Back to basics: electric vehicle charging and renewable energy

Design practices, codes and standards to consider when planning for electric vehicles and renewable energy sources

By Dan Peterson, PE March 13, 2024
Above-roof structural steel framing for photovoltaic at the University of Illinois at Urbana-Champaign, Electrical and Computer Engineering Building. Courtesy: SmithGroup

EV insights

  • The increasing prevalence of electric vehicles (EV) prompts a need for understanding EV charging infrastructure and the environmental considerations associated with the electricity grid’s composition.
  • Examining electric vehicle supply equipment (EVSE) reveals a spectrum of charging options, from Level 1’s slow “trickle” charge to Level 3 or DCFC for rapid long-distance travel, emphasizing the importance of strategic planning for sustainable transportation choices.

This article has been peer-reviewed.Recent developments may contribute to the adoption of electric vehicles (EVs) by expanding the accessibility of existing charging networks. A growing list of automakers who currently use the Combined Charging System (CCS) standard have agreed to adopt the North American Charging Standard (NACS). In turn, Tesla has agreed to make its Supercharger network accessible to other brands of EVs. Adapters will allow EVs with one type of charging standard to use stations that provide a different charging standard.

As the number of EVs on the roads continues to increase, it becomes important to know the key elements involved in the design and installation of EV charging infrastructure. Drivers of EVs might feel uncomfortable with the data indicating that 60% of the utility-scale electricity generation in the United States in 2022 was produced by fossil fuels. Their car of choice could in effect be running on coal power.

Along with understanding EV charging infrastructure, it is also prudent to become familiar with what goes into small-scale renewable energy installations, particularly those of the solar photovoltaic (PV) type. Both can help contribute toward a more sustainable future and both will need to be considered on projects with U.S. Green Building Council LEED certification goals.

Levels of EV charging stations

Terminology for EV supply equipment (EVSE) is important for engineers to understand.

Sticklers on semantics may say that Level 1 and Level 2 EVSEs cannot accurately be called “chargers,” because they simply provide alternating current (ac) power to the EV’s onboard charger, which then converts to direct current (dc) power and charges the battery. In this article the terms are essentially used interchangeably.

Level 1 EVSEs connect the vehicle to a standard 120 volt (V) outlet. This type of “trickle” charging can add around 4 or 5 miles of range per hour. When someone is working or sleeping while their car is parked in the same place for eight hours or more, it may be all they need. The U.S. Department of Transportation estimates that the average distance traveled per driver in a day is about 39 miles. It should be noted that in very cold conditions, most of the energy provided by Level 1 charging can go toward battery heating, severely limiting the rate at which the battery can be charged.

Level 2 EVSEs connect the vehicle to 208 or 240 V single-phase power. The equipment can either be hardwired or plugged into an appropriate electrical receptacle. They can add anywhere from 12 up to 80 miles of range per hour. That depends on the ampacity of the circuit, the power output of the charging station and the capacity of the onboard charger (which determines the ability and speed at which an EV can accept the charge).

Level 3 or dc fast-charging (DCFC) stations convert ac to dc and send the current directly to the vehicle’s battery. These stations are generally rated anywhere from 30 kilowatts (kW) up to 350 kW and can add over 100 miles of range in 30 minutes or less.

Figure 1: Extensive carport solar photovoltaic installation at River People Health Center in Scottsdale, Arizona. Courtesy: Kevin Korczyk, K2 Creative LLC

Figure 1: Extensive carport solar photovoltaic installation at River People Health Center in Scottsdale, Arizona. Courtesy: Kevin Korczyk, K2 Creative LLC

The intent for these stations is to allow EVs to make long-distance trips that are farther than the range of the vehicle. As such, they are typically installed along highways and major travel routes. They can charge a vehicle from a low state of charge up to an 80% charge in a short amount of time.

The time to charge from 80% up to 100% can take longer than the charge from 20% to 80%, so some stations do not allow charging past 80%; it would make more sense for the driver to continue their journey and charge again at a different location. Many EV manufacturers recommend regularly charging only to 80% to preserve the health of the lithium-ion battery anyway.

The time to charge will depend on the specific vehicle’s battery management system and what battery voltage and current it can accept. It can also be affected by battery temperature, battery capacity and the condition of the charger.

