ECHECCRRWH           The Efficient Conversion of Heat into Electricity

                                         using Convection Currents and Repeated

                                         Recycling of Waste Heat

The Dream Machine


Heat is converted into electricity with about 40% efficiency in power stations. Motor vehicles have efficiencies only ~20%. Solar energy conversion is typically below 10% using the most sophisticated and expensive technologies.

A new set of concepts is described below for the conversion of solar energy or combustion heat into electricity. No practical work has been carried out and no quantitative or theoretical calculation. The Williams engine is a design based purely on my understanding of heat and the kinetic theory of gases.


There are three unusual features:

  1. The system is driven by convection currents alone. There is no pump. Combustion and generation are at normal atmospheric pressure.

  2. The turbine produces electricity from both incoming air and outgoing hot gases.

  3. Efficient heat recovery from the gases leaving the turbine repeatedly recycles waste heat to prewarm incoming air.


It has been put to me that the second law of thermodynamics applies to all energy conversion imposing a maximum efficiency of DT/T. I maintain that the second law applies to a closed system as in the Carnot cycle but that in the apparatus described the turbine is simply driven by airflow. The maximum efficiency is then around 60% as in wind turbines or up to 80% as in the turbine component of the solar chimney. The Wells turbine achieves even higher efficiency.

If the second law does apply then for combustion gases at 500 C the maximum efficiency would be about 480/773 about 60%. But residual heat energy in the effluent gases from the turbine will be absorbed in the heat exchanger by incoming air. Such energy recovery systems can be over 95% efficient so that waste heat will be recycled a second, third .. time to achieve an eventual over 80% overall efficiency.

If the above configuration was used for solar energy conversion the temperature involved could be 20 C for ambient air and 30 C after solar absorption. If the second law applies this would give a maximum efficiency of 3%. But any heat rejected by the turbine will be reabsorbed in the heat exchanger and recycled into the incoming air. This will drive up the temperature of air entering the turbine imposing higher efficiency. Heat rejected at first presentation to the turbine will be reabsorbed a second, third .. 10,20 .. 100 .. times until air leaving the apparatus is reduced to just above ambient temperatures. By this repeated recycling of rejected energy, a cumulative efficiency of over 80% should be achievable. Indeed the only energy loss is in the warm air leaving.

Thus, whether the second law of thermodynamics applies or not, efficient recycling of waste heat should allow conversion of heat into electricity with over 80% efficiency. It may be that the above ideas are fundamentally flawed and that the Williams engine will produce very little electricity and only lots of hot air.

It is my contention however that the principles described will allow conversion efficiencies of over 80% heat into mechanical or electrical energy. The source of heat can be fossil fuels or solar energy. The principles should apply to motor vehicle engines, power stations, roof solar electricity and large scale solar farms. If that is indeed the case then that is global warming solved.


I would suggest that the apparatus outlined be called the Williams engine. If there are problems of copyright versus Formula One (!) then that it be called ECHECCRRWH the Efficient Conversion of Heat into Electricity using Convection Currents and Repeated Recycling of Waste Heat or more simply, the Dream Machine.


Dr Alan Williams

                                                                                                                                                                November 2000

E-mail address:  williams.a(AT)