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Making the switch to solar energy can help you lower or even eliminate your monthly electric bills while reducing your carbon footprint. However, before installing a clean energy system in your home, you must first answer an important question: “How many solar panels do I need?”
To accurately calculate the ideal number of solar panels for your home, you’ll need a professional assessment. However, you can estimate the size and cost of the system based on your electricity bills, energy needs and available roof space. Here are the general steps:
Read on for a full explanation of each step of the process. Or, to consult with a professional and start designing your system right away, you can click the buttons below to get connected with one of the best installers in the nation.
To determine how many solar panels are needed to power a house, several factors must be considered. For example, if there are two identical homes powered by solar energy in California and New York, with exactly the same energy usage, the California home will need fewer solar panels because the state gets more sunshine.
The following are some of the most important factors to consider when figuring out many solar panels you need:
Larger homes tend to consume more electricity, and they generally need more solar panels. However, they also have the extra roof space necessary for larger solar panel installations.
There may be exceptions to this rule — for example, a 2,000-square-foot home with new Energy Star appliances may consume less power than a 1,200-square-foot home with older, less-efficient devices. When it comes to installation, solar panels can be placed on many types of surfaces.
However, your roof conditions may limit the number of solar panels your home can handle. For example, if you have a chimney, rooftop air conditioning unit or skylight, you’ll have to place panels around these fixtures. Similarly, roof areas that are covered by shadows are not suitable for panels.
Also, most top solar companies will not work on asbestos roofs due to the potential health risks for installers.
Where there is more sunlight available, there is more energy that can be converted into electricity. The yearly output of each solar panel is higher in states like Arizona or New Mexico, which get a larger amount of sunlight than less sunny regions like New England.
The World Bank has created solar radiation maps for over 200 countries and regions, including the U.S. The map below can give you an idea of the sunshine available in your location. Keep in mind that homes in sunnier regions will generally need fewer solar panels.
© 2020 The World Bank, Source: Global Solar Atlas 2.0, Solar resource data: Solargis.
Households with more members normally use a higher amount of electricity, and this also means they need more solar panels to increase energy production.
Electricity usage is a very important factor, as it determines how much power must be generated by your solar panel system. If your home uses 12,000 kilowatt-hours (kWh) per year and you want to go 100% solar, your system must be capable of generating that amount of power.
High-efficiency panels can deliver more watts per square foot, which means you need to purchase fewer of them to reach your electricity generation target. There are three main types of solar panels: monocrystalline, polycrystalline and thin-film.
In general, monocrystalline panels are the most efficient solar panels, followed closely by polycrystalline panels. Thin-film panels are the least efficient.
If you want to know for sure how many panels you need, you can click below to connect with an EcoWatch-vetted installer and get a free estimate.
So, based on these factors, how many solar panels power a home? To roughly determine how many solar panels you need without a professional assessment, you’ll need to figure out two basic things: how much energy you use and how much energy your panels will produce.
According to the latest data from the U.S. Energy Information Administration (EIA), the average American home uses 10,649 kWh of energy per year. However, this varies depending on the state. For example:
To more closely estimate how much energy you use annually, add up the kWh reported on your last 12 power bills. These numbers will fluctuate based on factors like the size of your home, the number of residents, your electricity consumption habits and the energy efficiency rating of your home devices.
After you determine how many kWh of electricity your home uses annually, you’ll want to figure out how many kWh are produced by each of your solar panels during a year. This will depend on the specific type of solar panel, roof conditions and local peak sunlight hours.
In the solar power industry, a common metric used to estimate system capacity is “specific yield” or “specific production.” This can be defined as the annual kWh of energy produced for each kilowatt of solar capacity installed. Specific yield has much to do with the amount of sunlight available in your location.
You can get a better idea of the specific yield that can be achieved in your location by checking reliable sources like the World Bank solar maps or the solar radiation database from the National Renewable Energy Laboratory. To estimate how many kW are needed to run a house, you can divide your annual kWh consumption by the specific yield per kilowatt of solar capacity.
For example, if your home needs 15,000 kWh of energy per year, and solar panels have a specific yield of 1,500 kWh/kWp in your location, you will need a system size of around 10 kilowatts. Paradise Energy Solutions has also come up with a general formula to roughly ballpark the solar panel system size you need.
