3-In-1 Solar Calculators: kWh Needs, Size, Savings, Cost, Payback

Adequate solar panel planning always starts with solar calculations. Solar power calculators can be quite confusing. That’s why we simplified them and created an all-in-one solar panel calculator.

Using this solar size kWh calculator, together with savings and payback calculator, will give you an idea of how to transition to a solar panel-based system for your house.

Here’s the deal:

Solar energy is the future. However, everybody who wants to install solar panels has to know a thing or two about how big a system you need. This includes:

  • How many panels do you need for your house?
  • What kind of savings can you expect?
  • Are solar panels are even worth it?
  • Bonus: How much profit you can make with solar panels?

As you will see in our 10kW system in California example, you will likely make at least $74,497.84 profit in 25 years (check the calculation at the end of the article).

That’s why we have prepared 3 calculators anybody planning to transition to solar energy can freely and simply use. These include:

  1. Solar power kWh calculator. First of all, you need to determine what your annual electricity needs are and how big a solar system you need to meet them. This is the ‘How Many Solar Panels Do I Need’ calculator.
  2. Solar savings calculator. To figure out if installing solar panels is a financially viable option, you need to determine a solar savings calculator. This one calculates how much you save with solar energy-based electricity generation per year. Many households save more than $1, per year, for example.
  3. Solar panel cost payback calculator. Solar systems can cost anywhere from $5,000 to $2o,000. This solar payback calculator includes the cost of solar panels, any potential rebates, and annual electricity savings. Based on this, we can determine how quickly the solar panels pay for themselves. Usually, it takes 4-6 years for big self-sufficient home-based solar panels (for AC, electric car charging, etc), and 7-1o years for typical solar panels to pay for themselves; after that time, you’re basically getting free electricity directly from the sun.

Combined, these solar panel calculators will give you an idea of how big a solar system you need, how many kWh per year will it generate, how much you’ll save by switching to solar in the following years/decades, and if all of this is actually financially viable. This is all you need to make an informed decision.

Don’t worry (even if you’re making solar panel calculations for the 1st time):

We will guide you through the whole process. We will go calculator-by-calculator. You can simply input your figures and the solar panel’s calculators will dynamically estimate sizes, savings, and costs. Moreover, we include examples and links to articles with more in-depth explanations (with calculated tables for different solar irradiance areas, house sizes, and so on).

Let’s first start with an example of what kind of information you will get when you use all 3 solar calculators:

Example: Solar Calculator Outputs For An Average Home

Let’s say we have a standard 1,500 sq ft home. According to US Energy Information Administration, the average annual electricity usage for a residential home is 10,715 kWh/year (2020 data). For comparison, the average electricity usage in the UK is about 3.77 kWh/year according to Statista’s 2019 data.

We want to install a solar system that will take care of all the electricity needs of our house. That means that (in the US) such a solar system has to produce 10,715 kWh per year.

We will first use the solar power calculator to figure out what size solar system we need to generate 12,000 kWh per year. On top of that, we will calculate how much we save on electricity with this solar system. That will help us – using the 3rd solar panel cost calculator – to determine if solar panels are worth it.

Here are screenshots of all these solar calculations for an average US home:

solar panel calculator example

Positive note for this calculation: Solar panels last for 25 years. For the first 6.2 years, you are paying back a $10,000 initial investment. For the next 18.8 years, you are reaping the $1,624.84/year profits. In the lifespan of solar panels, these profits will accumulate to $30,546.99. Those are the numbers you will be able to calculate with these 3 solar calculators.

Let’s start by figuring out your annual kWh needs and how many solar panels you would need to meet them:

1. ‘How Many Solar Panels Do I Need’ Calculator (kWh Calculator)

First of all, you need to decide if you want to use solar power to:

  • Power all of your house’s electric appliances.
  • Power part of your house’s electric appliances.

In the past, homeowners wanted to use solar panels just to power a refrigerator or lights. With the increased efficiency of solar panels in the past years, more and more homeowners can decide to power all of their electric appliances with solar energy.

To adequately use the ‘how many solar panels do I need to power my house calculator’ below, you will need to estimate how much electricity you spend each year. Translation: How many kWh of electricity do you pay for per year?

According to the U.S. Energy Information Administration, a typical household spent 10,715 kilowatt-hours (kWh) of electricity in 2020. That’s about 893 kWh per month with an average monthly electricity bill of $117.78 (given $0.1319/kWh electricity price).

Now, if you spend 10,715 kWh, you have to build a solar system that will generate 10,715 kWh, right? That’s quite obvious.

What size of a solar panel system do you need for that? That’s what the solar panels kWh calculator will answer.

Here is how to use this kWh calculator in 2 steps:

  1. Figure out how much electricity you spend per year (in kWh). This is the ‘Annual Electricity Needs (in kWh)’ input.
  2. Figure out how many peak solar sun hours you get at your location (generally between 5 and 7 hours). This is the ‘Peak Sun Hours In Your Area (in Hours)’ input.

You just input these two numbers in the kWh solar calculator, and you will get the minimum size of a solar system you need to meet these electricity demands. Of course, you can play around with the number (use the slider) to get a feeling of how the size of a solar system changes, given different electricity needs and peak sun hours:

0.00 kW

Estimated Size Of Solar System To Cover 100% Electrical Needs


Here’s one example you can test out with this solar calculator. If you spend 16,420 kWh worth of electricity per year and live in an area with 6 peak sun hours, you will need a 10k solar system to be self-sufficient. You can plug these numbers in the calculator above and see the result:

solar size calculator

When you figure out how big a solar system you need, you have to look at financial viability. And that starts with calculating yearly electricity savings:

2. Solar Savings Calculator (2nd Solar Calculator)

The only way how to calculate if solar panels are worth it is to try to estimate how much your electricity bills will go down. You will also need the solar savings estimator to figure out after how many years the initial investment in solar panels will pay back (for the 3rd solar payback calculator).

