I don't know this for sure, because the power conditioning gear and service panel aren't visible, but I highly doubt that there is a battery system in this installation, so let's assume we're looking at a typical grid-connected (parallel) set up.
That means that all of the power generated goes to the utility, and none of the power is used by the billboard lighting, which after all is only on at night.
What could be wrong with that?
I suppose nothing, really, except that it goes to the heart of the issue of regulatory fairness and misuse of environmental perception. The sentiment goes: "I have solar PV panels on my home/business/facility, so I'm power/grid/environmentally neutral."
These installations are most certainly not grid neutral. There is still a utility service point, with transformer, distribution, transmission, and power plant infrastructure to support it.
The problem in California is that under net-metering tariffs, the bill board owner could "zero-out" their bill and pay for none of the carrying costs of that infrastructure. They simply have to size the solar PV to generate the same amount of power used by the lighting on an annual basis.
That means the neighbors do pay more, by the way, because they now carry the infrastructure costs. And that is the heart of my criticism, not of solar or distributed generation of any type, but of the manner in which it is treated in the regulatory arena.