The Municipality of Maribor, Slovenia, commissioned experts from the University of Ljubljana to prepare a study about the best economic and technical solutions for the electrification of a bus line in Maribor to achieve sustainability goals and improve air quality in the city.
The main results from the study are as follows:
- All associated costs for the electrification of bus line No. 6 in Maribor are lower than the purchase of new buses with diesel engines. The purchase of an e-fast charger for e-buses is more efficient than slow charging solutions, such as overnight charging of e-buses, considering the length and altitude difference of bus line No.6. This is the most reasonable way is to install two fast charging stations with at least 150kW or one charging station with at least 300kW. For occasional charging, the most efficient way is smart charging, which allows the level to be maintained in the appropriate phase to keep the battery in good condition. Fast charging stations at bus route termini should allow top-down charging with pantographs.
- The bidder for e-buses should offer to calculate the cost for the entire life cycle of the battery. The e-bus procurement tender should allow for sufficiently neutral technological requirements to allow bidders to choose different technological solutions that offer the most favourable battery and bus life cycle within the tender. The study analysed the characteristics of different types of batteries, namely LTO (Lithium - Titanate), NMC (Lithium Nickel Manganese Cobalt Oxide) and LMP (Lithium Metal Polymer).
- NMC batteries represent the most widely used batteries among the technologies analysed. They achieve lower prices per unit of stored energy, which means that they represent the cheapest initial investment cost in the acquisition of electric busses compared to LTO or LMP batteries for the same capacity. Due to their medium charging capacity, NMC batteries are used for both fast charging cases and a combination of fast and overnight charging. NMC batteries are not recommended for bus operation on longer daily routes and over longer periods of time, as a high depth of battery discharge leads to accelerated degradation of the battery cells.
- LTO batteries have a lower energy density, the main advantage is a lower degree of degradation, which leads to a longer battery life and allows high currents and thus charging and discharging power. The power density of LTO batteries is higher compared to NMC or LMP batteries, which means that they can be charged at higher powers with much lower absolute battery energy. This means that the actual capacity of LTO batteries is also about three times lower compared to batteries using NMC as cathode material or solid electrolyte batteries.
- Solid electrolyte batteries (LMP) represent a technology that achieves high or very high energy densities and thus high specific capacities. LMP batteries achieve a higher number of cycles and use at higher discharge rates. Due to the characteristics, which include low specific charge rates, the potential for high depths of discharge and the specifics of maintaining the operating temperature of the batteries, the use of LMP batteries in systems with night charging makes sense.
The original article was published on the Interreg EfficienCE webpage on 09 April 2021.
Photo: Municipality of Maribor