732Supermarket in Chicago

This example examines a 24-hour supermarket in Chicago with a peak load of 167 kW, an annual electricity bill of $67,500 (average of 5.7$ per kWh), and an annual gas bill of $566 (average of $5.90 per MMBtu) calculated using actual rates from a large utility in Chicago; the rates are time-of-use rates. Figure 7.3 shows selected weekday electrical load shapes for this facility. Note that the load shapes are much flatter than those for the restaurant presented in the previous example. Two different scenarios were examined for the Chicago supermarket: peak shaving and base-load control. Table 7.3 shows the comparative results from the analysis.

The peak shaving scenario used a single 50 kW microturbine with heat recovery, while the base-load scenario had three turbines. This example illustrates how optimal control can recognize the periods when it is expensive to purchase grid electricity. Threshold control does not recognize these and, in fact, will tend to operate during the periods of high load and corresponding high electricity costs. Optimal control, on the other hand, takes advantage of the time-of-use component and shows a clear benefit over the threshold control method. The rate of return on this investment is not as attractive as with the previous example due to the relatively low cost of electricity. As in the first case, optimal control performs best with either of the two control objectives. The difference between optimal control and the best threshold control is significant.

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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