Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

One year of experience on Eversource TOU rates

David29

Active Member
Supporting Member
Aug 1, 2015
2,294
1,976
DEDHAM, MA
I converted my home charging service to Eversource Time of Use (TOU) rates just about a year ago, so I thought I would report my experience over this first year.

I have a separate electric service for charging my car so all the power on the meter is for car charging, except for a small amount used for a security lamp.

With just about 11,000 miles driven in the past year, I have used a total of 4,501 kWh from Eversource in that time. My total cost of electricity was $809.82, which includes the energy cost, plus the delivery cost, plus the monthly fee ($9.99/month). That is an average cost of 17.99 cents/kWh. The TOU rate affects only the delivery portion of the bill. Compared to what I would have paid if the service had been on normal residential rates, I saved $96.15 or 10.6% of my total bill. More meaningful is that the savings is 20.5% of the delivery portion of the bill (i.e., including the monthly service fee but excluding energy). So, the savings is small, but it did not cost anything to switch to TOU rates, so I am glad I did it.

Although I tried hard to do most charging during the nighttime off-peak hours, I did use some peak period power during the year. In most cases this was for preheating or precooling the car. I used 159 kWh of peak energy, which is about 3.5% of the total power used. The penalty for using that power was $16.76 for the year – in other words, that is how much extra I paid to buy that power in peak period versus in the off-peak period.

My total savings would have been higher if I had driven more miles, of course. And my percentage savings would have been higher, because the fixed monthly fee would become a smaller part of each kWh’s cost. The monthly service fee is higher for TOU ($9.99/month) than for normal residential service ($6.43).

One other relevant point is that Eversource changed the TOU rates on January 1, 2017. The savings was much more under the 2016 rates than it is now. In my first month of TOU in late 2016, I saved more than 4 cents/kWh, while I saved an average of only 2.1 cents/kWh with the new rates. Savings are somewhat higher in the summer than in the winter, which is helpful since we are likely to drive more in the summer, and I am more likely to use peak period preheating in the winter.

Besides charging at home, we used Superchargers for trips away from home. According to my notes, we used just about 400 kWh of energy from Superchargers over the year, plus a small amount from Level 2 chargers here and there (not tracked). It is an amusing coincidence that our Supercharger energy use during the year was almost exactly the amount (400 kWh) being provided free by Tesla to cars that do not have free Supercharging.
 

dave4444

Member
Aug 12, 2017
72
96
NH USA
David, Does has the on-screen controls->trips->total energy values been useful for determining away-from-home charging amounts? I've been disappointed in the lack of historical data Tesla gives us, I'm sure the car knows when and how much I've charged for the life of the car (plus everywhere I've ever driven, but that's a different topic).

I've kept one of my trip counters never reset to track total usage since day 1 and my home EVSE keeps track of the kWH I put in from there. It's unclear how useful this is as I believe the trip consumption is for driving energy only, not idle/parked vampire usage, plus I think it's for output from the battery not input from charging (AC or DC). Some public chargers track and give you kWH output at the end of every session, but many don't (including tesla's annoyingly).
 

David29

Active Member
Supporting Member
Aug 1, 2015
2,294
1,976
DEDHAM, MA
The trick with superchargers, at least, is to log the data from the charging screen before you unplug the charging cable. get into the car, make your notes, then exit and unplug. If you do that, the charging screen does indeed tell you how many kWh you just took in. In fact, it does that for level 2 chargers as well, but I rarely bother.
You can also make a decent estimate of how much charge you got by noting the % charge when you start (or the miles of battery capacity of your display is set to distance) and when you finish charging. You just have to have the discipline to note the starting value before you plug in because the charging will start immediately and change the SOC. (And I admit that sometimes I am too eager to plug in and go to the rest room or food or coffee etc., especially if I have my spouse with me.)
 

David29

Active Member
Supporting Member
Aug 1, 2015
2,294
1,976
DEDHAM, MA
I converted my home charging service to Eversource Time of Use (TOU) rates just about a year ago, so I thought I would report my experience over this first year.

I have a separate electric service for charging my car so all the power on the meter is for car charging, except for a small amount used for a security lamp.

With just about 11,000 miles driven in the past year, I have used a total of 4,501 kWh from Eversource in that time. My total cost of electricity was $809.82, which includes the energy cost, plus the delivery cost, plus the monthly fee ($9.99/month). That is an average cost of 17.99 cents/kWh. The TOU rate affects only the delivery portion of the bill. Compared to what I would have paid if the service had been on normal residential rates, I saved $96.15 or 10.6% of my total bill. More meaningful is that the savings is 20.5% of the delivery portion of the bill (i.e., including the monthly service fee but excluding energy). So, the savings is small, but it did not cost anything to switch to TOU rates, so I am glad I did it.

Although I tried hard to do most charging during the nighttime off-peak hours, I did use some peak period power during the year. In most cases this was for preheating or precooling the car. I used 159 kWh of peak energy, which is about 3.5% of the total power used. The penalty for using that power was $16.76 for the year – in other words, that is how much extra I paid to buy that power in peak period versus in the off-peak period.

My total savings would have been higher if I had driven more miles, of course. And my percentage savings would have been higher, because the fixed monthly fee would become a smaller part of each kWh’s cost. The monthly service fee is higher for TOU ($9.99/month) than for normal residential service ($6.43).

One other relevant point is that Eversource changed the TOU rates on January 1, 2017. The savings was much more under the 2016 rates than it is now. In my first month of TOU in late 2016, I saved more than 4 cents/kWh, while I saved an average of only 2.1 cents/kWh with the new rates. Savings are somewhat higher in the summer than in the winter, which is helpful since we are likely to drive more in the summer, and I am more likely to use peak period preheating in the winter.