Generally, as the level of charging increases, the potential cost of the EV charging station will also increase. The price of the equipment, installation costs, electricity charges and maintenance will all need to be considered. Site-specific factors, like the distance of the EVSE from the electrical service and whether the service needs to be upgraded will significantly affect installation cost.

A basic Level 1 installation could be virtually free while a DCFC installation could cost anywhere from $50,000 to over $100,000. Aside from providing a higher amount of power, Level 3 EVSEs/DCFC also convert ac to dc to charge the battery more directly, which is part of why they are more expensive.

To illustrate the amount of power required for each type, let’s assume a 12 ampere (amp) 120 V, 1-phase load for Level 1 charging (roughly 1.44 kW), a 40 amp, 208 V, 1-phase load for Level 2 charging (roughly 8.32 kW) and a 60 amp, 480 V, 3-phase load (roughly 50 kW) for DCFC.

Six Level 1 chargers would equal the power required for one Level 2 charger. Six Level 2 chargers would equal the power required for one 50 kW DCFC. Thirty-six Level 1 chargers would equal the power required for one 50 kW DCFC.

Not all the power provided goes to charge the battery. Lithium-ion batteries stay their healthiest, most efficient and safest when they are kept from reaching extreme temperatures. The built-in battery management system and associated heating and cooling systems in an EV will take care of keeping the temperature within an acceptable range. That takes energy, so it is in a driver’s best interest to precondition the EV battery while it is plugged in when possible rather than drawing energy from the battery to do so.

Level 1 charging

The least expensive Level 1 installation would be at an EV owner’s home where they simply plug the EVSE that came with their vehicle into an existing receptacle. At a garage or parking lot associated with a person’s workplace, a Level 1 installation might look as simple as a receptacle on a dedicated circuit in front of a parking space. If in a wet location, the receptacle should be installed with a weatherproof while-in-use cover that is large enough to house the plugs for a variety of charging cords that EV drivers would need to bring.

Figure 2: Level 1 installation at the Phoenix Biomedical Campus Parking Garage, from 2015. The technology for electric vehicles has improved substantially in the past eight years, but this type of installation is still useful. Courtesy: SmithGroup

Figure 2: Level 1 installation at the Phoenix Biomedical Campus Parking Garage, from 2015. The technology for electric vehicles has improved substantially in the past eight years, but this type of installation is still useful. Courtesy: SmithGroup

NFPA 70: National Electrical Code (NEC) Article 625.54 (2020 and 2023) also requires that receptacles meant for EV charging be ground-fault circuit interrupter (GFCI) protected. The cost to the parking garage or building owner would include the installation of breakers, conduit, wire, National Electrical Manufacturers Association (NEMA) 5-20R receptacles, boxes and covers for however many parking spaces are allocated for Level 1 charging.

For an installation such as this, it is important to consider measures to deter theft of employees’ charging cables. Access control, surveillance and lockable receptacle boxes are a few ideas that can help. The U.S. Department of Energy wrote an article describing this issue and some mitigation strategies that EV owners can implement.

A marginally more expensive Level 1 charging installation would replace the receptacle with a stationary EVSE, likely hard-wired that includes the cord to plug into the vehicle. A pedestal-mounted Level 1 EVSE will generally be more expensive than a wall-mounted unit. One benefit to this approach is that it can provide a cleaner look without a variety of charging cords strewn about the parking area.

Also, EV owners do not have to worry about their own equipment being damaged or stolen. Site owners may consider the advantages to outweigh the slightly increased installation cost.

Level 2 charging

The installation of Level 2 charging stations can be a little more involved than Level 1. At the lower end, it is as simple as installing a breaker, conduit, wire, a special receptacle such as a NEMA 14-30 or NEMA 14-50 and the wall-mounted EVSE that is plugged into the receptacle. At public parking garages or workplace parking spaces, Level 2 charging stations will frequently be hardwired with a pair of circuits and dual connections for access from two adjacent parking spaces to cut down on the cost per port. A cable management system is commonly integrated into these stations to help keep cords off the ground.

Aside from charging cars faster, Level 2 charging stations can be networked and include a credit card reader. This can allow station owners to manage who can access them and to set a price for using them. It can also make it easy to see who is using the stations, how often and how much power is being used for charging cars, etc. Being part of a network of chargers from an EV infrastructure company (such as Tesla, ChargePoint, Electrify America, EVgo, Blink and others) allows EV users to find them more easily.

