If you google “solar panel efficiency”, you will instantly find several sources that all indicate that most (cheap!) solar panels are 15% to 20% efficient, whic

If you google “solar panel efficiency”, you will instantly find several sources that all indicate that most (cheap!) solar panels are 15% to 20% efficient, which is 50% higher than the number you’re providing. Top end residential solar panels are over 20% efficient, somewhere in the neighborhood of 22%. Specialized/research solar panels can reach efficiencies of over 40%. Also, energy density is not nearly as important as you seem to fundamentally believe. It’s pretty much all about cost and availability. In countries that use very little energy per capita, even just a single solar panel (with a small inverter and a lead acid battery) per person (or even per family) is life changing, giving them enough energy to run a small refrigerator, a light bulb, and a place to recharge their smartphone without having to go into town and pay someone. In deep urban environments, space is definitely at a premium, but I struggle to imagine that many people are excited to set up a dirty diesel plant in the town square when air quality is already bad enough due to heavily polluting vehicles running in the city center, let alone set up a small nuclear plant, even if wealthier countries would allow such a proliferation of nuclear technology and fuels. Once the nuclear fuel is spent, then you have this extremely toxic, dangerous waste that has to be put somewhere, and those people probably have a lot of other things on their minds, so you could just be rad poisoning their town by giving them nuclear if they don’t dispose of the waste properly. On the other hand, the rooftops are prime locations for solar panels and solar water heaters, and because 175W/m^2 of solar converted electricity is actually a ton of energy, it’s still plenty of power. Unfortunately, cost and availability are king. Wealthy countries are happy to sell old assets at a steep discount, and so shiny new solar panels have to compete with second hand fossil fuel plants / generators that don’t lend themselves to great air quality. Solar is an extremely sensible solution. Nuclear is not a clear answer at all for developing countries, unless you happen to have the design for a clean, portable cold fusion reactor in your pocket. Fission has a lot of problems that are manageable, but managing those problems takes significant money.