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EV Basics – What’s a kilowatt hour?

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Tesla Model S dash display

So what’s a kilowatt hour or shall we ask Watts a Kilowatt hour?

As more car buyers take the plunge into owning an electric vehicle (EV), it’s important to educate on the EV specific units of measure which differ greatly than your traditional gas burning vehicle. What is a kilowatt hour? How does it differ from a kilowatt? And why does this even matter?

Background

First, let me preface everything by saying that much of what I’m about to write is based on US specific units of measure since that’s what I’m familiar with. For instance, miles vs km and US dollars versus Euros. I’m also over simplifying and breaking things down to basic laymen terms so please cut me some slack if you already know all this!

If you receive a utility bill for your residence then you should probably be somewhat familiar with, or have heard of, a kilowatt (kW) and kilowatt hours (kWh) since that’s what electricity bills are measured on. Your EV is no different and uses these same units of measure although it’s probably something you haven’t paid much attention to in the past.

kW and kWh Units

Depending on the EV display you may see watt hours (Wh) or kilowatt hours (kWh) in some places and watts (W) and kilowatts (kW) in others. The kilo or k is a standard prefix meaning a thousand. So 1 kWh is 1,000 Wh. If you own your EV long enough you may just get to the next level, megawatt hour (MWh) which would be one million Wh!

Now for the fundamental definitions:

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kW is a measurement of power and kWh is a measurement of energy.

Energy is the amount of work that can be performed. kWh, calories, joules are all units of energy. A slice of pizza has 285 calories which is 0.33 Wh of energy that can be derived from that substance. Energy can be converted and change in form. For instance we can convert that slice of pizza to heat by setting it on fire. The fuel is the pizza, but don’t try converting it in your EV!

Tesla-Model-S-Dash-Energy

Power is the rate at which energy is generated or used. kW is a unit of power. When you accelerate in your EV you’re using power and when you decelerate with regenerative braking you’re generating power. The Model S dedicates half the speedometer display to the unit of power on the right side. There you can see how many kW you are using (indicator is orange) or generating (indicator is green) at any instance in time. It’s great to be able to see this however you can’t easily convert this into a cost. In order to do that, you’ll need to measure it over time and convert it into a unit of energy.

Power is similar to your speed. 50mph is your speed, but you have to maintain that for an hour to travel 50 miles. Similarly, 40kW is how much power you’re using and you’ll have to maintain that consumption for one hour to use 40kWh. If you spend half that hour at 40kW and the other half at 20kW you’ll end up consuming 30kWh. Power usage is constantly changing and will depend on driving habit as well as usage of onboard amenities such as your seat heaters or A/C unit.

A 100W incandescent light bulb used over 1 hour will consume 100Wh of energy. If you use that 100W bulb for 8 hours every day, it will consume 800W or 0.8 kWh per day. After 30 days, it will have consumed 0.8kWh x 30 = 24 kWh. After 365 days it will have consumed 292 kWh. Measuring your EV is done in a similar fashion but keep in mind that an EV can both use and generate power (regenerative braking) over periods of time. The difference or net power used (used – generated) is what you see reported on your EV display.

Units for Charging

Charging RateCharging your EV you transfers energy back into your battery so you’re effectively storing kWh for later use. EVs report charging in different ways but the most common is to report by kW and kWh added. So a charge rate of 6 kW is storing 6kWh for every hour of charge. If you’re charging at 6kWh and charge for 2 hours you’ll have an extra 12kWh added at the end of your charge.

When it comes to driving, we’re trained to think in terms of miles, but not all miles travelled are the same when it comes to energy usage since there are variations in terrain and elevations. Weather also plays a factor for each mile travelled. A kWh stored, on the other hand, is always the same. The main difference is how you use that kWh.

The Model S offers the option to display charge rate by kW and kWh or by miles. Not surprisingly most Tesla owners choose to display charge rate in terms of miles. However it’s important to note that there’s a huge assumption being made about how many miles you can drive on a Wh and that assumption needs to account for charging efficiency. Tesla uses their proprietary algorithm to compute this value.

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Tesla-Model-S-Limousine-Watts-on-Wheels

On Tesla’s online calculator they assume 300Wh/mile average use and a 90% charging efficiency. My own measurements show the average Wh/mile usage to be a bit higher (306 lifetime average) and the charging efficiency to be slightly less (81% last month).

What about Volts vs Amps?

Now you may be wondering how all this relates to volts and amps. This gets us back to the basics. One can calculate watts by multiplying volts with amps. W = V x A. So if you’re at a public charger and it’s charging at 199V and 30A (reference picture above), you’re essentially charging at 199V x 30A = 5,970W or about 6kW. This equates to 6kWh added after an hour of charging, but as we all know this is based on an ideal world where it charges at 100% efficiency with no loss. At 199V and 30A, the Model S is reporting this as a rate of 16 mi/hr.

Lets check that math:

5,970W/300Wh/mile standard assumption = theoretical 20 miles/hr charge rate. But that doesn’t account for charging efficiency. The Model S is reporting 16 mi/hr so its assuming an 80% charging efficiency (16/20) under these conditions.

Cost

Electric Costs

Utility bills price per kWh. Your electric company may break it down by distribution vs generation, time of use, etc. and then associate a different cost per kWh on each pricing tier. It seems complex but you can simplify this.

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To figure out your total cost per kWh just take your total amount of the bill and divide it by your total energy usage for the same period. That may include the various service fees, taxes, etc. but in the end you’re paying the electric company that total amount for those kWh regardless of what it’s derived from. Knowing this will help you calculate the costs for your road trips based on the kWh used.

