*6.5. Ongoing Development*

Currently, the functionality of the e-bike wireless charger has been proved in the laboratory. After this, measurements of the electromagnetic field radiated by the charger are going to be performed to verify the compliance to the International Commission on Non-Ionizing Radiation Protection (ICNIPR) that ensures safety to human beings [55]. The radiated magnetic field of the charger is expected to be within the limits for general public (27 μT) since the coils are placed on top of each other, and there is no gap in the free air. This is unlike in electric cars, where the coils have a flat arrangemen<sup>t</sup> with a larger gap [56]. Moreover, the rated power of this charger is considerably lower than the 3.3 kW minimum for electric cars as per SAE J2954 [57]. Hence, a lower radiated magnetic flux can be expected. Second, a kickstand with structurally integrated magnetics is being developed, which is sturdier for a longer lifetime.

#### **7. Environment Integrated PV System**

The solar panels, battery storage, and the AC, DC, and wireless charging are combined together to form an Environment Integrated PV system (EIPV) built on the university campus, as shown in Figure 2. Three cabinets of 1.39 m by 0.72 m are located inside the EIPV, which are used for storing the battery and the associated electronics for the inverter and MPPT converter and the DC e-bike charger and control circuitry, respectively. Integrating all the electronics and batteries inside the EIPV saves approximately 3 m<sup>3</sup> space that would have otherwise be required for external cabinets to house all the electronics and batteries. The key advantage of the EIPV is, therefore, the mechanical and electrical integration of all components resulting in a single structure that combines aesthetics, modularity, safety, functionality, ergonomics, and usability.

Figure 13a shows the solar MPPT converter, bidirectional inverter, grid islanding device, control, and protection circuity for both devices. Figure 13b shows the DC-DC converters for the e-bike DC charging, charging measurement circuit, and the Raspberry Pi central controller responsible for communicating with all the devices. The Raspberry Pi also reads data from all devices like

the VICTRON system, DC chargers, and weather station and logs them centrally into an Internet server [58]. The charging current and voltage are displayed on the monitor inside the e-bike station for user convenience.

**Figure 13.** (**a**) Grid Inverter, PV MPPT charger, protection, and monitoring circuit. (**b**) DC-DC converter, control, and protection for DC charging of e-bike.

#### *7.1. Energy Yield of the PV System and Load*

Figure 14 shows the measured monthly energy yield of a 2.6 kW PV system for one year over the period of October 2018 to September 2019. A total of 2378 kWh of PV energy is produced in this period, corresponding to a daily average of 6.5 kWh/day. The extreme differences in the PV generation between the seasons can be seen with 40 kWh generation in December compared to 315 kWh in June, up to an eight times difference. In terms of daily energy yield, there is as much as a 25 times difference, varying from 0.64 kWh/day to 15.4 kWh/day. It is also important to note the difference in yield between Figure 14, and Figure 5b due primarily to the difference in the meteorological conditions of 2013 and 2018/2019.

**Figure 14.** Monthly energy yield (in kWh) of the 2.6 kW PV system for the period of October 2018 to September 2019 and the corresponding load demand including losses (in kWh).

In terms of load demand, two e-bikes from the electrical engineering faculty are regularly charged at the location with occasional demand from other e-bikes, e-scooters, and the Twizy. The annual demand of the station was much lower than the theoretical analysis and was found to be 561 kWh/year or 1.5 kWh/day on average. The lower demand was due to a much lower baseload (limited use of light, converters going into sleep mode) and a lesser number of e-bikes than anticipated. The load also exhibited a seasonal variation primarily due to variation in usage of e-bikes with higher e-bike usage and charging in the summer.

From an economic perspective, an annual yield of 2378 kWh of PV energy results in a revenue of ~595€/year, assuming a net-metered feed-in tariff of 0.25 €/kWh. Charging a 500-Wh e-bike battery costs about 0.125 €/charge. Due to the custom design of the station, the net cost of all the electronics, including the PV, battery, and chargers was approximately 15,000 €, which resulted in a payback period of ~25 years. It must be noted that this does not include civil material costs of constructing the station and the cost of hours for research and development, which are significant [9]. To reduce the costs, the options can be to provide only AC charging, not including a battery, installing the PV on the rooftop, and using a single converter for both MPPT and grid feeding.

#### *7.2. Power Management of the Battery*

The integrated battery storage can be controlled with numerous power managemen<sup>t</sup> strategies based on the PV generation and grid conditions. One such strategy that has been implemented currently is shown below.


Based on this power management, Figure 15 shows the measured power profiles of the PV, battery, grid, and the battery SOC over one week in May with a few cloudy days. First, it can be observed that the solar power is used to supply the load on sunny days, feed at least 400 W to the AC grid, and to charge the battery from 50% to 100% SOC. Second, there is a dip in the PV generation in the afternoon due to shading from the nearby faculty building, as seen in Figure 5. Third, when the solar production is low/zero (especially in the evening and night), the battery discharges and feeds power to the AC grid. Lastly, when there is not enough solar production and if the battery SOC ≤ 50%, no power is supplied to the AC grid.

**Figure 15.** Measurement over one week in May: (**Top**) the generated PV power and power fed to the grid. (**Middle**) battery charging power (positive), discharging power (negative), the load, and power losses. (**Bottom**) SOC of battery.
