Solar vs. Grid Charging in Fresno
Buying a Tesla can dramatically reduce how much money you spend at the gas station, but that does not mean driving becomes free. The energy has to come from somewhere. For most Tesla owners who charge at home, that energy comes from one of two places: the utility grid or a home solar system. And the difference between the two can be substantial.
One of the most common mistakes we see homeowners make when purchasing an electric vehicle is forgetting to account for how much additional electricity the vehicle will add to their home. A Tesla is essentially a large battery on wheels. If you drive frequently and do most of your charging at home, your vehicle can become one of the largest electrical loads in your house. So how much does charging a Tesla actually increase your electric bill? Let’s break down the math.
How Much Electricity Does a Tesla Use?
There is no single answer because it depends on several factors. The biggest factor is simply how much you drive. Someone driving 500 miles per month is obviously going to use considerably less electricity than someone driving 2,000 miles per month. Your actual electricity consumption can also depend on the Tesla model, driving speed, weather, elevation, climate control usage, charging efficiency and driving habits. There are also small energy losses that occur during the charging process, meaning the amount of electricity pulled from your house can be somewhat higher than the amount that ultimately ends up stored in the vehicle’s battery.
For a homeowner who drives heavily and does essentially all of their charging at home, we may see the EV add approximately 500 to 800 kWh of electricity consumption per month. That is the range we are going to use for this example. It is important to understand that this represents a relatively high amount of driving. If you drive significantly less, your monthly EV electricity consumption can also be significantly lower.
The best way to estimate your individual cost is to determine how many kWh your vehicle actually uses each month and multiply that number by your effective electricity rate. The basic formula is simple:
Monthly EV charging cost = Monthly EV electricity consumption × Cost per kWh Once you know those 2 numbers, comparing utility charging with solar becomes very easy.
What Does It Cost to Charge a Tesla from the Utility Grid?
Let’s use an example electricity cost of $0.45 per kWh. Your actual utility cost may be higher or lower depending on your utility company, rate plan, location and the time of day when you charge. But $0.45 per kWh gives us a simple example to demonstrate how quickly EV charging can add to an electric bill.
- If your Tesla requires 500 kWh per month: 500 kWh × $0.45 = $225 per month
- If your Tesla requires 800 kWh per month: 800 kWh × $0.45 = $360 per month
That means our example homeowner could be spending approximately: $225 to $360 per month just to charge the vehicle from utility electricity. Over an entire year, that becomes: $2,700 to $4,320 per year.
That does not necessarily mean owning the EV is more expensive than owning a gas vehicle. To determine that, you would need to compare the charging cost against what you previously spent on gasoline and vehicle operating costs. But it does demonstrate something important: An electric vehicle can substantially increase the electricity consumption of your home.
Now Let’s Charge the Same Tesla with Solar
Instead of purchasing all of that electricity from the utility, let’s assume you have a properly designed solar and battery system where your blended cost to generate and manage that energy works out to approximately $0.22 per kWh. Again, this is an example.
Every solar system is different. The actual cost of solar energy depends on the price of the system, financing, production, equipment, system life, battery configuration and other factors.
But using $0.22 per kWh allows us to compare the exact same electricity consumption.
- At 500 kWh: 500 kWh × $0.22 = $110 per month
- At 800 kWh: 800 kWh × $0.22 = $176 per month
Our estimated monthly EV energy cost is now: $110 to $176 per month.
Compare that with our grid example:
- Utility charging: $225 to $360 per month
- Solar charging: $110 to $176 per month
Using these assumptions, solar reduces the effective cost of the electricity used to charge the vehicle by more than half.
What Does That Difference Look Like Over a Year?
Let’s take the comparison one step further.
- At 500 kWh per month:
Utility: $225 × 12 = $2,700 per year
Solar: $110 × 12 = $1,320 per year
Difference: $1,380 per year
- At 800 kWh per month:
Utility: $360 × 12 = $4,320 per year
Solar: $176 × 12 = $2,112 per year
Difference: $2,208 per year
Under these example assumptions, that is a potential difference of approximately $1,380 to $2,208 per year in energy costs. Over 10 years, assuming the example rates never changed, that would represent approximately $13,800 to $22,080. Real world utility rates, solar production, driving habits and other factors will change over time, so that should not be viewed as a guaranteed savings calculation. But it shows why homeowners with EVs should think seriously about where the electricity used to charge their vehicles is coming from.
When You Charge Your Tesla Matters
If you have solar and batteries, there is another part of this equation that is often overlooked. When are you charging the car? Imagine your solar system is producing a large amount of excess electricity at 1:00 in the afternoon. Your home does not need all of it. If your Tesla is plugged in, some of that solar production can go directly toward charging the vehicle. That is an excellent use of excess daytime solar production.
Instead of: Solar → Home Battery → Tesla you can potentially do: Solar → Tesla
The energy is being produced on your roof and consumed by a load at the house at essentially the same time. Whenever practical, this is how we prefer to see EV charging incorporated into a solar and battery system.
Why Not Just Charge the Tesla from Your Home Batteries?