Because these stations charge faster, one port can serve multiple users in a day. It is important to have a strategy in place to manage how long each user is parked and charging so that all those who wish to can access the chargers. If there is a time limit at the charging stations at an employee’s workplace, they will have to go and move their vehicle at some point during their workday. Some may not mind doing that, but others may prefer a dedicated parking space with a Level 1 charger so that they do not have to worry about moving their car before commuting back home.

Level 3 or DCFC

Lastly, DCFC stations have many of the same features as Level 2 charging. The difference is that they have high power requirements and provide dc power. They are only intended to be used for 30 minutes to an hour per vehicle by those traveling a significant distance. Some have a time limit to allow more users to charge. They are typically installed by EV infrastructure companies. It makes sense to see them installed along highway corridors, at or near gas stations, at shopping centers and coffee shops or on a company’s property operating a fleet of EVs.

Figure 3: Level 2 installation with signage at the IDEA Tempe Parking Garage. This garage has a mix of Level 1 and Level 2 with some spaces only for Becton Dickinson employees and others for public use. Courtesy: SmithGroup

Figure 3: Level 2 installation with signage at the IDEA Tempe Parking Garage. This garage has a mix of Level 1 and Level 2 with some spaces only for Becton Dickinson employees and others for public use. Courtesy: SmithGroup

Per NEC 625.41, the overcurrent protection for feeders and branch circuits supplying EV charging equipment shall be sized for continuous duty and shall not be rated less than 125% of the maximum load. Considering the output capability mentioned previously, the electrical service required for a station with one 50 kW charger would be around 80 amps at 480 V. A station with two 250 kW chargers would need a service of 800 amps at 480 V. Because of the substantial amount of power provided, most DCFC use a 480-V, 3-phase input. However, there are some available with a 208-V, 3-phase input.

The high power input for a dc fast charger may trigger NEC 625.43, which requires equipment rated more than 60 amps or more than 150 V to ground to have a disconnecting means that is lockable in the open position to be provided and installed in a readily accessible location.

Building codes and standards for EV charging

NEC: NEC Article 625 is the main standard on this topic for electrical engineers in the United States. As technology and infrastructure advances, there have also been updates to this section over the past few code cycles. For 2017, it was called “Electric Vehicle Charging System.” For 2020, it was renamed to “Electric Vehicle Power Transfer System.”

In addition to talking about EV charging, 2020 added references to “power export” and “bidirectional current flow.” This technology can allow EV owners to send power back to a load (referred to as V2L, vehicle to load), a building or home (referred to as V2H, vehicle to home or building), a utility (V2G, vehicle to grid), another vehicle (V2V, vehicle to vehicle) or all of these (V2X, vehicle to everything).

Currently, only a few manufacturers of EVs have bidirectional capability, but more are committing to it as standard in future vehicles. Similarly, few companies are developing or have developed bidirectional EVSEs for use in the United States. With this technology, there is the possibility to use EVs in conjunction with bidirectional EVSE as an optional standby system (must meet NEC Article 702) or an electric power production source (must meet NEC Article 705).

In either of these cases, the EVSE must be listed as suitable for the purpose (NEC 625.48). A hardwired connection is necessary for a bidirectional EVSE, as the GFCI protection requirement for EVSEs connected to a receptacle makes them unsuitable for power transfer in the other direction.

The 2023 NEC includes new informational notes, one of which refers to National Electrical Contractors Association 413-2019: Installing and Maintaining Electric Vehicle Supply Equipment. The term EVSE did not appear in the NEC previously. This year also allows for controls to limit the overall rating of a system through an Energy Management System or EVSEs with adjustable settings. The disconnecting means required in NEC 625.43 can be remote if a plaque is installed on the equipment denoting the location.

