Greentech Media

Energy storage is the backbone of the green technology economy. Storage technologies address power-source predictability, which many believe is a significant obstacle to the widespread adoption of green power-generation technology. Green energy-storage technologies also provide sustainable solutions for consumer electronics and transportation technologies.

Storage systems are grouped by storage method. Grid-storage technology is currently used to supplement diurnal power supplies, charging from nighttime base-load power and supplementing peak power demand during the day. When providing storage for green power generation, this technique would be reversed. Storage systems would charge during the day, collecting excess solar or wind energy, and would then provide base-load power at night.

Key Components

• Electrochemical - Electrochemical storage converts chemical energy into electrical energy and works in a way similar to fuel cells. A primary difference between fuel cells and electrochemical storage is the flow rate. Electrochemical storage maintains fuels and electrolytes outside of the reactor, pumping them through when electricity is needed. Fuel cells require a constant flow to generate electrical energy. The energy in electrochemical storage is determined by the amount of stored fuel, which can be recharged by processing through the reactor.
• Vanadium Redox Flow Battery- Flow batteries are designed primarily for large-scale grid energy storage. Charged electrolyte fluid stored in large tanks is pumped through reactor cells and reacted upon, converting chemical energy into electrical energy. Excess fluid is held in outside tanks and re-energized before it passes through the reactor. By adding new tanks, flow batteries are easily scaled up. Vanadium redox flow batteries solve ion leakage, which was a major problem in maintaining functional flow batteries.
• Zinc-Bromide Hybrid Flow Battery- Hybrid flow batteries differ from redox flow batteries in that hybrid flow batteries are limited in the amount of charged electrolyte they can process. Hybrid flow batteries require some amount of charged electrolyte to remain in the reactor, limiting storage ability and variable power output.
• Solid Oxide Fuel Cell (SOFC)- Solid oxide fuel cells operate at extremely high temperatures (700° to 1000° C). High operating temperatures negate the need for the platinum catalyst required in kinds of non-reformed fuel cells. Solid oxide fuel cells are currently stationary storage devices - due to the high operating temperature - but are useful in providing backup power to gas turbines through hybrid heat and power devices. SOFCs are also used for co-generating hydrogen (through excess fuel production in fuel electrolysis) and electricity. Current research is focused on decreasing their operating temperatures for use in automobiles and mobile devices.

Solid Oxide Fuel Cell (SOFC)
Bloom Energy	SiEnergy Systems LLC	Franklin Fuel Cells

• Integrated Mini Fuel Cell - A fuel cell's fuel-storage component often dwarfs the cell itself. One possible work around is storing hydrogen as methanol - liquid fuels store compactly - and freeing the stored hydrogen through a heating process. These are known as microchemical systems. Current research has developed the technology to process methanol in a series of concentric rings, with the core acting as a combustion unit that heats the rings to strip hydrogen out of the methanol solution. Integrated mini fuel cells can be as small as 5 centimeters in diameter, allowing them to fit into laptops, and can generate as much as 1000 watts/kg.

Integrated Mini Fuel Cell
Tekion	>Smart Fuel Cell

• Direct Liquid Fuel Cell - Storing hydrogen in sodium borohydride and combining that hydrogen with oxygen from the air is an efficient way of getting big power into compact spaces. Sodium borohydride has the advantage of high-capacity, small-volume hydrogen storage. It is also inflammable, alleviating a major concern with consumer-electronics fuel cells. A downside of this technology is that its power capacity is about the same as the most advanced li-ion batteries. Current research is focused on increasing the hydrogen content of the sodium borohydride, without increasing the boron-oxide byproduct. Some researchers have had success with adding ethylene glycol, a common ingredient in antifreeze.

Direct Liquid Fuel Cell

Medis Technologies