Low Temperature Stirling Engine for Waste Heat Recovery from Distributed Power Sources

"Since March 2006, Boulder, Colorado based Cool Energy, Inc. (CEI) has prototyped three generations of a novel low-temperature Stirling engine to generate electricity for low-to-medium temperature (100°C to 250°C) heat sources including solar thermal, geothermal and waste heat. With a marketing name for the SolarHeart® Engine, in its most recent operation in April, 2010, over 1800 watts of output electrical power was generated, exceeding its intended peak capacity. CEI’s main application focus with this engine has been a solar thermal system for distributed residential heating and power. This renewable energy system, the SolarFlow® System, consists of rooftop solar thermal collectors, the SolarHeart Engine, a solar thermal storage tank and associated heat exchanger plumbing to connect to conventional space heating and water heating systems. Integrated with the system is a Smart Grid compatible controller to calculate the optimal use of collected thermal energy in the building and deliver it as space hear, water heat, electricity or storage by the system. In a typical Solar Flow System installation, a roof-mounted 400-800 square foot array of evacuated tube solar thermal collectors is used with the SolarHeart Engine to provide up to 80% of the space heating, 95% of hot water, and 60% of the electricity needed annually by the home. This Solar Hear Engine is scheduled to be installed in the first pilot field solar Flow System in June 2010.

Concurrent with pilot installations, a final design for the SolarHeart Engine is being completed, whose output power is expected to reach 2000W at 250°C, with a peak thermal conversation efficiency of >20%. The engine also has applications for residential or building use of geothermal heat input, and can also be used to maximize the power output of distributed power diesel gensets by capturing their waste heat.

Cool energy’s roadmap includes higher output power Stirling engines for beneficial use of low temperature waste heat and renewable heat sources to target commercial and industrial buildings. In particular, the input heat (fuel) target is the abundance of low temperature waste heat (100-300C) rejected from fuel cells, microturbines, or diesel engines used for distributed or stand-alone electric power generation in buildings. EPA SBIR funding will enable Cool Energy to proceed with development of a 25 KWe Stirling Engine, at the opportune time when the current development of its lower output power Solar Hear Engine for use in residential and small commercial buildings is entering pre-commercialization stages.
"