Besides charging at home, we used Superchargers for trips away from home. According to my notes, we used just about 400 kWh of energy from Superchargers over the year, plus a small amount from Level 2 chargers here and there (not tracked). It is an amusing coincidence that our Supercharger energy use during the year was almost exactly the amount (400 kWh) being provided free by Tesla to cars that do not have free Supercharging.

One other thing I should mention. I did a quick estimate and it looks as if the energy cost per mile is about 8.5 cents/mile, for the miles not done with Supercharger energy. That is a depressingly high figure. It means there is no savings to operating my Model S compared to a gas car getting 30 mpg with gas at $2.50/gallon. This is a reflection of the extremely high cost of electricity in eastern MA.
 
  • Informative
Reactions: chjch

tga

Active Member
Supporting Member
Apr 8, 2014
4,043
3,032
New Hampshire
One other thing I should mention. I did a quick estimate and it looks as if the energy cost per mile is about 8.5 cents/mile, for the miles not done with Supercharger energy. That is a depressingly high figure. It means there is no savings to operating my Model S compared to a gas car getting 30 mpg with gas at $2.50/gallon. This is a reflection of the extremely high cost of electricity in eastern MA.
Are you sure on the math? That sounds high. I've been averaging 348 Wh/mi, o4 0.348 kWh/mi. At $17.99/kWh, that's 6.3 cents/mile (plus charging inefficiencies). At a local $1/hr chargpoint ([email protected] after voltage drop), I was estimating <6 cents/mile.

Eventually, we will get TOU pricing on generation, too. Then it gets interesting...
 
  • Like
Reactions: chjch

EdisonFire

Member
Sep 2, 2015
179
143
NJ
I don’t have time of use meter and pay .14/kWh in NJ. That is generation plus delivery. It seems your rate is very high for TOU metering
 
  • Informative
Reactions: David29

David29

Active Member
Supporting Member
Aug 1, 2015
2,294
1,976
DEDHAM, MA
Are you sure on the math? That sounds high. I've been averaging 348 Wh/mi, o4 0.348 kWh/mi. At $17.99/kWh, that's 6.3 cents/mile (plus charging inefficiencies). At a local $1/hr chargpoint ([email protected] after voltage drop), I was estimating <6 cents/mile.

Eventually, we will get TOU pricing on generation, too. Then it gets interesting...

It could be off a little, but not a lot, i think. The reason for the uncertainty is that I tried to adjust for the miles driven with Supercharger energy. trouble is, when we are on trips, some of the energy we use is from the initial charge at home and the final charge back at home after the trip, so it is hard to know exactly how many miles are driven exclusively in Supercharger (free) energy. One reason for the higher than expected cost could be that I have to pay Eversource for all the energy consumed, which includes the energy lost in conversion from AC to DC. The car only measures the energy taken out of the battery, not the energy that comes into the AC/DC converter.
 

dave4444

Member
Aug 12, 2017
72
96
NH USA
It could be off a little, but not a lot, i think. The reason for the uncertainty is that I tried to adjust for the miles driven with Supercharger energy. trouble is, when we are on trips, some of the energy we use is from the initial charge at home and the final charge back at home after the trip, so it is hard to know exactly how many miles are driven exclusively in Supercharger (free) energy. One reason for the higher than expected cost could be that I have to pay Eversource for all the energy consumed, which includes the energy lost in conversion from AC to DC. The car only measures the energy taken out of the battery, not the energy that comes into the AC/DC converter.

You're also paying to heat the wires between your utility meter and the car. Check the voltage as reported by your car right after you plugin (while still 0 Amps), and then once at full load. You can calculate the power going to heat wires from the voltage delta between 0A and full load (as reported on the dash/app). Note you're not paying for all of that as the resistance is spread across transformer->meter and meter->car, but it's good to know. A voltage reading on your panel/meter vs car would be more accurate.

I've seen some public chargers that drop 15V under 30A load, 450W of power is going to heat the air/ground/building not charge my car!
 
  • Informative
Reactions: David29

tga

Active Member
Supporting Member
Apr 8, 2014
4,043
3,032
New Hampshire
The reason for the uncertainty is that I tried to adjust for the miles driven with Supercharger energy. trouble is, when we are on trips, some of the energy we use is from the initial charge at home and the final charge back at home after the trip, so it is hard to know exactly how many miles are driven exclusively in Supercharger (free) energy.
When I first got the car, I didn't have home charging set up yet. I was using pay-to-charge chargepoints ($1/hr) and the local supercharger. At 200V (under load), I was getting 6kW = 6kWh/hr of charge = 6kWh/$1 charge ~= $0.17/kWh, which is about what I pay at home. I was estimating 5-6 cents/mile entirely on electricity I paid for, more like 2 cents/mile when free supercharging was included (most of my miles are roadtrips).

This reminds me, I need to order a kWh meter to install in-line with my HPWC.

You're also paying to heat the wires between your utility meter and the car. Check the voltage as reported by your car right after you plugin (while still 0 Amps), and then once at full load. You can calculate the power going to heat wires from the voltage delta between 0A and full load (as reported on the dash/app). Note you're not paying for all of that as the resistance is spread across transformer->meter and meter->car, but it's good to know. A voltage reading on your panel/meter vs car would be more accurate.

I've seen some public chargers that drop 15V under 30A load, 450W of power is going to heat the air/ground/building not charge my car!
FWIW, I loose 8-9V @ 24A. Only 1-2 is after the panel (ie, I see 7V drop at the source side of the 100A main breaker). I've got small Al overhead feeds (4Ga, I think), with a couple of splices and a decent run to the pole. An electrician who looked at it commented that I might want to upgrade that, even if I wasn't planning a service upgrade to 200A (or more).
 

Products we're discussing on TMC...

About Us

Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.

Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


SUPPORT TMC
Top