Plug In America |

Understanding Electric Vehicle Charging

Tom's picture

Trading a gas pump for a plug is a wonderful thing. It's far more convenient, takes less of your time, and saves you from breathing toxic fumes and smelling like gas for hours after fueling. Charging is a different experience than pumping gas and understanding the subtleties takes time. I've been driving electric for over two years and I'm still learning. Potential EV owners might want to get a head start on the learning curve, and maybe save a bunch of money as a result.

Mostly, I'll relate how charging works for a Nissan Leaf, a four-door, five-passenger hatchback with a range of about 100 miles, but I'll also mention other plug-in vehicles. The Leaf is intended for typical daily driving, which for 78% of drivers in the US means 40 miles or less per day. Occasional longer trips are possible and understanding charging will help you evaluate whether an EV will suit your driving needs.

Level 1 Charging

Level 1 Charging - Standard house outlet
Level 1 Charging - Standard House Outlet

Level 1 charging is the technical jargon for plugging your car into an ordinary household outlet. For a Leaf, this means about 4.5 miles of range per hour of charging, or about 22 hours for a full charge. Wow, does that sound terrible! But there's a problem with thinking this way: you'll rarely need to do a full charge from flat empty to full. If you drive 40 miles per day and charge overnight, you'll be back to full in 9 hours. When you're sleeping, it doesn't matter if it takes one hour or 9 hours to charge.

But what if you have to drive a lot one day, say 80 miles? Sure, it would take 18 hours to get a full charge, but with a 9-hour overnight charge, you'll be ready for your normal commute the next day. If you drive less than 40 miles per day or charge for more than 9 hours, you'll work back up to a full charge over the next few days.

If you need to drive 80 miles on consecutive days, you'll need an alternative. Maybe you'll drive your other car, that gas-burner you keep around for long trips, or if there's public EV charging in your area, you can charge away from home while you're parked to do your shopping or other errands.

Level 1 charging at work could also be a supplement for people driving over 40 miles per day, or even a substitute for those who can't charge at home (because they don't have a garage or fixed parking place, for example).

Since it's easy to get 40 miles of range charging overnight from 120V, Level 1 is perfectly suited for overnight charging of the Chevy Volt, a plug-in hybrid with a 40-mile all-electric range.

Although Level 1 charging is generally too slow for a road trip, it can be helpful as destination charging. Cathy and I drove 90 miles to San Juan Island, charged for a few days in a friend's garage when not cruising around the island, and left with a full charge. That was great, but I wouldn't want to have to wait for Level 1 charging in the middle of a travel segment.

Beyond range issues, Level 1 may not be suitable for primary charging in all cases. In extreme climates, more power may be required to maintain proper battery temperatures. In these cases, Level 2 charging may be more appropriate (see below).

DC Fast Charging

The Blink DC Fast Charge Station
Blink DC Fast Charge Station
photo by ECOtality

At the other end of the spectrum is DC Fast Charging, the fastest type of charging currently available. It provides up to 40 miles of range for every 10 minutes of charging. These stations are expensive (up to $100,000) and require more power than your house, so you'll never have one of these in your garage.

They are going to start appearing as public charging stations in the next year, beginning in the Leaf target areas. If there's one conveniently located near where you drive, you can get back up to 80% of a full charge while getting lunch or drinking a latte. Charging this fast makes it far more practical to drive beyond an EV's single-charge range in one day. It's still not going to make a one-day 800-mile drive practical, but a 200-mile drive with a couple of charging breaks can be quite doable.

Level 2 Charging

ChargePoint/Coulomb Level 2 Charging Station
ChargePoint/Coulomb Level 2 Charging Station

Between the cheap Level 1 and expensive DC Fast Charging stations sits Level 2 charging. Level 2 supplies 240V, like what an electric dryer or oven uses. It goes through a box and a cord that improves safety by waiting to send power to the plug until it's plugged into an EV. Level 2 allows for a wide range of charging speeds, all the way up to 19.2 kilowatts (kW), or about 70 miles of range per hour of charging.

