Workplace Charging - The Goldilocks Approach
Many companies are considering providing workplace charging for their employees and finding they are in new territory with many options to consider. We at Plug In America would like to share what we have learned having been involved for over 10 years in both using charging infrastructure as drivers and advising site hosts of all types in how to provide effective charging facilities.
There are many reasons a company may be considering providing workplace charging. It could be to attract and retain forward-thinking employees, to enhance a company's "green" image, to gain points toward LEED certification, or to raise awareness of electric vehicles.
Our analysis and recommendations are based on the goal of using workplace charging to increase the adoption of electric vehicles, which ties in with many of the reasons we find companies are considering making charging available in the workplace. Even when this is not an explicit goal at a given company, understanding the issues presented here may be helpful in evaluating charging options.
We also want to minimize the cost to the employer while meeting the goal of encouraging increased use of electric vehicles. These considerations include infrastructure costs, operating costs, maintenance costs, and efficient use of employee time.
There is certainly no one-size-fits-all approach that meets the goals and needs of every company. The ideas presented here are meant to serve as a starting point, a baseline plan that can be used to inform the analysis of corporate goals, infrastructure considerations, and employee interests.
Level 1 refers to charging at 120V. This can be from an ordinary outlet using a portable charging device or from a dedicated Level 1 station that has the proper electronics and plug to connect directly to a plug-in electric vehicle. For long term loads, like charging a vehicle, the current drawn is generally limited to 12A, which yields 1.44 kilowatts (kW) of charging.
Level 2 refers to charging at higher voltage, 208V to 240V. The current limit for Level 2 stations is typically 30 to 32 amps (~7 kW), but can be anything from 15A to 80A (up to 19.2 kW). In principle, Level 2 charging can be accomplished with a 240V outlet (NEMA 14-50, for example), but we strongly prefer charging stations for Level 2 to avoid a number of safety, liability, and usability issues.
DC Quick Charge This charging method bypasses the vehicle's on-board AC charging equipment and sends high voltage (300V to 400V) DC directly to the battery, at rates between 20 and 130 kW. These are expensive to install and operate, and are typically used for road trips or other situations where extra charge is needed in a hurry, not for a workday charging session.
The "Just Right" Fee
Problem: Free Reduces Availability
Free charging sounds like the best incentive to get people to consider electric vehicles, but the cost of electricity is not a barrier to EV adoption. An exact comparison with gas depends on a number of factors, but think of driving on electricity as equivalent to getting gas for less than $1 per gallon. Free charging makes the cost benefit more apparent, but has a couple of problems. First, it sets an expectation that charging will always be free, something that generally isn't sustainable. A short-term pilot with free charging can be very effective in kickstarting awareness of electric vehicles, and some companies may want to continue to provide free charging even as EVs rise in popularity.
However, if free charging drives demand to a level that can't be met, the resulting oversubscription can create problems that reduce EV adoption. Free charging motivates everyone to charge at work because it's cheaper than charging at home. Charging that is oversubscribed is undependable and therefore people who can't charge at home won't find it a viable option. The only people who can use free charging are those who don't need it because they have a more reliable alternative. This creates conflict between drivers who need charging to get home and others who just want to charge because it's free. This built-in conflict can even create a hostile environment at work. Who wants to get into a shouting match over fueling their car so they can get home?
When free charging leads to oversubscription and reduces charging availability for those who need to charge, it discourages EV adoption among those who could most benefit from charging at work.
Problem: Overly Cheap Charging Shifts Off-Peak Use to On-Peak
Like free charging, billing at a rate that's below the market price for electricity incentivizes shifting charging from overnight at home to charging at work during the day. As EV adoption increases, this puts extra strain on the grid and increases energy costs.
Problem: Overly Expensive Charging Can Hurt Adoption Or Usage
Paid charging billed far above the cost of electricity erases the economic advantage of driving electric. People who can't charge at home thus can't use this as a way to make driving electric financially viable. This therefore will not increase EV adoption. Likewise it can't substantially increase use of EVs if it makes driving electric cost more than burning gas.
Solution: Charge a Little Over Market Price
The solution is to provide charging billed at just a little above local home rates. This extends the economic advantages of driving electric to those who cannot charge at home. It also eliminates the incentive to shift charging from home to work, reducing the number of stations needed to satisfy demand. Together these benefits minimize the infrastructure cost of providing charging at work and focus the benefits on those who need it the most.
Note that billing for public charging is different; other issues are at play there.
What Technology To Choose?
Problem: Level 2 Infrastructure Requires Resource Management
A typical Level 2 charging station delivers enough power to add approximately 200 miles of electric driving range in a workday, far more than the average commuter needs to charge up. Thus, there's pressure to take time out of the day to go out and shuffle cars so the next car can charge. Employees at workplaces with oversubscribed Level 2 chargers have developed dedicated mailing lists and sophisticated notification systems to coordinate swapping vehicles at charging stations.
In the long run, employee distraction is probably the most expensive cost in providing Level 2 workplace charging, easily exceeding the cost of electricity and, over time, exceeding the cost of equipment and installation.
