Battery Backups & Generators (Home Energy Part 19)
Deep cycle lead acid batteries are still the most economic choice for renewable energy storage. If you would like power during an outage or to be off grid, they are a must. They are not without maintenance, as they need to be periodically refilled with distilled water. Also, it is important that they are stored in a climate controlled area with ventilation for the hydrogen. Hydrocaps can be used to limit some of the hydrogen venting, but it will not prevent it all. A good deep cycle lead acid battery that is maintained well can last 15-20 years.
A backup generator with a reciprocating internal combustion engine is more correctly known as a genset (a generator and motor set). There are many shapes and sizes and a variety of fuel types. A genset could be considered renewable if the feedstock was from biodiesel. However, most gensets are powered by gasoline, natural gas, propane, or diesel. Gensets are an inexpensive way to provide power during a short term blackout. 
2. Kemp, William H., “The Renewable Energy Handbook,” 2005.