The big question to ask when looking at how many solar panels do I need to power my home is whether you want to be completely self-sufficient in electricity or simply generate enough electricity to cover your major appliances at peak times.
Let’s look at a quick rule of thumb to work this out. Remember the more electricity you use, the more solar panels you’ll need to install.
How Many Solar Panels Do I Need For My Home?
The average US home needs 20-30 solar panels to cover its electricity needs. To estimate yours, use these 5 steps,
Determine your hourly energy needs
Calculate the number of daylight hours per day
Work out the daily electricity output by multiplying your solar panel wattage with the sun hours per day
Calculate the number of solar panels by dividing your daily electricity needs with the daily power output
Account for production losses and determine the size of your panel
The devil though is always in the detail, so with this in mind let’s dive in and use a 5 step guide to see how many panels you need.
Step 1: Work Out Your Total Electricity Use
First you must ask yourself, “what are my solar panel goals?”
You have two options to choose from,
- To have enough solar panels to be self-sufficient in electricity
- To be partially sufficient in electricity production to cover your primary appliances.
How To Be Completely Self Sufficient In Electricity
You will need to have the space and budget for the solar panels. See later on in the article how you can estimate this.
So, if you have the space, then calculating how much you need is simple. Just check your utility bill to find out your electricity use per month and that’s the kilowatt goal your solar panel system needs to generate.
How To Generate Enough Electricity To Cover Your Major Appliances
If you have limitations on putting up solar roof panels because of restricted roof or land space then you’re looking at becoming partially self sufficient in electricity.
First Let’s Get A Definition Of Watts and Kilowatts
In metric, 1,000 = kilo, so 1,000 watts equals a kilowatt. For instance, if you turned on a 100-watt bulb, it would take 10 hours to use one kilowatt-hour of energy. So this is our unit of measurement. Now let’s see how to work out what we need.
According to The Office of Energy Efficiency & Renewable Energy, there are a number of different formulas you can use.
The quickest way is to calculate how much electricity you need to just run your major appliances. To do this, you need the following information.
- Usage Time: Work out how many hours in a day you use each major appliance. For example, your fridge, TV or hot water.
- Device Wattage: Now check your appliance for a label that will give you its wattage.
Estimation: Multiply the wattage by the number of hours you use. This is your watt per hour.
Electricity Use By Appliance
Square Footage Of Your Roof
- TV
- Refrigerator
- Air Conditioning
Average kWh Electricity Needed
- 234 W watts per hour
- 225 W watts per hour
- 3500 watts per hour
Number Of Solar Panels
- 1
- 2
- 3
A Worked Example On How To Be Self Sufficient In Electricity To Cover Your Major Daily Appliances
The average US home uses 1.25 kWh per hour or 30kWh per day E.g. from 3 main appliances
Major Usage Time Per Day:
- TV = 4 hours
- Refrigerator = 24 hours
- Washing Machine = 1 hour
- Total of 29 hours
Device Wattage Per Day:
- TV = 234 W per hour
- Refrigerator = 225 W per hour
- Washing Machine = 225 per hour
- Total = 684 W per hour
Estimation Per Day:
Multiply the wattage by the number of hours you use. So to cover your major appliances you would need to generate
= 19.8 kWh per day or 19800 watts
Step 2: Calculate The Average Number Of Daylight Hours Per Day
Now that you know how many kWh you need to generate per day to either be self-sufficient in electricity, or have enough to cover your major appliances, it’s time to see how many solar hours you have available to generate that electricity.
This will also hinge on how much sun can get to your solar panel because of the shade on your roof, the pitch of your roof, where you live and the time of year. For the average sunlight hours in your area, it’s good to find out this figure from your local meteorological service.
According to the US Climate Blogspot the average is 15 hours a day in the U.S. but peak sun times can range from 4 hours in Massachusetts to 7 hours in Arizona. It is the peak time that you are interested in.
