How Many Solar Panels I Need For My House? - Find Easily

How many Solar Panels I Need to Power my Entire House -The ULTIMATE guide

How many solar panels I need

When Thinking about installing solar for your home, the first question that pops up in your mind is,…how many solar panels I need to power my house with Solar Energy? The answer is not as complicated as you think; you can power 100% of your house with Solar, and you would need roughly around 20 to 35 panels for an average home, around 2000 sq. ft.

The truth of the matter is, Solar panels are not a one-size-fits-all solution, like most technologies that are used in today’s world. We’ve to understand that the number of panels that you would need will depend on circumstances like Roof Space, Usage, etc and that will determine how many solar panels I need to power my entire house.

Here is a quick breakdown of the number of panels you would need for different size homes with average power consumption. On average, the kwh usage of electricity is based on 0.5 kWh per square foot. So, if you have a 2000 square foot house, your average kWh per month is 1,000 kWh.

Energy-Consumption-1
Average Energy Consumption per Month for different household sizes and recommended panels

What is your usage

So you’ve decided to go solar; first and foremost, you need to be checking what your usage is going to be. Also, one of the foremost things you need to be thinking about is how your users will be. Is it going to remain constant, or will it increase in the years to come since you’ve gone solar? Remember, when you install solar, you should be thinking about your current needs and if there is going to be additional usage in the future. Your electricity usage can be taken into account if you plan to start a family or you plan to bring in your parents to stay alongside you, or you’re planning to buy additional appliances that rely on electricity or Electric Vehicles as you know that Electric Vehicles are going to become a mainstay in the coming years

How do you find your usage and Define KWH and breakdown usage?

How does one find their electric usage, in general, is an excellent question for anyone to start who plans to go solar? You can actually use two ways to go about that. Some people prefer to go through the traditional way because they love to do calculations and be sure ( In actuality, this will help you to understand your energy use in your home in a more in-depth way and find things that are going to use fewer energy killers that can help you get rid of stuff.

  1. Traditional way
  • Figure out every electric appliance you use in your home, think in the South, electricity runs heaters, etc., don’t forget the lights you use regularly.  
  • You can find every device wattage label either on the device or at the back of the device.  
Usage-Details-1
Device Wattage labels at the back of a Sandwich press electric appliance (left and Energy Guide Ratings (right)
  • Alternatively, you could use this table to determine the wattage of individual devices. This table was used from Energy Savers [1].
Electrical AppliancesTotal Watts
Coffee Maker1500 watts
Microwave1000 watts
Toaster1100 watts
Dishwasher1800 watts
Washer500 watts
Dryer3000 watts
Iron1100 watts
Ceiling fan130 watts
Vacuum-Upright297 watts
Hair dryer710 watts
Laptop50 watts
Computer CPU68 watts
Computer Monitor LCD1500 watts
Television 19″-36″120 watts
Television 53″-61″180 watts
Default Energy consumption of various electric appliances. [1]

Now to calculate power consumption use the following steps to do it

Using the Coffee Maker as an example, The Coffee Maker uses 1500 Watts and is used a daily average of 2 hrs per day. This will give you the number of watt-hours consumed each day.

1,500 W × 2hr = 3000 Wh

  • But the reality is to calculate how much solar you need; you need to determine the kilowatt-hours (kWh), not watt-hours. One kilowatt is equal to 1000 watts, so to calculate how many kWh a device uses, divide the watt-hours by 1000, and you get your watts/hr.

3000 Wh / 1000  = 3kWh

  • Now we need to multiply that per month by 30 days, and you will be able to get an average of how much you use per month.

3kwh x 30 = 90kwh

  • Add all the cost of for individual devices and you will get the entire cost of all devices per month.

After we added up all the usage, the entire house uses approximately 37 kwh day..

  • Electricity Bills from Solar
    • Alternatively, there is a straightforward way to do that. Open up your electricity bill online from your provider or pull up your copy.
Electricty-Bill
Total Avg. Monthly Usage shown under Yearly Comparison in the bottom left of the Electricity bill

Where it shows the kwh  shows the total kwh used on a monthly basis.

In general, the average monthly consumption of electricity in the US is 2019. The average monthly electricity consumption for a home in the United States was 877 (paste Link here) kWh per month, 10,649 kWh per year.  This was based on the EIA estimates.

Solar Potential – Sunlight breakdown in a different area

The other aspect you would need to consider is the Solar Potential or Solar insulation in your area. Solar potential, also known as Solar radiation, is a term for the electromagnetic radiation emitted by the sun. This solar radiation can be turned into a useful form for human consumption in electricity and heat. But again, this is l based on the Technical solutions available to convert them into a useful form for human consumption and or based on the economic viability considerations. With that being said, Solar potential is different for different regions… See below the breakdown of solar potential or Solar insolation in the United States.

