How Many Solar Panels Do I Need?

How Many Solar Panels Do I Need?

Solar energy can transform your life, but it’s important not to overbuy. How do you choose the right number of solar panels for your home?

On average, solar energy costs around $2.50 per kWh and each panel can produce around 290 kWh per day. Your own energy usage goals and the local conditions here in Las Vegas will determine how many panels you need. In this article, we will cover some of the factors you should consider when calculating how many solar panels you will need.

Considering a rooftop solar panel installation? Work with the experts.
Contact Bell Solar & Electrical Systems today for assistance.

How Many Solar Panels Are Needed to Power an Average House?

When it comes to generating solar energy for your home, the most important factor to consider is the number of kilowatt (kWh) hours of electricity that you use in a year. According to the U.S. Energy Information Administration, the average home consumes about 10,972 kWh per year. This kind of usage would require somewhere between 28 to 34 solar panels to power the average home. However, you might choose to offset only part of your energy usage, which would require fewer solar panels.

How Many Solar Panels Do I Need?

If you’re asking yourself, “How many solar panels do I need?” you’re not alone. There are some factors that will make every home a little different when it comes to the number of panels they require. Here are some things to keep in mind when determining the size of your solar array.

  • Roof size
  • Location relevant to the sun 
  • Shade from nearby trees
  • Pools and hot tubs that draw a lot of extra power 
  • Hours of sunlight (Nevada can see an a see an average of 10 hours of sunlight per day during some stretches of the year)

It’s also imperative to understand what your goal is with your panels. Are you simply doing it to minimize your carbon footprint? Or are you trying to save as much money as possible? Most people want to do both, but you do need to know what percentage of your current usage you plan to offset with your new system.

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Factors That Affect Solar Panel Output

The amount of energy your solar system actually generates will be different than what it’s rated to produce. A solar calculator won’t necessarily capture the impact each of these factors can have on your system. The following factors will affect its output.

Average Solar Panel Size

The average rooftop solar panel is 65 inches long and 35 inches wide with few exceptions among major brands. Panel depth for most major brands ranges between 1.20 inches to 1.6 inches in depth.

Exceptions to these sizes can be found in the First Solar Series 5 panels, which are 73 inches long, 47 inches wide, and a razor-thin .22 inches deep. SunPower Corp: E20-327 panels are 61.3 inches long, 41.2 inches wide, and are a chunky 1.88 inches deep.

While solar panels’ sizes can vary between manufacturers, their reliability and efficiency are far more important factors that determine their output.

Average Solar Panel Output

Most solar panels produce 250 watts per hour, but this can range anywhere from 150 watts to 370 watts per hour depending on the brand. Panels with higher efficiency will cost more but are also of a higher-quality build than their less-expensive counterparts. Solar panels can degrade in efficiency by about 0.8 percent each year, according to a 2012 study by the National Renewable Energy Laboratory (NREL). Once you calculate solar panel wattage you expect to produce for your entire system, you’ll have a better idea of how bi your system should be.

Solar Cell Type

There are several different types of solar panels that are created using different materials or construction methods which impact their efficiency. Monocrystalline solar panels are often black and are made of one large silicon crystal which transmits electricity with higher efficiency than polycrystalline panels. This type, which is usually blue and has a mottled appearance, is made of many different silicon crystals molded together. These are less expensive than monocrystalline panels but can degrade over time as the electricity transfers between each crystal. 

Shade

In many ways, plain old shade will be a bigger factor in determining solar panel output than any of the technical specs. After all, if a panel isn’t getting any sunlight, it won’t be able to produce energy, no matter how thick or thin it is or what it’s made of. Your roof will need to be assessed to determine what type of shading each part of it can expect to receive throughout the day and across seasons. You may need to cut down nearby trees or install your panels on racks to optimize their sun exposure.

Temperature

High temperatures can reduce the efficiency of your solar array, which can be a concern given how hot Las Vegas rooftops get in the summer. In a laboratory setting, solar panels are rated at 77°F (25 °C), beyond which they lose an amount of efficiency that’s equal to their temperature coefficient (-0.35 and -0.5 for most mono- and polycrystalline solar panels).

Serious losses in efficiency, determined to be 20% or more, don’t occur until panels reach temperatures in excess of 149°F. However, even at these temperatures, your panels can still produce enough energy to cover a significant portion of your home’s energy usage or all of its needs if you build extra solar cells.

How Do I Calculate The Number of Solar Panels Needed?

The number of solar panels you’ll need will be determined by your daily kWh usage for your home. To get started, you will need to gather the previous year’s worth of electric bills. Start by figuring out your average monthly kWh that you use, then divide your average monthly kWh by 30 (days in the month). It’s important to note that this will be a starting estimate, and you should speak with an experienced and qualified solar contractor to confirm your numbers.

For example, if your average monthly kWh usage is 1,000, you divide that by 30 to get 33.3 kWh per day. If you use a 250 watt panel that puts out 1 kWh per day, then you would need  about 33 panels for your home. We are using fairly simple figures here to display how this calculation will work. Assuming you are using a 250 panel (which is most common) that puts out around 1kWh per day, your calculation should be pretty close.

Wondering How Many Solar Panels You Would Need to Switch to Solar?

Keep in mind, every home is made of many different factors (mentioned in the section above) that can alter calculations. You also need to set your own goals in terms of what percentage of usage you would like the solar panel system to offset. In order to come up with the most accurate projection of the amount of solar panels that you’ll need, it’s best to work with a skilled and  experienced solar contractor. This will ensure that you have the proper amount of panels to hit your energy consumption needs.

However, if you’re trying to maximize the value of your solar system, installation is the one place in the value chain where your decisions will have the greatest impact. A local installer that knows what to expect from Las Vegas’s unique weather and solar conditions, as well as your roof, can save you thousands of dollars over the life of your system. Let Bell Solar & Electrical Systems install your rooftop solar system to help you get the most out of it.

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