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Technology Corridor

How software controls can bridge the gap between wholesale market prices and consumer behavior.
Fortnightly Magazine - May 15 2003

small CHP or microgrid applications, it may often be attractive to customers to have the heat loads designed into the system at the time of project conception.

Thermal storage is also readily adaptable to HVAC systems-especially commercial cooling systems and their central chilled water plants. One conventional method is to use HVAC chillers with a thermal energy storage tank to shift peak loads. (See Jim Heller, "Load Shifting with Thermal Energy Storage," Navy ENews 95b, Naval Facilities Engineering Service Center, http://www.nfesc.navy.mil/) Even so, the analysis required to optimize HVAC operation is not trivial. Each of the key components of the HVAC system has its own energy efficiency value, which will depend on a variety of factors, such as load or humidity. Thus, an EMS offers the only practical method to achieve higher efficiencies and coordination with markets.

Overall, the optimal use of storage will require long-term contract arrangements and planning for DER operation. And a modular or pre-packaged CHP system may provide the key to successful integration of CHP in small-scale, microgrid applications.

For example, the packaged systems may contain a microturbine packaged with a desiccant-type dehumidifier and an absorption chiller. The advantage of using DER in air-conditioning applications is that the peak demand for the air conditioning typically coincides with the utility peak demand for power. A test of such a system is being performed at the University of Maryland for the Department of Energy.

Ancillary Services

One of the most exciting prospects of the microgrid controlled by the EMS is its ability to provide ancillary services, or reliability services. Microgrids located near urban centers could provide these services much more efficiently than distant generating stations because they would operate near the loads. Voltage regulation is one of the services under consideration in certain trial programs.

For many ancillary services, the EMS would make a decision in a day-ahead market as to whether it would be profitable to supply the service, and at what price. The EMS would then bid into the market and find out if the bid was successful. If successful, the EMS would plan to supply the service the next day.

One of the most significant services, spinning reserve, is sold like insurance. The microgrid would be paid for supplying the service regardless of whether it is called for, and it should be called for only infrequently (though a rapid, automatic response is required when called upon). The bidding and dispatching could be done automatically with only periodic operator oversight.

Reactive supply and voltage control are both required to regulate distribution voltage and to maintain bulk power system reliability, but whether microgrids can sell this service will depend on their size and the availability of a market.

Emissions Limits and Credits

When used in CHP applications, DER will both reduce and displace emissions from central electric power generation and from local heat generation. The EMS will make operational decisions that result in the lowest net emission production. These decisions will be directed by the net impact of the DER/CHP use, including displaced emissions and not just the