How to figure cost of electrical charging

Generally, a full charge will pull about 3 kWh from the wall.
If you don't have the concept of "baselines" (i.e. your rate per kWh is constant regardless of how much electricity you use per month), then simply multiply your rate by 3 and then again by the number of times per month you expect to charge. depending on your schedule, you might end up charging once a day, twice a day, or maybe even three times.

 

After you have some data on the EV Ratio, you can divide miles and kwh consumed to get miles/kwh, or kwh/mile($/mile) based on your own consumption. Make sure you add 15% to kwh consumed to adjust for the electricity lost between the power source and battery. You can then compare this to $/mile cost with gasoline.

You can also multiply your avg kwh price times kwh consumed times 1.15, and adjust for free charge stations.

 

buy a killowatt energy use meter.

 

here in CA we can get hour by hour readouts of electricity usage via PGE website. as others have mentioned a full charge consumes 3kwh. rate calcs are easy for flat rates, but many ev owners are on time-of-use w. tiers which is a pain to calc.

 

So for US average $0.12/kWh x 3 kWhr per charge up = $0.36 for ~10 miles = ~$1.80 per 50 MPG (eg; gallon)

You can adjust this for free charging scenarios etc.

 

This. Most fun you'll have plugging stuff in. Then apply the quick math. I've been getting closer to 3.4kWh per charge. Plus, you'll know (other than watching the clock) when the charge cycle is complete. $20 well spent.

 

Also, when looking at your cost per kWh, don't take the line item figure from your electric bill because there's other add-on's that increase the kWh cost. The most accurate way to get your true cost per kWh is take the bottom line of your utility bill (the "pay this amount") and divide that by the total kWh consumed. That will give you the true cost per kWh with all tarrifs, taxes, delivery fees, seasonal adjustments, etc... included.

 

This is not necessarily correct.
My bill for example has a flat delivery charge. There is no per kwh cost for delivery fees. Seasonal adjustments are reflected in the base kwh price, not an additional per kwh charge.
It is important to consider these if your bill works that way, so look carefully. Likewise it is important not to include them if they don't change on how many kwh you use.

 

Yeah, they're very sneaky around here- they say "why does everyone complain about our rates? We're are only 8-9 cents per kWh" but then they charge you another 8-9 cents per kWh for "Delivery and System charges" so now you're paying 18 cents per kWh before surcharges, etc. Once you add it all up and divide by total usage- our rate here is over 20 cents per kWh not the 8-9 cents they like to quote to the Public Service Commission and newspapers.

 

And then use it on all the rest of the things you plug in. See how much your TV is costing when it is off. See what drying a load of laundry in the dryer costs. So much fun.

 

If you use a 120 volt circuit, it takes 3 hours for a full charge. The circuit is rated for 15 amps current (priuskitty has reported that actual current draw is 11.7-11.9 amps- let's say 12). 12 amps x 120 volts = 1440 watts. For 3 hours, it is 1440 watts x 3 hours = 4320 watt-hours = 4.3 kWh. If you use a 240V circuit, it is 1.5 hours for a full charge and you end up with the same number. Just log the hours you charged and use the equation:

amps x volts x hours / 1000 = KWh (OK, I'm ignoring power factor.. the battery charger is an inductive and not resistive load and PF is not 100%... not sure what it is for the Prius Plug-in)​

If you are paying 10c/kWh, a full charge that gives 15 miles in EV mode driving will cost $0.43. That's 3c/mile. If gas is $4/gal and you get 50 MPG, that's 8c/mile in traditional gasoline hybrid mode. In general, the EV mode fuel costs are about equivalent to less than $2/gal gas. Looking at it another way, EV mode fuel efficiency is listed at 95 MPGe (gasoline equivalent- about 1.9x the traditional gasoline hybrid efficiency- so I figure the PF is ~95%).

 

i think your amperage is off.

 

it's not that simple b/c at the last 10 minutes of charging the amperage drops by half

 

drinnovation said: ↑

Yes I looked at the raw data earlier.. my comment was because I was thinking the spikes were so the car could better estimate the actual charge in the battery (its hard to get a good read while charging). Thus i expected the "finall fill", where they reduce current to charge more slowly as the balance cells/charge would occur right after one of those "spikes".​

Read more: http://priuschat.com/threads/attention-kill-a-watt-nerds.113900/page-4#ixzz2CoplS9A7

 

I believe you are right. I was "conservative" in my estimate- a device rated for a 15 amp circuit, of course, will draw less than 15 amps. My intent was to give a simple equation that would not require the purchase fo watt meters or other devices. If someone has used something like kill-a-watt, we could calibrate this equation. Maybe it is 13 amps or 11 amps...

 

11.72 amps

 

Or, have a separate electric meter installed, dedicated to only supplying juice to your PIP. This simplfies things.

DBCassidy

 

Also, a battery charger generally doesn't run full on the entire time. To get better than the rough numbers you give, one really needs to measure the actual flow (with for example a kill-a-watt).