Because it's difficult to install them at scale like that. For example, if you want to do a big solar project, you have to negotiate with the owner of every bu

Because it's difficult to install them at scale like that. For example, if you want to do a big solar project, you have to negotiate with the owner of every building you want to put panels on, you have to find a place in every building for inverters, you have to install metering, you may have to upgrade the grid to handle the extra power going out, then you have to have an account and customer service and payments for every building, and if the panels need to be maintained, you have to schedule a time and send out a crew. Then you also can't practically do certain things like install trackers, because they break more often and it's too expensive to maintain them if you have to have a crew go out there instead of your on-site maintenance people just go over to the broken tracker/panel. Overall the costs of rooftop solar are just more expensive than a central solar farm. Plus, you can site the solar farm where there is better sunlight and land is cheap. Ultimately this is the problem I have with solar: It puts an effective cap on our energy use. Solar will never be more than 100% efficient, and there is only so much land that it is reasonable to use, so if we say, wanted to expand our worldwide energy usage 10x, it's not really feasible.