691Control Techniques

Control of a fuel cell system must include an evaluation of safety, economics, and overall system (grid or local user) reliability and/or needs. The price of electricity, the impact to operations, and the cost of fuel and maintenance must all be taken into account. The goal of the control scheme is to determine whether or not the fuel cell should be operating during a particular period. Generally, a simple hour-ahead control method is sufficient if the start-up transients of the generator are not too inefficient. Chapter 7 presents some of the techniques that can be used to control on-site generation. Each of these could be applied to a fuel cell system. The control strategies include:

• Threshold control — always run if load demand is greater than a predetermined threshold

• Buy-back priority — used when power needs to be sold back to the utility

• Simple buy-back — power is sold back to the utility at a predetermined rate, measured by a separate meter

• Net metering — user pays utility for net power consumed

• Cooling/heating priority control — cogeneration

• Optimal control — minimizes cost over lifetime of fuel cell

• Complete optimization — optimizes fuel cell and complete system operation

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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