Solar panels create dc power.  Electric bike motors also use dc power, but bike chargers are designed for the ac power provided in a home.  They, convert ac power to dc power, so battery chargers are ac power. Charging the battery with a standard charger would require converting to ac power and then back to dc power. Forums on the internet say that there is no good way to change from dc to ac current and that I would lose a significant amount of power in this conversion. However, one website said that a pmw or mppt can charge a dc battery with  dc current, avoiding the loss of power from converting dc to ac and then back to dc. DC also has less risk of shock, which is good because I am in no way an electrician.

        We used an mppt because the mppt converts the power it receives into the exact  volts and amps required by the battery.  Our 52 volt battery can accept between 2.5 and 10 amps and exactly 58.8 volts.  The mppt also stops the current from flowing when the battery is full to keep it from overcharging and prevents reverse charging where the panels might otherwise draw power from the battery when there is no sunlight. 

         After doing the trip, I now think that a pmw is better because the mppt is programmed and only goes up to 48 V and we had a 52 V battery. If we had dumber technology - the pmw - whatever we would give it, it would condition.

        At first, we bought a cheap mppt and connected it to a solar panel, and it worked great - we were getting power! This mppt only went up to 10 amps, which was not enough for the amount of current we generated with the five solar panels.

       I found that if we run the solar panels in parallel the amps are added and the volts are constant, whereas in series the volts are added, and the amps are constant. In series, the 18.5 V x 5 solar panels equals 92.5 V. This would be a lot of volts and most mppts do not handle this many volts. Also, if one solar panel stops working in series, the whole current stops because amps are constant. Therefore, we wired the panels in parallel.

       Our mppt can handle 60 amps but not as many volts. Another mppt said it could handle 100 amps but did not specify a maximum voltage.  It was only 20 dollars. We hooked it up and it lit up for a few seconds before going dark (we burnt it out). Since the cheap one failed, my dad and I decided to get a heavy duty one from the American company Renogy.

       We learned how and then wired together our solar panels to produce between 25 and 35 amps and 18.5 V. Higher volts means thicker wires so we used 12 awg wires, which are 1.65mm in diameter and are rated for a maximum of 20 amps, far under the 5.5 amps flowing through most of our wires.