Physics 310 Spring 2019
ARRAY DESIGN
In order to have our 750W electric assist motor running off of solar, we need to look at the battery storage capacity and energy use. Currently, we have a battery that is 48V and is rated at 11Ah. This is true if we match the manufacture's testing which is charge/discharge the battery at 2.2A for 5-6 hours.
​
Donette is able to use her battery, on average, for 4 hours. This means that her average power use is 132 Watts since power is energy over time. Energy stored in the battery is (48V)*(11Ah) = 528 Wh. This energy divided by Donette's 4 hour use is the average power we need to be able to supply with the array, 132W. This makes our total energy use 528 Wh/day.
​
In San Luis Obispo, we get 5.5 kWh/m^2 of solar irradiation. Typical residential solar panels are 12% - 20% efficient at converting solar to electricity. Assuming a 16% efficiency, we are only able to use .88 kWh of the 5.5 kWh provided by the sun. Dividing our total energy requirement, 528 Wh, and the usable solar irradiation, 880 Wh/m^2, we get .6 m^2. This means that we need .6 m^2 of solar panels and we know that each solar panel is .21 m^2 so we would need 3 panels. Currently, we have three 50 W panels which gives us a 150 W rated array.
We could potentially get better solar panels but we must be able to meet the limitation set by the canopy, 1.2 m^2.
SUMMARY
Energy use : 528 Wh
Average Power use : 132 W
Array size : 150 W, 54 VMPPT
link to panel : 50W Panel (need 3)
FUTUREÂ RECOMMENDATIONS ON SOLAR
The two major requirements of this project is to provide Donnete with increased longevity of her bike and to keep weight low. So, any further solar improvements must be light weight and very efficient due to the limited surface area available.
While researching this project, we came across many similar alternative transport projects. One such project was one man’s 64 day electrically assisted bike ride from France to china, and in the article,  he mentions that many other solar powered E bikes used Sun Power’s C60 solar cell. See the further readings section for more. The C-60 Solar cell is an extremely efficient Mono Crystalline Silicon cell offering an incredible efficiency of up to 22%. It is also lightweight, flexible, and durable meeting all the requirements  for Donnete's Bike. We recommend a custom made traditional "glass" solar panel made from Sunpower's C60 solar cells.