You absolutely can. There are situations where charging an EV from stored battery energy makes sense. But think about what you are doing. You generated electricity from solar. You stored that electricity inside your stationary home battery. Later, you discharged the stationary battery and used that electricity to charge another battery inside your vehicle. Essentially, you are moving energy from one battery into another battery. Every time energy is converted, stored and discharged, there are efficiency losses. Those losses are normal and relatively small with modern equipment, but they still exist. There is also another important consideration. Your stationary batteries have limited storage capacity.
If you have 27 kWh of usable home battery capacity and your Tesla begins charging aggressively at night, the vehicle can consume a significant portion of that stored energy. That may leave less stored electricity available to operate the house overnight or provide backup power if the grid goes down. This is why we prefer direct daytime solar charging whenever it works with the homeowner’s schedule.
The Best Time to Charge an EV With Solar
If you work from home, this is relatively easy. Plug the vehicle in while solar production is strong and allow your solar system to contribute directly to the EV load. If you do not work from home, weekends can be another opportunity. Maybe the vehicle sits in the driveway for several hours Saturday or Sunday while the solar system is producing heavily. That is a great time to charge.
Modern energy management equipment can also provide increasingly sophisticated ways to coordinate solar production, battery storage, household consumption and EV charging. The overall objective is simple: Use as much of your own solar production as intelligently as possible.
What If You Have to Charge at Night?
Charging during the day is not realistic for everyone. A lot of people commute to work in the morning, return home in the evening and plug the car in at night. That is completely normal. If the vehicle needs to charge overnight and you are trying to avoid rapidly draining your stationary batteries, one strategy can be reducing the charging amperage when appropriate.
A Level 2 charger does not always need to operate at its maximum available amperage.
If the vehicle is going to sit in the garage for 8 or 10 hours, you may be able to charge it more gradually. For example, if you only need to replace a relatively small amount of energy before the next morning, there may be no reason to have the vehicle pulling at its maximum charging rate immediately after you plug it in. The exact strategy depends on your vehicle, charger, battery system, utility rate plan, household loads and how much energy you need before your next trip. Reducing charging amperage does not magically reduce the total kWh required by the vehicle, but it can reduce the instantaneous demand placed on the home’s electrical system and battery storage.
Your EV Needs to Be Included When Sizing Solar
This is one of the biggest mistakes we see when designing solar systems. Let’s say your house currently consumes: 12,000 kWh per year. A contractor designs the solar system around that number. Everything looks great. Then 6 months later you buy a Tesla. Suppose that Tesla adds another 6,000 kWh of annual electricity consumption. Your household has effectively gone from: 12,000 kWh per year to: 18,000 kWh per year. The solar system did not suddenly stop working. Your electricity consumption changed.
The system that was designed for the old house load is now undersized for the new one. That is why we always ask homeowners about future electrical loads when designing solar.
- Are you planning to buy an EV?
- Are you adding a pool?
- Are you installing another air conditioner?
- Are you building an ADU?
- Are you converting gas appliances to electric?
Your solar system should not only account for what you used yesterday. Whenever possible, it should anticipate how you expect to use electricity in the future.
How Much Additional Solar Do You Need for a Tesla?
This can be calculated using the same concept.
- If your Tesla consumes 500 kWh per month: 500 × 12 = 6,000 kWh per year
- If it consumes 800 kWh per month: 800 × 12 = 9,600 kWh per year
That means a high mileage household doing most of its charging at home could potentially add 6,000 to 9,600 kWh of annual electricity consumption. Your solar contractor can then determine how much additional solar capacity is required to produce that energy based on your location, roof orientation, shading, panel selection and expected production. This is why we prefer sizing solar from kWh consumption, not simply asking how many panels someone wants.
Solar Changes the Economics of Owning an EV
An electric vehicle eliminates trips to the gas station, but it replaces gasoline with electricity. Where that electricity comes from matters.
Using our example assumptions:
500 kWh from the grid at $0.45 = $225
500 kWh from solar at $0.22 = $110
And:
800 kWh from the grid at $0.45 = $360
800 kWh from solar at $0.22 = $176
That is a substantial difference.
And if you already own solar, buying an EV is a good reason to reevaluate whether your existing system is still large enough. If your solar was designed before you purchased the vehicle, the EV may be the reason your electric bill suddenly increased even though nothing is wrong with your solar system.
The Bottom Line: Designing Solar for Your EV
Charging a Tesla at home can add a significant amount of electricity consumption, particularly for someone who drives frequently and does most of their charging at home. For a high mileage driver consuming approximately 500 to 800 kWh per month, our example utility rate of $0.45 per kWh produces a charging cost of approximately $225 to $360 per month. Using an example solar energy cost of $0.22 per kWh brings that effective cost down to approximately $110 to $176 per month. But the smartest solar and EV strategy goes beyond simply installing enough panels. You also want to think about when the vehicle charges.
Whenever possible, we prefer having excess daytime solar production flow directly into the EV rather than storing that electricity in a stationary battery first and then transferring it into the vehicle battery later. If nighttime charging is necessary, charging can be coordinated around the home’s battery capacity, household consumption and utility rate plan.
At Supreme Solar and Electric, when we design a solar and battery system for a homeowner with an EV, we look at the entire energy profile of the house. We evaluate current consumption, annual mileage, EV charging, future electrical loads, solar production and battery storage. Because once you own an electric vehicle, your car is no longer separate from your electric bill. It becomes part of your home’s energy system.
Request a quote from Supreme Solar for solar and electric vehicle charging in Fresno.