Actually it helped a lot.
I found here the https://www.thesuntrip.com/wp-content/uploads/2019/02/Technical-Regulations-ST20.pdf
for the 2020 race to china.
Limits are
1155wh battery
<2,50 m² installed solar and 1,50 m² portable solar.
No charger
No night driving
The chosen engine should not...