Powerwalls are unique and efficient energy storage solutions. That said, they aren’t exactly cheap. It stands to reason why a homeowner would be eager to determine the number of solar panels they need to optimize their Tesla Powerwall setup.
As a soon-to-be or current Powerwall owner, you may already know that you can charge these products with regular AC electricity. But if you want to charge your Tesla Powerwall the fastest way possible, you’ll need to invest in some solar panels.
If you want to learn how to calculate the number of solar panels needed for a Tesla Powerwall across all U.S. States, along with some nifty charging tips, read on!
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How many solar panels are needed to charge a Tesla Powerwall?
Based on solar irradiation levels throughout the U.S., you’ll need 7-11 400W solar panels to charge your Tesla Powerwall to 100% in one full day. These figures equate to a solar system with a power output between 2.6kW-4.1kW depending on your location.
Now, let’s look at how you can calculate the number of solar panels needed for a Tesla Powerwall; this will provide you with a more accurate estimate for your household.
Note to our readers: As of October 2022, Tesla only sells the Powerwall bundled with Tesla Solar panels. In addition, the minimum solar array Tesla installs is 4.8kW or 12 x 400W solar panels —enough to fully charge a Powerwall in a day across all U.S. states.
Calculating the number of solar panels for a Tesla Powerwall
To calculate the number of solar panels needed for a Powerwall, you’ll have to obtain three pieces of information:
- Tesla powerwall capacity.
- Your location’s solar production potential.
- Tesla solar panel power output.
1. Tesla powerwall capacity
Our “Tesla Powerwall Capacity” article demonstrated that a Tesla Powerwall’s usable capacity is 13.5kWh. It can be extended up to 135kWh with 10 units in parallel.
2. Your location’s dolar production potential
The most crucial parameter for this calculation is solar production potential or Photovoltaic Output (PVOUT). PVOUT is expressed in kWh per kWp. For example, a 1kW solar panel setup with a PVOUT of 4 kWh/kWp can produce an estimated 4kWh.
Naturally, the more sun your area receives, the lower the number of solar panels your Tesla Powerwall will need.
The best way to determine your PVOUT is to use a prediction model like the one developed by Solargis for Global Solar Atlas. Simply enter your location, and the website calculates your potential solar production.
Related reading: Solar Panel Energy Production (State-by-state)
3. Tesla solar power output
A Tesla solar panels rate power varies between 395W and 405W. Our calculation considers a 400W solar module.
Now it’s time to calculate. Use the following formula to calculate the number of solar panels you’ll need:
Here’s an example:
Let’s consider a solar system located in California (PVOUT=4.9kWh/kWp) and a solar panel of 400W=0.4kW. By applying the above formula, we calculated that 6.89 or 7 solar panels are needed to fully charge a Tesla Powerwall.
Number of solar panels needed to charge a Tesla Powerwall across all U.S. states
We’ve applied the formula to all U.S. states (except Alaska, which doesn’t receive enough sun).
|U.S. State||Number Of 400W Solar Panels Required For A Tesla Powerwall||Power Of A Solar System (kW) Required For A Tesla Powerwall|
How long will it take to charge a Tesla Powerwall?
Charging a Tesla Powerwall takes between 3 and 8 hours, depending on your location’s solar irradiation and your system’s power.
Tesla recommends pairing the Powerwall with a 4.8kW solar system. During summer, you can fully charge the Powerwall in less than 4 hours with this system.
Usually, to determine the time it takes to charge a Powerwall, you divide the Powerwall’s capacity by your system’s power output. However, a solar system rarely operates at its maximum rated power. That’s why we rely on prediction models that calculate the average hourly profile for the power output.
Below is the hourly profile for an average day in August (the sunniest month) near Los Angeles.
The maximum power output for this 4.8 kW system is only 3.5 kW between 11 AM and 1 PM, far from its rated power.
Luckily, between 9 AM and 3 PM, the power output is above 3 kW, allowing the quick charge of the Powerwall.
