Solar Panel Calculator

Whether you want to help our planet or just save some money, the solar panel calculator might be just the tool you want to use. It's created to help you find the perfect solar panel size for your house depending on how much of your electric bill you'd like to offset.

If you're willing to make such an investment, it may be a good idea to compare the cost of going solar versus solar savings. Read on to learn more about it!

Why are solar panels for home use a way to go?

Undoubtedly, renewable energy has a number of benefits affecting several areas of our lives. Many countries are turning towards hydroelectric power or wind turbines depending on which best suits their natural environment. Why should you follow the trend? Let's see:

What solar panel size should I choose? Calculate your solar panel needs

Solar panel dimensions are critical if your roof is small or of an unusual shape. Why? These factors affect the usable area, so whatever you sacrifice in size, you'll need to make up for in efficiency. It may seem confusing, so let's go through the whole decision-making process step by step:

solar array output = electricity consumption / (365 * solar hours in a day),

where the electricity consumption is yearly and expressed in kWh (our energy converter can help if your electric meter uses other units). Solar hours in a day depends strongly on your location.

solar array size = solar array output * (bill offset / efficiency),

where both bill offset and efficiency are percentages.

required panels = solar array size * 1000 / (solar hours per day * panel output in watts).

Typically, the output is 300 watts, but this may vary so make sure to double-check!

area occupied = required panels * panel width * panel length,

where both width and length are in meters.

If the area occupied is smaller than your roof area, the system should fit just right!

How many solar panels do I need?

You can find the number of solar panels you need from the equation:

number of panels = system size / single panel size,

where system and single panel sizes are their wattages, not actual dimensions. The system size determines the power you expect from the solar panels.

The number of solar panels you need depends on the following factors:

So, for example, if you have a small roof, it might be a good idea to invest in fewer highly efficient panels.

Bear in mind that as long as the total power output fulfils your needs, it doesn't matter how many solar panels you have.

Cost of going solar vs. solar savings - an example

Photovoltaic cells are often advertised as an investment that saves you money in the long run. Although, as we've mentioned, each case is different, we can check it with an example.

Let's consider a nice house somewhere near Boston, Massachusetts. The average residential power use is 627 kWh per month, priced at 14.91¢/kWh. Rounding it up, we pay $94 for electricity monthly, and $1,128 yearly.

Now, the house has a gable roof, and one side of it is usually in the shade, so a solar panel power output there would be close to zero. It's better to exclude this bit completely. If the total roof area was 1750 ft2, halving it means that we have approximately 875 ft2 (81.3 m2) of usable area.

Inputting the data into the solar panel calculator shows us that to offset 100% of electricity bills, we need a solar array producing 7.36 kW, assuming 70% efficiency. The average installation cost for an 8 kW system is $25,680. Dividing this by yearly electricity cost, we see that the solar panels for home use would return the investment after nearly 23 years.

However, this is a bad scenario, as solar panels are more efficient when used closer to the equator. Bear in mind that often there are incentives that help offset the installation price. Moreover, we didn't account for inflation that causes electricity costs to increase. Although the final decision is yours, hopefully, our solar panel calculator can help you make an informed choice.


How to calculate solar panel output?

To find the solar panel output, use the following solar power formula:

output = solar panel kilowatts × efficiency × solar hours per day.

The output will be given in kWh, and, in practice, it will depend on how sunny it is since the number of solar hours per day is just an average.

How is the efficiency of solar panels calculated?

The solar panel efficiency is usually calculated from the formula:

efficiency = (Pmax / area) / 1000 x 100%,


How to calculate the solar panels needs for camping?

To determine your solar panel needs for camping:

How many solar panels to charge a Tesla?

Let's consider an upgraded Tesla Model S with a battery capacity of 100 kWh. If you used half of its capacity daily, then you'd need a solar array of approximately 14.99 kW, which translates to 13 solar panels to offset the costs entirely. This is assuming 4 solar hours a day, which is the yearly average for the US, and 300 W panels.

Madhu Raman and Michael Darcy