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Energy Storage: It's Not Just Load Leveling Anymore

Fortnightly Magazine - August 1998

outages, usually less than 30 minutes, to buy time for the transfer to backup generators. Uninterruptible power supply units provide back-up power and activate in cases of complete power outages, unlike the power quality systems that perform on-line corrections.

Upstream from the retail product services, energy storage can offer lower-cost options for ancillary services and capacity reserves, as well as avoiding transmission or distribution overload.

Electricity transmission companies or independent system operators must provide ancillary services to regulate frequency, manage voltage sags and provide area control to avoid damaging utility or customer equipment. Energy storage systems can provide several megawatts for more than an hour to correct generator and transmission line imbalances. Energy storage systems can be immediately available for reserve power, making them a more effective option than thermal plants and combustion turbines, which must be left in constant operation, meaning higher emissions and costs. Energy storage increases the ability of non-generating electricity providers to respond to demand spikes by delivering power until backup units are running.

Energy storage can help by extending the life of generating units by responding to load swings that would otherwise require a more rigorous duty-cycle from the unit. Similarly, in a peak power capacity applications, storage can be used to supplement generation during periods of peak demand. It also can assist power producers by mitigating stress on the wires.

At the generation end, energy suppliers must minimize costs, relying more on lower-cost resources. For example, some areas generate electricity for between 2 and 5 cents per kWh. Utilities may achieve required rate reductions by moving this lower-cost electricity to higher-cost areas such as Southern California. However, if large amounts of electricity are moved, reliability may be diminished due to overloaded transmission lines.

A storage system can support transmission systems by giving utilities the ability to increase energy transfer and stabilize voltage levels. The alternative -- building transmission and distribution lines -- is becoming more unattractive with tougher siting conditions and pressures to reduce capital expenses.

At the distribution level, when demand is excessive, equipment overloads, excessive voltage drop, poor power factor and increasing fault levels may occur. Storage can help protect and prolong the life of existing equipment by supplying real power and regulating voltages. Storage has the added benefit of allowing utilities to add capacity incrementally when and where it is needed to solve specific capacity bottlenecks.

The proliferation of green power products in newly competitive electric markets should also create demand for energy storage technologies.

For instance, energy storage increases the value of electricity generated from solar and wind resources by making it available regardless of when it was generated. For grid-connected renewable energy storage systems, energy storage can provide peak-shaving capability or reduce peak demand charges by charging from the PV array or, during off-peak hours, from the grid. In competitive markets, energy storage will allow customers to take advantage of net metering and avoid paying for electricity during high-cost periods.

Of course, grid-independent or remote power applications all employ energy storage to allow the intermittent resource to serve a required load.