How Much Solar Power Can You Generate?

Solar power generation has grown in popularity over the last decade. According to Pew Research Center, residential solar installations increased by 34% from 2020 to 2021 in the U.S. alone^[1]. Other sources suggest similar growth rates worldwide, with residential solar adoption increasing to around 3% globally^[2]. With solar energy becoming more affordable and accessible, many homeowners are considering installing solar panels. This guide will provide key information to help determine your home’s solar power generation potential.

Factors That Determine Solar Power Generation

There are several key factors that impact how much solar power you can generate from a solar panel system. These include:

Solar Panel Efficiency

The efficiency of solar panels determines how much of the sun’s energy can be converted into usable electricity. Typical residential solar panels on the market today have efficiencies ranging from 15-22%. Higher efficiency panels will produce more power from the same amount of sunlight ^[1].

Number of Solar Panels

The number and size of solar panels in an array also affects total power output. More solar panels means more surface area to absorb sunlight and generate electricity. The specifics depend on factors like roof space, but a typical 5kW solar array may have 16-20 panels.

Solar Panel Orientation

Optimally tilting solar panels to directly face the sun’s rays can increase electricity production by up to 25% compared to non-optimally oriented fixed panels ^[2]. Facing south is optimal for northern hemisphere installations.

Shading

Any shading, even partial, greatly reduces solar panel output. Installations should minimize obstructions like trees, chimneys, and nearby buildings to maximize sun exposure throughout the day.

Geography/Latitude

The sun’s energy increases the closer you are to the equator. So solar panels in southern climates like Arizona or Florida will produce more energy than identical panels further north in places like Minnesota or Maine.

Weather Conditions

Overcast days, as well as snow, rain, and other inclement weather reduces solar energy production. Very hot temperatures can also slightly decrease panel efficiency. The clearest, sunniest days are optimal for solar power generation.

Calculate Your Roof’s Solar Potential

There are several online tools available to help you estimate your roof’s solar energy potential. Project Sunroof from Google (https://sunroof.withgoogle.com/) allows you to enter your address and uses 3D modeling to analyze your roof size, pitch, and direction to determine the number of solar panels that can fit and how much sun exposure your roof gets throughout the year. The tool also estimates the potential electricity generation and cost savings based on your roof specifics and location.

Another option is the PVWatts Calculator from the National Renewable Energy Lab (https://www.hachettebookgroup.com/storey/test-home-solar-power-potential/). This tool allows you to enter details like your address, system size, panel tilt and azimuth, and other factors to estimate the solar output. It incorporates weather data for your location to account for cloud cover and sunlight hours.

When using these tools, key factors that influence solar potential include total roof square footage, roof pitch, direction the roof faces, and surrounding obstructions that may cause shading. South-facing roofs with a pitch around 30 degrees are optimal in the northern hemisphere. Calculating your specific roof’s solar potential helps determine realistic system sizes and energy output.

Solar Panel Types and Efficiencies

There are three main types of solar panels used in residential installations: monocrystalline, polycrystalline, and thin-film. The efficiency of a solar panel refers to what percentage of sunlight hitting the panel is converted into usable electricity. The most efficient solar panels use monocrystalline silicon cells and can reach over 20% efficiency, while polycrystalline panels are slightly less efficient at 15-18% typically. Thin-film panels using cadmium telluride (CdTe) or copper indium gallium selenide (CIGS) have efficiencies around 10-13%, but can be cheaper to manufacture.

According to experts, the most efficient solar panels for residential use come from Maxeon (sold through SunPower) and Canadian Solar. Maxeon’s SunPower panels use monocrystalline silicon cells and achieve up to 22.8% efficiency. Canadian Solar’s HiKu and BiHiKu panels also use monocrystalline silicon with efficiencies of up to 21.1%. These maximally efficient panels produce more electricity per square foot than their polycrystalline and thin-film counterparts.

While monocrystalline panels are the most efficient, polycrystalline and thin-film technologies have improved significantly in recent years. The type of panel can impact the payback period on a solar installation, so it’s important to weigh efficiency versus cost savings when choosing solar panels.

How Many Solar Panels Do You Need?

The number of solar panels needed depends on several factors like your home’s energy usage, the wattage of the panels, and the physical space available for the solar array. According to Energysage, a typical home needs between 17-25 solar panels to cover 100% of its electricity usage (1). The size of your home and your energy needs play a big role. An average 2,000 square foot home requires about 20 panels to meet its energy demands (2). However, energy efficient homes may need fewer panels, while larger homes over 3,000 square feet may need closer to 30 panels.

The wattage or output of your solar panels also affects calculations. Most homeowners install panels with 250-400 watts, with 300W as a common size. Higher wattage panels produce more energy, so you would need fewer panels. Calculate your home’s kWh usage, then divide by the kWh output of your panels to estimate how many you need.

