*1.2. State-of-the-Art*

The most common design for a solar e-bike charging station is to use the AC low voltage grid for power exchange between the PV and the EV. A solar inverter with maximum power point tracking (MPPT) feeds the solar power to the AC grid [15–19]. A standard e-bike AC power adapter is then used for e-bike charging. Even though there have been recent studies to simplify the complexity of the e-bike power adapter [20,21], the disadvantage of such designs is due to the unnecessary power conversion from DC to AC and back, even though both the solar panels and e-bike battery operate

on DC [18,22,23]. DC charging the e-bikes directly from the PV would reduce the power conversion stages, and it would not require the cyclists to bring the power adapter but only requires a DC cable. However, e-bike DC charging is still manufacturer-specific, and, therefore, no standard exists except for the consensus on typical battery voltage levels of 24 V, 36 V, and 48 V. The challenge is primarily due to lack of standard connectors and communication protocols for charging control and safety that exist between the power adapter and the bike battery, which varies across manufacturers.

**Figure 2.** (**a**) Front view of solar e-bike charging station showing solar panels. (**b**) Back view showing the charging status display screen, the e-bikes, and Twizy EV charging.

The next step for a more user-friendly and safer experience in e-bike charging would be the transition from plug-in charging methods to wireless charging. This solution was already proposed in Reference [24], where a 100 W e-bike wireless charger has been demonstrated to have an efficiency above 90%. A considerable number of e-bike wireless charging systems use flat-air coils to realize the power transfer [24–28] because they are lightweight. However, air coils might produce a magnetic field higher than the safety limit for the general public in their proximity [29]. Other solutions use a ferromagnetic core to improve the coupling between the coils [30–34], but, at the same time, they introduce extra elements on the e-bike, which do not have any other purposes. In Reference [35], a review of solar-powered wireless charging systems for light electric vehicles is presented and shows 400 W–5 kW designs operating at a resonant frequency in the range of 8.7–100 kHz with a 2.8–20 cm air gap and an efficiency in the range of 75–95%.

Lastly, two key features that distinguish the charging station are the physical design of the structure and the use of energy storage. The usual method to install solar panels is to place them on the parking lot or the rooftop or façade of buildings, while the less common technique is to use a dedicated solar park-port [15–17,36]. The critical design tradeoffs are the cabling losses, construction/installation costs, accessibility, and need for large electrical cabinets to store the electronics. This becomes even more relevant for charging stations with battery storage due to their large size and weight. Most of the existing e-bike charging stations lack an integrated battery storage. This prevents the station from being used in an off-grid mode, especially on days where the solar insolation is very low during the year [18].
