Ripasso Energy derives its technology from submarine engines developed by Kockums. Ripasso’s systems generate electricity from concentrated solar power with world-record efficiency. The engines are hybrids, allowing various fuels to be used when the sun is not shining. And commercialization is underway.

”Renewable energy sources such as solar and wind have many advantages, and they are becoming increasingly competitive as price keeps falling. Still, renewables have a well-known drawback in the fact that production is not continous, but varies over the day and between seasons. Energy storage may provide a solution, but not until the technology is developed further. Therein lies our opportunity”, says Gunnar Larsson, CEO and founder of Ripasso Energy.

”We have developed a stirling engine that can produce electricity around the clock. Solar is the primary power source, but the hybrid engine is capable of utilizing gas or liquid fuels when there is not enough sunlight”.

World-leading submarine technology

The mirror dish focuses the sunlight to the stirling engine. The engine first converts heat to mechanical work, then to electricity. Photo: Ripasso Energy.

The stirling engine was invented 200 years ago by the Scottish clergyman Robert Stirling. The technology is based on alternate heating and cooling of an enclosed gas to drive pistons, converting heat to mechanical work. Kockums has developed the engine type for use in military submarines for 30 years, and their engine is the world-leading in this application. The stirling engine can be powered by practically any energy source, and it can be virtually vibration free. The acoustic properties provide an important advantage in submarines, making the movement more difficult to track by sonar. Engines in solar power applications, where acoustics are less of an issue, are not entirely quiet.

While the stirling engine makes for excellent conversion from solar energy to mechanical work – and, via a generator, to electricity – manufacturing the engine is expensive. Volume production will be needed to bring the cost down and make the technology competitive. Still, compared to a combustion engine, the construction is less complex and easier to mass produce.

”With exclusive licence from Kockums, we have developed a unique hybrid adaptation of the Stirling engine that can harness solar energy as well as a wide range of fuels. The technology is proven in the context of submarines, and Kockums has successfully developed sealing solutions that allow high efficiency. Since the heat energy source is external to the Stirling engine rather than generated by internal combustion, the components don’t get dirty and maintenance intervals can be prolonged to 6 000 hours. We estimate at least 25 years of service life”, Gunnar Larsson says.,

Ripasso’s energy system consists of a parabolic mirror dish, slowly rotating to follow the sun. The sunlight is reflected to a 33 kW stirling engine in the focal point, heating enclosed hydrogen gas to drive pistons. The system provides alternating current directly without the need for additional DC/AC converters, water cooling systems or complex central units. The system converts concentrated solar radiation into electrical energy at a high rate of efficiency.

”The total solar-to-grid quality efficiency of the system is above 30 percent and in our test facility in South Africa, a world leading efficiency of 32 percent was demonstrated a couple of years ago. Thanks to the hybrid adaptation, solar energy can be complemented with biogas, waste gas or other fluid fuels at times when solar radiation is not available. None of our competitors can offer a solution that can match ours in availability or utilize different energy sources in the same system. After four years, results from the pilot plant have been very convincing, both operationally and maintenance-wise”, Gunnar says.

Experience from the truck industry

The hybrid technology, allowing solar to be combined with other fuels, is one of Ripasso’s advantages; another is the lesson learned from submarine engine development, according to Gunnar Larsson. Photo: Ripasso Energy

”Together with Sibbhultsverken in Skåne, we have worked hard to lower the cost of production. Sibbhultsverken has manufactured transmissions for Scania, and we are using standard automotive components as much as possible to drive down cost to a competitive level. The current production process is easily scalable. When we reach a production volume of 100 to 1000 unites per year, the price will be  favorable compared to alternative technologies”.

”In the years to come, we will produce systems for commercial facilities. We are planning sixteen solar hybrid projects on Sicily together with our Italian partner, Horizon.”

Ripasso Energy is expecting that an order for at least 100 engines will be completed in 2018:

”We will have our first commercial facility in operation within less than a year’s time. It will serve as an important reference for the viability of our technology. The potential is huge and the annual value of the market is 50 billion SEK. Our technology offers higher efficiency and reliable power delivery, making it attractive”, Gunnar Larsson says.

The article was published in May 2017.