Offset 100% of Your Energy Usage
In general, typical homeowners will need somewhere between 28 and 34 solar panels (referred also as modules) to cover 100% of their energy needs. The exact number of panels you can or should install varies based on several factors, including how much energy your household consumes, the size of your roof, where you are located, what size and type of panels you plan to use, and so forth.
Fortunately, it’s not terribly difficult to calculate how many solar panels would be optimal for your home. Let’s dive in.
100% Solar Energy Generation Is Not Always Possible
Depending on your exact situation, covering 100% of your energy consumption with solar power just may not be feasible. However, even if you cover only a portion of your consumption with solar energy, it can still make economic sense to proceed with the installation.
Fortunately, most solar incentives still apply whether you are installing a system to provide 10% or 100% of your energy, and every little bit helps against not only your monthly electric bill but also as an environmentally friendly energy source.
Basic Charges Are Unavoidable
Keep in mind that even if you design and install a solar energy system that can offset 100% of your energy consumption, you will still have to pay basic charges from the utility company if your system is grid-tied. These may include a monthly base charge or minimum charges.
Talk to your utility company ahead of time to determine what your power bill will look like if you choose to go solar, and be sure to ask them about their net metering policy.
The first step to determining how many solar panels you will need to power your home or business s to figure out how much energy you already used within the last 12 months, measured in kilowatt-hours (kWh). Most utility companies give you your total energy usage on your electricity bill, but if not, take a look at a handful of bills from different parts of the year, average those kWh amounts, and multiply by 12 to find your estimated annual consumption.
Calculation: kWh per month x 12 months = yearly consumption
The average household in the United States uses around 10,400 kWh each year. For Oregon and Washington, it is slightly lower.
Oregon: 10,812 kWh per year
Washington: 11484 kWh per year
As a reference point, a kilowatt-hour is equal to 1,000 watts of power being used for one hour. In practical terms, if you have 10 lights in your house that all have 100-watt light bulbs (10 x 100 watts = 1,000 watts) and you leave them all on for one hour, you’ve used one-kilowatt hour.
How Much Energy Do Everyday Household Items Consume?
Generally, we don’t think too much about how much energy household items consume, since we just plug them in and know that they’ll work. So, let’s look at a few of the most common and largest power draws in typical homes.
A standard refrigerator uses about 600 kWh per year, which usually requires two panels to produce. An air conditioning unit uses around 215 kWh annually while central air conditioning uses around 1,000 kWh, requiring less than one and about three panels respectively. To charge an electric vehicle at your home, you’ll need about 10 panels to produce 3,000 kWh. Finally, if you plan to operate a pool or hot tub using solar energy, you’re looking at 2,500 and 3,300 kWh respectively, or 8 and 11 panels.
Estimate Your Solar Generation Potential
Next up, you’ll need to calculate how well solar panels can generate energy based on your location to determine your solar production ratio. The amount of sunlight will vary If you live in a more sunny part of the country like Arizona or California, your solar panels will obviously produce more energy than if you live in a less sunny area like Oregon and Washington state, where the same size and number of panels will produce less electricity in the same time period.
Production Ration By State
Mid-Atlantic (e.g. MD, PA, DC): 1.1-1.35
Midwest (e.g. IL, MI, MN): 1.1-1.3
Mountain West (e.g. CO, UT): 1.3-1.6
Northeast (e.g. MA, CT, RI): 1-1.3
Pacific Northwest (e.g. WA, OR): 1-1.15
Southeast (e.g. FL, GA, NC): 1.2-1.5
Southwest (e.g. TX, AZ, NM): 1.5-1.8
West Coast (e.g. CA): 1.4-1.8
Data from EnergySage.com
Now that you have determined your consumption and your state’s ratio, you can simply divide your consumption in kWh by the solar production ratio, and then divide that number by the wattage of the panels that you intend to use.
For example, let’s say you use 11,000 kWh per year, the production ratio of your location is 1.5, and you plan to use 250-watt panels.
Calculation: 11,000 / 1.15 = 9565 and 7,333 / 250 = 38.26 solar panels
If you round to 38 panels, that should cover your annual energy consumption. This translates to a solar energy system that is roughly 7.5 kW.
Determine Usable Roof Area
Now that you know how many solar panels you need to cover your annual energy consumption, you need to make sure that there is room on your roof to hold that many panels. The amount of room required depends also on how efficient your solar panels are. To produce the same amount of energy, high-efficiency solar panels require less space than medium efficiency panels, which require less space than low-efficiency panels.
Generally, every 5 kW of solar panels requires about 250 square foot of roof space, plus or minus based on efficiency. For our 7.5 kW sample system that we calculated above, that means you would need around 375 square feet of south-facing roof surface that is not shaded by trees or other structures.
How-To Be More Accurate?
As we outlined above, you can get a good estimate of the number of solar panels you’ll need simply by calculating your annual energy consumption and determining the solar production ratio for your location.
However, the best way to find out exactly how many solar panels you would need is to contact us at Sunbridge Solar for a free consultation. Our experts will ask you a series of questions to formulate a professional estimate of both the size of the solar energy system that would be necessary as well as a cost estimate for installing it.
Is Solar Energy Worth It?
It certainly is, and you don’t have to live in a super sunny area either to save money. Obviously, the more sun you get, the more efficient your solar system, but you can still produce plenty of power in less sunny locations by using higher efficiency panels or increasing the size of your solar array by adding more panels.
Frequently Asked Questions
To wrap up, let’s answer some common questions we get asked a lot.
As we’ve covered above, the square footage of your home isn’t relevant to the calculation of how many solar panels you need - rather, it depends on your annual energy consumption. Check your utility bill and use the calculations we’ve outlined earlier in this article to determine the right number of panels for your home.
While this depends on several factors including your location and the size of panels you install, you will need roughly 24 250-watt panels to produce 1,000 kWh each month.
Somewhere between 20 and 35 panels will power the average United States home. But we can’t stress this enough - it all depends on what your average annual energy consumption looks like and how much sun you get. If you only use $50 worth of electricity in a month you’d need a significantly smaller system than your neighbor that is using $250.
Different states have different requirements about how close to the edge of your roof you can install solar panels and what types of fire access walkways you need to build in, but in general, every 5 kW of power requires about 250 square feet of roof space. Keep in mind that this number changes based on the efficiency of your panels.
Again, it depends on what your energy consumption will be. If you plan to run all the same appliances that you do in your grid-tied home, you can calculate the number of panels you’ll need for your off-grid home.
However, you may want to add extra panels to offset the lack of backup grid power. When there is no sun for an extended time period, you’ll have no power at all at your off-grid home unless you have a hefty battery system.