However, the charging stations being put in with federal grant money don't support the full range of Level 2 charging and max out at 6.6 kW or around 26 miles of range per hour of charging.

Both Level 1 and Level 2 charging stations simply deliver household electricity to the car. Electronics on board the car transform the wall power into the proper form to charge the battery. This bit of electronics built into the car also has a maximum power rating. The first model-year Leafs can only use 3.3 kW, about 12 miles of range per hour, or about 8 hours for a full charge from empty. The Chevy Volt's on-board charger is also limited to 3.3 kW, although its smaller battery pack gets full sooner.

Nissan recommends that you install a Level 2 charging station at home. That's a reasonable thing to do if you don't mind spending about $2,000, just consider it part of the cost of the car. Early buyers in the Leaf target markets may be able to get into The EV Project and get a free Level 2 charging station plus an allowance toward the install cost. Failing that, there's a 30% federal tax credit (up to $1,000) for installing EV charging, which can make it less expensive. Still, if you are planning to use your EV for a daily commute of 40 miles or less per day, you should at least consider using Level 1 charging at home. You can always add a Level 2 charging station later if you decide you need it.

There will soon be 20,000 public Level 2 charging stations (limited to 6.6 kW) installed mainly in the Leaf target areas. Even if you only have Level 1 charging in your garage, if you're in the early rollout areas, you should have access to convenient Level 2 charging available while your car is parked and you're doing something else. These charging stations will make it possible to drive 60 miles to a baseball game and pick up about 50 miles of range in 4 hours while you're having fun, thus easily driving over the single-charge range while always keeping a healthy reserve.

Charge Time and Battery Capacity

It's misleading that charging times are generally quoted as time for a full charge. While it does take about 22 hours (Level 1) or 8 hours (Level 2) to charge a Leaf from empty to full, you're not likely to do that often because  you will rarely arrive home with a fully depleted battery. It doesn't matter if you're driving a 40-mile Volt, a 100-mile Leaf or a 240-mile Tesla Roadster, if your commute is 40 miles, you'll only need about 9 hours (Level 1) or 3 hours (3.3 kW Level 2) to charge.

When we bought our Tesla Roadster, we got the high-power 16.8 kW Level 2 charging station, which can charge the car in 3.5 hours. After driving the car for a few months, I realized it's all but pointless to have such a big charging station in our garage. It's rare that I drive over 40 miles in a day. The 16.8 kW charging station can restore 40 miles in under 40 minutes. I want that charging speed when I'm making a long trip, not when I'm sleeping at home. In fact, I manually drop the power I pull from the charging station to about 7.5 kW because it's a little nicer to our electrical panel and the grid, and my typical overnight charge is still under 2 hours. Ignoring the fact that Tesla is still using the now-incompatible proprietary charging plug they picked before there was a chosen standard, most people buying a Tesla Roadster today would be well-served to buy a 6.6 kW charging station for home.

3 Roadsters Sharing the Charging Station at Burgerville
3 Roadsters Sharing the Charging Station at Burgerville

Level 2 Charging, Road Trips, and Charging Speed

Already, Ford has announced that the upcoming electric Ford Focus will support charging at 6.6 kW, and is making fun of the Leaf's 3.3 kW Level 2 charging limit. By the time Ford actually starts delivering the electric Focus, Nissan may have already upgraded the Leaf to 6.6 kW charging. I don't think it will be long before mainstream EVs are capable of even faster charging. The Tesla Roadster can charge at 16.8 kW, which combined with a larger battery pack makes 400-mile drives possible even without DC Fast Charging. Given that Level 2 charging costs 1/10 of what a DC Fast Charger does, I can imagine a lot of driving being supported by full Level 2 charging stations in areas that can't justify the investment in DC Fast Charging.

