As more homes throughout the country consider installing solar panels, one question commonly asked is, “how many solar panels do I need?”. Well, it depends – there are a few factors that go into determining how many solar panels you would need to power your home or business; home energy usage, roof or property surface area, orientation of your roof and geographic location. In this piece, we’ll break it down for you.
How much solar energy do I need?
When determining how much solar energy you need; your home’s average energy usage is the first thing to look at. According to the U.S. Energy Information Administration, in 2019, the average electricity consumption for a U.S. residential utility customer was 10,649 kWh. That’s an average of about 877 kWh per month. To understand your own usage, a good rule of thumb is to look back at your total energy consumption from the last twelve months on your utility bills. Most utility bills provide this information. Divide that number by 12 and you have a great estimate of what you’ll need your solar panels to generate each month.
Where you live also plays an important role in how many solar panels you’ll need. For example, states in the northeast endure longer winters accompanied by shorter days during cooler months. Residents in these regions will most likely need more solar panels to generate the same amount of power as residents from sunnier and warmer climates would. It’s important to understand how many peak hours of sunlight your geographic location receives on average.
Factors That Affect Solar Panel Output Efficiency
All things being equal, the design of the solar panel determines how efficient it is. This, in turn, specifies how well each square foot can convert sunlight into energy.
For example, gridlines on most panels reduce the active surface area. Therefore, they are not as efficient as those without them. In addition, grid panels are susceptible to peeling, further reducing efficiency.
Quality plays a role, too. For example, if the construction is subpar and introduces corrosion and cracking, it can also impact the ability of the panel to absorb sunlight.
But as a rule of thumb, expect residential solar panels to give you between 150 – 370 watts. This translates to an average solar panel’s wattage per square foot of 15 watts.
How Much Do Solar Panels Cost on Average?
The average cost of a solar panel is around $0.65 to more than $2 per watt for high-end models. That means an average 6 kW system will set you back up to $12,000, depending on the location. This is exclusive of installation costs, which can bump the price up by another $5,000 – $10,000.
As a rule of thumb, PV systems in warmer locations are cheaper but require more panels, while the opposite is true with colder climates.
Fortunately, tax credits and incentives can cut solar panel installation costs and provide further savings throughout their lifespan.
How Many Solar Panels to Power a House?
When estimating how many kilowatts of solar do I need, it’s important to consider the size of your home. A home size of 1500 sqft would consume an avg. of 633 kWh/month, on the other hand, a 3000 sqft home would consume an avg. of 1185 kWh/month. An average homeowner would need about 28 to 34 solar panels to fully offset their electricity usage. The chart below is an estimate of the number of panels you could potentially need based on the size of your home.
*Data from the Residential Energy Consumption Survey.
How many solar panels do I need for a specifically sized solar system?
To determine the number of panels you need to achieve a given solar system size, divide it by the wattage of each panel (which averages around 320 watts).
For example, if you’re aiming for a 4 kW system, you’ll divide 4 kW (or 4,000 watts) by 320 watts to get 12.5. Round up the answer to 13, which is the number of panels you need.
How many solar panels do I need for common appliances?
You can also determine the number of panels you need on a per appliance basis. This approach is helpful if you want to add panels because of increased usage or when buying a new appliance.
To calculate this, divide the average annual wattage of the appliance by the panel wattage. For example, a 600 kWh refrigerator would need two solar panels (600 / 320)
Summary: Step-by-Step Guide to Determining Solar Panel Needs
Here are the steps to figure out the question, “what size solar system do I need?”
1. Measure your annual kWh usage or the yearly electricity consumption of your house. You can either consult a year’s worth of monthly electric bills or use the average American house consumption figure of 10,649 kWh / year as an estimate.
2. Figure out your panel wattage, which is how much electricity your panel produces under ideal conditions. For simplicity’s sake, you can use 320 watts as an estimate.