How to charge a Tesla Powerwall the fastest way possible
The Tesla Powerwall is designed for fast charging. Its maximum charging power is 5kW, which means it can reach full charge in:
13.5kWh/5kW = 2.7 hours (less than 3 hours).
Here are two ways of the fastest ways to charge your Tesla Powerwall:
- Plug it into utility electricity with an instant power output of 5kW.
- Connect to a solar system capable of reaching 5kW peak power.
Naturally, the larger the solar system, the faster the Powerwall will charge. We’ll use a prediction model to determine a solar system’s peak power. Here’s an example:
Our research shows that with 7.2 kW of solar panels (18 x 400W solar panels), you can reach an average of 5kW between 10 AM and 2 PM, except in January and December. This would allow for the fastest possible charging of your Powerwall.
Factors that influence a Tesla Powerwall’s charging time
The most efficient way to charge a Tesla Powerwall is through solar panels. They convert sunlight into electricity that the Powerwall stores. Consequently, the charging time of your Powerwall is directly related to the power output of your solar system.
The factors that influence a Tesla Powerwall’s charging time are the same ones that affect a solar panel’s power output.
Factors that influence a solar system’s power output
Solar panels are variable generators. Their electricity production is related to the following factors:
High temperatures negatively affect a solar panel’s efficiency. Solar panel manufacturers have introduced the temperature coefficient that expresses the decrease in power for every increase in deg°C.
Consider a 400W solar panel with a temperature coefficient of -0.29 %/°C. The panel’s surface can reach up to 60°C (140°F). That’s 35°C more than its rated operating temperature of 25°C. Therefore, the power loss at 60°C is:
35 x 0.29=10.15%
and the maximum output is:
400W – 10.15%= 359.4W
The easiest way to decrease the temperature is to allow enough space between the solar panel and your roof for the air to circulate.
Some systems also involve spraying water on the solar panel to cool it down.
2. Local shadow
Contrary to popular belief, solar panels can produce electricity in the shade (without direct sunlight). However, their output can be 2-3 times lower than when exposed to direct sunlight.
Consequently, you must ensure that your solar system receives direct sunlight during the most productive hours: between 9 AM and 3 PM.
3. Solar irradiation at the location
Solar irradiation is the number one factor affecting solar panel production and it relates to your location on the planet.
The solar potential in the U.S. varies from 5.2kWh/kWp in Alabama down to 3.3kWh/kWp in Wyoming. That’s a massive difference of 60%.
You’ll need to oversize your solar system in states with low solar irradiation to reach higher power output.
4. Solar panel tilt
Solar panels have a much better power output when directly facing the sun and the sun’s position continuously changes depending on the time of day and season.
Although some solar systems are equipped with solar tracking devices, the vast majority of solar installations are fixed. Therefore, you must tilt your panels to the optimal angle to achieve the highest solar exposure throughout the year.
The closer you get to the equator, the flatter your solar panels must be (0 deg angle). For example, the recommended tilt in San Diego, California, is 31deg vs. 44deg in North Dakota.
Find out the right tilting angle on Global Solar Atlas.
5. Solar panel orientation (azimuth)
Our article discussing solar panel direction demonstrated that to optimize exposure to the sun, a solar panel must face south in the Northern Hemisphere and north in the Southern Hemisphere.
Note to our readers: We are referring to the geographical south and north. These are slightly different from magnetic south and north on a compass.
The Tesla Powerwall is one of the market’s best domestic Energy Storage Solutions (ESS). Thanks to its 13.5kWh capacity, it can seamlessly help you get through power outages. In addition, coupled with Tesla solar panels, it enables you to save money in states with high electricity prices.
In this article, we calculated that you’d need 7-11 solar panels (400W) to charge your Tesla Powerwall in one day. This can take 3-8 hours, depending on the size of your solar system.
Finally, to charge the Powerwall the fastest, you’ll need to:
- Maximize your solar system power output.
- Avoid local shadow.
- Face your panels south (in the Northern Hemisphere).
- Find the right tilting angle.