April 27, 2022

How Many Solar Panels Does it Take to Charge a Tesla?

Tesla has addressed the renewable energy gap in the automotive industry by manufacturing one of the most highly adopted electric vehicles on the road today.

How Many Solar Panels Does it Take to Charge a Tesla?

Over the past decade, solar energy has gained incredible traction as a method to provide renewable, clean energy to power one’s home. With this availability, individuals have found tremendous benefit in the ability to supplement one’s electricity bill, contribute to a green initiative, and even become more self-reliant by building electrical systems that are off the grid. In parallel to this massive move in consumer renewable energy, Tesla has addressed the renewable energy gap in the automotive industry by manufacturing one of the most highly adopted electric vehicles on the road today.

Through a truly incredible engineering feat, Tesla has designed an all-electric vehicle that is faster and more luxurious than many of its gas-powered contemporaries. Founder Elon Musk - who also started other green-forward and society-benefiting companies - isn’t stopping at electric-powered cars. Elon envisions fostering a green energy future state that empowers individuals to power their homes and vehicles independently through renewable energy sources. One of the primary ways to move towards this goal is to enable a system where consumer solar panels facilitate Tesla charging, effectively dropping the cost of energy for driving aTesla to zero.

Today, as Tesla owners look to build these closed-loop energy systems, there are many questions concerning the requirements to build such a system. In the following sections, we’ll look at design considerations and provide an example of  how to determine the number of solar panels required to charge a Tesla using those considerations.

  1. Tesla Design Parameters
  2. State of Charge
  3. Battery Capacity
  4. Target Tesla Energy Requirement
  5. Solar Panel Design Overview
  6. Solar Power Overview
  7. Solar Power Rating
  8. Solar Panel Efficiency
  9. How Many Solar Panels Does it Take to Charge a Tesla?

Tesla Design Parameters

Before we can assess how many solar panels it takes to create a closed-loop charging system for a  Tesla, we must first assess how much electricity is consumed, on average, when charging.  To determine how much electricity will be needed we must first set the following  parameters: State of Charge, battery capacity, and the target Tesla energy requirement.

State of Charge

State of Charge denotes the upper and lower limit of battery state. For example, a common State of Charge for a Tesla owner may be 20% to 80%, which means a depth of discharge to 20% and a charge limit target of 80%. Of course, the State of Charge is going to vary depending on each individual’s unique driving requirements. A Tesla owner who has a 10 mile daily drive to work will have a much different charge requirement compared to a Tesla owner that drives 40 miles to work for their daily commute.

For our example, we will assume a State of Charge of 20% to 80%.

Battery Capacity

Another major consideration is Tesla battery capacity, which varies from model to model. For instance, the Tesla Model X comes equipped with a 100 kWh battery, whereas the Tesla Model 3 comes equipped with a 50 to 75 kWh battery. Of course, meeting a State of Charge of 20%-80% is going to consume more energy for the Model X over the Model 3 due to the capacity difference. Also, it’s important to keep in mind that all lithium-ion batteries are going to exhibit a charging efficiency of less than 100%. This means that although a lithium-ion battery may be rated at 75 kWh, a Tesla driver may only reap 90% efficiency or a maximum of 67.5 kWh of potential energy in the battery.

For our example, we will assume a battery capacity of 75 kWh.

At 90% efficiency, this provides a total available energy of 67.5 kWh.

Target Tesla Energy Requirement

Taking into consideration the previously stated calculation parameters, we can determine how much energy in kWh is required to charge a 75 kWh rated battery at 90% efficiency (67.5 kWh) and a State of Charge requirement of 60% (80%-20%) by using the calculation below.  We’ll later use this total in kWh to determine how many solar panels are required to meet that required energy consumption.

Total required kWh = State of Charge X Battery Capacity = 67.5 kWh X .6 = 40.5 kWh

Solar Panel Design Overview

Now that we’ve determined the energy consumption required to power a Tesla on a daily basis to be 40.5 kWh, let’s investigate how many solar panels are needed for a closed-loop solar energy system to meet that requirement.

Solar Panel Overview

A solar cell, also known as a photovoltaic cell, is an electrical device that is designed to convert energy from the sun into electricity. Through an electrochemical process, solar cells capture photons emitted from the sun’s rays and convert it into electrical energy. In doing so, this electrical energy can either be used to power appliances in the home or can be stored as potential energy by charging a bay of lithium-ion batteries. In the case of our example, Tesla owners can benefit from the use of capturing solar energy via solar cells and convert that solar energy into electricity which can then be used to charge the Tesla battery.