Lastly, physically fit panels based on your usable roof or ground space. Panels vary in dimensions but are roughly 5 by 3 feet. Make sure to space panels properly to avoid shading each other. In summary, carefully consider these factors and use solar calculators to determine the right solar panel system size for your home.

Sources:
(1) https://www.energysage.com/solar/how-many-solar-panels-do-i-need/
(2) https://www.solarenergyworld.com/how-many-solar-panels-are-needed-to-run-a-house/

Optimal Solar Panel Orientation

Proper orientation of solar panels is crucial for maximizing power generation. The optimal solar panel direction is true south in the northern hemisphere and true north in the southern hemisphere. Facing panels directly south (in the northern hemisphere) allows them to receive the most direct sunlight over the course of a day.

Tilting solar panels at an angle can also increase energy production. The optimal tilt angle depends on your latitude. For most residential installations in the U.S., tilting panels between 30-45 degrees provides good year-round solar exposure [1]. The lower your latitude, the lower your optimal tilt angle. Use this general guideline: your optimal tilt angle is roughly equal to your latitude.

At northern latitudes above 25 degrees, tilting panels at latitude + 15 degrees in winter and latitude – 15 degrees in summer can boost output during different seasons. Some panel mounts allow seasonal tilt adjustments to maximize energy gains.

Utilizing tilt and direction optimized for your location will enable your solar array to capture the most sunlight possible throughout the year.

Shading and Obstruction Considerations

Shading from trees, buildings, and other obstructions can significantly reduce the amount of sunlight reaching solar panels, diminishing energy production. According to Deege Solar, even a small amount of shading, such as a single tree branch, can reduce output by up to 25%.

Trees typically cause the most shading issues. The location, height, distance, foliage density and overlap with the solar array all impact the degree of shading. Evergreens and dense trees result in more shading than deciduous trees. Proper siting and placement can avoid or minimize obstruction from trees.

Nearby buildings and structures can also cast shadows onto panels depending on time of day and location of the sun. The collective impact depends on the shading percentage and duration. Weather events like storms and cloud cover lead to temporary shading that affects daily and seasonal generation.

A solar site survey and shading analysis determines the obstructions and helps optimize the system design. Strategic inverter selection, panel placements and microinverter/optimizers on each panel can mitigate shading losses. Keeping panels obstruction-free through selective tree trimming and relocating obtrusive objects also helps maximize solar output.

Geography and Solar Potential

The amount of solar energy available varies significantly across different regions and climates. According to the Solar Energy Industries Association’s State-By-State Map, some of the top states for solar energy potential include California, Texas, Florida, and Arizona. These states tend to have high numbers of sunny days per year as well as large expanses of open land suitable for solar installations.

Areas at lower latitudes closer to the equator generally have higher solar potential. The southwest United States region has an excellent solar resource due to its latitude, arid climate, and clear skies. Northern states farther from the equator, like those in the Pacific Northwest, have lower solar potential due to more cloud cover and precipitation. However, even some northern states can still generate significant solar energy if panels are angled properly.

Higher elevations also receive more solar irradiation than lower elevations. Other geographic factors like coastal fog and average snowfall will impact the viability of solar at a given location. Overall, examining the average peak sun hours per day and solar irradiation maps can give a good indication of an area’s solar generation potential.

Average Output Estimates

The average output of a solar panel depends on several factors, most importantly the panel’s nameplate capacity and efficiency. Most residential solar panels today range from 250-400 watts, with higher wattages representing more power production capacity.

In ideal conditions, a 250 watt solar panel can produce around 1.5 kWh per day. Over the year, this works out to around 500-550 kWh annually. Higher capacity panels like a 400 watt model could produce 800-900 kWh per year (Sunrun).

However, solar panels rarely operate at their full rated capacity. Capacity factors for residential solar average around 15-20%, meaning panels produce 15-20% of their rated output over a year after accounting for nighttime, weather effects, and other losses. This brings the average annual production down to 120-130 kWh for a 250 watt panel.

When paired with solar batteries, excess daytime solar production can be stored for use at night. This increases self-consumption and offsets the capacity factor losses. With sufficient battery storage, annual panel production can near the ideal output.

Conclusion

In closing, determining your home or business’s solar power generation potential requires evaluating several key factors. The most important considerations are your available roof space, panel efficiency and orientation, geographic solar irradiance levels, and obstructions like trees or other buildings. With careful planning and high-efficiency solar panels, even homes with less-than-ideal conditions can generate a meaningful amount of electricity from the sun. While solar may not meet 100% of your needs, the clean energy produced daily from your roof leads to lower electricity bills, reduced carbon emissions, and greater energy independence. Weighing the many benefits of solar power versus the upfront costs makes installing a system an increasingly smart choice for homes and businesses everywhere.