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Demand Management

powerlineCommercial and industrial firms are increasingly falling under time-of-use rates that are raising their energy costs. By using on-site energy storage, individual stores and facilities can lock in lower rates, through peakshaving, as part of their overall energy management strategies. Zinc-Flow units can both support improved power quality, and can provide a means to reduce the cost of energy.

Power Quality
Zinc-Flow units can provide an on-site cache of power to protect against power sags, or provide a ride-through capability to an on-site generator in the event of a sudden interruption in power. The discharges from the Zinc Flow unit in this application can range from less than a second to 30 seconds. Power quality is a growing problem for US businesses; with estimates ranging upwards of $150 billion each year in lost production or damaged equipment from poor power quality. Both industrial and commercial firms suffer from these conditions; while transient power fluctuations disrupt and damage industrial batch-processing (lost work product) and continuous processing (schedule disruption) commercial firms are also feeling the impact as fault-intolerant information technology spreads throughout the firm. Voltage sags and swells are the most common power quality problem, and these events can come from obvious external sources as lightning strikes, but also not so obvious internal sources as large electrical loads (motors, etc.) suddenly switching on and off. Surprisingly, the majority of power disruption events do not last long: an EPRI study on the Analysis of Utility Disturbances found that 98% of all events less than 30 seconds and more than 90% of power quality disturbances last for less than 2 seconds.

Peak Shaving
DatacenterThe original desire by commercial and industrial firms to simply have lower energy bills has been joined by the desire to prevent volatile power prices from affecting the bottom line; for many firms, even a small rise in energy costs could wipe out hard won efficiency improvements; worse yet is simply an unpredictable price. Conservation programs have been used for many years to reduce enterprise energy costs, but they have two drawbacks: many do little to counteract the specific high-use periods that drive demand charges, and those load-shifting programs that do quickly begins to interfere with production operations.

Peak shaving allows customers to directly reduce their utility bill through arbitraging power stored from off-peak periods to on-peak. By doing so, energy storage technologies can allow firms to engage in load shifting without the subsequent effects on the production schedule. The total use of energy (kWh) would not be affected, but the firm's costs would be lower because of the lower use during higher priced periods of the day (if the firm's tariff has multiple levels). By maintaining such a cache of energy on-site, the energy storage facility can also be integrated with other energy management strategies gaining favor such as a demand response program to provide a greater flexibility to the firm to reduce its usage cost of energy.

Besides arbitraging low cost power, a customer's demand charges can be reduced. Demand charges are based on the highest power usage (kW) during the month, even if only used for the 5 minutes. Therefore, reducing the highest peak demand can quickly add up as demand charges can many times represent half of a customer's total electricity bill in some locations. Of interest to many retail establishments, highly cyclical loads such as cooling loads can increase the demand charge component of the bill dramatically. For this reason, even for many firms where their overall cost of energy is only a small part of overall costs, what is commonly found is that certain components of their energy usage may be well suited to incorporating an energy storage component.

2003 CBECS (Commercial Building Energy Consumption Survey), US Department of Energy, Table A5.
EPRI Distribution System Power Quality Monitoring Project (DPQ Study)

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