Solar-Irradiance
US Solar Irradiance [2]

  You can see the reddest area has the highest potential for generating the highest solar energy

Calculating Peak Sun Hours

One of the most important factors that influence your usage will be the Solar potential of your solar modules exposed to sunlight at a given time. Solar modules or solar panels will need sunlight to produce their maximum output. Although, on cloudy days, your solar panels / solar modules will be exposed to less solar power. Somewhere close to 40% lower on those days.

It is important to understand that Peak sun hours are not the same as the number of hours from sunrise to sunset. Rather it is the average of the Solar Radiation or Solar Insolation received throughout the day. Its unit of measurement is Kwh/m2 per day. A peak sun-hour is defined as an hour of sunlight that offers 1,000 watts per square meter. Peak sun hours describe the intensity of sunlight in a specific area. For example, if a location gets 4 PSH (kWh/m²), the area gets 4 hours of solar power when the average intensity of sunlight is 1000 watts/meter². This number increases as we get closer to the equator and, more generally, during the summer months. Peak power happens when the solar rays are at right angles or perpendicular to the modules. As the solar rays deviate from the perpendicular, more and more energy is reflected rather than absorbed by the modules. In general, it’s more difficult to produce energy during the winter because of shorter days, cloudiness, and sun position in the sky.

STATESSUN POTENTIALSTATESSUN POTENTIAL
Alabama3.5-4Montana4 – 5
Alaska2 – 3Nebraska4.5 – 5
Arizona7 – 8Nevada6 – 7.5
Arkansas3.5 – 4New Hampshire3 – 3.5
California5 – 7.5New Jersey3.5 – 4
Colorado5 – 6.5New Mexico6 – 7
Connecticut3New York3 – 3.5
Delaware4North Carolina4 – 4.5
Florida4 – 4.5North Dakota4 – 4.5
Georgia4 – 4.5Ohio2.5 – 3.5
Hawaii4 – 5Oklahoma4.5 – 5.5
Idaho4 -5Oregon3 – 4.5
Illinois3 – 4Pennsylvania3
Indiana2.5 – 4Rhode Island3.5
Iowa4South Carolina4 – 4.5
Kansas4.5 – 5South Dakota4.5 – 5
Kentucky3 – 4Tennessee4
Louisiana4 – 4.5Texas4.5 – 6
Maine3 – 3.5Utah6 – 7
Maryland3 – 4Vermont3 – 3.5
Massachusetts3Virginia3.5 – 4
Michigan2.5 – 3.5Washington2.5 – 5
Minnesota4West Virginia3
Mississippi4 – 4.5Wisconsin3.5
Missouri4 – 4.5Wyoming5.5 – 6
Sun Potential of all the states within the US [3]

General Estimate for the size of the solar energy system you need for your home.

Since you have come up with several kwh used per year for your usage, you can determine the exact size of the solar system you would need to power your entire home. If you want your solar system to account for 100% of your energy consumption, here is how the calculation would work:

  • 37 kWh per day x 100% = 37 kWh.

Now use the Solar radiation / Solar Insolation or PSHs to determine how big of system you would need to have your 100% of your energy needs covered

For. Eg. In California, if you use the following formula

Daily Usage (kwh) / PSH (kwh/m2)

  • 37kwh / 5.82 kwh/m2= 6.35 kw

Now you’ve to accounts for standard energy losses of solar PV systems:

  • 6.35 kW x 1.3 (increase size of PV system by 30%) = 8.25kw

Once you’ve figured out the size of your system, which is 8.25kw, you need to divide your kW output based on the total number of panels/modules you plan to use on your system. For that, you would need to determine the size, type, weight of the panel, and the area required to place the panels on the roof. Generally, home users would need to understand what kind of panels they would need to use.

Type of the Panel

There are 2 most commonly used solar panels in the residential solar industry.

Solar-Panels
Monocrystalline Solar Panels (left) and Polycrystalline Solar Panels (right)
  • Mono-Crystalline – The easiest way to distinguish these panels is black in color. These panels are made of monocrystalline solar cells, a single silicon crystal, which gives them a uniform structure and a high purity level. As a result, you end up in higher efficiency solar panel with a sleek black look. But there is a drawback to these, that they are more expensive and resulting in the solar system being more pricier.
  • Poly Crystalline – These panels are dark blue in color. Polycrystalline solar panels are made from silicon which comes from multiple sources. As a result, it gives them an uneven blue color. The process is quicker and easier and leads to less wastage of resources, as it utilizes tiny bits of silicon. The effect of it makes it less expensive, but also the efficiency goes down as well. 
  • Thin Film Solar panel – A thin-film solar panel is a semiconductor coat deposited on glass, plastic, or metal. These coated solar thin films are fragile, making them flexible, lightweight, and adaptable to many surfaces. They have a higher tolerance than their crystalline panels, making them more resistant to damage from hail, golf balls, rocks. Typically, thin-film solar panels operate more efficiently in low-light conditions, but their efficiency in normal light tends to be lower than crystalline panels. The three most common types of thin-film solar panels are amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS) or gallium-free CIS.

