Renewable Energy, Solar Photovoltaic (Home Energy Part 13)
Renewable energy is a form of energy capable of being regenerated by natural processes at meaningful rates. Sunlight, wood, wind, and flowing water are all forms of renewable energy. 
Solar photovoltaic cells convert light from the sun directly into electricity. PV cells are essentially transistors or integrated circuits on steroids. It’s a silicon wafer about the size of your thumbnail that holds several million transistors and other electronic parts. PV cells start out the same way as chip circuits, but they are kept in the oven until they’re much larger. 
Solar PV is the backbone of renewable energy systems for homeowners.  Solar electricity is typically the most expensive means (not including any subsidies) by which humans generate electricity. However, there are some instances where it can be much cheaper than conventional electricity. For example, when building a new home more than a couple of tenths of a mile away from a power line, it is often cheaper to install solar in an energy efficient home, then pay to hook up to the electrical grid. These “hook up” charges can run in excess of $50,000. 
Off-grid systems use batteries, typically lead acid, inverters, charge controllers, and of course the solar panels to convert, store, and produce usable electricity. In other instances, for example to take advantage of subsidies, or net metering it may make sense for a homeowner to be grid connected. Grid connected systems do not require batteries, however without batteries any power outage will leave these homeowners without power. A third option is available for the grid connected to also have a battery backup. This is a nice option for those homeowners who would like to take advantage of subsidies and net metering, but would also like the resiliency of having access to power during outages.
Most solar PV manufacturers provide a written guarantee of 20-25 years, although the modules should last well past the guarantee. Modern PV modules do lose power production each year; however it is typically less than 1% per year. Maintenance is pretty simple and can be summed up in three words. Let it rain. 
Solar PV systems can be a great way to insulate homeowners from future electricity price increases, and grid failures if paired with a battery backup, as well as build independence and resiliency. Solar PV systems are expensive, but they can payback over time, given their long life span. Below is an example of the 2012 ROI on a 10 KW system without a battery backup in PA:
$7.00 per watt, total cost = $70,000
30% Federal Tax Credit= $21,000
Adjusted Price= $49,000
PA power production: Appx. 12 MW per year (Provided full sun site, good pitch, and direction)
Electricity saved= $1800 per year at .15 per KWH
AEC’s (Alternative Energy Credits): $400 per year
Savings: $2200 per year
2. Kemp, William H., “The Renewable Energy Handbook,” 2005.
3. Chiras, Dan., “The Homeowners Guide to Renewable Energy,” March 2006.