Читать книгу Maintaining Mission Critical Systems in a 24/7 Environment - Peter M. Curtis - Страница 61

The fact that electrical energy is most easily stored in batteries as DC is the primary reason power conversions is necessary when AC distribution is used in the data center. The two types of batteries that are most commonly used in conjunction with a UPS are lead‐acid wet cell (flooded) and valve regulated lead‐acid (VRLA) or variations thereof. Lithium ion batteries are gaining popularity since they have excellent weight to power density, can cycle or discharge many times without losing capacity, do not off gas during charging, and have a longer life than VRLA’s. They are mainly being deployed on smaller UPS’s below 300kW, and some state or local city codes have special requirements or are hesitant to allow them to be installed in buildings since they are a newer and thought of as unproven. This will change over time as more and more installations become common. For additional information, see Chapter 10 – UPS.

Another storage technology are flywheels that store kinetic energy and can discharge DC power to a UPS. Conventional batteries and flywheels are covered in more detail in the UPS chapter. Also worth mentioning here are some new battery storage technologies called Zinc‐Bromine Flow Batteries and a megawatt‐class of batteries that use a sodium‐sulfur electrolyte – which are both, by nature, DC sources. Both of these batteries have the potential to be used in grid‐storage class applications and may undergo many deep discharges without suffering ill effects.?? Various battery manufacturers are developing battery storage banks so that excess power produced from solar panels or other renewable sources during the day can be used at night, or other sources like hydropower can charge batteries at night for discharge during peak daytime hours reducing demand loads on fossil fuel plants. For additional information, see Chapter 10 – UPS.

As of this writing, sodium‐sulfur batteries have already been installed at several locations globally, including a wind farm in Japan and a bus depot in Garden City, NY. Zinc Bromide batteries have yet to prove themselves in anything more than a handful of demo installations, but the technology seems promising for the storage of electricity from intermittent sources and load‐leveling applications, similar to sodium‐sulfur batteries.