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Solar Power Calculator: Understanding The Numbers


Owning a home that generates electricity from the sun is a win for you and the planet. You want to make sure it's done right.

Using an online solar panel calculator can give you an estimate for how much a solar energy system will cost to install and how much money you could save in the long run. We’ll review the key factors that go into that calculation.

Step 1: Find Your Number Of Sun Hours

Graphic showing peak sun hours.

Source: Palmetto

First, you need to find out how much solar energy is available to capture in your area. This is typically measured in the number of sun hours per day. A sun hour describes the average 1,000 watts of power the sun emits per square meter. The average number of sun hours in the United States ranges between 3 to 5, depending on proximity to the equator and local climate. You can get an idea of your location’s sun hours in the graphic above.

The number of solar panels you need depends on both the number of sun hours you get, the quality of the system you choose and your energy consumption.

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Step 2: Determine Your Energy Usage

Next you need to know how many kilowatt-hours (kWh) you consume in a year. Any solar panel kWh calculation should account for efficiency.

A great place to start is with your energy bills from the last year to understand just how much you consume. For what it’s worth, the average American home consumed about 10,715 kWh in 2020. That’s an average of about 30 kWh daily.

There are a few other questions to consider. For example, think about whether you’re planning any home renovations that will include moving appliances from gas to electric power. Also, consider what you could do to reduce electricity usage, such as sealing your air-conditioning ducts, updating your insulation, switching to Energy Star appliances and switching to LED bulbs in your light fixtures. These changes, among others, will get you further on what solar energy you can produce.

Step 3: Choose Your Solar Panel System

Once you have your goal energy production in kWh per year and the number of sun hours you get per day, you can choose a solar system size.    

The final major variable in any solar panel cost calculation will be the quality of the panel. While most panels are the same size, their wattage can vary from 250 and 400 watts.

Choosing the right type of inverter can also translate into more energy production. Some solar panels come with micro-inverters on each panel to reduce the loss of energy and simplify any future system expansions.       

Efficiency is also important in choosing solar panels. Today’s most-efficient panels that are widely available convert 15 – 20% of the solar radiation they receive into power. That’s up from about 6% in older models.

It’s also important to decide whether you want a grid-tied system or an off-grid solar panel system. With the grid-tied system, your solar panels feed energy into the utility grid, which also allows you to draw energy from the grid at night and during other times when your system may not produce enough power. Grid-tied systems are by far the most common.

While off-grid solar panels allow the greatest amount of energy independence, they’re also the most expensive. You’ll need extra panels to generate enough power to charge batteries, which will then power your home at night, on cloudy days and other times when your system production falls short.

Step 4: Putting It All Together

Now that you have an idea of what goes into calculating the size of a solar panel system, let’s run through an example.

Erica has a home in Pennsylvania. She wants a grid-tied system for her 1,600 square-foot home. She’s also thinking about getting an electric car in the next few years. What size does she need?

Her area received a yearly average of 4.46 peak sun hours per day. She has made some smart efficiency upgrades to her home. She was able to figure out that her daily energy use was an average of 24 kWh by referencing her monthly energy bills over the course of a year. To accommodate an electric car in her future, we’ll add an extra 6 kWh of electricity use per day, which is more than enough for her 15-mile daily commute.

Let’s plug the numbers in:

(Estimated 30 daily kWh usage/4.46 peak sun hours per day) X 1.15 = 7.7 kW system size

We multiplied by 1.15 to add a 15% efficiency cushion into the system. What do your daily electricity usage and local peak sun hours tell you about your system needs?

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Solar Panel FAQs

What are some incentives for solar panels?

As part of the Department of Energy’s push to grow renewable energy in the United States, the Internal Revenue Service allows eligible taxpayers to claim a tax credit of up to 30% of the cost for solar energy systems on their federal taxes. This can mean a huge solar tax credit for projects installed through 2032, but the tax credit will drop to 26% in 2033 and to 22% in 2034.

Always consult a tax professional to find what works best for your individual situation.

Keep in mind that this is only the federal tax credit. State governments and utility companies often have benefits for solar homeowners, as well. For example, Arizona is currently exempting that purchase of solar equipment from sales tax.

What if I plan to buy an electric car?

The future is here. It's entirely feasible to run your electric car off solar energy instead of fossil fuel-generated grid electricity. That said, it will require additional power and panels. Electric car batteries range from about 30 – 100 kWh. Consider your driving habits to determine how many kWh an electric car will add to your usage. A helpful figure to remember is that electric cars average about 3 miles per kWh.

Be sure to talk to the solar company you work with about any potential large appliance or electric vehicle purchases. They should be able to advise on how future energy use will impact your system.

Should I get a backup battery?

More homeowners are expressing interest in batteries for their solar projects. There are a few reasons why:

  • They want energy storage to go off-grid.
  • They want to be able to power their home in a blackout.
  • They want to use energy from the battery to power their home during peak hours, which can further reduce electricity costs for a grid-tied solar home.

If any of these situations align with your goals, be sure to mention it when consulting with a solar expert to design your system.

The Bottom Line: Solar Energy Pays For Itself

The cost to install a solar energy system is going down, while the efficiency is going up. Depending on where you live, your electricity rates may be going up as well. A home solar system could give you the chance to save money and help the environment at the same time.

If you’re feeling ready to look into solar panel installation, reach out to one of our solar energy experts to get an accurate solar power calculation.

Rocket Solar does not provide legal or tax advice. The information herein is general in nature and should not be considered legal or tax advice. Consult an attorney or tax professional regarding your specific situation.

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