Solar Panel Rating

It’s important to know, as one embarks on his journey, that not all solar panels are made equal. Solar panels are designed to produce a certain value of electrical power measured in Watts. Solar panels are often advertised as 200W or 300W. This solar panel rating defines how much power the solar panel can generate. If a solar panel is rated at 300W, for example, and that solar panel converts the sun’s rays into electricity for one hour, this would then yield 300 watt-hours.

Solar Panel Efficiency

Another consideration while trying to determine how many solar panels are required to build a Tesla charging system is solar panel efficiency. Solar panel efficiency denotes how efficiently a solar panel can convert the sun’s rays into electricity. As users start to research this topic, they’ll stumble across two distinct areas that affect solar panel efficiency - inherent efficiencies due to limiting electrochemical processes and environmental factors that influence efficiency.

Inherent Inefficiencies

Many Tesla owners who are new to solar power efficiency may be surprised at the shockingly low efficiency rating of solar panels. Most consumer solar panels offer a 20-30% efficiency rating, but can even be as low as 12%! This efficiency rating means that these solar panels are only converting at most, 30% of the sun’s rays into electricity. It’s important to note that this inherent limitation has already been calculated into the power rating of commercial-grade solar panels. So before you go multiplying your solar power output by 30 percent to calculate efficiency, hold off, as it’s already been accounted for.

Environmental Inefficiencies

Like the inherent inefficiency of solar panels, environmental inefficiencies should also be taken into consideration when determining how many solar panels are needed. Environmental inefficiencies represent exterior environmental factors that degrade solar panel efficiency. Examples of environmental inefficiencies include dust, low temperatures, cloud coverage, obstructions blocking direct sunlight, and so on. All of these exterior factors play a major role in the efficiency of solar panels.

To make a conservative estimate, we’ll assume a 25% degradation of efficiency due to environmental factors. We’ll use this degradation factor in our calculation in the following section.

Solar Inverter Inefficiency

Lastly, the efficiency of the solar inverter needs to be considered. A solar inverter is an electrical device that converts the electrical energy drawn from a solar panel into a constant dependable amperage and voltage to be applied to a Tesla charger. It's critically important to add an inverter into the design scope of a project, because without one, unregulated voltage spikes could pose serious harm to your vehicle and home. A typical electrical inverter is going to clock in at around 95% efficiency.

For the purposes of our example we’ll assume an electrical inverter efficiency of 95%.

How Many Solar Panels Does it Take to Charge a Tesla?

Now that we’ve gathered all of our critical data, we’re ready to  determine how many solar panels are required to charge a Tesla. Remember, for our example, we need our solar panel system to generate a total power output of 40.5 kWh. Of course, retrace the steps above to align this power value specifically to your requirements.

For our example, we have decided to use 250W solar panels. At 250W, it will take six solar panels to create 1.5KW of energy (250W * 6 panels = 1,500W = 1.5KW). However, remember  the inefficiencies discussed above. If we assume 75% efficiency due to environmental causes and 95% efficiency at the inverter, this will leave us with a panel efficiency of 1.091K. We got to this number by multiplying 1.5KW (energy created by six 250W panels) by .75 (environmental efficiency)  by .97 . For the means of this example we’ll round that to 1KW per six 250W panels. Finally, let’s make a general assumption of 4 hours of direct sunlight, to generate power for the Tesla in question. So, 1KW at 4 hours, yields 4 KiloWatt hours per 6 solar panels.

Here’s our final example walk through:
6 solar 250W solar panels produces 1.5KW

1.5KW * .75 * .97 = ~1KW (accounting for inefficiencies)

4 hours of sunlight yields 4KWh per 6 panels

To arrive at ~40KWh one must use 6 X 10 or 60 250W solar panels.

After our lengthy analysis and thorough investigation, we’ve arrived at ~60 solar panels to do the trick!  Now you can walk through the steps we’ve outlined in this article to determine the number of solar panels needed for your unique charging requirements.

What Type of Solar Panels does Tesla Use?

Tesla's solar panel manufacturer is Hanwha Solar.

Next Steps

We hope this article has given you the tools to  answer the question “How many solar panels does it take to charge a Tesla?”  If you would like to learn about when to charge your car, as well as how it charges, check out Optiwatt. It is a free app that can schedule your car to charge for the cheapest price. If you are looking to learn more, consider reading our comprehensive guide to best charging practices, The Comprehensive Guide to Maximizing your Tesla’s Battery Efficiency and Battery Life.

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