Stirling Solar Power Generators

In addition to SEGS, ISCCS, PV, and updraft tower methods for collecting solar energy, Stirling solar dish systems are also used (Figure 1.38). These units focus the Sun's energy onto H2 in sealed Stirling engines. As the H2 is heated to 732°C (1,350°F), it expands and drives the pistons of the engine. Stirling engines are used on submarines because they are quiet (no combustion takes place). In solar applications, their main advantage is their high efficiency (30%), which is nearly double that of the best PV collectors. These closed systems do not need to be refilled, only their mirrors need washing every couple of weeks. The operation can be fully automated including start-up in the morning, shutdown in the evening, tracking the Sun, and remote monitoring over the Internet.

The present cost of a 25 kW, 944 ft2 stand-alone prototype unit is about $150,000. This price is likely to drop as production volume rises. Stirling Energy Systems, Inc., is operating a six-dish test unit at Sandia National Laboratories and has contracts for full-size power plants. Their construction started in 2008 and will be completed in 2012. A 500 mW plant will be built at Victorville, California, in the Mojave Desert for Southern California Edison. This construction is estimated to take 3-4 years. The plant will consist of 20,000 dishes over a 4,500 acre area. Another 300 mW plant will also be built at Imperial Valley, Calexico, California, for San Diego Gas and Electric on an area of 2,000 acres.

The Stirling engine contains a fixed quantity of gas (H2) that is moved back and forth between the hot and the cold ends of the engine. As the gas is moved, it expands and contracts, and this change in volume is used to drive

Stirling Plant Engine

figure 1.38

California Edison's 25 kW dish/Stirling system, McDonnell Douglas/Southern California. The 944 square foot concentrator consists of 82 spherically curved glass mirrors, each 3 ft by 4 ft. The United Stirling 4-95 Mark II engine (four cylinders of 95 cc displacement) uses hydrogen at a maximum gas pressure of 2,900 psi. This engine delivered 25 kW output at 1,000 W/m2 insolation. (Courtesy of Stirling Energy Systems—SES.)

figure 1.38

California Edison's 25 kW dish/Stirling system, McDonnell Douglas/Southern California. The 944 square foot concentrator consists of 82 spherically curved glass mirrors, each 3 ft by 4 ft. The United Stirling 4-95 Mark II engine (four cylinders of 95 cc displacement) uses hydrogen at a maximum gas pressure of 2,900 psi. This engine delivered 25 kW output at 1,000 W/m2 insolation. (Courtesy of Stirling Energy Systems—SES.)

the engine. In Figure 1.39, the hot end (which is heated by the Sun) is on the right, and the cold end (cooled by the ambient air) is on the left.

In phase #1 of the cycle, when most of the gas is in the "power piston" (the hot end on the right), the gas is heated by the Sun and it therefore expands, forcing the power piston to the left. This is when the engine does the work,

Solar Energy Piston

at Crankshaft figure 1.39

One version of the Stirling engine, with the "power piston" on the hot (right) side of the engine and the "displacer piston" on" the cold (left) side.

at Crankshaft figure 1.39

One version of the Stirling engine, with the "power piston" on the hot (right) side of the engine and the "displacer piston" on" the cold (left) side.

figure 1.40

Solar satellite collector planned by Japan for 2040.

figure 1.40

Solar satellite collector planned by Japan for 2040.

and the higher is the hot-end temperature, the more work it does. In phase #2 of the cycle, as the gas expands, it forces more gas into the "displacer piston" (the cold end on the left).

In phase #3 of the cycle, the gas is cooled by the ambient air in the cold end, while the displacer piston compresses the gas. Cooling contracts the gas (lowers its pressure), which makes it easier to compress it. In this phase of the cycle, energy is consumed by the engine (but less than the energy that was generated in phase #1). The lower the temperature, the less energy is consumed in compressing the gas.

The displacer piston on the cooling end on the left controls the direction in which the pistons move. It determines if most of the gas is in the piston on the right or left. In phase #4 of the cycle, the displacer piston on the left moves the compressed gas back into the power piston on the right. As the gas is returned into the power piston, it is heated at this hot end by the concentrated solar energy, and the cycle repeats.

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.

Get My Free Ebook


Responses

  • andreas
    How to Build Your Own Solar Powered Stirling Generator Plant?
    1 year ago

Post a comment