If you plan to invest in solar panels, one of the most important considerations is how many solar panels you need. Of course, this is directly related to how much electricity you need or expect your panels to produce.
The issue is that your roof is only so large. So before you can invest in solar panels, you need to think about how many solar panels you can fit on your roof and if the number of solar panels will meet your energy needs.
This article will help you calculate your roof size. We’ll also look at the size of standard solar panels, and once we’ve done this, we can then figure out how many you can fit on your roof. Of course, factors other than roof and panel size will decide how many panels you need.
How Many Panels Can You Fit on Your Roof? How Many Do You Need?
We want to determine how many solar panels can fit your roof and how many you need. There are a few steps to determine these figures.
- Determine how much electricity you need those panels to produce. This is going to be based on your current electricity consumption.
- Determine how much electricity your standard panels can produce. This will determine how many panels you will need to meet your energy requirements.
- Determine the average size of solar panels.
- Determine the overall size or area of your roof. This will, in part, determine how many panels you can fit.
We can then determine how many solar panels you need to meet your needs and if you can fit them all on your roof.
Note that we will be making some generalizations because:
- Not all roofs are the same size or shape.
- Not all solar panels produce the same amount of electricity.
- Not all solar panels that produce the same amount of electricity are the same size.
Therefore, we need to generalize these numbers.
Our step-by-step process below will use average estimates. However, we want to provide a real-life step-by-step example using real numbers, so we have to use general figures and averages to perform our calculations.
Determining Your Energy Requirements
First, you need to determine how much power your solar panels need to produce. This is done by looking at your monthly energy bill or statement. This will tell you exactly how much electricity you use monthly and yearly.
This will allow you to determine how many solar panels you need to meet your energy usage requirements.
For the record, the standard amount of energy used by a single household in the US is roughly 903-kilowatt hours per month. So, let’s assume that you need your panels to produce 903-kilowatt hours per month (we will round this down to 900 to make calculations easier).
The Solar System Size You Need to Meet Your Energy Usage
Now that you know how much electricity you need, you can determine the required size of the system. Most solar panels are 250 watts or 0.25 kilowatts.
A standard 5kW system will produce 20-kilowatt hours per day or 600-kilowatt hours per month. However, remember that output will also depend on peak sunlight.
The standard peak sunlight used in this calculation is 4 hours. So, if a 5kW system gets 6 hours of peak sunlight per day, it would generate 30 kilowatt-hours per day or 900 per month.
If you only get 4 hours of peak sunlight per day, to get to those 900-kilowatt hours, you will need a 7.5kW solar system. With 4 hours of peak sunlight, a 7.5kW system would produce 30kWh per day or 900 kWh per month.
Knowing how much electricity a specific size solar system can produce is essential. First, however, we now need to determine how large that system will be in terms of the area covered.
The Size of the Solar Panels
For the purposes of this calculation, we will assume that you get the standard 4 hours of peak sunlight, and you need a 7.5kW system to fully meet your energy needs.
Of course, you also need to consider how large the solar panels are. For instance, different brands might have solar panels of differing sizes. For example, LG, Tesla, and Panasonic solar panels vary slightly in size.
That said, as long as they have the same wattage, they should all be roughly the same size. For example, most 250 watt solar panels measure approximately 1.44m2.
Since 250 watts equal 0.25 kilowatts, to get a full 7.5-kilowatt system, you would require 30 solar panels. So, 30 solar panels of 250 watts a piece would create a 7.5kW system. This, with 4 hours of peak sunlight, should produce 900 kWh monthly.
How much space will you need to accommodate 30 solar panels, each 1.44m2? The answer is 43.2m2. And the next step is to figure out how large your roof is and if it can accommodate the panels.
How to Calculate the Size of Your Roof
Below we have provided an easy step-by-step formula to calculate the size of your roof.
There are three measurements that you need to perform this calculation.
- You need to know the highest point of your roof (A).
- You need to know the distance from the horizontal apex to the eaves (B)
- You need to know the length of the apex of the roof (C).
You now need to use this formula, A2 + B2 = X2. Plug the values as listed above into the equation. Here, you are solving for X (the distance from the edge to the apex of your roof).
Then, take C (length of the apex) and multiple it by X (distance from the edge to the apex).
This will provide you with the area of your roof. Remember to subtract about 30 cm or 12 inches from the roof’s edge. You can’t install solar panels right on the edge of the roof.
The Average Size Roof in the US – How Many Solar Panels it Can Fit?
Obviously, all houses are different, so we have to generalize here again. The average roof size of a residential home in the US is 1,700ft2 or 157.94m2. Now we can put everything together.
- To meet the needs of an American household, a solar system that can produce 900 (903) kWh monthly is needed.
- Based on the average 4 hours of peak sunlight per day, this would require a solar system of 7.5kW.
- A single solar panel is usually 250 watts. This means that to generate 900kWh, you would need a total of 30 panels.
- Each panel is roughly 1.44m2. This means that 30 panels would take up 43.2m2.
Based on the average size of a roof in the US, 157.94m2, you could fit just under 110 panels. However, you need only 30 panels of 250 watts each to generate 900kWh per month. If you want to take advantage of net metering, you can install more solar panels than you need.
Moreover, maybe you only get 2 hours of peak sunlight per day. If this is the case, you would technically need a 15kW system to meet your 900kWh monthly needs, twice the size of a 7.5kW system. A 15kW system would need 60 panels, each 250 watts. To accommodate this, you would need 86.4m2 of roof space.
Conclusion
If an average panel is 1.44m2, and the average roof is 157.94m2, you could potentially fit over 110 panels on your roof. However, this is likely more than you will ever need to power your home.