Design Review: Solar Cell Array Design

SC7 Array Design Review

Frank Wang

Why did we need to redesign the array?

The FSGP regulations have changed.

Previous regulation:
  • 6m2 Array
  • No Supplementary Array

Current regulation:

  • 4m2 Array
  • 2m2 Supplementary Array

SC6 Array Design

SC6 was made using 3 string array: red, green and blue. Red marks the front of the car. The cells are connected by wires and enclosed in 3x4 modules. The array is divided so that each string can supply reasonable voltage to the car if one gets cut out. The cells are in 3x4 modules because bypass diodes are used to maintain connectivity upon module failure. They do cause a small voltage drop across them (~0.3V) which limits the number of them we want to use as they effectivelly lower output voltage. 

SC6 Array

Design Constraints

The available area on the top shell is constrained by

  • Regulations
  • Shell shape 
  • Canopy placement

MPPT input voltage has to be adjusted for maximum efficiency. The MPPTs NUsolar has have a minimum input of 36 volts. Each cell can generate about 0.6 volts.

The number of modules/bypass diodes needs to be optimized for best performance with minimal voltage drop

SC7s workable surface

SC7 Array Iterations

Iteration 1

Similar layout to SC6s array using 3 modules and 3 strings. However, due to smaller array size, the output voltage of ~50V was too close to the minimum input value of our MPPTs.

Iteration 2

3 modules were used to make this layout as well but unlike the iteration 1, it only uses 2 strings which means this array only needs 2 MPPTs. The modules would have been connected with shoe-string wiring and the output voltage would have been ~80V which is significantly above the minimum MPPT input. However, the irregular module placement would have led to difficult wiring.

Iteration 3

This design uses 6 different modules and 2 strings to achieve ~80V output voltage. The front of the car will be relatively complex and the rest will be regular so the wiring will be easier. 

The supplementary array uses same modules as the array. It will fold along the vertical edges and be stored in the back of the car during racing and used for stationary charging.

SC7 main array
SC7 supplementary array

Next Steps

  • Receive feedback from the manufacturer D2
  • Consider using straight wires instead of zigzagging wires
  • Use laminated bypass diodes and larger pannels

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