OK - the real basics… Do you have a flat roof or a sloped roof that faces south or almost south? Is much of the roof unshaded for most of the day? Is the roof in good condition? (Or in some cases a PV system can be mounted on the ground.)
That's a big one... and actually a physics question. There are good sources on the internet for learning this. Here is a good one from the National Renewable Energy Lab: PV intro by NREL. In short photons from the sun knock loose electrons present in a solar PV panel, and the panel is designed to gather those electrons and give them a circuit on which to do work, i.e. make electricity.
No. There are systems with solar collectors that heat water. These can provide hot water for a home, business, or even a swimming pool. Ask M3E about these systems, too! A solar collector can be made to heat air, water, I guess just about anything. Systems that heat things rather than make electricity are called solar thermal systems.
In most cases, no. A typical PV system whenever possible is tied to the utility grid. When it's dark or the solar system is not producing enough power, whatever is needed comes from the utility company.
Your PV system will operate efficiently for more than 25 years. A PV module has an expected lifetime of over 30 years. The inverter may have to be replaced once or twice during the life of the system.
Solar PV systems are "scalable." For each particular project a system size (and therefore capacity) is determined by such things as how much space, how big a budget, and how big an electric bill you have to begin with. So, you put in a smaller system; you save some. You put in a comparatively larger system; you save more.
At the times the solar system cannot provide enough power for your building load (nighttime, for example) kiloWatt hours flow through the meter and in to your building from the utility company. When there is light and the solar system is making more than enough power for building needs, electricity flows out through the meter and onto the grid. The meter nets together the kilowatt hours that come in with the ones that go out.
PV systems require much less maintenance than conventional generators. The panel collectors are typically guaranteed for 25 years or more and require no maintenance. The inverter life is typically at least 10 years. The most common cause of problems is a failure in the electronics - the inverter, and overcurrent protection components. If the installation is done well, these will serve for a very long time as well. If you think you should test certain of these occasionally, get an expert and never test an electrical system alone. Think safety first, and always.
For a PV system, availability involves some uncertainty because of the variability of sunlight. If there is light, the PV system will produce. System design uses an estimate of the average amount of sunlight at the installation to calculate an annual output in kilowatt hours.
For safety reasons, if your local utility grid is out, a grid-tied solar PV system will shut down as well.
If you are grid-tied (most likely), the power you need comes from the electric company at these times.
Incentives differ for residential, commercial, non profit, and public properties. The best way to check out current incentives is to visit www.dsireusa.org.
Of course, this depends on the size of the system. For a "typical" sized residential system in Washington County MD (every jurisdiction has its own rules) once a contract is signed the schedule would be something like this: Structural Engineer review of the roof - 2 weeks; Permit from the County - 2 weeks; Final design, material ordering, etc. 2 weeks; construction of system 3 weeks; utility interconnection 1-2 weeks. So from start to finish... about 3 months.
Of course, this depends on size, type of roof or ground mount, degree of difficulty to tie to the existing electrical system, etc. Systems are generally expressed in terms of cost per Watt. A Watt is 1,000 kilowatts (kW). Here are some price ranges you could reasonably expect: