What Solar Panel Size Do I Need?

What Solar Panel Size Do I Need?

Thinking of making the switch to solar energy and getting rid of your monthly electric bills? Many homeowners are now considering installing solar panels to run their appliances on solar power and be kinder to the environment. But before you start setting up your solar system, it's crucial to know what size solar panels you'll need to buy so you can estimate how many solar panels you’ll need. In this post, we share the general steps you can take to determine how to correctly size your solar system and select the right panels.

Content Index

How Many Solar Panels Do I Need?

When determining the solar energy you need for your home or business, you’ll first need to look at your average energy use. According to the U.S. Energy Information Administration, the average consumption for a U.S. residential utility customer was 10,649 kWh. That’s around 877 kWh every month.

You can calculate your own total energy consumption for the last 12 months on your utility bills. Most utility bills offer this information. Now, divide that number by 12 to get your monthly average consumption. That’s the amount you’ll need your solar panels to produce each month.


You can divide this number by 30 to get your daily kWh usage and by 24 to get the hourly average electricity usage. 

Once you establish your hourly, daily, or monthly average energy usage, you must consider other factors that will affect the size and cost of the solar system.

This includes:

  • Your available roof space. Your roof condition may influence the number of solar panels your home can handle. for example, if you have a chimney, skylight, or rooftop air conditioning, you’ll have less space to place the panels. Additionally, roofs covered by shadows won't be effective for solar panels.

  • The amount of sunlight your home receives. Different regions receive varying amounts of direct sunlight, and this will influence the energy that will be converted into electricity. States like New Mexico and Arizona have a higher output than areas like New England, which are less sunny. Therefore, you must understand how many peak hours of sunlight your geographical area receives on average.

  • The wattage of the solar panels you want to use. High-efficiency solar panels deliver more watts per square foot, meaning you’ll purchase fewer to reach your power output target.

How to Measure the Efficiency of a Solar Panel

The efficiency of your solar panels is the amount of solar energy converted into electricity, from the energy absorbed from the sun. Nowadays, due to technological advancement, solar panels can reach an efficiency level of 30 percent or more.

To calculate the efficiency of a solar panel:

Efficiency (%) = Power rating (Watts)/surface x 100


Watts is indicated on the solar panel, and

Surface means the surface area of the panel.

Let’s say you have a solar panel rated 320 watts, and its surface area is 1600 square meters. Its efficiency will be;

Efficiency = 320/1600 x 100 = 20%


How to Calculate kWh (Kilowatt Hour)

Another factor you’ll want to know is the kWh of the solar panel to get an estimate of how much power it can generate in a day and month.

To calculate the kWh, you’ll need to know the exact number of hours you get direct sunlight in your area and then multiply it by the power rating on the panel.

Example calculations

Calculating kWh of a 50-Watt Solar Panel

Let's take an example where your region gets direct sunlight for six hours. The kWh will be calculated as follows:

kWh = 50 watts x 6 hours of direct sunlight = 300 watts per hour, which is 0.3 kWh

Therefore, assuming you have five 50-watt solar panels, the total amount of energy you can expect will be; 0.3 kWh x 5 = 1.5 kWh. A 50-watt solar panel can be ideal for outdoor solar lighting or garden lights due to the low amount of energy they generate.

Calculating kWh of a 250-Watt Solar Panel

kWh = 250 watts x 6 of direct sunlight = 1500 watts per hour, or 1.5 kWh

Therefore, in this case, just one 250-watt solar panel produces the same amount of energy as five 50-watt solar panels.

Remember, the amount of energy your home uses will fluctuate, depending on the energy efficiency rating of your home appliances, the size of your home, and your electricity consumption habits.

Therefore, if you need a 10-kW solar installation using 250-watt solar panels, you will need 40 panels. Your formula will look like this: 10,000 / 250W = 40 panels.

Calculating kWh of a 350-Watt Solar Panel

A 350-watt solar panel will generate;

kWh = 350 watts x 6 hours of direct sunlight = 2100 watts per hour, which is 2.1 kWh

To get a 10-kW solar system installation using 350-watt solar panels, you’ll need 28 or 29 solar panels. That is, 10,000/350W = 28.5 solar panels.