So, carrying on with our example,
Hours Of Peak Sunlight Per Day
Local Average Amount Of Sunlight In Your Area:
4 winter hours – 6 summer hours of peak sunshine on average per day for your area.
Number Of Hours Solar Panel In The Shade Per Day:
1 hour in the shade in the summer and 2 hours in the winter.
Pitch Of The Roof Affecting Available Sun Hours:
It has no effect on the available peak hours
Estimation Of Peak Sunlight Hours Per Day:
- Local peak hours = 6 hours
- Minus Hours in the shade = 4 hours
- Effect of roof pitch on peak hours = 0
- = 2 winter hours – 5 summer hours available
Step 3: Work Out The Daily Electricity Output Of A Solar Panel Using Peak Sunshine Hours
This is where things start to get interesting as you work out the base amount of electricity your solar panels produce per day. This isn’t the final amount, but I’m getting ahead of myself.
The average solar panel produces between 250 – 400 watts per hour. However, not all solar panels are created equal. In our guide, “What Types Of Solar Panel Do I Need?”, we looked at some advantages and disadvantages of each type of solar panel. Here’s a summary.
4 Types Of Solar Panel: Advantages And Disadvantages
Factors To Consider With A Solar Panel
- Energy Efficiency
- Life Expectancy
- Ease Of Installation
- Roof Space Required
- Quality Of Materials
- Cost
Thin Film Solar Panels
- Low Energy Efficiency
- Low Durability
- Easy
- Low Space Efficiency
- Low
- Low
Polycrystalline Solar Panels
- Medium Efficiency
- Medium Durability
- Medium
- Medium Efficiency
- Medium
- Medium
Monocrystalline Solar Panels
- High Energy Efficiency
- High Durability
- Medium
- High Space Efficiency
- High
- High
Solar Shingles And Solar Roofs
- Medium Efficiency
- High Durability
- Difficult
- Medium Efficiency
- High
- Very High
For a more complete look at choosing the most suitable solar panel for your needs, check out the article:
So, as you can see, the wattage your panel produces per hour depends on the above factors. As we carry on with our example we will work out the solar panel output per hour and per day.
Daily Electricity Output Of Your Solar Panel
Amount Of Watts Produced Per Hour:
400
Available Sun Hours:
From the previous Step #2 = 2 winter hours – 5 summer hours available
Estimation:
- Local peak hours
= 2 winter hours – 5 summer hours - Multiply the solar panel wattage of 400W with the peak hours
- = 800W in the winter – 2000W in the summer available per day
Step 4: Calculate The Number Of Solar Panels And The Solar Panel System Size You Need
Let’s now work out how many solar panels you need based on the two different sustainable energy goals we discussed earlier.
To calculate how many solar panels your home needs to cover its electricity usage, you need to divide your daily electricity usage from Step #1 by the daily power output of your chosen solar panel, from Step#3. Divide the electricity output of a solar panel by your daily electricity usage
Carrying on with our example:
How Many Solar Panels Do I Need To Cover My Daily Electricity Needs?
To Be Completely Self Sufficient In Electricity:
30kWh or 30000 watts per day
To Generate Enough Electricity To Cover Major Appliances:
19.8 kWh per day or 19800 watts
Daily Power Output Of Major Appliances In Your Home
800W in the winter – 2000W in the summer available per day
Estimation To Be Self Sufficient In Electricity:
- = 37.5 solar panels to cover the winter hours
- 15 solar panels to cover the summer hours
Estimation To Generate Electricity For Major Appliances:
- = 24.75 solar panels to cover the winter hours
- = 10 to cover the summer hours
Step 5: Account For Electricity Production Losses On Your Solar Panel
We’re nearly there. As I mentioned earlier, not all solar panels are created equal, as some are more energy efficient than others. This inevitably comes down to:
- Quality of manufacture
- The materials used
- The amount of sun hours in your location
- The type of solar panel used
The efficiency of a panel is based on how well a panel can convert sunlight into energy. Most solar panels provide an energy efficiency rating between 10 and 25 percent, which is the percentage of solar energy that is being converted into usable electricity.
