Some critics of solar power say that solar panels don’t produce electricity on cloudy days. This claim is false. Solar panels can still can produce 10–25% of their typical output on a cloudy day. Obviously, this amount is much less than during periods of direct sunlight, but it is not nothing.
We may assume that solar panels thrive in hot, sunny weather, but too much heat can actually reduce solar panel output 10–25%. So, very hot weather isn’t the best condition for them. “The problem is, most solar panels’ power outputs start to degrade if the temperature of the panel goes over about 25°C. This is why, if you look at the specification label on a solar panel, most manufacturers quote the solar power output at a panel temperature of 25degC.”
This is why a solar power system might be more effective in San Francisco than in much hotter Las Vegas, even though Vegas has more sunny days. San Francisco is well known for its fog, so it might be easy to assume that solar power wouldn’t do well there. However, rooftop solar power systems in San Francisco do function well. The amount of direct sunlight is reduced by fog and clouds, but solar panels function better at cooler temperatures, so the electricity output in San Francisco is still significant. Using a home solar power system there can save approximately $1,500 per year on utility bills, according to an analysis conducted by SolarCity.