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You Call That A Charger? – MW-Scale Chargers as DERs

Charles Botsford, PE's picture
Program Manager CWB Energy Solutions

Mr. Botsford is a professional chemical engineer in the State of California with 30 years’ experience in engineering process design, distributed generation, and environmental management. He has a...

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  • Jun 29, 2022

This item is part of the DER and Management Systems - June 2022 SPECIAL ISSUE, click here for more

You Call That A Charger? The device in Figure 1 is commonly called a Level 2 EVSE, or Electric Vehicle Supply Equipment. It isn’t technically a charger, but a set of electronically controlled contactors. The charger is what converts alternating current (AC) to direct current (DC), either on-board the EV or at a stationary device. So, “You Call That a Charger?” No. However, when we talk about DC MW-scale chargers, “Now That’s A Charger.”

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Figure 1. Level 2 EVSE – You Call That A Charger?

EVs as DERs

Electric Vehicles (EVs) are perhaps the ultimate distributed energy resource (DER):

  • EVs are distributed…in fact, they’re everywhere
  • EVs are energy resources…they have big batteries on board, and the capability to provide every type grid service that conventional energy storage does
  • Best of all, the use of energy storage from EV battery packs is much cheaper than battery farms. As EVs are used increasingly for grid services, this will provide a major benefit to the already low-cost economics of renewables penetration.

To date, the EVs-as-DERs discussion has centered on light-duty EVs for grid services. For example, the California investor-owned utilities Pacific Gas & Electric and Southern California Edison are conducting technology pilots to demonstrate AC vehicle-to-grid (V2G) and DC V2G, which will unleash the full power of light-duty EVs to stabilize the grid. This comes at a perfect time, with updates to IEEE 1547, California Rule 21, and the adoption in 2021 of the Society of Automotive Engineers (SAE) J3072 standard for AC V2G.

The light-duty discussion is good. As the saying goes: there’s strength in numbers. California, the US, and the world have many millions of light-duty EVs. California is expected to grow its current EV population of greater than 1M EVs exponentially to 25M by 2030.

Grid-Connected EVs

The bulk of EV charging, light- and heavy-duty, happens during off-peak hours, when the grid is least stressed and power is cheapest. This makes EVs an excellent sink for renewable power generation, and a perfect grid resource.

The impact of a single light-duty EV relative to the grid is insignificant. However, 25-50M EVs in the US by 2030, will provide significant grid services, whether from simple managed unidirectional charging or from bi-directional DC V2G and AC V2G charging.

With light-duty capacity of EV packs in the 50-100kWh range and heavy-duty EV packs upwards of 500kWh, this translates to over 1,000 GWh and 150 GW of usable EV battery storage and power [1].

The bulk of grid-connected EV services will come in the form of managed unidirectional charging, which is a very low-cost way of supplying grid services. DC and AC V2G will provide higher value services to the grid, but may only be needed for local and niche applications. One example of DC V2G would be a medium-duty delivery fleet that charges and discharges while in the depot. An example of AC V2G would be grid services supplied by an employer during workplace charging.

The grid services provided by EVs and their chargers include [2, 3]:

  • Peak shifting
  • Peak shaving
  • Supply capacity and firming
  • Frequency regulation
  • Spinning, non-spinning, and supplemental reserves
  • Reactive supply and voltage control
  • Transmission upgrade deferral
  • Congestion relief
  • Distribution upgrade deferral
  • Power quality
  • Power reliability
  • Demand charge management
  • Demand response
  • Time-of-use management

source: Cochran Inc.

Figure 2. MW-Scale Shore-Power for a Cruise Ship

Okay, shore power to a cruise ship isn’t technically a charger, either. It’s AC power just like the “charger” in Figure 1. However, it’s an example of a potential MW-scale DER, especially as ships and other heavy-duty vehicles become electrified.

