Load Managing EVs in Smart Buildings

Although most of the vehicles on the road are conventional ICE cars, EVs are making inroads into this market. This will cause grid issues as the additional loads the electric vehicles will require are likely to cause additional stress on infrastructure. How can society prepare for this and avoid the problem?

There will need to be many more charging stations, particularly as “range anxiety” is one of the major reasons for not changing to an EV. Many people will opt to charge their vehicles at home. Can large residential buildings cope with the loads?

The answer is yes, providing the load management is sophisticated enough.

An electric vehicle generally charges at a 3-phase charging station with up to 11 kW, if the driver hasn’t reduced the charge limit manually. So, if one EV needs 11 kW charging power, two require 22 kW, and 50 would be needing 550 kW. That is just the EVs. Assuming the 50 residential consumers are using an equal amount of power and we can double it to 1100 kW.

However, there are some practical factors which can help us. All the EVs will probably not be charging at the same time at full capacity. In the same way that all fifty apartments will not have the stove, oven, washing machine, home cinema and other appliances running all at once. The power supply calculations take account of this. Based on the empirical values of the network plus a security margin, so that peak usage will be met with sufficient power.

In the example of fifty EVs with 11 kW charging power, the diversity factor is about 28 per cent. Instead of the projected total of 550 kW we actually need 155 kW of input.

If the parking garage of this apartment block has sufficient charging points for 20 or more EVs to charge simultaneously, the power load would shoot up. To avoid overloading the building’s electrical system, a control unit would have to limit how much power could be used for charging.

There are two types of load management available: static and dynamic load management. In static load management, the charging stations have a fixed upper limit. This maximum power is equally distributed among all plugged-in cars. This is to ensure the load on the building, including the residential load, is not too high.

In dynamic load management, the charging station’s control unit interacts with the building’s energy metering system. It thus reacts in real time to the energy requirements in the residential apartments—which always take priority—and allots the remaining power to the plugged-in vehicles. This intelligent load management allows management to further reduce the connected load in new buildings and to utilize it more efficiently. For example if many home appliances are used in the early evening, less power is available charge the electric cars. As the energy demand in the apartments drops at night, the EVs can use more power and will be sufficiently charged in the morning. Power peaks are thus avoided.

An example of this system is in the Austrian city of Vienna. KEBA Energy Automation has launched the project Urcharge (Urban plus Charge) in partnership with the energy provider Linz AG, the housing association Neue Heimat, the Vienna University of Technology, and the environmental management agency ETA. In a six-month project, it proved that it is possible to keep fifty EVs and one hundred charging stations in a large residential building in constant use without increasing the power input. The most important findings of Urcharge were that power could be supplied to the building’s electrical system at all times and that the occupants did not notice the load management’s software's application when charging their electric vehicles so the power needs of all customers were satisfied.