Is Level 1 (120V) charging less efficient than Level 2 (240V) charging?

The charging efficiency refers to the proportion of electricity obtained from the electric grid that is successfully stored in the vehicle's battery, expressed as a percentage. There are two main components that affect this efficiency, delivery losses and the efficiency of the electric vehicle charging system.

Delivery Losses

This is the energy that is lost on the way to the electric vehicle, this inefficiency is usually extremely low, especially if the charger is installed close to the electrical panel.
No electrical equipment is 100% efficient, in other words there are always some energy wasted and not used directly for the purpose that the equipment was designed for. Electric vehicle chargers are no different, very minor energy is wasted inside the charger to run it's electronic components such as the display, card reader, connectivity components and etc.

We recommend you look for electric vehicle chargers that are 'Energy Star' certified.

A Level 1 outlet allows almost all of the energy in the wire to be transferred directly to the vehicle, whereas a Level 2 charger may have internal components that consume power, such as LED screens and card readers. Load-balanced Level 2 chargers, in particular, which require constant communication to optimize power delivery, are less efficient than dedicated outlets, which are simpler and more straightforward.

Electric Vehicle Losses


Charging efficiency of the vehicle depends on two important factors:
  • Ambient Temperature
  • The vehicle's "Battery Management System (BMS)"

Ambient Temperature

Batteries have a sweet spot when it comes to optimum charging temperature. In climates where the ambient temperature is lower/higher than the battery's optimum charging temperature, the battery management system inside the vehicle will try to get the batteries to that optimum temperature and hence in the process wastes some energy. This process happens for any level of charging regardless of how fast or slow the charger may be.

Battery Management System (BMS)

The efficiency of the charger ultimately is defined by the vehicle's BMS. The external EV chargers don't do anythings magical to be more efficient, the only task of an EV charger is to provide the exact amount of power that is requested from the BMS, nothing more nothing less! It's the BMS that can have inefficiencies in it's design that would result in the vehicle's batteries receiving less power than was delivered by the EV charger.

There has been a study done in 2014 on a Nissan Leaf (one of the first EVs that hit the market) that mentions that "On average, Level 2 charging was 5.6% more efficient than Level 1 (89.4% vs. 83.8%)".

Efficiency becomes irrelevant when the car gets fully charged during the time it's plugged in. A charger with an efficiency of 89% is good as a charger with 81% efficiency if they both fully charge the vehicle before the driver gets back.

That's why the research article also mentions that the impact of the efficiency differences is biggest for short term chargers, not for overnight/daily charging.

"These results suggest that the impact of the observed efficiency gains may be biggest at public charging stations, where charging times tend to be short and climatic conditions more variable, rather than residential charging."

In residential settings where residents pay directly for the electricity they use, the inefficiency of the charger may be of less concern to the property owner because they will receive payment for the amount of power consumed by the vehicle, regardless of how inefficient the charger may be.

Keep in mind, given the 5.6% inefficiency, the difference in the cost of electricity is about 7 cents per day for a full charge which is negligible for the electric vehicle owner.

A Level 2 charger installation in a property incurs significantly higher ongoing costs compared to a Level 1 outlet. Ultimately, the higher cost is passed on to the resident, resulting in a higher usage rate. As a result of this, residents typically prefer a slightly less efficient Level 1 charger with lower usage costs over a slightly more efficient Level 2 charger that comes with higher usage costs.

In other words, given the same of power is delivered to the vehicle to get it fully charged, the client may be paying ~7 cents more per day on a level 1 charger due to inefficiencies but has to pay ~50 cents more to use a Level 2 charger due to higher maintenance/service costs which is passed on to them.

The researchers concluded by stating that additional studies on a greater number of vehicles are necessary to obtain a more precise outcome.

"Future research should consider the relative efficiency of DC Fast charging and wireless charging, as well as how charging efficiency varies among vehicle models"




What about efficiency of the power grid itself?


One of the most important factors this research fails to take into account is the fact that higher power charging puts a lot of pressure on the power grid itself which makes the overall system a lot less efficient. So even though the effective power that the vehicle receives may be slightly higher for the Level 2 charger but the adverse effect of the high power Level 2 charger on the power grid is detrimental.

To combat this, utilities usually recommend/fund smart charging systems that can balance the load so the pressure on the grid can be reduced. These so called 'load-balanced' solutions often provide lower than Level 1 (120V) charging speeds which defeats the whole purpose of installing a Level 2 (240V) charger in the first place.


Usability of the chargers


Outlets are more usable in colder climates because they have fewer moving parts

The usability of the chargers are also often neglected when it comes to ambient temperature comparisons. Because a charger that has a built-in cable is more prone to freezing and hence becoming unusable than a simple outlet in a cold climates.

Outlets have been successfully field tested for decades in cold cities in which they are called block heaters: