Introduction

Perhaps one of the most significant technical challenges facing renewable energy systems is development and deployment of large-scale energy storage. Presently all types of renewable energy sources generated by wind, solar, oceanic current, and tidal energy are harvested only during limited hours of each day. For instance, as discussed in the first chapter of this book, solar photovoltaic power is only generated during solar insolation periods, which average a few hours per day. Likewise, wind energy production, because of the unpredictable nature of wind streams and turbulence, is unpredictable, whereas use or demand of electrical power requires availability of 24 hours a day. Therefore, storage and availability of uninterruptible and consistent electrical power generation can be considered as one of the most important challenges and obstacles that must be overcome.

In general, large energy storage systems fall into the following main four categories:

• Mechanical technologies – Compressed air, flywheel, and pumped storage hydroelectric systems

• Electrochemical process – Batteries and charge capacitor systems

• Thermal process – Molten salt and solar ponds

• Chemical process – Hydrogen generation