253 Technical Developments and Outstanding Barriers

Stirling cycle engines have developed considerably in recent years. The free-piston configuration has served as an enabling technology for a great deal of energy conversion development. Stirling Technology Company (STC) and Sun Power Inc. are the leading developers of free-piston Stirling cycle engine generators with capacities ranging from 10 W to 5 kW. These generators have demonstrated maintenance-free operating lives far beyond that of gasoline or diesel engine generators. Ongoing endurance testing has proven so far that these generators can run continuously without maintenance for over six years, about 55,000 hours, with no observable degradation in performance. The potential operating life of these generators is well over twenty years. Similar prototype engines are currently available to utilities and other interests for evaluation, while the designs are being refined to lower costs and prepare for mass production. Development work is also under way to produce more reliable and cost-effective balance-of-plant equipment.

Advancement of engine technology is paralleled by advancements in the design and performance of the linear alternators used to convert the piston motion into electricity. Recent work has lead to more efficient and easier to build alternators that drive down cost while enhancing generator performance. Much of the current development work is aimed at bringing the cost of the generators down by making them ready for mass production. A large scale production run of 1 kW generators is planned for 2002, with limited production of 3 kW generators to follow.

Despite the numerous advantages over other technologies, Stirling engines do have some limiting characteristics that must be considered. The primary limitation of cost-effective, free-piston Stirling generators is power generation capacity. As mentioned previously, engines with capacities over 5 to 7 kW require costly and complex heat exchangers and piston mountings. The scale of current generators is similar to most portable generation systems. For this reason, Stirling generators are best used when small amounts of power are required continuously over a long period of time, such as for a remote telecommunications site or in a home or small office building. With their high reliability and silent operation, Stirling generators lend themselves well to being located in such places. The development of Stirling micro-cogeneration systems, where both heat and electricity are supplied at the same time, makes placement in residential and small business sites very practical. It is also possible to operate multiple Stirling generators in parallel to fulfill a larger power requirement.

Stirling engines are also somewhat larger and heavier than IC engines of similar capacity, primarily due to stroke limits of the piston mountings and the need for a safe, hermetically sealed pressure vessel. For this reason, it is best to consider Stirling generators for applications where the system will not need to be moved frequently by hand. However, lighter-weight engines are being developed as space probe power systems, and the technology is certain to find its way into commercial generators.

Stirling generators can provide tangible alternatives to small IC engines and add a whole new level to power distribution. Information about current developments in Stirling generators and supporting technology can be obtained by contacting STC and other companies who manufacture Stirling engines and generators.

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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