MW-Scale EV Charging

You wouldn’t necessarily think of a cruise ship as a DER, or a train, or a plane for that matter. However, heavy-duty vehicles are more than ever being included in the electrification discussion. While heavy-duty EVs, including trucks, buses, trains, ships, airplanes, construction equipment, and port equipment may not have the population of light-duty EVs, more and more of these electrified vehicles are being developed and commercialized by manufacturers. California Governor Newsom signed an executive order for drayage trucks to be zero emissions by 2035 [4]. This same executive order also mandates 100% zero emission sales of light-duty vehicles by 2035 and heavy-duty vehicles by 2045. Many states follow California’s lead in emissions controls and transportation electrification.

This will be an excellent opportunity to convert heavy-duty diesel-fueled vehicles into grid-serving DERs.

SAE Heavy-Duty Charging Standards

Three SAE standards are set to enable heavy-duty EV charging:


SAE J3105 is an existing standard that allows for mechanized conductive charging up to 1000VDC and 1200A, or 1.2 MW. J3105 has three connector types, the first two primarily for buses, and the third for trucks:

  • J3105-1 – a pantograph overhead mounted system (conductor moves down to the EV)
  • J3105-2 – a pantograph mounted on the vehicle (conductor moves up from the EV)
  • J3105-3 – a pin-and-socket where the pin moves into the socket mounted on the EV

The pantograph systems have generally been designed for electric buses, in which a defined route enables opportunity charging along the way at bus stops; The pin-and-socket (J3105-3) system has been considered more appropriate for heavy-duty trucks. The J3105-3 pin-and-socket method for connection is shown below:

source: Staubli

Figure 3. SAE J3105/3 Pin and Socket Diagram

One potential application of the J3105 charging method would be for a port yard hauler, also called a UTR, with a 300kWh pack. To charge this pack from 20 to 80% state-of-charge (SOC), or 180kWh in 15 minutes would require 720kW. Hey, not even a MW. The pack chemistry would require the ability to charge at a 4c rate, but that’s just possible with today’s lithium iron phosphate packs over that SOC range.

Depending on the duty cycle, a 300kWh battery pack for a yard hauler would likely satisfy a full day of operation. Most of the charging would occur overnight, with opportunity “fast charging” taking place when needed. For grid services, the yard hauler might be connected to an overnight bi-directional DC “trickle charger” at 50kW, which would allow port vehicles to provide DC V2G services.


SAE J2954/2 is a heavy-duty inductive (wireless power transfer) charging standard (in process) that allows high-power charging. In practice, heavy-duty inductive charging has been deployed for many years at up to 300kW, with a 1MW DOE-funded project in the works. The light-duty corresponding standard, J2954, was adopted late 2020. To date, transit buses have been the primary market for this charging technology, with one California transit agency logging over 1.3M miles of revenue service. A schematic is shown below for transit bus wireless power transfer.

           source: WAVE

Figure 4. SAE J2954/2 Wireless Power Transfer Diagram

Inductive charging for transit buses is a well-proven method for “opportunity charging”, or charging while the bus is in service. An example of charging using J2954/2 would be for a transit bus with a 400kWh pack to charge over a 20-80% SOC for a 240kWh charge in 15 minutes. This would require 1MW of charging power.

A 400kWh battery pack for a transit bus would satisfy many types of daily routes considering a bus would get on the order of 0.5 miles/kWh, or about 160 miles. Overnight charging would top off the pack, while opportunity “inductive fast charging” would enable extended operations throughout the day.


The standards development for SAE-J3271 began in early 2022, but the basis for the high power charging technology and communications protocols have been in development for many years, and is also known as the Megawatt Charging System, or MCS. J3271 allows for charging up to 3000A and 1500V, or 4.5MW. The goal of SAE J3271 is to enable conductive charging systems to be used for heavy-duty vehicles on land, sea, or air.

                        source: [5]

Figure 5. MCS Charger at EVS 35 in Oslo, Norway

An example of charging using J3271 would be for a class 8 drayage truck with a 600kWh pack to charge over a 20-80% SOC for a 360kWh charge in 10 minutes. This would require 2.2MW of charging power. With the usable energy from a 600kWh pack, a class 8 drayage truck could travel well over 200 miles, which would easily satisfy short haul daily runs from the Port of Los Angeles to California Inland Empire warehouses. Overnight “trickle charging” at 50kW would enable a full charge, while opportunity “fast charging” at MW-plus charging rates would enable a seamless transition for longer-haul runs.


