How Much Area is Required for a 1 kW Rooftop Solar PV System?

A 1 kW rooftop solar PV system requires approximately 100 ft2 of shadow-free area. The estimation accounts for leaving some space between the modules, mounting hardware clearance, and the inverter installation as well.

So the actual PV module array will occupy only a certain portion of this area we are about to discuss.

Please keep in mind that the calculation below is based on an ideal installation scenario in which the solar PV system is mounted at the perfect angle and there is no shading from trees or buildings.

The array uses an MPPT charge controller and has a module efficiency of 15% – 20%. If you have more shading, less ideal conditions, or a lower efficiency module, you'll need to adjust the calculation accordingly.

Here is how we came up with the 100 square feet number for a kilowatt system:

A typical 400 Watt monocrystalline solar panel measures approximately 79″x39.5″ and covers about 21.65 ft2 surface area.

In ideal conditions, 3 of these panels would be sufficient to generate a little over a kilowatt of power. However, in the real world, you'll want to factor in at least a 40% derate to account for losses. Having the 4th panel will give you a little more cushion reaching the kilowatt mark.

That means you would need 21.65 x 4 = 86.60 ft² of available surface area for a kilowatt system. This is the safe number of panel surface area you would need to generate a kilowatt of power.

But as we said before, you'll want to factor in some additional space for the inverter, mounting hardware, and wiring. So a more realistic estimate for the total area required would be 100 ft².

The important factors that can affect the output of your rooftop solar PV system and the amount of area required are:

Charge Controller Inefficiencies

An MPPT charge controller has a typical 94% – 99% efficiency, while a PWM controller is about 70%. Your solar PV array can only be as efficient as your charge controller.

To give an example, if you have a PWM controller with 70% efficiency and your solar PV array is able to produce 1000 Watts in full sun, you can only expect to get 700 Watts delivered to your batteries.

However, if you upgrade to an MPPT controller with 97% efficiency, you would now be able to get 970 Watts delivered.

As you can see, the type of charge controller you use can have a major impact on your system's performance thus how many solar panels you will need.

The direction your roof faces

The direction your roof faces also impacts how much area you will need for your solar PV system.

If your roof doesn't face south but instead faces east or west, you'll need more area to generate the same amount of power.

The reason for this is that the angle of the sun at the south-facing location will be much more perpendicular to the solar panels than at the east or west-facing location.

The type of your solar panels

There are a few different solar panel technologies available on the market: monocrystalline, polycrystalline, and thin film. You can use monocrystalline or polycrystalline solar panels for a rooftop PV system.

Thin-film solar panels are much less efficient than mono and polycrystalline panels and therefore you would need a lot more area to generate the same amount of power. Thus, we are keeping thin film out of the conversation for now.

We also know monocrystalline panels are more efficient than polycrystalline panels. So, if you're using monocrystalline panels, you will need fewer panels or less roof space to generate the same amount of power.

Temperature

Solar panels work best when the temperature is around 25 degrees Celsius which is they are typically tested. So, if you're in a considerably hotter or colder climate, you will need to account for that when calculating the performance of your solar PV system.

Because a lower-performing solar array means you'll need more panels to generate the same amount of power. This will translate into needing more roof space for your solar PV system.

System Losses

Every solar PV system will have certain inefficiencies or losses. There will be losses sourced from wiring, connectors, and inefficiencies in the panels themselves.

This isn't something you should be concerned about if you have followed the best practices for wiring and have chosen high-quality solar panels. However, you should strive to reduce inefficiencies as much as possible.

For example, building a higher voltage system (using a 24V instead of 12V) will reduce the losses in wiring. However, unless you plan these types of upgrades during the design phase of your system, you will likely be stuck with the inefficiencies.

The system configuration also has a significant impact on the size of your system. If you're using a series connection, each panel will be outputting at its rated voltage. But if you're using a parallel connection, the panels will be combined to create one big array with a higher current.

Both parallel and serial wiring of solar panels have their advantages and disadvantages. However, these configurations will directly impact how much roof space you need for your solar PV system.

Shading Losses

Shading from trees, buildings, and dirt can have a significant impact on the performance of your solar panels. If you have significant shading on your roof, it will be necessary to adjust the size of your system accordingly.

In fact, shading losses can be so significant, that can completely invalidate the economics of a rooftop PV system.

For example, a 25% uniform shading on your solar PV array can cause around 50% loss in power generation. And a 50% uniform shading can cause a whopping 90% loss in power generation!

You can check our post here that explains how does shading affects solar power generation.

However, all solar PV systems will likely experience some shading that should be accounted for when sizing your system.

Panel mismatch tolerance

Mismatch loss is defined as a loss induced by minor changes in the electrical properties of the installed modules, expressed as a fixed percentage reduction in the system's DC power output.

According to industry standards, mismatch losses can range from 0.01% to 3% depending on the system configuration and string length.

Number of panels in the array

The number of solar panels in the array makes difference in the amount of energy that can be produced by the system and in the physical size of the array.

If you use 100 Watt solar panels, the number of solar panels in an array is ten. If you use 250 Watt solar panels, the number of solar panels in an array will be four.

Although, the physical size of the array will be smaller with the 250 Watt solar panels, using 100 Watt solar panels will actually offer better shading tolerance.

This is due to the fact that shaded panels in a string will not drag down the power output of the entire string as much if the wattage of each panel is lower.

However, there is always a compromise with everything. Using smaller but more solar panels will result in more wiring and connector losses. This can also create unnecessary complexities you have to manage.

Losses due to panel & roof geometry

The panel geometry also has an impact on the size of your system. Solar panels come in a variety of shapes and sizes, but they are typically rectangular.

There aren't many roofs that perfectly fit to accommodate the designed shape and size of solar panels. This often leads to gaps and unused spaces on the roof that should be accounted for when calculating the amount of roof space that you need.

If your roof has a lot of obstacles, you may need to alter your original calculations to change the number of panels and/or the size of the array.

Conclusion

So as you can see, there are many factors that need to be taken into account when sizing a rooftop solar PV system. It's not as simple as just looking at the rated power output of the panels and multiplying it by the number of panels you need.

Each factor has a unique impact on the size of your system, and you need to account for all of them when sizing your system.

Taking all of this into account, a minimum of 100 square feet is required to consistently produce 1000 Watts (one kilowatt). This number allows you to account for everything we've discussed so far.