Figure 4: Level 2 charging installation at River People Health Center with a carport photovoltaic canopy in the background. Courtesy: SmithGroup

Figure 4: Level 2 charging installation at River People Health Center with a carport photovoltaic canopy in the background. Courtesy: SmithGroup

LEED: For U.S. Green Building Council LEED v4.1, one point is available for EVs under the location and transportation category. It involves providing charging infrastructure for EVs for on-site parking and can be achieved by adhering to one of two options:

  • Install Level 2 or greater Energy Star-certified EVSE to serve 5% of all parking spaces (or at least two, whichever is greater). Clear signage must be used to identify these spaces. The EVSE must also “be capable of responding to time-of-use market signals (e.g., price).”

  • Provide EV-ready infrastructure for 10% of all parking spaces (or at least six, whichever is greater). This means providing a dedicated electrical circuit for each space with the capacity, conduit and wire for Level 2 or greater charging, routed to an electrical box or enclosure near each required space.

For the second option, the only part missing is the EVSE. When the building owners see more demand for EV charging, they can purchase and have the equipment installed as needed. Note that Level 1 charging infrastructure does not qualify for this LEED credit.

Renewable energy

One of the reasons drivers switch to EVs is to help reduce greenhouse gas emissions and smog. As such, it is likely also important to those same people that the power source for their EV is not contributing to air pollution. Increasing the amount of power produced by renewable energy sources can help.

For more on this topic and how the use of renewable energy sources can drastically reduce the greenhouse gas emissions of passenger vehicles, read a 2021 white paper titled A Global Comparison Of The Life-Cycle Greenhouse Gas Emissions Of Combustion Engine And Electric Passenger Cars by the International Council on Clean Transportation.

Solar power

At the utility scale in the U.S., the main renewable energy sources from the greatest to least amount of kilowatt-hours (kWh) produced include wind, hydropower, solar, biomass and geothermal. Utility-scale solar PV power produced 141 billion kWh in the U.S. in 2022. Small-scale PV systems produced around 61 billion kWh. This data appears to support the general idea that wind energy is more favored by large-scale operations while solar power is scalable to a project of almost any size, including smaller commercial and residential buildings.

The remainder of this article will review the basics of solar power, specifically PV systems, which accounted for 45% of all new generating capacity in the first half of 2023. Harnessing the power of sunlight is one of the best ways to expand renewable energy production.

For reference, below is a list of building code sections that relate to solar energy:

  • NEC Article 690 Solar Photovoltaic (PV) Systems.

  • NEC Article 691 Large-Scale Solar Photovoltaic (PV) Electric Power Production Facility.

  • NEC Article 705 Interconnected Electric Power Production Sources.

  • International Building Code Section 3111 Solar Energy Systems.

  • International Fire Code Section 1205 Solar Photovoltaic Power Systems.

  • International Energy Conservation Code (IECC) Appendix CB: Solar-ready Zone — Commercial Provisions (not mandatory unless the jurisdiction specifically adopts the appendix).

  • IECC Appendix RB: Solar-Ready Provisions — Detached One- and Two-family Dwellings and Townhouses (not mandatory unless the jurisdiction specifically adopts the appendix).

  • International Green Construction Code 3.2 On-site renewable energy systems.

LEED v4.1 has up to five points available under the energy and atmosphere category when on-site renewable energy is produced or when off-site renewable energy is procured for all or part of the building’s annual energy use.

PV installations

It is important to understand the objective of a PV project before beginning design. There may be goals for LEED certification or net zero energy, to meet local codes, to eventually save money on the power bills or to show that renewable energy is important to an organization.

Knowing that purpose can help determine the extent of the PV for the project. It is also important to establish whether it is to be a grid-tied or a standalone system. Refer to NEC Article 690 for specific requirements for solar PV systems. It has also been revised significantly in the last few code cycles, so pay attention to the language used in the version relevant to the project.

Figure 5: Above-roof structural steel framing for photovoltaic at the University of Illinois at Urbana-Champaign, Electrical and Computer Engineering Building. Courtesy: SmithGroup

Figure 5: Above-roof structural steel framing for photovoltaic at the University of Illinois at Urbana-Champaign, Electrical and Computer Engineering Building. Courtesy: SmithGroup

At a basic level, each PV installation will need the following:

  • Solar panels/PV modules.

  • Racking system.

  • Inverter(s).

  • Conduit and wiring.

  • Connection to electrical equipment.

