totally different paradigm than conventional relaying.
No fully developed EMS exists today. Yet manufacturers already are introducing products into the market that can serve as building blocks for a highly versatile EMS (see sidebar, p. 58). Soon that may open the door to physical energy systems more attuned to market realities.
A Bare-Bones Concept
Under the concept of a microgrid as developed by the Consortium for Electric Reliability Technical Solutions (CERTS), the microgrid never exports power to the grid but is operated only as a controllable load. The generators thus need a minimum of overview control. Each is programmed with control characteristics that allow them to function together to provide a high-quality source of power under a range of operating conditions. The generators are given only basic dispatch commands by the EMS. Other functions the EMS can perform include:
- Intelligent energy storage, based on special weather-related or process needs;
- Full optimization of combined heating and power (CHP);
- DER functionality without a dedicated generator control system, because the EMS will dispatch only voltage and power;
- Microgrid operation based on the energy market predictions for both gas and electricity;
- Optimization of heating, ventilation and air conditioning (HVAC) through advanced control strategies;
- Minimized pollution based on sophisticated algorithms that consider CHP and displaced emissions;
- Enhanced power quality where, for example, a loss of grid power causes a seamless transfer to standalone power involving only a loss of non-critical loads within the microgrid;
- Support of the future grid through an array of ancillary services, such as voltage regulation and reserve power.
Even without supplying power to the utility, the microgrid still can supply significant services to the utility. The ability to control load is extremely important to a utility during times of system stress. Reducing 5 MW of load in an overloaded feeder can do more to restore local voltage than supplying 10 MW of generation from a distant generator. The ability to control load enables a powerful control of voltage. Also, the ability to control power factor enables voltage control.
Thermal Energy and Storage Microgrids that feature CHP can provide a 30 percent improvement over conventional power plant efficiency. That can produce a total system efficiency of 80 percent, by using thermal energy that otherwise would be wasted. Any additional thermal energy contributions to commercial and industrial (C&I) processes would only improve cost savings further. The thermal energy produced by reciprocating engines, gas turbines, microturbines, fuel cells, and stirling engines, etc., all can be used for systems and appliances that rely on thermal energy (e.g., air and water heaters and handlers, chillers, steam turbines and heat recovery boilers and generators).
Several manufacturers of CHP systems now package systems starting as small as 25 to 30 kilowatts. However, the small size of these systems will present unique challenges in making efficient use of thermal energy, compared with the use of steam from larger, 50-MW combined-cycle plants, which are used often to supply steam for larger local uses, such as heating of dormitories, heating petroleum in a refining operation, or cooking in a food processing industry. In