When considering going solar, one of the most commonly asked questions is 'How do cloudy or rainy days affect solar panels?' It's obvious that clouds diminish the effects of solar energy, right? Well, yes and no. Allow me to explain:
By far, the greatest hindrance to solar energy production is shade. Shade that falls on your solar panels can definitely diminish their output. Depending on how the system is set-up, shade that falls on a single cell of a single panel can reduce the efficiency of the entire system.
Generally speaking, the rating of your solar panel is dependent upon direct sunlight during peak hours of solar activity. So, if your panels are rated at 325w then that means that each panel will produce 325 watts per hour of direct sunlight during peak hours. When thunderstorms roll in, casting a shadow on your system, it can effect your solar production by 20-50%, depending on the darkness and thickness of the cloud coverage. However, under other circumstances, particularly when a cumulus cloud comes between the sun and your system an interesting effect is observed. The energy production of the panels actually increases SLIGHTLY ABOVE THE MAX OUTPUT of the system for a BRIEF period of time. This is due to the panel's ability to absorb diffused, as well as reflected light. The albedo, or the amount of diffused light proportionate to the effects of direct sunlight on a surface, actually increases the total overall solar energy and, at times, can add to the total solar production. Albeit briefly, the effects are still interesting to note.
That being said, shade from clouds, trees, or other obstructions can reduce your overall output. During cloudy or rainy days, most systems will still produce enough energy to power their homes during the day, though they might produce fewer 'credits' to power their home throughout the night. With a grid-tie system, homeowners accumulate credits for the excess energy produced by a solar home that is then sold back to the utility company. These credits are then used by the homeowner during times when there isn't enough solar energy to power the home, like at night-time and during the winter. This is called net-metering and it is generally required by the utility company in order to go solar.
The moral of the story is this: while shade from clouds may affect your solar panel's ability to produce electricity, it is by no means enough to negate the overall benefits of the system - even during years with higher than usual rainfall. Having a solar expert out to evaluate your home is the first step, and they will be able to let you know if going solar is right for you.