04 January 2012
“It’s cheaper to generate an electron than to store one,” said Jim Greenburger, executive director of the US-based National Alliance for Advanced Technology Batteries. “The function of storage is to help the generator to deliver steady power.”
When the ability to create an electron from sunlight is easier, more efficient and possible at various scales, there’s good reason to explore how best to tie stored solar energy into the electrical infrastructure. Energy storage helps balance operating reserves, acts as a supplement when new transmission lines can’t be built, provides black-start power after system failure and provides power quality and stability. The following is a look at the state of the art in battery research, who’s involved and what we can expect from each.
Researchers around the globe are making headway developing batteries for large-scale, and grid-capable solar energy storage.
Zinc air battery chemistries is one of the most interesting things Greenburger has seen recently. EOS Energy Storage of Easton, Pennsylvania, is developing a high-energy rechargeable zinc-air battery for use in the grid. It’s expected to store three times the energy of lithium-ion batteries for half the cost. Initial manufacturing is expected next year with megawatt-scale systems delivery is anticipated for 2013.
These batteries use a porous electrode allowing air inside the battery where a catalyst helps form hydroxyl ions at an oxygen-electrolyte interface. The ions help oxidize a zinc electrode, creating current. During recharging, zinc oxide is converted back to zinc and oxygen is released. Aside from its stability and planet-healthy lack of toxic metals, zinc air batteries have promise for electrical vehicles as well.
Aquion Energy, based in Pittsburgh, Pennyslvania, is developing what it calls a low-cost, ambient temperature sodium-ion battery. It uses an electro-chemical couple said to be capable of thousands of deep discharge cycles with little or no loss of capacity and an efficiency of more than 85%. It uses thicker electrodes (carbon anode and sodium cathode), a sodium-based aqueous electrolyte and less-expensive separators and current collector materials. The battery uses no hazardous materials. The plan is to build units with a capacity between 10 kWh and 100 kWh that can perform for more than two hours. Aside from being 100% recyclable, the battery is expected to withstand discharge abuse, incur low maintenance costs and can be assembled in open-air environments. It is expected to cost less than a third of lithium-ion technology. Aquion hopes to release a commercial grid-enabled battery in 2012.
Paul Denholm, a systems analyst for the National Renewable Energy Laboratory (NREL) said that while lithium-ion (li-ion) batteries have been primarily used for electric vehicles and smaller applications, the technology is gaining interest from companies looking to develop them for the grid. The primary issue is their high cost.
Researchers at the University of Leeds in the UK have licensed a new material and process that could simplify the manufacture of li-ion cells to Livermore, California-based PolyStor Energy Corporation. Electrovaya Inc., a Canadian manufacturer of nano-structured polymer li-ion battery platforms started work in late 2011 on a project to build a 1.2 mWh storage system at a Manitoba research facility using end-of-life li-ion batteries from electric vehicle (EVs). The Korean manufacturer, LG Chem Power Inc., signed a deal with Swiss power and automation company ABB to supply li-ion batteries for a storage system in Europe. The first set of batteries for the project is expected by late 2012.
Yi Cui, a materials science and engineering professor at Stanford University, recently developed nanowire anodes for li-ion batteries. The electrode is said to be 99% efficient and offer 10 times higher specific charge capacity of existing carbon anodes, maintaining 83% of their charge after 40,000 cycles. (Lead-acid batteries last for just hundreds of cycles, while li-ion batteries typically last for 1,000.) The new electrode uses the same principle as li-ion, but accomplishes it using abundant and inexpensive elements. Yi Cui says the new battery will use a water-based electrolyte rather than the solvent typically used in li-ion batteries.
For any solar energy to supplant the burning of fossil fuels to create electricity, storage technologies will have to be less expensive and at least as reliable as our current system.
“There are a wide range of maturities for the sodium sulfur (NaS) battery,” according to Denholm of the NREL, explaining that NGK Insulators, based in Japan, builds cells for grid-tied systems. A 4 mWh system currently provides transmission backup for an almost 70-year-old infrastructure in the event of a line outage for about 4,000 people in Presidio, Texas. It’s the first of its kind in Texas and the largest in the US. This molten-metal type of battery has high energy density, high efficiency (89–92%) and long cycle life. While made from inexpensive materials, it operates at high temperatures (300 to 350 degrees C) and must be contained in concrete structures.
“Even though lead-acid chemistry is over a hundred years old there are people doing some new things with it to make it competitive,” Denholm said. Greenburger agreed, explaining, “Everybody in the business keeps waving their hands, saying lead-acid is the cheapest.” The latest research into lead-acid chemistries will be explored in a future article on Solar Novus Today.
Written by Jonathan Gourlay, Contributing Editor, Solar Novus Today