3. Estimate your production ratio, or how much electricity your panel produces based on the average sunlight. You can compute this by dividing your system wattage by its electricity output in a year. Or you can use the US estimate of between 1.3 and 1.6.
4. Plug the data into the formula: Panel number = kWh usage / production ratio / wattage
For example, let’s say your house has an estimated 12,800 kWh consumption. Assuming a production ratio of 1.6 and 320-watt panels, you would need:
12,800 kWh / 1.6 / 320
Or 25 panels total.
Some homeowners might also ask, “how many square feet of solar panels do I need?” To answer this question, you first need to know that an average residential solar panel is around 17.5 feet. Then multiply this figure by the number of panels you need based on the steps we just outlined.
Thus, in our above example, a 12,800 kWh consumption will need 437.5 square feet of solar panels (or 25 panels x 17.5 feet)
Before we get into the examples, it’s helpful to note that a home’s power usage isn’t entirely dependent on its square footage. Instead, the number of residents and their energy habits play a much bigger role.
But for the sake of people asking, “how much solar power do I need?” in terms of square footage, we’ve illustrated the examples in these terms.
Example 1: how many solar panels do I need for a 1000 Sq Ft Home?
Let’s assume the consumption of a 1,000 sq ft home with four residents and average usage to be 690 kWh per month or 8,280 kWh per year.
With a panel wattage of 320 and a production ratio of 1.4, the number of solar panels you’ll need is:
Solar Panels = 8,280 / 1.4 / 320 = 18.48
Or 19 solar panels.
Example 2: how many solar panels for 2500 Sq Ft Home?
Let’s assume that our 2,500 sq ft home houses five people with regular energy usage habits. The estimated consumption would then be 1,131 kWh per month or 13,572 kWh per year.
Again, considering a 320W panel and a 1.4 production ratio, plugging the numbers in the equation gives us:
Solar Panels = 13,572 / 1.4 / 320 = 30.29
Or 31 solar panels.
Solar Panels kWh Calculator
You can use the calculator below to quickly determine your solar panel needs based on your average monthly kWh usage and the nearest city from your house. The latter helps better gauge the amount of sunlight you receive based on your location.
Solar panel calculator
Solar Panel Square Footage Calculator
Alternatively, you can also figure out the number of solar panels you need based on the square footage. This is useful if you plan to install solar panels on a new house and haven’t tracked your monthly electricity consumption yet.
However, no calculator will do this for you directly since there’s no correlation between square footage and consumption.
But there’s a workaround. You can use the calculator below to get the predicted monthly kWh usage based on the number of people living in the house and their energy consumption habits:
Once you get the estimated monthly kWh usage, simply plug it into the solar panel kWh calculator above.
Not all roofs are suitable for solar panels
Apart from estimating how many solar panels you need, you should also consider the weight of the panels themselves.
On average, a single panel weighs around 40 pounds, adding around 2.8 pounds per square foot for a typical pitched roof and 5 pounds for flat roofs. Therefore, you need to make sure that your roof can support this added weight. You also need to consider the material, age, and structure of your roof.
According to the National Renewable Energy Laboratory of the U.S. Department of Energy, approximately 50% of homes can’t support rooftop solar panels. Community solar programs are a common way for many homeowners, businesses and renters to go solar without actually installing anything on their roof. Participants can subscribe to a nearby solar farm and pay a lower price for the electricity sourced from it. Through Community Solar with Nexamp, the process is similar to determine the size of a subscribers’ share of a solar farm is similar to determining the number of rooftop solar panels. We simply analyze a subscriber’s last 12-13 months of energy usage and recommend a suitable allocation of our farm for them to subscribe to at a discounted rate. The end goal is to offset as much of a subscriber’s annual electricity costs as possible.
At the end of the day, the number of solar panels you’ll need to see potential savings is unique to your home’s energy usage. Interesting in seeing how much you could save by joining our community solar program? Reach out to us by visiting our community solar page or call us at (800)-945-5124.