Change the environmental requirements for cars. Require that each car installs solar panels on its roof.
As this article by Bloomberg shows, Ford has just built a “concept car” with a solar panel roof. It has between 300 and 350 Watts of capacity.
Let’s go with the lower number of 0.3 kW, on average. Just as the requirements to reduce CO2 emissions under EU law are calculated on average, this would obviously also depend on how much area is available, which would be different for various car models.
Last year’s new car registrations in Germany were 2.95 million units. If each of those had a 0.3 kW solar roof, we would get an extra 0.885 GW of new capacity each year.
Since most of those 2.95 million new cars are still running on stinking gasoline, those solar panels would not directly power the motor, as with electrical or hybrid vehicles (still stuck at 1.6% of the market). But they would reduce the load on the automotive alternator, which in turn of course will help save gasoline.
Also, I fully expect cars and trucks to move from stinking gasoline to electrical motors in my remaining lifetime (only a couple of decades). Once that happens, every kWh necessary to power the motor and generated by the roof solar panels won’t need to be generated somewhere else.
There are over 1 billion cars World wide. Put 0.3 kW on every one of them and you get 300 GW extra capacity, more than all stationary capacity of the World combined right now.
I like the idea so much, if I had to decide this alone I would require solar panels on the hood and the sides of cars as well.
This might even qualify as an innovative technology under Article 12 of Regulation 443/2009.