March 11, 2018 Solar Energy Written by Greentumble Editorial Team
Solar Panels on Rooftop
If your community is like many others today,

you’re seeing more and more solar panels installed on your neighbors’ rooftops. Solar photovoltaic system installations are booming. If you’re starting to think about saving money on your electricity bill with clean solar energy, you’re probably questioning, “How many solar panels will I actually need?”.

If you're in the early stage of shopping for solar, use the calculator below to learn more about how much money can a solar roof save you based on your location and household size.

The first step in finding out the size of a solar system that will generate enough power to meet your energy consumption is to calculate the amount of electricity you use as this can vary a lot from household to household.

As an example, let’s assume two families live next door to each other in 1,000 sq ft homes. A single guy lives in Home A and he often spends evenings out in the city with friends or looking for his soul mate. Being alone, and most of the day out, he doesn’t use much electricity and pays about $50 a month.

In Home B, two parents live with a teenage kid. They are using the heater or air conditioner often during the day and use electricity to filter their swimming pool, meanwhile the teenager is always on his iPad or watching TV. Since more people are living in the house and their way of life requires more energy, they pay $200 a month on electricity.

So even though the houses have the same size, the family in Home B would need to consider installing more solar panels to make up for their electricity usage than the single guy in Home A.
In your case you can think of it like this: The more energy your home uses, the more energy has to be produced by your solar PV system. Therefore, the more solar panels you are going to need.

How much solar power will you need?

To find out your average energy usage, check your past utility bills. More precisely the last 12 months of your bills (so you include summer and winter months as energy consumption varies throughout the year). Look for the total number of killowatt-hours (kWh) you consumed every month.

Calculate Energy Consumption

Sum the numbers up and divide them by 12 to get the average. An easier way to determine your total energy consumption for the past year is to simply call your utility company and ask them to provide you the details.

Based on the data available from the U.S Energy Information Administration, in 2013 the average family home in the United States consumed about 900 Kwh of electricity per month. That’s 30kWh per day.

Obviously your household can consume more or less electricity depending on how big your house is, how many family members live in it, the appliances you have and how energy efficient you are.

How many kWh can solar panels produce and how many panels you need on your roof?

The amount of power (kWh) your solar energy system can produce depends on the number of solar panels that can absorb solar energy and convert it into electricity.

Assuming you are going to choose standard-efficiency solar panels, here are the most common sizes for residential solar systems and their kWh production potential to give you an idea of how many panels you would need for your house.

    • A 3kW solar system which consists of 12 panels can produce an average of 4200 kWh per year. You will need a roof space of about 194 sq ft for a 3kW system.

    • A 5kW solar system which consists of 20 panels can produce an average of 7000 kWh per year. You will need a roof space of about 340 sq ft for a 5kW system.

    • A 10kW solar system which consists of 40 panels can produce an average of 14,000 kWh per year. You will need a roof space of about 680 sq ft for a 10kW system.

Keep in mind that the amount of power your solar system can produce depends on how much sunlight your roof receives and your location. For example California has more sunny days annually than Washington. In this case if you live in Washington you would need a bigger solar system to get the same power as you would get with a smaller system in California.

The Renewable Resource Data Center provides average daily total solar resource information on grid cells by state and it’s free to use so check it out.

Few things about solar panel output efficiency

Solar panel type and quality make a significant difference in terms of solar output and efficiency. Not all solar panels are the same. For instance, monocrystalline photovoltaic (PV) solar panels are known to be the most efficient solar panels on the market, but also the most expensive. Their two main advantages over the other panels such as polycrystalline or thin-film panels is that 1) they absorb more sunlight than conventional cells and their output efficiency is not affected that much by temperature and 2) they occupy less space. These an ideal option if you have enough roof space for standard (polycrystalline) panels.

On the other hand, polycrystalline panels are cheaper, they are less efficient and therefore occupy more space, but offer a better return on investment than monocrystalline panels.

Because of these wide differences in quality and efficiency, it’s up to you to decide which solar panels are right for your home. The main takeaway is that, the more efficient the panels are, the more power they can produce, and the fewer you will need on your roof to get the same energy output with polycrystalline or thin-film solar panels. Overall, if money is not an issue, monocrystalline panels are the best option.


How much energy do you want to offset with solar?

Typically most people want to offset as close as possible to 100 percent of their consumption. However, not everyone can afford to offset all energy consumption with a stand-alone solar system as it can get quite expensive.

Small solar systems on house rooftops

Installing a smaller system and participating in the net metering program is still a great way to reduce your electricity bill up to 50 percent or more.

How net metering works?

Let us assume that you are gone in a vacation with your family. The solar system still generates energy when you’re gone but since you are not using it, it’s being automatically sent back to the grid and you get credits for it. As a result, your electricity bill will decrease according to how many credits you have.

Knowing the answers to the above questions will give you a good understanding of the number of panels needed to achieve your daily energy production goals — or at least a realistic range.

If you're in the early stage of shopping for solar, use the calculator below to learn more about how much money can a solar roof save you based on your location and household size.