Personally, I'm disappointed we're spending so much money installing these 6.6 kW public charging stations rather than full-speed Level 2 chargers when most of the expense is usually just running the wires and buying the fancy box. A typical commercial Level 2 install runs around $10,000 for a charging station that's connected to a network and capable of billing the user. Cranking those charging stations up to the 19.2 kW limit would add a small incremental cost, perhaps 10% to 20%, and would allow for much faster charging. If you're a business owner installing a charging station and have to dig a trench and/or run conduit, even if it's just a for 6.6 kW unit, I strongly recommend planning for running 100A wire later without having to retrench or replace conduit so that upgrading to a 19.2 kW charging station will be much less expensive.

Comments

Anonymous's picture

Level 2 charger cost about $100

I modified my level 1 charger that came with the Leaf and have used it as a Level 2 for nearly 2 years, Cost about $100 and works like a dream!! The idea of a $2000 level 2 charging outlet is crazy!!! If you want details email me directly at rdoctors at g****l.com
Anonymous's picture

Availability / duration

Can you comment on the following issue: I plug my EV into a public charging station and go off to do my business. The car is sitting there all day - how does this affect other users who drive up expecting to charge their vehicles? There's a public charging station about 4 blocks from where I work - perfect as I wouldn't mind parking there, plugging in, walking to work and then coming back at the end of the day. But I'm sure that wouldn't be allowed?
Dan Cohen's picture

DC

Hi Tom: I live on Maui where we pay around .25/kW. I had an EV (ex airport) 25 years ago with lead-cell batteries. I'd like to get an EV again, and I wonder - would it be possible to charge Lead-cell batteries off a PV system, then charge an EV from the battery-bank? I believe I had 16 6V deepcycle batteries in that old Honda 600 van, which used to sell for about $50 ea/ probably double now. Seems like DC to DC should be a mucher faster charging time. Our local power company charges thousands just to evalutate hooking up a PV-metering system, and they do not pay for excess electricity produced beyond homeowner's consumption. Mahalo! Dan
themotorman's picture

solar yes!!

YOu can charge directly from the solar panels. You need to have enough panels to produce at least 2.5 volts x number of cells. e.g for your 16 x6 = 96 cells you'd need a system that puts out 2.5 x 96 volts = 240 volts. You then need someway to stop charging when the cells are charged as overcharging is bad for them. The simplest would be a controller ( Arizona windsun ) have them and are very helpful for off grid applications. For best battery life you need to have a cell balancing method and again they are available.
Dan Cohen's picture

spelling

*much faster*
Dave Mann's picture

Who Pays and How?

All excellent information. Many thanks for the run down. I am in a target area (3 miles from Nissan HQ, actually). Question is, in the case of public charging stations, will credit/debit cards be required? After all, someone has to pay for the electricity being used to charge the vehicle. How are the charging stations collecting payment now that they are being installed?
Tom's picture

Billing for Charging

Billing for charging is a very complex issue, worthy of a whole different article at least. Here are some quick thoughts for now... - Electricity is cheap, so cheap it's often more expensive to pay for billing infrastructure than it is to give the electricity away. - The cost of electricity given away is an investment in our future independence from oil and represents a public good. - Sites that install charging to encourage EV use would often rather have free charging stations that get used to raise awareness about EVs than paid stations that don't. - Businesses often want to attract customers and the minor cost of a little electricity is more than made up for in increased business. - For stations that do bill for charging, there are many options such as charge network membership cards, direct credit card support, or premium parking rates for spots that offer charging. We're in a delicate phase now where charging infrastructure is being installed to promote electric vehicle ownership, which in turn will create demand for charging. As ownership increases to the point where infrastructure needs to be reserved for those who really need to charge, we'll likely see a shift in billing practices. At the same time, businesses may find it necessary to offer free or inexpensive charging to attract customers from a wider geographical area.
Michael's picture

