Finding the number of solar panels needed to cover a certain amount of kWh per month might seem like an easy task. However, this is further from the truth. There are some significant factors that affect the number of solar panels you need in your home.
Firstly, you need to know that the load provided by the manufacturers is not always accurate. There are at least 23% loss of efficiency in your solar panels. Therefore, when calculating the load of your solar panels, don’t forget to subtract the losses.
Another major factor that affects the number of solar panels needed is the irradiance of the situation sun in different locations. During the day, different locations experience different sun peaks at different times. This largely affects the sizing of solar panels.
If you calculate your load without putting into consideration this two factors then you will either over size or under size your system.
Below is a step-by-step you use to find the number of solar panels you need in your home.
Step 1: First find your home energy use in Kwh per month (this is what is provided on the electricity bill). You can calculate this by multiplying Kw by 30.
Step 2: Multiple the 23% losses by the load. You can also multiple the load by 1.4
Step 3: Multiple the figure found in step 2 with 12 to find the load per year.
Step 4: Find the annual irradiance in your location
Step 5: Divide the load per year with the annual irradiance to find the number of solar panels you need in your home.
In this guide, you will learn how to incorporate each factor named above when sizing your solar PV system. You will also get to know some of the best solar panels kWh calculators that will help you reduce the work done on sizing your system.
STICK AROUND TO FIND OUT MORE!
1. How do you calculate square footage for solar panels?
To find out the total square footage needed by your solar panels, you will need to multiply the number of solar panels you need by 17.55 square feet ( which is the standard size of most solar panels in the market).
Most homes needs at least 15 solar panels. So, to find the total square footage for your solar panels you will multiply;
17.55 square foot × 15 solar panels = 263.25 square foot.
This however is just an estimate. You might find your self needing more solar panels than 15 or your solar panels being larger or smaller than 17.55
2. Solar panels kwh calculator?
Sun watts calculator uses the data you provide to estimate the kWh of your system per month. What you need for you to use this calculator is know the kwh per year, the solar watts per day which is provided on the website, and the % of the electricity bill to offset.
3. Factors Affecting the number of Solar Panels you need for your home?
Instead of wasting your time going through all Google searches, consult with an installation company in your area. However, we will look into the top four things your installer will tell you.
So to help you save some coins let’s get started.
How is your electricity usage.
If you are transforming from electricity use to solar, you need to match the power your appliances usage. So check your utility bill and use solar guides to find out how much power you need.
What is the size of the available roofing area? Is there a lot of shading?
If you come from a place with surplus of sunlight, you might find yourself buying fewer solar panels than a person in another state will the same roofing area but too much shading. Consult with installers in your individual state to get the estimates. You can also get the data on how many hours of sun exposure can you get in your area from Renewable resources data center.
How efficient are your solar panels?
Most solar panels have wattages between 150-370. So, to match the load needed in your home, you might find yourself buying more solar panels. Invest on buying the high grade solar panels as they have the capability to generate more electricity in a small surface area. High grade solar panels are expensive.
Does your area your area allow net metering?
There are some areas where you are allowed to connect your solar panels to the Grid through a process known as net metering. When you connect your solar panels to your grid, you receive credit for saving electricity when you use solar energy.
Net metering allows you use solar energy when the sun is hot. Unfortunately, you cannot use solar energy at night when the sun is out.
How is the weather in your area
Does your area experience more sunny days or cold days? Is the sun reliable? Since solar panels harvest energy from the sun, the weather plays a major part when deciding the number of solar panels you need in your home.
If there is surplus of sun in your area, then you might end up installing less solar panels than a person who lives in cold places. Consult with installers in your area to know what to expect with your solar panels.
The size of solar batteries
Some people prefer storing more power in solar batteries for when need arise. In order to fully charge this solar batteries efficiently, you need to match the power of the solar batteries with the solar panels. Otherwise, you might end up over charging or discharging your solar batteries.
Check the rating of the solar batteries and ensure the solar panels can power them.
Do you have charge controllers installed
If you have solar charge controllers in your system, then you don’t need more solar panels than a person without charge controllers. There are two types of solar charge controllers: MPPT and PWM.
A PMW matches the current and voltage of the solar panels and the solar battery. So if your battery needs 12V, your solar charge controllers will send 12V from the solar panels. If you don’t have enough solar panels your solar battery may not charge effiently.
MPPT on the other hand can send more charge to the solar battery. However, it cannot overcharge the battery.
When installing solar panels, check the type of charge controllers your have installed. If you do not have charge controllers installed
The physical size of solar panels
Huge solar panels occupy large surface area than small solar panels. They also collect more solar energy than smaller ones. So if you are considering buying large solar panels, you will buy less solar panels than a person buying smaller solar panels.
You need more small solar panels to fill a large surface area.
The brand of solar panels
Different brands of solar panels manufacture solar panels with different efficiency. So if you are buying from renown solar panel company, you might end up buying less solar panels but spend more.
