# Design of a Modular Energy Production-Storage System for a Sustainable Bicycle
## 5 Conclusions  
In this paper, a modular integrated system has been designed and built capable of producing energy at any speed (even at low speeds of 9 km/h) and storing it for later use. The system is capable of charging its own batteries and powering the devices that are connected to the USB charger from a speed of 9 km/h. An outstanding feature of this design is the modular integration of the different modules: dynamo, USB charger, batteries, solar panel, etc. From a construction point of view, the system allows the simple and efficient integration of all components using only one extension cable. Finally, the end product is ergonomic, easy to use, and priced below the market. A Li-ion battery (IMR 26650) with a capacity of 5250 mAh has been used with a voltage of 3.7 V, and at a price much lower than the market price (approximately forty-five dollars). This battery allows more than 500 charge cycles. Although LiFePo4 batteries offer much higher life cycle values, they do so at the cost of a sacrifice in weight and volume [51,52].  
Other very valuable aspects of this design have been the final appearance (maximum integration in the bicycle with the least visibility of the product); the ability to replace batteries by the user; the Bluetooth connectivity; and the power output (about 2 A of output are supplied). Although the total weight is 0.2 kg, this is similar to the model with the highest output current (the Forumslader provides 2.9 A), although in the design presented, the capacity of the batteries has been doubled. The modular integration with different devices such as the battery pack or solar panels also stands out. Current models on the market do not perform this integration.  
The design can be improved in the future by creating a tailored solar panel. Also, the appearance can be improved by better encapsulation and USB connection while maintaining a degree of IP protection. The creation of an App for mobile devices would be another added value to the USB charger. This would require an electronic redesign to integrate a Bluetooth communication module. Finally, the cost of the battery module must be reduced because, although it offers some installation features on the bicycle that conventional products do not have, this device is slightly above the market value.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14020523/s1](https://www.mdpi.com/article/10.3390/app14020523/s1)]([https://www.mdpi.com/article/10.3390/app14020523/s1](https://www.mdpi.com/article/10.3390/app14020523/s1)).  
Conceptualization, J.S.V. and J.A.V.-M.; methodology, J.S.V., F.C. and J.I.M.-M.; software, J.A.V.-M.; validation, J.S.V., J.A.V.-M., F.C. and J.I.M.-M.; formal analysis, F.C. and J.I.M.-M.; investigation, J.S.V. and J.A.V.-M.; resources, F.C. and J.I.M.-M.; data curation, J.A.V.-M. and J.I.M.-M.; writing--original draft preparation, J.S.V., J.A.V.-M., F.C. and J.I.M.-M.; writing--review and editing, J.S.V., J.A.V.-M., F.C. and J.I.M.-M.; visualization, J.A.V.-M. and J.S.V.; supervision, F.C. and J.I.M.-M.; project administration, F.C.; funding acquisition, J.S.V. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Institutional Review Board StatementNot applicable.  
Informed Consent StatementNot applicable.  
Data AvailabilityStatementData are contained within the article and supplementary materials.  
Conflicts of InterestThe authors declare no conflicts of interest.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Model** & **Aesthetics** & **Capacity** & **Current** & **Weight** & **Battery** & **Solar** & **Stable** & **Drag Force** & **Bluetooth/App** & **Price** & **Total** \\ \hline Final Design & 2 & 4 & 2 & 1 & 1 & 1 & 1 & 0 & 4 & 16 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Designed model evaluation scores.