Billing for Charging

Tom, I think that if you examine your own home utility bill you'll find that electricity is not so cheap. The often quoted $0.11/KWHR as the national average cost for electricity doesn't represent the full cost of "delivered" power, which includes transportation and distribution charges, plus the multitude of fees charged by the utility companies. Also, as your consumption over your baseline goes up, so does the rate charged. My guess is that the average person pays around $0.20/KWHR for delivered power, and if they buy and start charging an electric car at home, that rate will go up considerably with their increase in daily consumption. Even at a flat $0.20/KWHR, charging your Leaf with a half-charge per day, 12 KWHRs, for a month works out to $72 added electrical cost on your electric bill. The notion of "giving away" power is not a sustainable one--subsidizing private transportation costs with taxpayer-provided electricity in the case of public charging stations, or company-provided electricity in the case of private charging stations, does not encourage energy conservation, charger time sharing, or the ethical concept of paying for what you use. In the case of taxpayers, they are already subsidizing the cost of the electric car and the cost of the public charging infrastructure, should they really pay for the electric car owner's fuel too? Owners of fossil fuel vehicles will not be too keen about subsidies for electric cars when they are paying for their own fuel, including the fuel taxes for maintaining the road infrastructure. Billing for charging does not have to be a complex issue: The bill needs to cover the cost of the electricity used in KWHRs, a fee to the owner of the charger for its cost and maintenance, a transaction fee for the services provided by the biller, and a fee to cover road use taxes that is based on mileage. When it's all said and done, the real cost of charging your electric vehicle at your home and at public or corporate charging stations, will not be much cheaper than the cost of gasoline.
Anonymous's picture

On electricity costing what gasoline costs.

We have an especially economical EV, and PG&E has a special rate for EVs; four cents per KWH. But putting that all aside, and assuming the very high use of electricity per mile (we figure we use one KWH per five miles; more or less; less than five on the freeway at high speeds, more in town at or below 40 mph) that you quote, the difference in cost per mile for electricity versus gasoline is MUCH greater than you suggest! We figure we AVERAGE one cent per mile (quite a bit less, actually, when we measure it) in our EV, and about 10 to 15 cents per mile in our (very economical) gas-burner! So, get real - in addition to a huge savings in pollution, we get a very real, large savings in cost per mile (and our EV is maintenance-free - check the brakes after about 40,000 miles, the tires when they lose tread - that's it!).
Tom's picture

Billing for Charging

Michael, trust me, I've looked at our utility bill. Our top marginal rate is 10.3561 cents per kWh. We pay another 1.25 cents for green power and 1.3593 in taxes and fees, less 0.339 cents in credits, for a total of 12.6264 cents per kWh. Our base rate is a few cents cheaper than that.

Under your scenario, putting 12 kWh into a LEAF every day for 30 days would mean driving 40 to 50 miles per day. Let's take the low number and call it 1,200 miles per month. At our top electric rate, we'd pay $45 dollars in electricity. At $4 per gallon, that same 45 dollars would buy 11.3 gallons. So to get the same cost is a gas car, I'd need to get 106 MPG. Even at 20 cents per kWh, that's equivalent to 62 miles per gallon.

Taxpayer subsidies for oil far exceed those for electric cars. Since 1973, the US has spent about $90 billion per year to secure foreign oil fields and oil routes. That's over $1 per gallon. That doesn't count our oil-motivated wars in the middle east, tax breaks to oil companies, or the healthcare costs associated with burning oil and the urban air pollution it causes.

Finally, I didn't say electricity needs to be free. I said that business may make a better return by offering free charging to attract customers. We went on a vacation recently and had to choose between two B&Bs. They both said they would allow us to charge overnight, but one wanted to charge us $20 for $1.60 worth of electricity, the other said it would be free. The one that gave us free charging got our business and made much more than $1.60 on the deal. Businesses should do what makes sense, but it requires some thought to get it right.

