 2,000-square-foot home?

The number of solar panels needed for a 2,000-square-foot home will vary depending on several factors, such as the panel type, its efficiency, and the amount of energy your home requires. We estimate that a home this size will use around 28–34 solar panels. 

Can solar panels run without a battery?

Yes, solar panels can run without a battery if the system is connected to an electrical grid. During the day, the solar panels generate electricity, which is either used directly in your home or fed back into the grid. At night or when your panels don’t produce enough, you’ll draw power from the grid as usual.

How many solar panels do I need for 1,000 kWh per month?

How many solar panels you need for 1,000 kWh per month varies depending on the specific panels you install and where you put them. Higher efficiency panels produce more power per panel, reducing the total number you need. The amount of sunlight your roof gets also impacts the number of panels you need.

Is 10kWh enough to power a house?

In most cases, 10 kWh is not enough to power a house. The typical U.S. home uses around 30 kWh per day, so 10kWh would not be enough to meet most people’s daily needs.


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