Solar panels

Solar panels convert light to dc electricity via semiconductor technology through the PV effect, which means the creation of voltage and/or current in a material upon exposure to light. PV cells are combined in series and packaged together in a waterproof PV module. The modules are connected to each other in series to form a string and multiple strings are connected in parallel to create an array. Obviously, this is the electricity-generating part of a PV system that is easily identified wherever it has been installed.

Racking system

The support structure for the PV modules is commonly called the racking system. Structural steel framing will be a common element of the racking system whether it is a rooftop, ground mount or carport system. For flat roofs, a ballasted system — one that uses heavy material to counter wind load and hold the panels in place — is also an option. Each has pros and cons that are to be weighed during design. Analysis of the weight and wind loads by a structural engineer is also crucial. The spacing, tilt angle, shading and direction the PV modules are facing, as well as the location, should all be considered as they will affect the energy production of the system.

Carport systems are especially desirable in hot climates due to the shade they provide. If installed in conjunction with EV charging stations, they can also provide visual assurance to EV owners that at least part of the energy used to charge their car is from the abundant renewable energy provided by the sun.

Inverters and wiring

Inverters convert dc to ac power (the opposite of when providing power to an EV). They can be grouped into three types: micro, string and central. Micro inverters are implemented at the module level so will be rated at a wattage higher than a single solar panel, which may be from 300 Watts (W) to 700 W. A string inverter is connected to strings of PV modules and can be rated from 3 to 50 kW or more. A central inverter is a large inverter rated from around 100 kW up to 1 megawatt (MW) used for utility-scale systems and is typically implemented in conjunction with combiner and sub combiner boxes that all feed into it.

A PV system will have a mix of dc wiring and ac wiring, the extent of which depends on where the inverter is in the system. All wiring methods must conform to NEC 690.31.

Electrical equipment connections

Some of the electrical equipment needed on the dc side may include:

  • Combiner boxes: These connect multiple strings in parallel and include a fuse for each string.

  • Fused disconnect: This is a disconnect for the PV array located between the array and the inverter.

On the ac side, electrical equipment may include:

  • Fused disconnect between the inverter and the ac power distribution panel.

  • Utility service disconnect between the utility and the ac power distribution panel. This is not required in all cases and may instead be a breaker in an electrical panel.

Figure 6: Carport solar photovoltaic installation at DPR Construction’s Arizona headquarters. Courtesy: Gregg Mastorakos, Mastorakos Photography

Figure 6: Carport solar photovoltaic installation at DPR Construction’s Arizona headquarters. Courtesy: Gregg Mastorakos, Mastorakos Photography

What else do you need to know about PVs and EVs?

There is much to consider and coordinate when designing a PV system that is outside the scope of this article. Here’s a nonexhaustive list of what was not covered:

  • Rapid shutdown requirements for PV systems. See NEC 690.12 for this very important requirement for a readily accessible switch that reduces the shock hazard for emergency responders.

  • Roof space coordination, including access, pathways, smoke ventilation, penetrations and equipment locations.

  • Modeling the PV system for energy production estimates in kilowatt-hour and the array size in kW.

  • String sizing, including calculations for the maximum voltage (NEC 690.7).

  • Circuit sizing and current (NEC 690.8).

  • Overcurrent protection (NEC 690.9)

  • Sizing an inverter: A typical dc to ac ratio is between 1.2 and 1.25, meaning the inverter is slightly undersized compared to the PV array. This is done to account for various system losses and to save on equipment costs. If the ratio is too high, then power clipping occurs when the dc power produced is higher than the inverter’s rating.

  • Utility interconnection, whether at the load side or the supply side: coordinate early with the power company and meet code requirements (NEC 705). This will significantly affect how the system is designed.

  • Incorporating battery storage into the system.

  • Building-integrated PV.

Though not covered in this article, federal and utility incentives are available for both solar and EV charging installations that can help them to fit in a project’s budget.

The EV and renewable energy technologies are not new; however, they continue to expand in exciting ways. Synergizing the two is an excellent way to help secure a greener future. Each EV charging station that is installed makes a switch from a vehicle with an internal combustion engine to an EV make even more sense. Dependence on fossil fuels is reduced with each PV installation. As design professionals become more familiar with designing these systems, owners will become more comfortable including them in their facilities.


Author Bio: Dan Peterson, PE, is a senior electrical engineer at SmithGroup with more than 17 years of experience designing electrical systems.