EV Charging and the Effects of Cold Temperatures

At cold temperatures, electric vehicles struggle to charge. This is due the internal resistance of the battery, as represented in the illustrated figure below. The electrons are stored in the battery and when the battery is in use a chemical reaction occurs, as a result, a current is produced, which does the useful work of the system. However, that chemical reaction could be severely impacted by cold temperatures. Temperature is a measure of heat at molecular level and heat is the movement of molecular particles in the surroundings. Considering this, when the temperature drops, the chemical reaction slows down because of the decrease in molecular motion caused by colder temperatures. The lower the temperature, the higher the internal resistance of the battery. With greater battery resistance, more current will be required to charge the battery.

Image result for internal resistance of the battery

Figure 1: working of battery                                                        Figure 2: internal resistance of a battery

The relationship can be understood through Ohm’s law, as V=IR. Both V (voltage) and I (current) are directly proportional to each other in this scenario, but current (I) has an inverse relation with the resistance (R). An increase in the resistance will decrease the current, making it harder for a charger to feed the battery.

As per reports made public by Yutaka Motoaki and his colleagues, data was analyzed from a fleet of Nissan Leaf Electric Vehicles operated as taxis across 500 Direct Current Fast Charge (DCFC) contingencies in temperatures ranging from 15 to 103 degrees of Fahrenheit. It was found that at 77 degrees, a DCFC charger was able to charge the battery from zero to 80 percent capacity in just 30 minutes, which is a normal fast charging rate, but at 32 degrees it was found that some extreme degradation in charging time occurs. Specifically, the battery’s state of charge was 36 percent less in the same amount of time, and with more drops in temperature, the longer it took to charge the battery. The charging rate of the battery was approximately three times slower in colder temperatures compared to the warmer conditions. Based on Motoaki collected data, it can be inferred that an EV owner may experience longer charging times due to cold weather. Because of this, high elevation regions and the northernmost areas of the United States are considered as the places where cold temperatures could influence charging time the most.

Furthermore, it was concluded by Motoaki that colder temperature only impacts EV drivers in a certain way. For example, those who charge there EVs at home in the warm garage and use them for commuting in a single charge range might not experience much inconvenience as compared to charging them in a colder environment.

Motoaki’s research gives rise to the question faced by both EVs owners and charging infrastructure providers. For example, the location or abundance of charging framework may need to be different in colder regions, and electric utilities might consume electricity at different levels based on seasonal changes in climate.

According to Motoaki the research is based on a certain type of vehicle (Nissan leaf) and a single type of the charging system, a 50KW DCFC. Climate temperatures may have a different result for Tesla vehicles or EVs from manufacturers other than Nissan. Different manufacturers and models have different system designs in the vehicles they produce. Tesla uses Battery Thermal Management (BTM) technology which preheats the battery before charging. This allows the battery to be charged at more optimal level.

Charging Stations:

Electric vehicle charging stations control the energy transfer to the battery of the EV. Generally, charging is based on power levels and the charging mode. The SAE (Society of Automotive Engineers) and the International Electrotechnical Commission (IEC) have categorized electric vehicle chargers based on their various power levels and charging modes. With respect to power level, there are three basic levels of charging stations that are available to charge an electric vehicle. The battery capacity of first EV models released fluctuates from 20 to 60KWh, but newer models, such as the Tesla Model X and the Ford Lightning have battery capacities of 100kWh and 150kWh respectively.

Level 1 Chargers: Comprises of a single-phase AC system with a max current of up to 3 kW. To charge a 20 kWh electric vehicle it would take an estimated 7 hours to fully charge the battery. Level 1 chargers require a ground fault interrupter and over current protections to avoid mishaps. These kinds of charging stations are located in domestic households and at workplaces.

Level 2 Chargers: These chargers consist of 3 phase alternating current (AC) with a charging power of up to 24 kW. It takes roughly 2 hours and 45 minutes to fully charge an average 60 kWh EV battery. For both level 1 and level 2 chargers, the actual connector used to plug an EV in comes in the form of either type 1 or type 2 connector, with the exception of Tesla models which have their own unique connector. Type 1 and 2 converters can be purchased to make Tesla models connectable on non Tesla chargers. Level 2 chargers are typically located at public charging stations hosted on hotel and other public properties. They can also be installed at home if the residence is equipped with typical 240v capabilities.