The efficiency of a solar panel is concerned with area, not power. A 10% efficient 200W panel and a 15% efficient 200W panel will both produce the same amount of power. Where things differ is in the size of the solar panel.
So, you would expect the 15% efficient solar panel to be smaller than the 10% efficient panel.
If you want to get a more realistic idea of the number of solar panels you need, it’s important to take solar panel efficiency into consideration.
In the final part of our example, we’ll see how this works.
Final Consideration Of The Number Of Solar Panels Do I Need To Cover My Daily Electricity Needs
High Quality And High Energy Efficiency Solar Panel:
Monocrystalline Solar Panels with high energy efficiency of 20%
Low Quality And Low Energy Efficiency Solar Panel:
Thin Film Solar Panels with low energy efficiency of 10%
Estimation Of The Number Of Solar Panels:
The 20% efficient solar panels would be half the size of the low energy efficient panels
Frequently Asked Questions Concerning How Many Solar Panels Are Needed To Power A House
How Many Solar Panels Do I Need Per Person?
As we have previously discussed, how many solar panels you need depends on how much electricity you consume. As a rough guide, we have put together this table that breaks down the average consumption by person.
Number of People Living in The House
- 1
- 2
- 3
- 4
- 6
Monthly Electricity Consumed In The House
- 70kWh
- 141kWh
- 212kWh
- 283kWh
- 353kWh
Number Of Solar Panels Needed In The House
- 4
- 8
- 12
- 16
- 22
How Home Size Affects The Amount Of Solar Panels Needed?
Other than higher electricity usage, one of the main factors to take into consideration is your roof size.
Depending on the size, structure and type of roof you have, will influence how many solar panels you can install. As an illustration, PV solar modules usually measure about 3 feet by 5 feet. That means each one needs about 15 square feet to sit comfortably on a roof.
Assuming a mid range, average sized solar panel that produces 250 watts
How Many Solar Panels Can Be Fitted On A Roof
Square Footage Of Your Roof
- 1000 square feet
- 2000 square feet
- 2500 square feet
- 3000 square feet
Annual kWh Electricity Generated
- 4700 kWh pa
- 9500 kWh pa
- 12000 kWh pa
- 14000 kWh pa
Number Of Solar Panels
- 15
- 30
- 38
- 44
After determining this, you then use the 5 Step formula above. Multiply your household’s hourly energy requirement by the peak sunlight hours for your location and divide that by your panel’s wattage.
How Many Kwh Can Your Solar Panels Produce?
It depends on the quality and type of solar panel, but on average you are looking at 200-400 watts per hour. To work out how much each panel will produce for you per day multiply your peak hours of sunlight by the manufacturers declared wattage produced by the solar panel.
As an example, 6 hours of peak sunlight per day multiplied by 300 watts from a solar panel = 1,800 watts or roughly 1.8 kilowatt hours per day. Which works out at 657 kilowatt hours of energy per year from each panel on your roof. This is variable as it also depends on the season and weather.
Summary Of How Many Solar Panels Do I Need For My Home
So when working out how many solar panels do I need to provide electricity for my home you need to determine your solar panel goals by choosing one of two options:,
- To have enough solar panels to be self-sufficient in electricity
- To be partially sufficient in electricity production to cover your primary appliances.
Once you have decided on your goal you then follow this 5 step process to see how many solar panels do I need for my home.
Step 1: Determine your hourly energy needs
Step 2: Calculate the number of daylight hours per day
Step 3: Work out the daily electricity output by multiplying your solar panel wattage with the sun hours per day
Step 4: Calculate the number of solar panels by dividing your daily electricity needs with the daily power output
Step 5: Account for production losses and determine the size of your panel
When Looking For Solar Panels Which Solar Contractor Is Right For You?
Whatever your circumstances, never compromise on quality as solar panel installation is a tremendous investment.
If you would like to see how the leading suppliers compare against each other click on the link at the bottom of the page.
