Hybrid systems can increase fuel efficiency in urban areas by up to 30%. The most common hybrid systems seek to harness braking energy in kinetic or electrical recovery systems, and then use it when the primary engine would be operating inefficiently. Hybrid systems for large vehicles are expensive, hard to retrofit, and without subsidy the economics are insufficiently attractive for them to be deployed.
However, typically vehicles lose about two thirds of the available energy in their fuel as waste heat. Heat recovery technologies to capture high-grade waste heat have been developed, but in urban settings insufficient heat is generated to make these technologies economically viable.
There is an alternative. A Dearman engine working alongside a diesel engine – a heat hybrid. Dearman technology is capable of offering a unique combination of heat recovery and hybrid power, delivering similar levels of fuel saving to other hybrid systems, but at a much lower cost, resulting in a comparatively rapid payback.