Does it need to be sunny every day for my solar panels to work?
No. Solar panels will produce more power on sunny days than on days with clouds, fog or rain. But the solar panels will still produce power on days with clouds, fog or rain. Typically when you are provided with a solar proposal for your home a software program is utilized that takes into account the type of solar panels and equipment that will go on your home and factors such as azimuth (the direction the panels face — south, southwest, etc.), pitch (the angle at which they are installed), amount of sun they will receive (takes into account tree shading, location on globe, etc.) and typical weather for your region. All of these will affect the production of the system as a whole. So, typically the proposal outlining how much your system would produce is taking into account, or estimating, all of the factors that will affect the amount of electricity your solar panels will produce. Seasonal changes in weather can ultimately influence this number over time, but, a 5-percent difference would be considered high. – Micah Breeden, Chief Financial Officer of Allterra Solar in Santa Cruz, California
What happens if my panels produce extra energy?
This question has a two-fold answer, though each utility company handles this differently, so you will want to contact your utility provider for details on how they handle this.
If you produce more power on a Tuesday in the summer than you used at your home. Your utility company will apply credits to your account for the excess power that your system produced and sent out to their grid. For example, if you produce 20 kWh and use 10 kWh on a given day, your utility company will credit you for 10 kWh on your account. The rate at which they credit you is the same rate at which they would charge you at the time you are sending excess power to their grid. Typically you get credited at a higher rate than when you buy power back as the rates in the day time (when your solar system is producing lots of power) are more expensive than in the evening (when you have to buy power since your system is off).
If at the end of the first 12 months of your solar system being operational your system has produced more power than your home has consumed, then your utility company will likely pay you for that excess power. Some companies will pay you at the wholesale rate, rather than the amount they credit your bill. The wholesale rate is typically around $0.03/kWh, so, it is not in your best interests to install more solar power than you typically consume in your home. – Micah Breeden, Chief Financial Officer of Allterra Solar in Santa Cruz, California