Today in our environmental science lecture, we're discussing renewable energy sources. One interesting case is the small town of Greensville, which switched to solar power in 2015. Initially, the town invested in solar panels for public buildings, but they faced a problem: energy storage. Batteries were expensive, so they partnered with a nearby university to develop a more efficient storage system. By 2018, they reduced costs by 30% and now supply 70% of the town's electricity from solar. However, the professor notes that the main challenge remains cloudy days, when output drops significantly. Despite this, the project has inspired neighboring towns to adopt similar plans.
❓ What was the main problem Greensville faced after installing solar panels?