Here is how you go thinking about this:

  1. Before solar panels, you paid $1,319 for 10,000 kWh of electricity. (Average price of $0.1319/kWh)
  2. With solar panels, you will generate 10,000 kWh of electricity. That means that you won’t have to pay $1,319 for a year’s worth of electricity; your solar savings are thus $1,319/year.

With this next solar panel savings calculator, you will be able to easily estimate your yearly solar savings on electricity. You will need 3 figures to do so:

  1. Solar system size. That’s what we calculated in the 1st Solar Power Calculator. Example: 5kW, 8kW, 10kW, or even 15kW system.
  2. Peak sun hours in your area. We have already used that in the 1st solar calculator. Example: Most households get 5 to 7 peak sun hours.
  3. Electricity cost. That’s the price per kWh in your area. Example: Annual average electricity price is $0.1319/kWh. In your situation, it can be more than that or less than that. Check your electricity bill or search for the electricity costs in your area online.

When you have all of this information, you’re ready to use this solar power savings calculation (you can play around with numbers a bit as well):


Total Annual Savings On Electricity


Ok, here’s how this savings calculator works:

Let’s say we live in sunny California that gets 6.75 peak sun hours per day. We plan to install a 10kW solar system and would like to estimate how much will this solar system save us every year. We also need to know the price of electricity; according to the U.S. Energy Information Administration, the price of electricity in California in September 2021 was $0.2344 for residential use.

We plug all of this into the solar panel savings calculator and get this result:

Solar Savings Calculator

That means that we will see $4,331.27 yearly savings with this 10kW solar system.

Those are quite high savings, right? However, the initial investment into a 10kW system was even higher. The next question you need to answer is this:

How many years must I use the solar panels for them to pay off?

Basically, we need the solar payback calculator to figure that out. Here it is:

3. Solar Payback Calculator (3rd Solar Calculator)

We know that by installing a solar system, we will pay a lot less (or even $0/year) for electricity. However, for the solar system to make financial sense (or profit, as it does in almost all cases), we need to look into how much we paid for the whole system.

Electricity savings will accumulate year over year. When do these savings offset the biggest con of solar panels – the initial investment?

We’ll use a ‘Solar Payback Calculator’ to determine that. To use it adequately, you will need to input 3 figures, namely:

  1. Cost of the solar system. This goes without saying; solar panels can cost $5,000, $10,000, $20,000, or even $50,000, depending primarily on the size of the solar system you’re about to install, and secondarily on the brand, location, contractors, and so on. You just need to get the total initial investment all tallied up.
  2. Rebates for solar panels. That’s a bonus you might be eligible for, depending on your state’s policies. If you get a subsidy for installing solar panels, the solar savings calculator below will deduct those rebates from the initial cost of the solar system.
  3. Annual savings on electricity. That’s what we calculated in the 2nd calculator. That’s the yearly solar panel savings estimation.

When you input all of these 3 factors in the solar payback calculator, you will get results after how many years your initial investment into solar panels will be recuperated. In essence, solar panels pay for themself in electricity savings, you just want to estimate after how many years you will recuperate all those costs and actually start profiting from your solar system.

Here’s the solar payback calculator:

0.00 Years


As we have stated in the introduction, the bigger 10kW+ solar systems will pay for themselves in 4 to 6 years. The smaller system will need 7-10 years to pay for themselves.

You can easily check that with this calculator. Let’s use our ’10kW in California example’:

We know that we save $4,331.27/year with that solar panel system. According to EnergySage, a 10kW solar system in California costs anywhere from $23,900 – $29,300. You also know that California offers federal Investment Tax Credit (ITC) for solar panels. Currently, it’s at 26%.

Let’s say we pick the priciest 10kW solar system in California that costs us $29,300. We get 26% rebates (tax credits); that’s a $7,618 reduction in price already.

If we put all of this into the solar payback calculator, we get this result:

Solar Payback Calculator

That means that even the most expensive 10kW solar system in California will pay for itself for 6.8 years. That means that your whole investment will be recuperated in less than 7 years.

Here’s the interesting part:

Today’s solar panels last for 25-30 years. For the first 6.8 years, you will have a net loss with the solar panels. For the next 17.2 years, however, you will have a net profit from your solar panels (we took a 25-year lifespan of solar panels here).

Now you can calculate how much you will profit by installing this solar system. Here’s how you do that:

Profit From Solar Panels = 17.2 years × $4,331.27/year = $74,497.84

That’s a huge number. In fact, that’s the solar power profit calculated if the prices of electricity stay the same. Price per kWh is likely to rise due to inflation and other factors, so in reality, you can even hit $100,000 of profit just by installing solar panels on your house.

That there is the true power of the solar system.

$100,000 Profit + Saving The Planet

These savings/profits and zero carbon footprint are exactly why so many people are thinking about switching to solar. It saves the planet AND it makes for not only a financially viable but for a profitable investment.

To have a good understanding of how solar panels investment will play out, however, you need to calculate a bit. That’s why these 3 calculators are here for.

Do You Need Help With Solar Panel Calculation?

Hopefully, everybody can use these calculators and get a good grip of the solar panel numbers.

In case you have any questions about the calculations, or you would like for us to help you calculate a bit, you can use the comments below.

Just describe your situation (the more numbers, the better) and we’ll do our best to help you out.

Thank you.

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