711 Threshold Control

In threshold control, the generators run whenever a building's electrical load is greater than a predetermined threshold. The number of generators initially installed is equal to the difference between the annual peak and the threshold divided by the nominal power output of each installed unit:

Number installed = kWPEAK - ^threshold kWPER UNIT

If the electrical load of the building is greater than the threshold, then the number of generators operating is equal to the number required to reduce the grid load to the threshold limit:

Number operating = kWBUILDN - kWthreshold kWPER UNIT

A problem with this control method is deciding where to assign the threshold limit during system design. A high limit means that the generator is used only for peak shaving and the number of operating hours may be small. A low limit forces the generators to run more often and is akin to base loading. A threshold of zero indicates that the generators will try to operate whenever possible. This specific case is referred to as always-on control.

Thresholds are established during design by finding the best financial return given energy requirements as they are known during design. The trade-off is between capital investment in DG hardware versus savings in utility bills, both taken over the economic lifetime of the DG equipment. Of course, process or building usage often changes drastically during system lifetime, and the installed DG controller must be intelligent enough to operate the DG system optimally no matter how building usage has evolved from the initial design upon which the initial threshold was based.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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