Level 3 Chargers: Level 3 charging stations are based on direct current (DC) and have a power output of up to 300 kW. These chargers provide a fast charging option and can charge smaller EV batteries in 20-30 minutes. Lever 3 charging connectors, also referred to as Direct Current Fast Chargers, fall under SAE J1772, CHAdeMo, and IEC 62196 type 2 standards (as shown in the pictures. Fast charging stations are typically connected directly to the grid and have transformers and rectifiers to convert alternating current (AC) into direct current (DC) voltages to charge EVs batteries. Ideally, Direct Current Fast Chargers (DCFCs) can be placed at locations alongside highways, as long as the grid is equipped to handle their demand, to quickly charge EVs. They can essentially serve as electric fuel stations, similar to conventional gas stations. DCFC facilities will be essential to help grow the use of EVs. It should be noted that fast charging comes at higher costs as it requires stronger currents and more advanced electrical infrastructure. The faster charging of batteries also has also been found to decrease the lifetime and capacity of batteries.

Figure 3: Charging connectors: IEC Type 4/​CHAdeMO (left); CCS Combo 2 (center); IEC Type 2 outlet (right)

Figure 4: EV charging block diagram

Locations for charging stations:

The location of EV charging stations is an essential detail to consider. For example, power losses can be greatly reduced if a charging network is established near grid substations. Charging station capacity and available locations to charge multiple electric vehicles are some of the core parameters in the analysis of the economic viability of electric vehicles. When an electric vehicle is connected to the station, the control system works on the basis of several variables. These include the state of charge (SOC) of the battery, current levels, and the energy cost from the grid. Electric vehicle charging stations are becoming more common, but charging infrastructure is a large barrier to adoption in the EV space. Another important aspect to consider is charging the time of the car. If a station is full of cars, wait times can add up as drivers wait until the electric vehicles ahead of them in the queue have completed their charging. Consequently, when choosing a charging station, it is vital to select the least loaded, or busy station to reduce the waiting time and grid demand.

Charging stations in New York:

The New York State Energy Research and Development Authority (NYSERDA) announced financial grant awards in 2012 and 2013 to dozens of organizations to install Level 2 electric vehicle charging stations, or Electric Vehicle Supply Equipment (EVSE), across the New York State. NYSERDA and New York State established a goal to construct a state-wide network of up to 3,000 public and workplace charging stations to support up to 40,000 plug-in vehicles on the road by 2018. As of July 2021 there are over 2,500 level 2 and 3 charging stations across the state containing a total of over 6,200 charger plugs. These stations serve the 15,000+ EVs registered in the state. To assist the success of the program New York State has assisted with installation costs, revised regulations to shed light on charging station ownership rules, and lead research and demonstration projects on new EV technologies and policies. A large majority of the EVSE projects have been funded by NYSERDA, with additional funding available and more likely to be approved moving forward.

Figure 5: EV charging stations in New York state

Adverse Effects of Winter on Charging Stations in New York:

As discussed, cold temperatures can negatively influence EV driving range and charging capabilities. In addition to equipment and car efficiency issues, New York State’s colder winter months can make charging cords less flexible and more challenging to properly coil. The snow accumulation that is common in several areas of the state can lead to issues with snow plowing and equipment maintenance, as shown in figure 6. Without adequate consideration of winter conditions throughout the planning phase, the framework could potentially obstruct plowing of the parking spaces and lead to equipment damage. The use of retractable cord systems can significantly reduce the potential for plow damage. In addition, all stations should be cleared of snow regularly, to make them visible and convenient to use.

Advanced planning can go a long way toward reducing installation and maintenance costs. Successfully locating stations in a convenient spot to both EV drivers and maintenance personnel can prevent future issues. As more stations are installed, electricians and installation contractors are increasing their knowledge on EV technology and have grown their insight on installation best practices.

Figure 6: winter impact on charging station in New York

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