By Jillian Jordan
One of the biggest problems in the renewable energy game is the issue of energy storage when using an intermittent, or variable, power source. Solar photovoltaics (PV) and wind turbines have come a long way since their inception and new, affordable innovations are underway which boost their marketability through reliable storage when the sun is not out and the wind is not blowing.
The need for grid-level storage is nothing new, but demand for power is growing along with increase in businesses and population. A combination of systems such as pumped-storage hydroelectricity, Compressed Air Energy Storage (CAES), thermal storage and a liquid metal battery — to update the traditional Lead-acid and Lithium Ion — may be the start to a bigger integration of renewables to the existing power grid. Some believe energy storage to be the missing link in an effective smart grid. Though conservation and demand response methods will most likely mitigate the need for larger storage in the future, let’s take a look at the promising technologies that are already being utilized and those that are up-and-coming that may contribute to the emerging “energy internet”.
Second only to conventional pumped hydro in storage capacity is Compressed Air Energy Storage, or CAES — one of the leading methods to storing energy produced by wind turbines. Since wind tends to blow more during the night hours, it is important to take advantage of this source of power and use it when it is most needed. CAES does this by taking the excess, off-peak wind power to pump air into salt mines, depleted gas reservoirs and water aquifers or other naturally occurring geologic formations that are sealed for safety. These reservoirs are typically 2,500 to 6,000 feet underground.
Since this type of storage is limited to geography in specific regions, high-pressure capacity holding tanks are also fabricated to store the compressed air for use during peak hours of energy use. However, naturally occurring reservoirs are the most economically feasible. During peak hours, the compressed air is released and heated, turning the turbines to create power when needed. CEAS systems have a large-scale use and capacity at 50 to 300 mega watts, which can be used with gas turbines to produce the same amount of power as traditional methods while requiring 66 percent less natural gas. This offers a considerable drop in CO2 and a substantial cost savings to the utility. SustainX of Seabrook, New Hampshire has worked on capitalizing on this existing model and updated it with a new and innovative isothermal CAES that will go further in capturing the heat from the process and will not require reservoirs, using pipeline or pressure tanks.
When it comes to storing energy from solar photovoltaics, thermal storage is one popular option and has increased the use of solar power in our nation’s energy grid. Thermal storage can be done using water, molten salt or even molten glass among others. Similar to capturing wind power, thermal storage captures heat to be used at peak times. Molten salt energy storage has more efficient properties to holding heat than water and the capacities being generated for grid-level energy needs are proving to be promising. The liquid salt is passed through panels to gather concentrated solar rays. The molten salt is then kept in insulated storage tanks and pumped into steam generators when needed. Heat capture tops out during the day and the power can be saved for use at night when the sun is not shining during rainy days and long nights. When used in tandem with large-scale Concentrated Solar Power (CSP) technologies, (such as those designed by eSolar of Burbank, California) power is generated with a zero emissions benefit and massive storage capacity, making solar much more feasible in terms of marketability.
The newest player to the energy storage game is a liquid metal battery designed by Professor Donald Sadoway and his team of students at MIT. Recently, Sadoway presented a TED Talk that explained the solution he found to the energy storage conundrum keeping renewables in limited use on the grid. The concept of the liquid metal battery uses magnesium, antimony and molten salt electrolyte to build giant, cost-effective, batteries with a high capacity for energy storage. One 36-inch battery can store four kilowatt hours and these could then be stacked and placed into a 40-foot shipping container with a total capacity of two mega watt hours, which could meet the energy needs of 200 households in one day. The integration of this emissions-free energy storage system (now in beta with a company under the name AMBRI) could allow renewables to play an equal part in the grid and would be a catalyst to their rapid growth.
Given the innovations by companies like SustainX, eSolar and AMBRI, these new technologies in energy storage combined with emerging policies for a smart grid system are bringing us closer to a clean energy revolution than we ever were before.