On the hand, if you buy cheap solar panels with less efficiency, you will have to buy many solar panels to match the efficiency of your system.
How is are the solar incentives and rebated in your local state?
If your state give tax credit to solar energy users, you might get a huge discount depending on the square footage of your system.
This means you can buy more solar panels than a person from another state which don’t give tax credit to their citizens. Remember you are receiving a 26% tax credit from the federal government. Therefore, you can spend the discount to buy more solar panels.
*Note that this factors differ from state to state. Check with your local installing company to get guidance on what to do when installing solar PV system in your individual state.
4. How many solar panels do I need for 200 kwh per month?
When calculating the number of solar panels you need, you need to know your annual energy use and the sun irradiance in your area. You also need to account for 23% power loss to experienced by solar panels.
To aid in this calculations, we will take the average solar irradiance to be 4kWh/m2. You can however, use this guide to find the irradiance in your region for closer estimation.
- 200W
Energy generated annually: 200W× 4kWh/m2× 365=292kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 200kWh per month×12= 2400kW
Number of solar panels needed: 2400kw/ 225kWh/year= 11 solar panels
- 250W
Energy generated annually: 250W× 4kWh/m2× 365=365kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 200kWh per month×12= 2400kW
Number of solar panels needed: 2400kw/ 365kWh/year= 7 solar panels
- 400W
Energy generated annually: 400W× 4kWh/m2× 365=584kWh/year
23% loss: 77/100×584kWh/year= 450 kWh/year
Energy needed: 200kWh per month×12= 2400kW
Number of solar panels needed: 2400kw/450kWh/year= 6 solar panels
- 500W
Energy generated annually: 500W× 4kWh/m2× 365=730kWh/year
23% loss: 77/100×730kWh/year= 562 kWh/year
Energy needed: 200kWh per month×12= 2400kW
Number of solar panels needed: 2400kW/562kWh/year= 5solar panels
5. How many solar panels do i need for 1,000 kwh per month?
- 200W
Energy generated annually: 200W× 4kWh/m2× 365=292kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 1000kWh per month×12= 12000kW
Number of solar panels needed: 12000kw/ 225kWh/year= 53 solar panels
- 250W
Energy generated annually: 250W× 4kWh/m2× 365=365kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 1000kWh per month×12= 12000kW
Number of solar panels needed: 12000kw/ 365kWh/year= 33 solar panels
- 400W
Energy generated annually: 400W× 4kWh/m2× 365=584kWh/year
23% loss: 77/100×584kWh/year= 450 kWh/year
Energy needed: 1000kWh per month×12= 12000kW
Number of solar panels needed: 12000kw/450kWh/year= 27 solar panels
- 500W
Energy generated annually: 500W× 4kWh/m2× 365=730kWh/year
23% loss: 77/100×730kWh/year= 562 kWh/year
Energy needed: 1000kWh per month×12= 1200kW
Number of solar panels needed: 12000kW/562kWh/year= 21 solar panels
6. How many solar panels do I need for 1,500 kwh per month?
- 200W
Energy generated annually: 200W× 4kWh/m2× 365=292kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 1500kWh per month×12= 18000kW
Number of solar panels needed: 18000kw/ 225kWh/year= 80 solar panels
- 250W
Energy generated annually: 250W× 4kWh/m2× 365=365kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 1500kWh per month×12= 18000kW
Number of solar panels needed: 18000kw/ 365kWh/year= 49 solar panels
- 400W
Energy generated annually: 400W× 4kWh/m2× 365=584kWh/year
23% loss: 77/100×584kWh/year= 450 kWh/year
Energy needed: 1500kWh per month×12= 18000kW
Number of solar panels needed: 18000kw/450kWh/year= 40 solar panels
- 500W
Energy generated annually: 500W× 4kWh/m2× 365=730kWh/year
23% loss: 77/100×730kWh/year= 562 kWh/year
Energy needed: 1500kWh per month×12= 18000kW
Number of solar panels needed: 18000kW/562kWh/year= 32 solar panels
7. How many solar panels do I need for 2000 kWh a month?
- 200W
Energy generated annually: 200W× 4kWh/m2× 365=292kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 2000kWh per month×12= 24000kW
Number of solar panels needed: 24000kw/ 225kWh/year= 107 solar panels
- 250W
Energy generated annually: 250W× 4kWh/m2× 365=365kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed 2000kWh per month×12= 24000kW
