Maximum Speed under Solar Power

 If we assume 100% loss is due to aerodynamic drag.

The drag coefficient Cd is equal to the drag D divided by the quantity: density r times half the velocity V squared times the reference area A.

Cd = D / (A * .5 * r * V^2) 

V^2 = D / (A * .5 * r * Cd)        (1)

 https://www.grc.nasa.gov/WWW/K-12/airplane/dragco.html

Using r = 1.1644 kg/m^3  which is the value for air at STP, which is 30 degC.

For Stella Lux, 1.12 m x 1.76 m x 4.52

https://en.wikipedia.org/wiki/Stella_(solar_vehicles) 

Cd = 0.1019, using Stella Vie shape which is more aerodynamic.

A = 1.97 m^2

If the power loss, L is 1 kW, equivalent to 5 m^2 of solar panel,

D V = 1Kw => D = 1 kW / V

Inserting D into (1):

V^3 =   1 kW / (A * .5 * r * Cd)  = 8556.3

V = 8556.3 ^ (1/3)    =  20.5 m /s = 74 km / h

 

For Transparent Car, 1.5 m x 1.7 m x 5 m

 Cd = 0.1050, for ratio of height to width of 0.3 and ground clearance of 0.2 m.

A = 2.55 m^2
V^3 =   1 kW / (A * .5 * r * Cd)  =6415.0

V = 10152.28 ^ (1/3)    =  18.5 m /s = 67 km / h

 

For Transparent Car, 1.2 m x 1.7 m x 4 m

Assuming Cd = 0.1050 because similar height:length ration, and ground clearance of 0.2 m.

A =  2.04 m^2

V^3 =   1 kW / (A * .5 * r * Cd)  = 8, 018.8

V = 10152.28 ^ (1/3)    =  20 m /s = 72 km / h

 

For Transparent Car, 1.3 m x 1.7 m x 4 m

 

The actual MicroCFD for a similar shape with a height of 1.3 actually calculates:

Cd =  0.1328 because its length is only 4 m with wheelbase of 2.5. Ratio of height: length = 0.325

A = 2.21 m^2

V^3 =   1 kW / (A * .5 * r * Cd)  = 5,852.4

V = 5,852.4 ^ (1/3)    =  18 m /s = 65 km / h

 

For Transparent Car, 1.3 m x 1.7 m x 4.5 m

 Estimated Cd = 0.105

V =  19.5 m /s = 70.1 km / h

Conclusion

The 1.5x1.7x5 m car is more impressive and roomy. This is the Toyota Rav4 class.

For the World Solar Challenge, there is a limit of 5 x 1.6 x 2.2 m only.

2.2.1   When driving in a straight line, the solar car must fit inside a right rectangular prism
5000 mm long, 2200 mm wide and 1600 mm high, with the base of the prism coincident
with the ground.

Hopefully, by using supercapacitors, tiltable solar panels, and cooling air energy recovery, we should be able to tip the balance. The hull volumes of the Stella cars are not impressive.

Weight is not really a factor in the loss. It only affects rolling loss but rolling loss is only a small percentage of total loss. Slower acceleration may determine the time taken to reach a destination. With supercapacitors, we can increase acceleration tremenndously, at least for a short while.

If we are able to design a refrigeration system that allows the car to generate  a net power gain when the car is stationary, while collecting heat energy, it will be very impressive.

We may try to put the turbine generator pointing upward because high temperature air rises. Or add a small fan to push air through the aircon radiator which will then drive the generator.

The best option is therefore the  1.3 m x 1.7 m x 4.5 m. It is not too high that it violates the maximum overall height of 1.6 m at the highest ground clearance. Not too low, to allow more room for the solar panels to be tilted.