Schematic Figure Of Stirling Engine In Solar Powered Stirling Engine

Dish/engine technology is the oldest of the solar technologies, dating back to the 1800s when a number of companie s demonstrated solar powered steam-Rankine and Stirling-based systems. Modern technology was developed in the late 1970s and early 1980s by United Stirling AB, Advanco Corporation, McDonnell Douglas Aerospace Corporatio n (MDA), NASA's Jet Propulsion Laboratory, and DOE. This technology used directly-illuminated, tubular sola r receivers, the United Stirling 4-95 kinematic Stirling engine developed for automotive applications, and silver/glas s mirror dishes. A sketch of the United Stirling Power Conversion Unit (PCU), including the directly illuminate d receiver, is shown in Figure 6. The Advanco Vanguard system, a 25 kW e nominal output module, recorded a record solar-to-electric conversion efficiency of 29.4% (net) using the United Stirling PCU [1,11]. This efficiency is defined as the net electrical power delivered to the grid, taking into account the electrical power needed for parasitics, divide d by the direct normal insolation incident on the mirrors. MDA subsequently attempted to commercialize a system using the United Stirling PCU and a dish of their own design. Eight prototype systems were produced by MDA before the program was canceled in 1986 and the rights to the hardware and technology sold to Southern California Edison (SCE). The cancellation of the dish/Stirling program was part of MDA's decision to cancel all of their energy related activities, despite the excellent technical success of their dish/Stirling system. The MDA systems routinely converted sunligh t incident on the concentrator's mirrors to electricity with net efficiencies of about 30%. Southern California Edison Company continued to test the MDA system on a daily basis from 1986 through 1988. During its last year of operation,

Crankshaft

Crankshaft

Kinematic Stirling Engine
Figure 6. Schematic of the United Stirling 4-95 Kinematic Stirling engine.

it achieved an annual efficiency of about 12%, including system outages and all other effects such as mirror soiling . This is also a record for solar energy systems. Without outages, an annual efficiency of over 23% was determined t o be achievable [12-15].

In the early 1990s, Cummins Engine Company attempted to commercialize dish/Stirling systems based on free-piston Stirling engine technology. The Cummins development efforts were supported by SunLab through two 50/50 cos t shared contracts. (SunLab is a "virtual" laboratory composed of the solar thermal programs at Sandia National Laboratories and the National Renewable Energy Laboratory.) The Dish/Stirling Joint Venture Program (DSJVP) was started in 1991 and was intended to develop a 5 to 10 kWe dish/Stirling system for remote power applications [16] . The Utility Scale Joint Venture Program (USJVP) was started in late 1993 with the goal of developing a 25 kWe dish/engine system for utility applications [17]. However, largely because of a corporate decision to focus on its cor e diesel-engine busi ness, Cummins canceled their solar development in 1996. Technical difficulties with Cummins' free-piston Stirling engines were never resolved [18].

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