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Comprehensive Guide To Accurately Sizing Your Solar System

As businesses and individuals embrace sustainable energy solutions, harnessing the power of the sun through solar panels is a key step towards a greener future. Therefore, getting the size of your solar system right is vital for optimal energy production and cost-efficiency. 

In this guide, Ethical Energy Solar walks you through the essential factors to consider when determining the appropriate solar panel size for your setup. Armed with this knowledge, you’ll be able to make informed decisions that maximize your solar investment while minimizing your environmental impact. 

Let’s power up your solar journey together. 

Understanding Solar Panel Dimensions

Solar panels for residential use have dimensions around 65 inches by 39 inches, occupying approximately 17.5 square feet. These dimensions vary based on the manufacturer, wattage, and technology, impacting how many panels can fit on a roof and overall solar energy system. Accurate understanding allows for better integration into existing structures and optimal solar energy production.

How To Size A Solar System: Step By Step

Determine Your Average Monthly Kwh Usage

Begin by collecting your electricity bills from the past year. Each bill details your monthly kilowatt-hour (kWh) consumption. Add up the kWh for each month and then divide the total by 12 to find your average monthly usage. This step provides a clear snapshot of your typical electricity needs, aiding in the accurate sizing of your solar system.

Calculate Your Daily Kwh Usage

Calculate your daily kWh usage by taking your average monthly kWh usage and dividing it by 30. This provides an estimate of your daily energy consumption. 

A common blunder is overlooking variations in seasons and daily usage patterns. Be cautious not to base your calculation on a single month; instead, use a year’s data for a more accurate representation of your daily usage.

Estimate The Amount Of Sunlight Your Solar Panels Will Receive

Identify your location’s average daily sunlight hours. This information is often available online or can be provided by your solar installer. Do not overestimate sunlight hours, as this could lead to an oversized or undersized solar system. Also, consider any shading from trees or nearby buildings that might affect the solar panel’s exposure to sunlight.

Account For Inefficiencies

When accounting for inefficiencies, think of it as adding a little extra buffer to make sure your solar installation performs as expected. A good rule is to increase your calculated solar system size by about 10-20%.

This extra bit covers any small losses that can happen due to things like wiring or weather. It’s like having a spare tire in case of a flat—it’s always good to be a bit more prepared. 

Don’t cut it too close to your exact calculated size. It’s better to have a little extra than to fall short and not get all the energy you need. 

Full Or Partial Offset?

If you aim for a full offset, calculate your average monthly kWh usage. For a partial offset, decide what percentage you want to cover, like 50%. Then, size your solar system accordingly. You can potentially eliminate a big chunk of your electricity bills, which means more savings and a pat on the back for being eco-friendly. 

The big mistake here is either overestimating or underestimating your offset. Too much and you might invest in a bigger system than needed. Too little, and you won’t see the savings you expected. Balance is key. 

Determine How Many Solar Panels You Need

To know how many solar panels you need, check the wattage of each panel and divide that into your daily kWh usage (we’ve calculated this earlier). This gives you the number of panels needed to cover your daily energy needs.

If you do this right, you’ll have just the right amount of solar panels, and you’ll see a significant drop in your electricity bills. High-five for saving money and the planet!

Methods To Calculate Solar System Size


PVWatts, a prominent tool developed by National Renewable Energy Laboratory (NREL) is favored for its ability to accurately estimate solar system size. Taking into account critical factors such as geographical location, roof tilt, potential shading, and the type of solar panels to be used, PVWatts provides a comprehensive analysis. 

By predicting energy production based on these variables, it assists in fine-tuning the solar system size to optimize solar efficiency. 

Solar Reviews Calculator

Solarreviews offers an online calculator that factors in location, energy usage, and sunlight availability. It provides a rough estimate of the solar system size suitable for your energy needs and location.

This rough estimate serves as an initial guide, aiding you in making informed decisions about the potential solar system best suited for your location and energy needs.

Solar Power Company

Engaging a solar power company involves a comprehensive assessment by professionals. At Ethical Energy Solar, we’ll consider your energy consumption, location, roof orientation, and shading to design a solar system that fits your needs accurately. Our expertise ensures an optimal solar system size tailored to your requirements. Contact us today for further information!

Factors That Determine The Best Solar Panel Sizing

Energy Usage

Analyze your average daily energy consumption (in kilowatt-hours, kWh) to accurately size a solar system that aligns with your specific needs and effectively offsets your energy bills. 

By carefully reviewing historical energy usage data, considering peak consumption times, and factoring in any potential future changes in energy usage patterns, you can design a solar panel array that optimally caters to your unique household or commercial energy requirements.

Available Sunlight

The amount of sunlight your location receives, measured in peak sunlight hours per day, profoundly impacts solar panel sizing and how much solar energy you need. Regions with more sunlight require fewer panels to generate the desired energy, whereas regions with less sunlight will need a larger panel array to compensate for the reduced solar exposure.

Solar Insolation And Weather

Understand how weather patterns and seasonal variations affect solar insolation, enabling precise sizing to ensure consistent energy production throughout the year.  Cloudy regions might necessitate larger solar systems to compensate for reduced sunlight during certain periods.

Roof Characteristics

A south-facing, unobstructed roof with ample space is ideal for maximizing solar panel deployment. Besides, efficient use of available roof area is crucial in determining the number of panels a roof can accommodate.

System Losses

System losses can occur due to factors like wiring, inverter efficiency, and panel degradation over time. Yet, accounting for these losses ensures that the solar system is sized to produce sufficient energy, factoring in these inevitable inefficiencies.

Battery Storage

Adequate battery storage ensures a reliable power supply, especially during periods when sunlight is unavailable, such as at night or during cloudy days. This capability significantly impacts the overall design and size of the solar system. 

With an efficient and sufficiently sized battery storage system, excess solar energy generated during peak sunlight hours can be stored for later use.


What Size Solar Power System Do You Need?

Determining the size of your solar power system depends on factors like energy consumption, location, and sunlight availability. An accurate assessment considers your average energy usage and specific solar panel efficiency to size a system that meets your needs while optimizing cost efficiency and environmental benefits.

What Is The Size Of A Solar Panel?

Solar panels vary in size, but a standard residential solar panel typically measures about 65 inches by 39 inches or around 17.5 square feet. However, panel sizes can differ based on the manufacturer, wattage, and technology used. Higher-wattage panels are generally larger and more efficient in capturing solar energy.

How Many Panels Do I Need For My Home

To calculate the number of panels you need, divide your home’s average daily energy consumption (in kilowatt-hours) by the solar panel’s wattage. Consider factors like solar panel efficiency, hours of sunlight in your location, and weather patterns. It’s best to consult a solar expert to accurately determine how much power your household utilizes to gauge the right panel quantity.

How Do I Calculate What Size Solar System I Need?

First analyze your average daily energy usage (in kilowatt-hours). Next, consider the amount of solar array your location receives per day (in peak sunlight hours). Divide your daily energy usage by the peak sunlight hours to estimate the size of the solar system (in watts) needed to cover your energy needs efficiently.