Robert Stirling's engine patent

A technology with a history

The Stirling engine is an invention conceived over 200 years ago. It has, however, not been used to the extent that we predict will be the case in the coming years. Improvements to the technology itself, coupled with the overall shift in society towards less use of fossil fuels, will lead to more people using the Stirling technology and its unique benefits.

The engine itself is a heat engine. This means that its basic principle revolves around taking a difference in temperature and converting it into mechanical action. To achieve this, gas is kept in a closed canister. Various parts of the canister are heated or cooled, resulting in the gas in the respective parts either expanding or contracting. The change of volume is used to force a piston back and forth, which in turn can power something else, such as a flywheel. In the case of Ripasso Energy, the motion is used to power a generator, delivering electricity.

Stirlingmotor in Betrieb

Unique characteristics

In the field of climate-smart and cost-effective power generation, the Stirling engine has a number of aspects making it especially well-suited. These are characteristics either not shared at all with other engine technologies or that are more pronounced in the case of the Stirling engine. For example, the Stirling engine can be powered with virtually any source of heat. It is quiet and close to completely free from vibrations. Heat, whether it is from concentrated sunlight or from combustion, is applied to the engine only externally, meaning outside the engine itself. Above all, the Stirling engine has a remarkable capability of converting heat energy to kinetic energy. This aspect, the exceptional efficiency with which it accomplishes the conversion of energy forms, has lead to that the engine developed by Ripasso Energy retains the unofficial world record in solar energy to grid-quality electricity efficiency of 32 percent. This number is almost twice as high as for conventional solar panels.

Ripasso solhybrid

Hybridised technology

Capitalising on the fact that the engine can be powered by virtually any fuel, Ripasso Energy has developed a hybridised engine where solar energy is combined with some other fuel during the dark hours of the day. Practically any fuel in liquid or gas form can be used, such as LNG, biogas, ethanol and more. Since the engine itself is a closed system and only heated from the outside, different fuels can be gradually phased in or out based on availability.

PWR BLOK inside1

Large number of fuels possible

The fuel insensitivity of the Stirling engine, due to the heat only being applied externally, means that residual and flare gases also can be used to generate electricity. These gases – common biproducts in certain industries – have up until now not had any finically viable area of use. As a result, they are today simply burned in a process called flaring. This is an enormous waste and on the global scale, the energy content of the gas being flared each year is estimated to be that of the yearly power consumption of the entire African continent (OPEC Bulletin 5/15). The Stirling technology will make it possible to burn the gas while at the same time extracting its energy content. Moreover, this can be done at a price much lower than the current price of power at most markets.


Large-scale production benefits

Historically speaking, the main drawback of the Stirling technology has been the high production cost. Since the start in 2008, Ripasso Energy has developed and adjusted the engine for large-scale production. This has been done together with our manufacturing partner, Sibbhultsverken Group AB, a company with extensive experience from manufacturing parts for the automotive industry. The Stirling engine found in the products of Ripasso Energy has very low maintenance costs and price of the engine itself falls rapidly as production volume increases.