Y-Machine      

Further Development: Novel Stirling Engine

The Concept

Sunvention’s SunPulse engines have proven that it is possible to efficiently transform solar radiation to mechanical and electrical energy at relatively low temperatures and small temperature differences. It has become possible to produce efficient machines with relatively simple technology.

So that these machines can be constructed in simple workshops and in the so-called Third World, normal air at atmospheric pressure was chosen as a working fluid. The resulting engines are relatively large, and run at low rotational frequency.

To achieve higher output power in the range of several 10s of kW, it is necessary to make the engine smaller. This means either increasing the pressure of the working fluid (air) and/or increasing the rotational frequency of the engine. The Y-Machine represents such a development of the SunPulse engine.
A working pressure of 200 bar was chosen, which implies a 200-fold size reduction over the SunPulse engine at the same rotational frequency. The rotational frequency was deliberately kept low to achieve a very long engine lifetime and good thermodynamic transfer efficiency.

To do so, it was necessary to develop a novel heat exchange system for both the hot and cold sides, capable of effective heat transfer at temperatures below 100 degrees Celsius. This is very elegantly achieved through a combination of a liquid displacer piston and the use of a few quirks of physics.

Each pair of cylinders is expected to produce 5 kW

The Y-Machine can therefore transform heat from high-quality flat panel collectors, such as vacuum tube collectors, into mechanical and electrical energy. As heat from solar collectors can easily be stored in the form of hot water, it becomes possible to construct solar engines which run around-the-clock. This is a very important aspect of local autonomy. Such systems are cheaper, longer-lasting and more robust than photovoltaic systems coupled with electrochemical batteries.

Its novel heat exchanger also enables the Y-Machine to operate very well in reverse for refrigeration or as a heat pump. Refrigerants, as usually used for vapor-compression chillers, are not needed. Heat is transferred directly from the working fluid (air) to the heat transfer medium (water). Space-heating or cooling is easy using conventional piping and heating or cooling elements.

Sunvention is developing a 5kW Y-Machine to pilot-production stage by early 2012. It will be possible to electrically couple Y-Machine modules together to achieve higher output powers (5,10,15,20 kW).

The Y-Machine can also operate at higher temperatures, such as are generated for example in the lens system of Sunvention’s EPG, or using precision fixed-focus pneumatic mirrors developed at Sunvention. Higher efficiencies can be reached than are possible with flat panel collectors, but the simple non-pressurised water system must then be replaced with either a hot oil system such as is used in the EPG, or a pressurised water system. The necessary modifications are being developed.

For long periods without sun, the system includes an additional biogas or biomass burner. The Y-Machine can then supply buildings or settlements with energy around the clock, also in developed countries.