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How Much Power Do We Need?
A rider at the Tour de France level puts out 300 W at a high pace and our bike is heavier, but we could each put out 125 W consistently. After looking at formulas on power vs. speed online, we found the ratio is a logarithmic curve. My dad’s electric bike is 350 W and he said he can go 20 mph all day without using full power (his bike is lighter). We decided if we can sustain 400-600 W in addition to the power we generate, then we could maintain 25 mph. Therefore, we want an average 500 W for the motor.
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Converting sun power to dc current has inefficiencies: a 100 W panel is never perfect, so we expected about 75% efficiency on a sunny day. It would lose another 5% in the mppt and the wires. If we have 5 or 6 panels, this means we would get about 350 W or 425 W coming into the system. Then, we would lose another 5% going into and out of the battery. If we use 500 W an hour and collect 300 W an hour, then as long as we have a big battery and charge it while we are resting, we should have enough power. We planned to ride 6 hours a day and rest 4 hours a day, which means 600 W for 6 hours a day going 25 mph = 125 miles traveled a day. Based on this I conservatively estimated we could go 110 miles a day. With this in mind, we built the trailer to handle 5 panels. These panels are 100 inches long when put next to each other, so we built the trailer to be 96 inches long and 36 inches wide using 8 and 3 foot aluminum pieces. As a result, the panels hang two inches off of each side.