How To Calculate Solar Electricity Bill

To determine the amount of solar power you need, you first need to find out how much electricity you use by looking at your power bills for the past year. If you don’t have access to these bills, don’t worry – you can get an estimate by using our solar design service.

Once you know how much electricity you need, you can use our solar power calculator to figure out how many solar panels you’ll need. You can decide how many solar panels you want to get based on your energy needs, how much space you have, and your budget.

You don’t have to completely replace all of your current electricity use with solar power, but you can generate up to 120% of your previous year’s usage. If you increase your energy use, your utility company can help you adjust your solar panel system accordingly. We’re here to help you find the best balance between your energy needs and budget.

How to Calculate Solar Energy Offset

There is a straightforward equation at the core of this:

  • To calculate your solar energy offset, divide the amount of yearly solar electricity generated in kilowatt-hours (kWh) by the amount of yearly electricity consumed in kilowatt-hours (kWh).
  • Once you have the answer, multiply it by 100 to get the percentage of solar energy offset.
  • For instance, if the solar energy offset calculation yields 1, the percentage is 100%. If it’s 0.5, the percentage is 50%. And if it’s 1.5, the percentage is 150%.
  • A perfect solar energy offset is when your home uses the same amount of electricity over a year as your solar panels generate. This would give you a solar energy offset of 1 or 100%.


In a year, your solar panels produced 9,420 kilowatt-hours (kWh) of electricity.

In a year, your home consumed 8,640 kWh of electricity.

9,420 kWh / 8,640 kWh = A solar offset of 1.090, or 109%.

Performing those calculations with historical data is a simple task. If you have solar panels already installed, you can determine how much electricity your home used and how much your solar panels generated. However, things become complicated when you need to predict the number of solar panels required to achieve your desired solar offset if you don’t currently have solar panels installed.

Factors That Impact Solar Panel Offset

Estimating the solar panel offset can be challenging as it is based on historical data and future assumptions. Several factors can affect these estimates, including:

Roof Size: The maximum number of panels that can be installed may be limited by the size of your roof.

Solar Seasonality: The quantity of sunlight that your roof receives throughout the year can limit the amount of electricity that your panels can produce.

Utility Regulations: Utility companies can limit the extent to which a system can provide an offset.

Battery Storage: Saving your excess solar generation from the daytime can enable you to use that electricity at night when your solar panels are not generating power. This can alter how you utilize net metering.

The degree of solar offset that you desire may be challenging to attain, depending on the amount of energy you consume and the amount you have the potential to generate.

Steps To Calculate How Much Solar You Need

Calculating the required amount of solar power has never been easier with our simplified solar services. Our “Calculate How Much Solar” page provides a simple way to determine how much solar power in kilowatts (kW) is needed to produce the kilowatt hours (kWh) of energy consumed on your property.

To estimate the size of your solar system, you will need three pieces of information to calculate the required solar kilowatts:

  • Your utility power bill for the last 12 months
  • The solar hours per day for your location
  • The percentage amount of the power bill you want to be covered

Let’s now take a closer look at each item to gain a better understanding.

Your Power Bill

To calculate your energy consumption accurately, you need to gather monthly power bills for the past year. Follow these steps:

  • Look for the kilowatt hours (kWh) consumed for each month on the power bill. If there’s a summary chart, you might find your total kWh there.
  • If there is no total, add the kWh for each month, and enter the sum into #1 on our Solar Power Calculator. Avoid using commas or decimal points.
  • For instance, the average household in the USA uses 30 kWh per day, which translates to 11,000 kWh per year. Enter 11,000 into field #1 of the calculator.

Solar Hours Per Day

To calculate how much solar power you need, you need to know the solar hours per day in your location. The average solar hours per day in the USA is 4-6 hours, but it varies depending on the season and your location. To find the solar hours per day for your state and nearest city, scroll down on the Solar Power Calculator page. For instance, let’s say we’re using Birmingham, Alabama, which has 5.26 solar hours per day. Enter this value into #2, Solar Hours per Day.

