Interested in going solar? You might be wondering how many solar panels you need.
A quick Google search will give you an estimate based on the square footage of your home, but what’s more important is understanding how much power you use. No two households are the same, so you should design a custom solar system that meets your unique needs.
To help you determine how many solar panels are right for your home, below we’ll take a look at:
- Your daily kilowatt hour (kWh) usage
- The amount of direct sunlight you receive
- Your roof size and positioning
- Solar panel efficiency
With a clear understanding of these factors, you’ll be able to create a solar panel installation that’s both effective and provides long-term energy savings.
Your daily kilowatt hour (kWh) usage
“Kilowatt-hour” (kWh) refers to the number of kilowatts of energy you consume per hour. This is how electricity is measured by your power company, and it’s the easiest way to determine how much power you use, and therefore how many solar panels you need to supply it.
Take a look at your most recent power bill and you’ll see exactly how many kilowatt-hours your power company charged you. Most homeowners are billed on a monthly basis, but we recommend reviewing your day-to-day usage. (Note: If your bill doesn’t show daily figures, divide your monthly kilowatt-hour usage by 30.)
Why is knowing your daily kilowatt-hour usage important? Because you use electricity to run appliances and keep the lights on every day, and it’s crucial to ensure that your solar panels can sufficiently meet your daily energy requirements.
In the above example, a homeowner used 28 kilowatt-hours (kWh) of power during peak usage. The month was August, so they were running AC to keep their home cool. Since your heating and cooling systems will draw the highest amount of power, it’s wise to review your daily kilowatt-hour usage on days when you were running them.
Based on this number, we can reverse engineer the size of the solar system needed.
First, divide 28 kilowatt-hours by 12 hours of sunlight:
28 kilowatt-hours / 12 hours = 2.33 kilowatts
Second, multiply 2.33 kilowatts by 1,000 to calculate the amount in watts:
2.33 kilowatts x 1,000 = 2,333 watts
Per hour of sunlight, we can see that the average hourly wattage for our solar system is 2,333 watts. Most residential solar panels are sold in 100 – 400 watt increments, so to determine how many panels are needed, divide 2,333 watts by your desired solar panel wattage.
Example: 2,333 watts divided by 300 watt panels = roughly 7 – 8 panels.
Now, in a perfect world with 12 hours of 100% direct sunlight, you might be able to get away with these figures. But unfortunately for most homeowners, this isn’t the case.
To supply this amount of power, you’re probably looking at 2 – 4 times the number of 300-watt solar panels. Why? Because the amount of direct sunlight your home receives throughout the day will change.
We’ll explain more below.
The amount of direct sunlight you receive
As a rule of thumb, the less direct sunlight your home receives, the more solar panels you will need.
For example, San Diego experiences more hours of direct sunlight than cloudy Portland, Oregon. To generate equal solar power, a Portland homeowner will need a larger solar panel installation.
Moreover, the sun rotates throughout the sky each day, which means that even in sunny climates, you’ll only receive 100% direct sunlight for a few hours per day.
At 4 o’clock, for example, your 300-watt solar panel might be reduced to 30% efficiency, and you’ll need two or more 300-watt panels to make up the difference.
While this can be a deterrent for homeowners skeptical about the return on investment, we like to advise a couple things:
- Net-metering. At peak sunlight hours, homeowners don’t often consume all of the solar power they’re generating. To make use of this power, many cities offer “net-metering” programs, through which homeowners can sell their unused solar energy to the local grid. In return, they’ll receive a credit on their monthly power bill, which can off-set the extra energy costs incurred on cloudy days, or even in winter.
- Solar batteries. For maximum efficiency, many homeowners choose to install a home battery along with their solar panels. That way, when you’re not using 100% of your solar power, your battery will store the excess energy, which you can draw from at a later time— including nights, cloudy days, and power outages.
For more information, visit our solar batteries page.
You can also schedule a free solar estimate at any time, and our solar experts will guide you through the entire process!
Your roof size and positioning
While it’s possible to install a ground-mount solar panel system, the majority of homeowners install solar panels on their roofs. For this reason, the size and positioning of your roof will impact your solar panel needs.
For example, smaller roofs require panels with greater efficiency, simply because there isn’t enough space to accommodate a larger solar panel array.
Additionally, depending on how your roof is laid out, your solar panel needs will change. Is it angled facing east? Majority flat? Or partly shaded by large trees? If you study your roof and then place your panels in smart positions, you may not need as many because you can capitalize on where the sun hits them directly.
Solar panel efficiency
Last but not least, the efficiency of your solar panels will greatly impact the number you need.
Not all solar panels are created equal, and if you purchase panels that are more energy-efficient, you won’t need as many.
At Photon Brothers, we’re proud to offer industry-leading REC panels, which are the most advanced on the market today. Not only do they come with a 25-year warranty, but they also have the lowest rate of warranty claims in the industry.
With age, the efficiency of most solar panels will decrease. But even after 25 years, REC panels still produce 92% output.
As you can see, it pays to invest in solar panels that will serve you for decades to come.