A 60-cell mono or polycrystalline module averages a power output between 250 and 350 W, which has an efficiency of more near 18 or 19%. Comparatively speaking, one would need many thin-film modules and a larger area to produce the same power as a similar group of mono or polycrystalline silicon modules, as they are just more consistently dependable for the majority of solar markets. Hence, they are the dominant panel choice. To that extent, Monocrystalline panels produce better power purely because of fact that they have greater efficiency than polycrystalline panels. So people who have limited roof space should think about using Monocrystalline panels as the efficiency of these panels helps in getting more power from a system with limited roof space.

Size and Weight of the Panel

Solar panels come in different sizes and weights. But most brands stick to panels that have the same size and weight. These solar panels generally have 60 cells, and their typical measurement is 65 inches x 39 inches. Although some commercial solar panels are being used in the residential industry, they generally have 72 solar cells. These cells are interconnected in a series fashion in a sealed weatherproof package which is called the module. Most standard panels are between 260W and 325 watts DC STC, while SunPower manufacturers high-efficiency equipment in the range of 327 to 400 watts.

Since we’ve assumed the size of the system to be 8.25kW, and decided to go for a 280 W Standard Size Solar panel.

                        Number of Panels = Size of the System / Standard size of the module

Panels = 8250 / 280 W = 29.4

We would require 29 Solar panels of 280W to get to an 8250 kW system. This system would generate roughly 37 kwh per day, which would power 100% of your energy usage.  

Weight is another consideration that should be considered when trying to determine whether a rooftop can handle solar. Most residential PV modules weigh about 40 pounds each. Weight can range anywhere from 33 pounds to 50 pounds, depending on the manufacturer.

Roof Space

Before-Solar
Roof Space before Solar Panels are installed

Another factor that people need to consider is how much roof space you have on your roof. Bigger the roof, the chances of putting all the panels you need on the roof…But chances are you might have a smaller roof, or your southern exposure may not be enough, and so you might have to figure out if you have the space to calculate solar. [1]

Total Power Output = Total Area x Solar Irradiance x Conversion Efficiency

8750 = Area x 1000 x 0.20

Area  = 43.75 sq.meter

Solar Irradiance = The solar power per square meter at the Earth’s surface is (1,000 W/m^2).

Conversion Efficiency = Solar Panel efficiency is anywhere between 0.18 to 0.20

Location of the Roof

Solar panels produce more electricity when exposed to maximum sunlight and not obstructed from any shading. To understand the best output for a solar energy system, you must determine the location and position of the home or building. In general, the southern direction is the ideal place for solar panels. The panels can get more sunlight in this direction.  The solar panel should project to the true south. If you place the solar panels facing the east or west, you will get the sunlight for a limited time.

Shading

Another factor to consider is shading on the room if any obstructions like chimneys, trees, and adjacent buildings cast a shadow over the ideal locations for those roofs because the power output will be significantly less than the original.

Tilt Angle on Roof

When it comes to perfect roof pitch for solar panels, the rule of thumb is that it should equal the latitude of the location of the installation (Think the sunlight needs to hit the solar panel at a perpendicular angle). However, if this angle isn’t possible, pitch angles between 30 and 45 degrees will work. They will definitely provide the most optimum output for a Solar Energy system production of a solar array. For this reason, flat-roofed homes are ideal.

After-Solar
Roof After Solar Panels are installed

Recap

  • Find your average daily usage in kilowatt-hours (kWh) or find your monthly usage from your monthly electricity bill.
    • Find your Peak Sun hours (kwh/m2) per your state or nearby city.
    • Decide the wattage of the panel. Anything between 250 – 325 W would be considered the standard size.
    • Use the Formula to Calculate the Size of the system.

Size of the system = {Daily Usage (kwh) / Peak Sun Hours (kwh/m2)} x 1.30

Number of Panels = Size of the System / Standard size of the module

  • Find the Roof Space required

Total Power Output = Total Area x Solar Irradiance x Conversion Efficiency

  • Determine the South location of the Roof

Final Thoughts

The bottom line is that Electricity generated by Solar can power your home, and it makes complete financial sense in the long term to get solar for your home. But, like everything in life, Solar is not a size fits all kind of model. There are constraining factors such as Roof Space, South Facing Roofs, Sun hours (if you live in the upper part of the country), and financing of the system, renters, deed restrictions, etc., that prevent you from having a rooftop solar energy system for your home. So other options are available in the market to get Solar. One of those options is Community Solar, and if you want to understand it better, take some time to read our article on Community Solar.

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