The electric utility pilots to bring light-duty EVs onto the grid as DERS are exciting and will pave the way for a robust market for energy storage from EVs. As heavy-duty EVs using MW-scale charging mark their presence, they will contribute inexpensive MW and MWh to the grid, pushing aside stationary battery storage. This will be a boon to accelerate the penetration of renewables generation both on land and offshore, and enable the smooth replacement of diesel-fueled heavy-duty vehicles.


1. Sheppard, C, J. Szinai, N. Abhyankar, A. Gopal, Grid Impacts of Electric Vehicles and Managed Charging in California, Energy Analysis and Environmental Impacts Division, Lawrence Berkeley National Laboratory, November 2019.

2. Chhaya, S., etal, “Distribution System Constrained Vehicle-to-Grid Services for Improved Grid Stability and Reliability”, Final Project Report, California Energy Commission, Publication Number: CEC-500-2019-027, March 2019.

3. Vehicle-Grid Integration Working Group, Final Report to the California Joint Agencies, CPUC DRIVE OIR Rulemaking R.18-12-006, June 30, 2020.

4. Newsom, G., Executive Order N-79-20,, January 19,2021.

5. Hampel, C., “CharIN Show MW Charging System Commercial EVs”,, June 14, 2022.

Jim Stack's picture
Jim Stack on Jun 29, 2022

Trucks and Buses are rolling now that could use that Megawatt charging. A lot more are coming. Being able to have large MegaWatt Battery Storage systems in place will be key. I can't wait to see some of these trucks on the roads. 

Charles Botsford, PE's picture
Charles Botsford, PE on Jun 29, 2022

Thanks Jim. Electrified transit buses have been around for many years. Electrified drayage trucks (Class 8) are in demonstration mode currently, but we'll see lots starting in 2024. 350kW chargers are being installed for light-duty EVs, but will serve as "slow" chargers for heavy-duty trucks and off-road vehicles until the higher power chargers arrive, again around 2024.

Rao Konidena's picture
Rao Konidena on Jul 7, 2022

FERC approved the California Independent System Operator (CAISO) Order 2222 proposal on June 17, 2022, with some revisions. This FERC Order 2222 enables distributed energy resources such as aggregated EVs to participate in CAISO markets. The minimum size requirement is 100 kW. So, any aggregated EV greater than 100 kW by itself or with the help of an aggregator can participate in CAISO markets. Since there is no capacity market run by the ISO, there is no capacity market for EVs to participate.

Benoit Marcoux's picture
Benoit Marcoux on Jul 7, 2022

Hi Charles. 

Insightful, as always.

I'm not sure if there are a lot of opportunities for V2G with MHD vehicles, beyond school busses, which are conveniently unused in there summer. For other commercial vehicles, I see few instances when the battery might be full and could be discharged into the grid, but not needed later on for commercial activities. For example, a delivery truck need its full battery in the morning for the day's run, coming back late in the day with a depleted battery, missing both the morning and evening peaks. Thoughts?

Charles Botsford, PE's picture
Charles Botsford, PE on Jul 7, 2022

Hi Ben,

That's the beauty of unidirectional managed charging: the EV battery doesn't discharge back to the grid, and you get essentially the same grid services as V2G, except you need roughly three times the kWh. Most EVs as DERS, even MD or HD, will use unidirectional charging exclusively, and this will be of tremendous benefit to the grid. V2G is still useful, but more for localized niche applications such as when the power goes out at your house or business, or the utility shuts off power to millions of customers because they fear high winds might cause a wildfire.

Benoit Marcoux's picture
Benoit Marcoux on Jul 8, 2022

True, especially to avoid charging during the evening peak. Not so useful for the morning peak, if the MHD EV got charged overnight. 

Charles Botsford, PE's picture
Thank Charles for the Post!
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