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How Many Solar Panels Are Required to Power a House?

Learn how to do your own solar panel system sizing for your house. Equations, data, analysis, and more interesting information.

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Carlos Huerta
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More and more people are interested in powering their homes with solar energy. In the United States, more than 2 million houses are using photovoltaic energy. Therefore, if you want to use this power source in your home, you will surely ask yourself several questions, and one of them will surely be the number of panels that are required to power your home.

It can be estimated that an average house needs around 20 to 25 solar panels to cover basic electricity consumption. However, to calculate the exact number of panels that are required to supply your home electrically, these factors must be taken into account: the amount of energy you need in your home, the amount of sun peak hours (HSP) in your geographic area, and the power rating of your solar panel.

In the following article, we will address this issue and find some answers to the question above. However it is important to know this will be a general estimation. Particular factors and conditions that may affect your PV system such as shading should be analyzed individually for every case.

What Do I Need For My Solar Panel Sizing?

To take full advantage of the panel system that you will install in your home, you will want to know how to size it correctly, since this system has to supply your energy use patterns without oversizing it.

Therefore, the main factors to consider in learning how to determine the exact number of solar panels your home requires are explained in detail below.

In addition, a solar panel sizing exercise will be carried out, calculating the solar needs, estimating the size of the system, and selecting the panels that allow you to obtain the benefits of the photovoltaic installation.

Electricity Consumption Of Your Home

There are two ways to obtain the electricity consumption of your home. The first is the simplest because it is nothing more than looking at your utility bill, in which you will find the number of kilowatt-hours (kWh) that you use per month and per year in your home. If you want to know the average daily use, divide the annual value by 365. You may also check on the website of your utility to see in detail your energy consumptions throughout the year. 

The second way involves estimating the power demand and the hours of consumption for each device in order to obtain the energy consumption. Average power of typical loads in a home can be seen as shown in figure 1. This calculation is generally performed by design off-grid photovoltaic systems.

Figure 1. Appliance Consumption. Source: Unbound Solar

The electricity consumption varies a lot according to your location and the habits of usage. For example, in hotter areas (located to the south) you are more likely to consume a lot of energy in air conditioning units. While in colder areas (located to the north) more energy is consumed in heating units during winter. This is particularly important to consider at the time to size an off-grid system 

If you have no idea how much energy you could be consuming, you can take 10,649 kWh which according to the US Energy Information Administration (EIA) is the consumption of an average home in the US.

Where Are You Located?

The location of your house is essential to take into account when sizing the number of solar panels you need in your house since depending on the level of solar exposure you have, there will be fewer or more panels.

It must be taken into account that solar panels work at their maximum power when they are exposed to direct sunlight, this usually happens during peak hours of sunlight. So depending on your location peak sunlight hours can vary.

By definition, a peak sun hour (HSP) is referred as the amount of equivalent hours that have an irradiance value of 1000 W/m2, which is close to the maximum irradiance value that can be obtained on a surface on Earth (see figure 1). Keep in mind that HSPs are not the same as the amount of hours of sunlight. Depending on where you are, you may receive 6 to 8 hours of sunlight but peak hours of sunlight can be close to 4.

Figure 2. Map of solar irradiation in the United States. Source: SolarGIS

The impact of peak hours of sunlight will be directly proportional to the energy produced by your panels. For example, cities like Phoenix may have more peak hours of sunlight, while in other cities such as Seattle, the opposite happens.

To find out the peak hours of sunlight that your residence has, you can use the NREL’s online platform, which is the data center for renewable resources and provides such information by state and major cities in the United States.

How Many Panels Do I Need?

Taking the values ​​of energy and peak hours of sunlight, it is possible to proceed with the calculation of the solar panels. To do this, the daily energy requirement (kWh) of your home is divided by the multiplication between the peak hours of sunlight (HSP) for your area and a derating factor (associated with PV losses) of 0.7, the formula would then be:

The value obtained represents the power size of the system. To determine the number of panels as such, you have to choose the type of panel to use and take into account its technical characteristics, specifically its nominal power to divide the power of the whole system between the nominal power of only one and thus obtain the quantity of panels:

As an example we have the case of a house which energy demand is 10,649 kWh per year (average in the US) and it is desired to cover the demand with solar panels. Therefore, it is first necessary to convert this annual energy to daily energy as follows:

Assuming this building is located in the state of Florida, United States, the annual solar radiation would be close to 5.74 kWh / m2 / day or what is equal to 5.74 peak hours of sunlight. Therefore, according to formula (1) we have the following:

Now, to know the number of panels, the formula (2) is used, but first you have to select the type of panel to use. For the purposes of this example, the most important thing to take into account is the nominal power, in this case we will choose a high-end module of 400 W, Canadian Solar Inc. brand (see figure 3 panel data).


Table 2 Datasheet of Panel. Data Source: Photovoltaik Forum

So, having all the values ​​to use the formula (2), we can say that the panels that are needed for this case are:

So, taking into account the number of solar panels, you can calculate the space they will occupy in and the average cost of the installation. An online tool that can be used to calculate a photovoltaic system is the NREL PVWatts platform. The results will vary slightly when compared to manually calculated results but they will give a good reference of the number of panels that would be needed to meet demands, particularly for those who are not tech-savvy on the solar word as to use software tools.

Conclusion

The number of panels that are required to power your home is one of the most frequent questions that many users ask when they are in the initial stage of buying solar energy.

Now you have the necessary information to calculate the number of solar panels you will need for your home. However, it is always recommended that a professional in the area analyze in detail all the factors that affect the sizing of the photovoltaic system in general, from the number of panels, inverters, and other elements that may affect.

Frequently Asked Questions

Which Factors Can Affect The Solar System Production?


The energy production of a solar system can be affected by factors such as the amount of sunlight exposure that the panels receive, the size of the system, as well as the efficiency and other atmospheric factors such as temperature and climatic variations.

Which Parameters Should I Take Into Account When Selecting A Solar Panel?


To choose the type of panel to be used in your solar installation, the following technical factors must be considered: the type of photovoltaic cell, dimensions, efficiency, power, current and nominal voltage.

Are There Any Limitations When Sizing A Solar Panel System?


The main limitations that exist when sizing a solar panel system have to do with the budget, shading factors, the space available for installation, obstacles, roof penetration, soiling losses, and fire setbacks established by local jurisdictions.

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Author Bio

Electrical Engineer with background in solar PV designs for residential and commercial projects as well as power systems development. Fan of renewable energy topics and projects. Technical writer for papers, articles and research in related topics to sustainability and especially solar power.

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