Problem: Simultaneous Level 2 Charging Risks Utility Demand Charges
If there's enough Level 2 charging that shuffling cars during the day isn't needed, then the vast majority of EVs will get their full charge in the first couple of hours in the morning. Because of this, compared to a more gradual charging method, a company's exposure to utility demand charges is tripled or worse, another hidden cost that can exceed the more obvious electricity, equipment and install costs.
Problem: Level 2 Billing Schemes Create Problems
There are three basic ways to bill for charging, and none of them work well enough to be the predominant billing method in the workplace.
Billing by energy delivered, kWh, is the closest model to selling gasoline by the gallon, but when demand for charging is high and turnover is required to get everyone charged, then the scarce resource isn't the electricity, it is the opportunity to charge. Billing by energy use doesn't incentivize people to unplug when their vehicle is done charging.
Billing by hour is the obvious solution for getting people to free up the charging station when they are done charging, but is unfair because some vehicles draw energy at twice the rate, or more, of others.
Billing by session, like $5 per charge, combines the worst attributes of the above for Level 2 charging: it offers no incentive to move after charging is complete and is even more unfair than billing by time.
Problem: Networked Billing Stations Raise Costs
Stations with built-in billing and network connectivity provide a number of valuable benefits. In addition to enabling billing, they can also control access, collect data on use, and allow remote monitoring for maintenance issues. Many site hosts choose to install these sophisticated stations for these other benefits even when they provide free charging.
However, these stations add costs both for the equipment purchase and operating expenses, which can be problematic when used to provide daily charging for drivers who can't charge at home.
The incremental cost for charging units with billing can equate to the cost of electricity for years worth of charging. Passing that cost on to users of the stations puts up a barrier to EV adoption for those who can't install a simple charging station at home.
Because electricity is so inexpensive, billing overhead alone can double the cost of providing charging. Again, passing this cost on to users discourages those who can't charge at home from driving electric.
Solution: Fixed-Rate Parking Pass And Simple Charging Stations
With Level 1 charging, billing can be handled by having employees pay for a parking pass at a fixed monthly rate that allows them to use the charging. Charging for 8 hours will yield about 35 miles of range, which is enough for most commutes. So the billing rate could be set to be just a little above the cost for 8 hours of Level 1 charging, or about 11.5 kWh. If someone needs only six hours, they are overpaying by 33%, which is still far better than paying double at a billed Level 2 station. Because charging takes most of the day, there's no need to run out and shuffle cars around, and exposure to demand charges is also lowered.1
EV drivers can do the legwork needed for enforcement by reporting violators to facilities. Facilities can then issue a warning or call a tow truck.
Simple outlets (NEMA 5-15 or NEMA 5-20) are very inexpensive and may already be available in employee parking lots. If already available, providing charging can be as simple as adopting policy for giving permission to employees to use the existing outlets. These outlets need to be on dedicated circuits, which need to be rated for at least 15 amps and preferably for 20 amps. They should be situated such that charging cords won't cause a tripping or ADA hazard.
Dedicated Level 1 Stations
Level 1 charging stations have a number of advantages. Charging stations use J1772 connectors which are designed for thousands of plug/unplug cycles, are weather-resistant, have built-in ground fault protection, and communicate the maximum safe charging level to the car. In addition, a dedicated charging station is preferable to connecting the car to a simple outlet with a charging cord; the cord takes time to retrieve and put away, and is a potential theft target. Ideally charging is fast and convenient: 10 seconds to plug in and you're done.
Although Level 1 charging stations are more expensive than outlets, the cost of the stations may not add much to the total cost of installing charging infrastructure when new wiring is required.
Level 2 For Increased Availability
Level 1 may not be sufficient to meet everyone's charging needs, so some Level 2 should also be available, but at a higher billing rate than Level 1. Low power Level 2 stations (12 to 15 amps) can be administered in the same way as Level 1 stations, using inexpensive stations and controlling access via parking passes sold at a slight premium to an assumed 8 hours of charging per day at the local daytime utility rate. Higher power Level 2 stations (30 amps or more) can be provided for those who occasionally need charging, and can be billed at higher rates to cover the costs of more sophisticated stations needed for time-based billing.
DC Quick Charging For Edge Cases
DC Quick Charging can also make sense as a safety net for those odd cases where someone needs to charge quickly. This could be on site at the workplace for large companies or just conveniently located nearby.
Generally speaking, workplace charging should consist of mostly Level 1 charging, billed at just above the cost of 8 hours of charging per day, with some Level 2 available at a higher billing rate. Even though Level 1 charging stations and installation may not be any less expensive than non-billing Level 2 stations, this will meet the goal of increasing EV adoption and use while minimizing infrastructure costs, utility demand charges, and lost employee time.
1In some cases, peak utility rates may tip the balance toward Level 2 charging which finishes early in the work day. Providing lots of paid Level 2 is fine if it really makes more sense than Level 1.
This post is also available as a PDF.
Updated February 20, 2015.