Power Bill Offset

To determine the appropriate size of solar kit that can generate the amount of electricity you consume, you need to provide the final piece of information, which is the percentage of your electricity bill you want to cover. You have the option to choose between 50%, 80%, 100%, or 150%. For the purpose of this example, let’s assume you want to cover 100% of your electricity bill. To enter this information, input the whole number into the third section, and avoid including the % symbol. Thus, for the example, you should input #1 as 11000, #2 as 5.26, and #3 as 100. After entering this information, click on the “calculate” button.

The answer you receive, in this case, is 7.64. This indicates that a solar kit with a capacity of 7.64 kW or 7,640 watts can generate 11,000 kilowatt-hours per year in Birmingham, Alabama.

Now that you know how to calculate the necessary kW size for your solar kit, you can proceed to find more details and the price for the solar kit. To do this, click on the red link to “View Solar Kit Sizes,” or select “Solar Kit” from the menu and then choose “Solar Kit Sizes.”.

Calculating Your Actual Solar Savings

When you get a Solar PV system installed, your power bills may look different at first. Some people think they are only saving the amount of power they sell back to the grid, but actually, most of the savings come from using solar power instead of buying electricity from Synergy.

There’s a misunderstanding about how much money the Solar PV system saves you and how it shows up on your power bill. The Feed-In Tariff you get paid is only for the solar power you don’t use, which is sent back to the grid. If you use solar power when it’s produced, you don’t have to pay the full price for electricity, which is where the biggest savings are.

On your Synergy bill, the credit you see is only for the solar power you sold back to the grid. It doesn’t show the total amount of power your Solar PV system generated or how much of that solar power you used. There are also other charges on your bill, like the cost of the power you bought from Synergy and a daily supply charge, which you have to pay whether you use power or not.

So How Do I Calculate How Much I Have Actually Saved?

Solarweb is the most efficient and straightforward method for calculating the amount of power generated by your Fronius system. To use this service, you must have consumption meters connected to your home Wi-Fi. Alternatively, you can determine your actual savings by tracking your inverter’s production over a billing period and subtracting the power fed back to the grid, as displayed on your bill. This will give you an estimate of the amount of power you have consumed from your solar panels. It is crucial to use your power during daylight hours by performing activities such as cooking, heating, cooling, washing, downloading, drying, and charging. Avoid the mistake of consuming more power and aim to shift your usage to sunlight hours while conserving power when the sun is not shining. To learn more about energy-saving tips, please visit our Energy Saving Tips page.

Related: How Much Will Solar Panels Reduce My Electric Bill

Frequently Asked Questions

How do you calculate solar power consumption?

To determine the energy output needed from your solar panels each hour, divide your average hourly wattage requirement by the number of daily peak sunlight hours in your location. For example, a typical U.S. household that consumes 900 kWh per month in an area with five peak sunlight hours per day would require solar panels capable of producing 6,000 watts.

How do you calculate a 5kW solar system?

If you opt for 415W panels, you’ll require 12 solar panels to create a 5kW solar system. This will yield approximately 4.98kW. To accommodate these panels, you’ll need a roof space of at least 23.7m², as each panel is approximately 1.8 meters x 1.1 meters.

How do you calculate kW for solar panels?

If you want to achieve a particular solar system size, you can figure out the number of panels required by dividing the size by the average wattage of each panel, which is roughly 320 watts. As an illustration, if your target is to build a 4 kW system, you would need 12.5 panels, which is obtained by dividing 4 kW (equivalent to 4,000 watts) by 320 watts.

How many solar panels is 4 kW?

The commonly used residential solar panel system is the 4 kW, which consists of 16 panels, each measuring about 1.6 square meters (m2). In optimal conditions, each panel is rated to generate approximately 265 watts (W) of power.

What size is 1 kW solar?

The dimensions of a home solar panel with a capacity of 1 kW are 65 x 39 inches.