Choosing the right solar system size

Choosing the right solar system size

If you prefer using solar energy, the first step you should take is determining the appropriate solar system size for your home. It is tricky to overstate the influence of the size of the solar system on solar energy processes. The size of the solar system will decide: 

  • The total cost of installing solar panels 
  • The amount of roof space required
  •  The percentage of electricity bills that can offset 
  • The total financial savings over the life of the panel’s 

In other words, you first need to calculate the solar system. Size can determine if solar power is worth going for.

So what exactly does “size of the solar system” mean?

What factors affect the size of the system you need? How can you easily calculate the correct size of the solar system for your home? We answer all these questions on this blog.   What exactly does the size of the solar system mean? In the solar industry, the term “solar system size” is used to describe the ability of a solar panel system to generate electricity. A   300-watt solar panel system can generate 300 watts of electricity, while a 6 kilowatt (6000 watts) solar system will generate 6000 watts under standard conditions. Let’s look at the key terms used here:

 “Standard” conditions

-These are the specific conditions required for solar panels to operate at full load or “maximum output”.

Solar cells must have exactly 1000 watts of sunlight hitting them per square meter, and they must operate at a constant temperature of 77°F (25°C). These specific conditions reproduced in the laboratory are technically called “standard test conditions (STC)”. 


Watt is a unit of measurement for electricity production. When we talk about the size of solar panels or solar systems, we refer to the watts of direct current (DC). Now that you realize these terms, solar panel specifications and solar system quotes will make more sense. For example, you will see a solar panel described as “300-watt nominal DC output at STC”; in simple terms, we call it a 300-watt panel. When we put together 20 panels with this power to create a solar system, we get a solar system that is 6 kilowatts (6 kilowatts) in size! Now that we know the measured value of the term “size of the solar system”, let’s compare the three methods used to calculate it.

3 ways to calculate the size of the solar system

Now, back to the big question, how do you find the size of the solar system that fits your home? We introduced three methods for sizing solar systems and evaluated the advantages and disadvantages of each technique: 

  • PVWatts
  • SolarReviews Calculator
  • Quote from an installer.

1. PVWatts 

PVWatts was developed by the National Renewable Energy Laboratory (NREL) Tools online), Department of Energy National Laboratory. PVWatts uses historical solar irradiance and meteorological records to perform photovoltaic (PV) analysis on buildings worldwide. Based on your location and building characteristics, PVWatts provides an accurate hourly breakdown of system output. This is a powerful tool whose calculations are used by solar companies to develop advanced solar energy estimates and analysis and consumer-oriented tools such as the SolarReviews calculator. 

The biggest flaw of PVWatts is that it doesn’t calculate the size of the solar system for you; you have to use the tool to calculate it yourself. This requires some reverse engineering, requiring you to divide your total annual energy use by the amount of solar energy that a 1 kW panel can generate. We will guide you through this process on this blog.

2. SolarReviews Calculator

The SolarReviews calculator is designed for the convenience of homeowners. Uses advanced satellite imagery from your roof, powerful proprietary artificial intelligence, and access to a vast database of utility rates and electricity usage to generate rough estimates of solar energy. It will give you all the essential information to use solar energy with relatively high accuracy based on your address and monthly electricity bill. 

SolarReviews has several primary advantages over PVWatts, including 

  • Ease of use – This calculator can quickly tell you the recommended system size for your roof without you having to do the calculations yourself or speak to someone in person. 
  • No Measurement: SolarReviews can take into account the effects of your roof angle and direction, your roof angle (spacing), and roof direction without the need for physical measurements.
  • Provide Cost Estimate – Shows the estimated cost of using cash or loan to purchase the recommended size of the solar system.
  • Real-Time Pricing Option: The SolarReviews calculator allows you to view real-time prices for pre-selected solar installers in your area. No other solar calculator available for consumers to use online can provide this combination of accuracy, functionality, and Ease of use.

3. Solar energy company

The third way to calculate the size of the system is to ask the solar installation company to do it for you. Solar companies can combine tools such as PVWatts with on-site assessments of their roofs to develop the most accurate solar panel production forecasts. A reputable solar company is happy to calculate the solar system that suits your energy needs and provide you with free estimates for your consideration. To ensure that you only talk to solar companies with a good track record, use SolarReviews to discover the best solar companies in your regions. Suppose you are an intelligent consumer who likes to be prepared when talking to suppliers. In that situation, you can do the following: Use the SolarReviews calculator to see the estimated value of the size of the solar system.

What factors determine the size of your solar system? has five critical factors for calculating the size of a solar system:

  • usage
  • sun and weather 
  • roof features
  • system loss 
  • battery storage 

The energy you consume is the most critical factor in determining the size of the system solar needs. It is designed to adjust the size of the solar system to offset 100% of the electricity consumption, thus maximizing the savings because it means that you will no longer buy electricity from the utility company.

Sun and Weather

This factor is highly location-dependent. If we compare Peak Sun Hours (PSH) measurements to the average amount of sunshine (also called sunshine) received at a location, we see that the sunny city of Tucson, Arizona gets 7.5 7.9 PSH. This is more than twice as rainy and sunny as Seattle, Washington, at just 3.3 to 3.9 PSH. This means that, under all conditions, the Seattle system must be twice the size of Tucson! Any method you choose to calculate the size of the solar system will take into account the peak hours of sunshine at your location. PVWatts has access to the National Solar Radiation Database, which has many years of solar radiation and meteorological data. The   SolarReviews calculator and your local solar company can access the same data set through PVWatts. 

Roof Features

The direction (“azimuth”) and pitch (“pitch”) of the roof will determine the direction and angle of the solar panels. These two factors, especially the order, will have a considerable impact on solar energy production. System loss You will not be able to use the total DC output of the solar panel; that is because all solar power systems will experience system loss.

Battery storage 

Adding battery storage to a solar system will also significantly impact the solar system’s scale. How much will affect the size of the solar system you need depends on the following factors: The amount of required backup power Only want a few hours of emergency lights? Or, if there is an extended power outage, do you need enough solar battery storage to power your entire home for 2448 hours? The first will not have much impact on the system scale. Still, the latter option will require you to have a system scale large enough to cover your daily power consumption and fully charge the battery, even when solar power is low ( For example, cloudy days in winter). 

Battery efficiency

Every time electricity enters or leaves the battery, there will be a small amount of power loss. The total loss you can expect will vary greatly, depending on the type of battery configuration you choose.

Read our blog on Is solar battery storage right for my home?

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