Anonymous's picture

Thank you for your posts -- I'm convinced

Just want to thank everyone who contributes to this wonderful web site. I was trying to decide if I want my next car to be an EV, and now I am sure. (Also, I test drove the Nissan Leaf yesterday and loved it!) I am going to join your organization and do what I can to help get our country less and less dependent on fossil fuels. This will take decades, but I have faith that my young children will one day breathe cleaner air and have no idea how to fill up a gas tank.
Kimberly Madrigal's picture

Multifamily Requirements

Terrific article Tom. I really learned a lot. Since you're willing to offer reasoned opinions, here is a question for you: In a 6-unit Santa Monica, CA apartment building with 2-40amp switches reserved for common area usage, would you recommend a level 1&2 charger be installed for potential/future EV-driving residents or just a level 2? Why? Keeping the future and the building location in mind, do you think one charger is enough? Thanks again for providing such wonderful information.
Anonymous's picture

Multi-family units

For multi family use, you want as much charging speed as you can get. For the time being get 100 amp wire installed along with the 100 amp switches on the panel. But for the Charger itself, get 40 amp charger which is the higher end of the market right now. This will charge a car in 4-5 hours from empty or 1-3 hours for most uses and freeing up more time for others to use it. If you have two 20 amp chargers you will end up with people parked there for as much as 8-10 hours at a time which limits the amount of charging you can physically do. I'd put 4-6 parking spaces and a charger in the middle of each 2-3 parking spots so you can just unplug from one and plug into the other. I'd also make sure whatever charging station you use can show if the car is full or not so people don't just randomly take each others charging away.
Tom's picture

That's a good point. Charging

That's a good point. Charging at multi-family dwellings may have higher speed charging requirements to enable sharing than home charging where there's a dedicated charging station. Keep in mind that the charging rate is limited both by the charging station and the car. A 2011 Nissan LEAF can only charge at about 15A not matter how much current the charging station can supply. Faster charging vehicles are coming. The upcoming Ford Focus and later versions of the LEAF will support ~30A charging, while the Tesla Model S will support 80A charging. So it's definitely good to be thinking about the future when trenching or running conduit - avoid redoing expensive install work if faster charging rates are needed in the future.
Tom's picture

There are a number of issues

There are a number of issues with multi-family units: access to charging for EVs for owners, access for owners with wheelchair or other requirements, etc. Plug In America did an online conference about this very subject last week: http://www.pluginamerica.org/press-release/ev-charging-multifamily-housing Perhaps that will get posted online. It's a hot topic and it's all too easy to just plant a charger near a parking spot and end up with it not being usable. As for Level 1 and/or Level 2, I'd recommend a Level 2 charger. If there's a proper outdoor outlet in the vicinity, I wouldn't bother paying much extra to add Level 1 to a charging station. Unless you want to add charging right away to enhance the property value, I'd take a cautious approach and not make a big investment until there's a resident with a need. For anyone building a new unit, I'd recommend running wire to accommodate full Level 2 charging on a 100A circuit.
Kimberly Madrigal's picture

Multifamily Requirements

Tom, thanks for your input. We are in the early stages of a building systems retrofit and I had never really thought about the electrical requirements for an EV charging station before. I'm grateful to you and to Plug In America for providing such good information.
Colby's picture

The EV Charging at

The EV Charging at Multifamily Housing video is now on YouTube. http://www.youtube.com/watch?v=79ShT3YUVVA
Kimberly Madrigal's picture

Multifamily

Hi Colby, yes, I attended the multifamily session in Santa Monica and it was very edifying. Unfortunately, it was a bit light on information for multifamily (apartment building) owners and was definitely more focused on condo owners and residents. Sad really because there were a number of apartment building owners like me in the audience who were desperate for information. Perhaps Plug In America will convene another panel to address the specific concerns of apartment building owners. . .