Weight is not the most important for efficiency.

I notice that the participants spent too much effort to reduce weight but failing to notice the large Stella Vie. Somehow they forget about the law of physics. We must go back to physics when we want to determine the best solutions.

A heavy vehicle may be slow in acceleration or when climbing up hill, but they do not cause any energy loss. Efficiency is a matter of energy lost that cannot be recovered. Aerodynamic drag is one of them. Since aerodynamic drag contributes to 90% of all losses, it is therefore the most important. This is quoted by a few participants.

https://www.fueleconomy.gov/feg/atv-ev.shtml 

In the above site, wind resistance contributes to about 35%. No mention about weight at all.

Experience also inform us that heavy vehicles need not be inefficient. Take a look at Tesla cars. They are all very heavy because they have a large battery but they are still very fast and very economical.

My personal experience is similar. When I drove a Range Rover from Sandakan to Kota Kinabalu, I though I will spend more than double my normal fuel cost. It turned out to be only slightly more despite climbing up to Mount Kinabalu.

But if we drive in town, that car will kill you. Not so for Tesla cars or any hybrid cars that have regenerative brakes.

So the problem is not the weight, but the lack of regenerative braking. High performance also does not mean inefficient. It is just the laws of physics. Whatever energy that is sent to the car is converted to kinetic energy. If you brake normally, this kinetic energy will be lost forever. If you have regenerative braking, no problem at all.

For the World Solar Challenge, I was told that there was a large section which is hilly. We need to climb up a hill. I am sure it is not as high as Mount Kinabalu. It may take up more energy climbing up, and slow as well, so little kinetic energy, but potential energy increases.

If you go down hill, then you should go as fast as you can, without doing any braking. Not even regenerative braking. Because regenerative braking cannot convert all the potential energy back to chemical energy in the battery.

The problem is that there is a speed limit along the journey so you cannot drive too fast. We need to resort to regenerative braking or KERS, kinetic energy recovery system. Our only hope is to increase the conversion efficiency even more.

This applies to all cars, heavy or small. If small and light cars do not recover their potential or kinetic energy, they will surely lose a lot of energy in the process.

How to improve conversion efficiency? Use supercapacitors. Supercapacitors have low internal resistance, so low loss when used or charged. Easy to use. Just put them in parallel to the Lithium Ion batteries. Take special precaution only when charging. Better use voltage protectors when charging. No need to protect when discharging.

Spercapacitors are heavy and expensive, so limit them to just the kinetic energy of your car. If we have a car with 1000 kg of mass, the number of 300 F capacitors required is 33, to store energy equivalent to the kinetic energy of a 1000 kg car travelling at 20 m/s or 72 km/h.

 0.5*1000*20^2/(0.5*3000*4) = 33