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Elon Musk seemingly confirms Cybertruck gift to 13-year-old cancer fighter

Diagnosed in 2018 with a rare form of brain and spine cancer with no cure, the teen has undergone 13 surgeries by the time he was 12.

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Credit: Tesla

Elon Musk has seemingly confirmed that he will be sending a Tesla Cybertruck to 13-year-old Devarjaye “DJ” Daniel, a 13-year-old Houston boy fighting brain cancer. The teen was recognized as an honorary Secret Service member by U.S. President Donald Trump during his address to Congress on Tuesday. 

A Chance Meeting

The Tesla CEO’s Cybertruck pledge was mentioned during DJ’s short interview with CNN’s Kaitlan Collins. When Collins asked the 13-year-old what he told the Tesla CEO, DJ answered that he asked for a Cybertruck.

“I said, ‘can you do me a big favor, when you get back to Houston can you send us a Cybertruck down there?’” the cancer fighter stated.

Daniel noted that Musk responded positively to his request, which was highlighted by Collins in a post on X. Musk responded to the post with a heart emoji, suggesting that he really will be sending a Cybertruck to the 13-year-old cancer fighter.

Teen’s Cancer Battle Inspires

Diagnosed in 2018 with a rare form of brain and spine cancer with no cure, Daniel has undergone 13 surgeries by the time he was 12. During his speech, Trump highlighted the 13-year-old’s long battle with his disease. 

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“Joining us in the gallery tonight is a young man who truly loves our police. The doctors gave him five months at most to live. That was more than six years ago. Since that time, DJ and his dad have been on a quest to make his dream come true,” Trump stated.

Daniels officially received an honorary badge from U.S. Secret Service Director Sean Curran, to much applause during the event.

Surprisingly Partisan

While Daniels’ story has been inspiring, Trump’s focus on the 13-year-old cancer fighter has received its own fair share of criticism. MSNBC host Nicolle Wallace, while referencing Daniels’ love for law enforcement, noted that she is hoping the 13-year-old never has to defend the U.S. capitol against Trump supporters. “If he does, I hope he isn’t one of the six who loses his life to suicide,” Wallace stated.

Anti-Musk and Trump accounts on X have also thrown jokes at the cancer fighter’s honorary badge, with some dubbing the 13-year-old as a “DEI hire” that should be looked into by DOGE.

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Tesla owner highlights underrated benefit of FSD Supervised

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Credit: Tesla

Elon Musk has been pretty open about the idea of FSD being the difference maker for Tesla’s future.

If Tesla succeeds in achieving FSD, it could become the world’s most valuable company. If it doesn’t, then the company would not be able to reach its optimum potential.

FSD Supervised’s safety benefits:

  • But even if FSD is still not perfect today, FSD Supervised is already making a difference on the roads today.
  • This was highlighted in Tesla’s Q4 2024 Vehicle Safety Report.
  • As per Tesla, it recorded one crash for every 5.94 million miles driven in which drivers were using Autopilot technology.
  • For comparison, the most recent data available from the NHTSA and FHWA (from 2023) showed that there was one automobile crash every 702,000 miles in the United States. 

FSD user’s tale:

  • As per an FSD user’s post on social media platform X, FSD Supervised was able to help him drive a relative to a medical facility safely even if he was exhausted.
  • During the trip, the driver only had to monitor FSD Supervised’s performance to make sure the Tesla operated safely.
  • In a vehicle without FSD, such a trip with an exhausted driver would have been quite dangerous. 
  • “This morning, Tesla FSD proved to be an absolute godsend. I had to take my brother-in-law to the hospital in Sugar Land, TX, which is 40 miles away, at the ungodly hour of 4 AM. Both of us were exhausted, and he was understandably anxious about the surgery.
  • “The convenience of sending the hospital’s address directly from my iPhone to my Tesla while still inside my house, then just a single button press once inside, and 40 miles later we were precisely in front of the hospital’s admissions area.This experience really underscores just how transformative this technology can be for society,” Tesla owner JC Christopher noted in his post.

Don’t hesitate to contact us with news tips. Just send a message to simon@teslarati.com to give us a heads up.

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Tesla Optimus “stars” in incredible fanmade action short film

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Credit: @SoKrispyMedia/YouTube

There are few things that prove an enthusiast’s love towards a company more than a dedicated short film. This was highlighted recently when YouTube’s SoKrispyMedia posted a 10-minute action movie starring Optimus, Tesla’s humanoid robot, as well as several of the company’s most iconic products. 

The video: 

  • Shot like a Hollywood action flick, the video featured a rather humorous plot involving a group of thieves that mistakenly targeted a Tesla Model 3 driver. 
  • The Model 3 driver then ended up speaking to Tesla for assistance, and some high-octane and high-speed hijinks ensued.
  • While the short film featured several Tesla products like the Model 3, Superchargers, and the Cybertruck, it is Optimus that truly stole the show.
  • Optimus served several roles in the short film, from an assistant in a Tesla office to a “robocop” enforcer that helped out the Model 3 driver.

Cool inside jokes: 

  • The best Tesla videos are those that show an in-depth knowledge of the company, and SoKrispyMedia definitely had it. 
  • From the opening scenes alone, the video immediately poked fun at TSLA traders, the large number of gray Tesla owners, and the fact that many still do not understand Superchargers.
  • The video even poked fun at Tesla’s software updates, as well as how some Tesla drivers use Autopilot or other features without reading the fine print in the company’s release notes.
  • The video ended with a tour de force of references to Elon Musk products, from the Tesla Cybertruck to the Boring Company Not-a-Flamethrower, which was released back in 2018.

Check out SoKrispyMedia’s Tesla action short film in the video below.

Don’t hesitate to contact us with news tips. Just send a message to simon@teslarati.com to give us a heads up.

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