You can simply divide your annual kWh by 1,200 and you will get the kilowatts of solar capacity needed. So, if the energy consumption reported on your last 12 power bills adds up to 24,000 kWh, you’ll need a 20 kW system (24,000 / 1,200 = 20).
Once you know the system size you need, you can check your panel wattage to figure how many panels to purchase for your solar array. Multiply your system size by 1,000 to obtain watts, then divide this by the individual wattage of each solar panel.
Most of the best solar panels on the market have an output of around 330W to 360W each. The output of less efficient panels can be as low as 250W. So, if you need a 10-kW solar installation and you’re buying solar panels that have an output of 340W, you’ll need 30 panels. Your formula will look like this: 10,000W / 340W = 29.4 panels.
If you use lower-efficiency 250-watt solar panels, you’ll need 40 of them (10,000W / 250W = 40) panels. Keep in mind that, although the cost of solar panels is lower if you choose a lower-efficiency model over a pricier high-efficiency one, the total amount you pay for your solar energy system may come out to be the same or higher because you’ll have to buy more panels.
Solar panels produce no carbon emissions while operating. However, the EIA estimates fossil fuels still produce around 60% of the electricity delivered by U.S. power grids. Although the initial investment in solar panels is steep, renewable energy systems make sense financially for many homeowners.
According to the Department of Energy, they have a typical payback period of about 10 years, while their rated service life is up to 30 years. After recovering your initial investment, you will have a source of clean and free electricity for about two decades.
Plus, even if you have a large home or find you need more solar panels than you initially thought you would, keep in mind that there are both federal and local tax credits, rebates and other incentives to help you save on your solar power system.
If you want to know for sure how many panels you need, you can click below to connect with an EcoWatch-vetted installer and get a free estimate.
After you estimate how many solar panels power a house, the next step is calculating the roof area needed for their installation. The exact dimensions may change slightly depending on the manufacturer, but a typical solar panel for residential use measures 65 inches by 39 inches, or 17.6 square feet.
You will need 528 square feet of roof space to install 30 panels, and 704 square feet to install 40. In addition to having the required space for solar panels, you’ll also need a roof structure that supports their weight. A home solar panel weighs around 20 kilograms (44 pounds), which means that 30 of them will add around 600 kilograms (1,323 pounds) to your roof.
You will notice that some solar panels are described as residential, while others are described as commercial. Residential panels have 60 individual solar cells, while commercial panels have 72 cells, but both types will work in any building. Here are a few key differences:
Some of the latest solar panel designs have half-cells with a higher efficiency, which means they have 120 cells instead of 60 (or 144 instead of 72). However, this doesn’t change the dimensions of the panels.
The efficiency of a solar panel is affected by a number of factors, but two of the most prominent are the type of panel it is and how much sunlight it receives.
If your aim is to produce 2,000 kWh of energy a month, you’ll need to do a few quick calculations to determine how many solar panels you need. As a general rule of thumb, you can divide your annual kWh needs by 1,200 to calculate your ideal system size. In this case, 2,000 kWh per month x 12 months = 24,000 kWh per year.
24,000 kWh / 1,200 = a 20 kW system. But how many solar panels are in a 20 kW system? The number of solar panels you’ll need will depend on the power output of the panels. The best solar panels have output ratings between 330W and 360W, and the lowest-producing panels typically have a 250W output. Let’s say you purchase panels with an output of 340 watts.
You’ll need to divide your total system wattage by your panel wattage to determine how many panels to order. So, 20,000W / 340W = 58.8 panels. If you purchased 250W panels, your formula would look like this: 20,000 / 250 = 80 panels.
When deciding how many solar panels you need for your home — especially if you’re installing a large system — you’ll want to take into consideration how much weight your roof can support. Standard solar panels typically weigh about 44 pounds.
The lightest panels are under 35 pounds, and heavier models come in around 50 pounds. If your roof can’t support the number of panels you need, you can look for lighter panels, more efficient panels (so that you need fewer of them) or alternative placements, like installing a ground-mounted solar system.
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