There will probably be a significant reduction in the hashrate, at least in the early phase. That's expected because Bitcoin mining right now is heavily dependent on other sources. Miners can't just shift to solar power overnight. But I believe it will catch up eventually and a new hashrate record will be hit. 

I think the issue with solar power when used in Bitcoin mining is it's unstable nature. Bitcoin mining is energy-demanding and operates 24/7 while solar power isn't around the clock and is also dependent on the weather.