Whether solar or other low-emission power sources are profitable for the companies or industries who make them is beside the point; the true economic impact is how it affects everyone across the board, including all the global benefits of cutting emissions and mitigating climate change. That's why subsidizing them is sensible. It's worth being in the red if it eliminates fossil fuel use, whether the market likes it or not.
The real issue is whether they're actually low-emission at all, by the same reasoning. The mining and manufacturing involved in producing, distributing and maintaining them does not generally run on solar power, just as electric cars are usually just a diversion from fossil fuels in the tank to fossil fuels in a power plant.