Number of solar panels needed: 24000kw/ 365kWh/year= 66 solar panels
- 400W
Energy generated annually: 400W× 4kWh/m2× 365=584kWh/year
23% loss: 77/100×584kWh/year= 450 kWh/year
Energy needed: 2000kWh per month×12= 24000kW
Number of solar panels needed: 24000kw/450kWh/year= 53 solar panels
- 500W
Energy generated annually: 500W× 4kWh/m2× 365=730kWh/year
23% loss: 77/100×730kWh/year= 562 kWh/year
Energy needed: 2000kWh per month×12= 24000kW
Number of solar panels needed: 24000kW/562kWh/year= 43 solar panels
8. How many solar panels do i need for 2,500 kwh per month?
- 200W
Energy generated annually: 200W× 4kWh/m2× 365=292kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 2500kWh per month×12= 30000kW
Number of solar panels needed: 30000kw/ 225kWh/year= 133 solar panels
- 250W
Energy generated annually: 250W× 4kWh/m2× 365=365kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 2500kWh per month×12= 18000kW
Number of solar panels needed: 30000kw/ 365kWh/year= 82 solar panels
- 400W
Energy generated annually: 400W× 4kWh/m2× 365=584kWh/year
23% loss: 77/100×584kWh/year= 450 kWh/year
Energy needed: 2500kWh per month×12= 30000kW
Number of solar panels needed: 30000kw/450kWh/year= 67 solar panels
- 500W
Energy generated annually: 500W× 4kWh/m2× 365=730kWh/year
23% loss: 77/100×730kWh/year= 562 kWh/year
Energy needed: 2500kWh per month×12= 30000kW
Number of solar panels needed: 30000kW/562kWh/year= 53 solar panels
9. How many solar panels do i need for 3000 kwh per month?
- 200W
Energy generated annually: 200W× 4kWh/m2× 365=292kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 3000kWh per month×12= 36000kW
Number of solar panels needed: 36000kw/ 225kWh/year= 160 solar panels
- 250W
Energy generated annually: 250W× 4kWh/m2× 365=365kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 3000kWh per month×12= 36000kW
Number of solar panels needed: 36000kw/ 365kWh/year= 99 solar panels
- 400W
Energy generated annually: 400W× 4kWh/m2× 365=584kWh/year
23% loss: 77/100×584kWh/year= 450 kWh/year
Energy needed: 3000kWh per month×12= 36000kW
Number of solar panels needed: 36000kw/450kWh/year= 80 solar panels
- 500W
Energy generated annually: 500W× 4kWh/m2× 365=730kWh/year
23% loss: 77/100×730kWh/year= 562 kWh/year
Energy needed: 3000kWh per month×12= 36000kW
Number of solar panels needed: 36000kW/562kWh/year= 64 solar panels
- How many solar panels do i need for 4000 kwh per month
- 200W
Energy generated annually: 200W× 4kWh/m2× 365=292kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 4000kWh per month×12= 48000kW
Number of solar panels needed: 48000kw/ 225kWh/year= 213 solar panels
- 250W
Energy generated annually: 250W× 4kWh/m2× 365=365kWh/year
23% loss: 77/100×292kWh/year= 225kWh/year
Energy needed: 4000kWh per month×12= 48000kW
Number of solar panels needed: 48000kw/ 365kWh/year= 132 solar panels
- 400W
Energy generated annually: 400W× 4kWh/m2× 365=584kWh/year
23% loss: 77/100×584kWh/year= 450 kWh/year
Energy needed: 4000kWh per month×12= 48000kW
Number of solar panels needed: 48000kw/450kWh/year= 107 solar panels
- 500W
Energy generated annually: 500W× 4kWh/m2× 365=730kWh/year
23% loss: 77/100×730kWh/year= 562 kWh/year
Energy needed: 4000kWh per month×12= 48000kW
Number of solar panels needed: 48000kW/562kWh/year= 86 solar panels
The table below shows a summary of the number of solar panels each system need and their correspond rated Wattage
| 200W Solar Panels | 250W Solar panels | 400W SolarPanels | 500W Solar panels | |
| 200 kWh | 11 | 7 | 6 | 5 |
| 1000 kWh | 53 | 33 | 27 | 21 |
| 1500 kWh | 80 | 49 | 40 | 32 |
| 2000kWh | 107 | 66 | 53 | 43 |
| 2500kwh | 133 | 82 | 67 | 53 |
| 3000 kwh | 160 | 99 | 80 | 64 |
| 4000 kwh | 213 | 132 | 107 | 86 |
*please note that these figures are only for rough idea. Always get the advice from subject experts to calculate proper value for your home.
Conclusion
The number of solar panels installed in a solar PV system determines how well your system works. If you have a large load, you will need many solar panels than a person with the same home size but a smaller load. A system with charge controllers is capable of charging solar batteries even in cold weather. You might therefore need to buy less solar batteries than a person whose solar PV system don’t have a charge controller.
The guide above helps you to calculate the number of solar panels you need depending on the size of your load and other factors. Hope you get to learn something new.
Eng. Matthew Joseph Nandirio is the Founder of walkingsolar.
After graduating from the University of Houston in 2002, matt started working as a Solar Electrical Engineer for several multi-national solar energy companies.
He has a wide range of experiences including solar system requirement analysis, planning, maintaining, debugging and even solar device development through research.
He now shares his 20 years of expertise through his articles on the walkingsolar website.
Further, he is also the author of two books on Solar Technology, “Solar Power for Villages” and “DIY Solar System for Dummies”.
