Related Interests - Sterling & Fresnel Come Calling

Seems that if a person has a good Amateur Radio interest that they are also prone to have a generalized interest in technology.

I’m in that large class of Radio Amateurs, having plenty of “tinkering projects” going!

A couple that have caught my recent attention are the low-temperature differential Sterling Engines being experimented with, and with Thermal Generation (of heat and/or electric power) by Fresnel lens.

In the Sterling world some device are now running with a Δt (Delta-t for Differential in Temperature) of just a few degrees.  The small Δt sterling engine opens the possibility of meaningful power from from energy differentials like the change at evaporation, or from ambient summer air to water temperature in a body of water.  Obviously more energy than can be gained shouldn’t be required to co-locate or create the situation where an usable Δt occurs.  Though where a parasitic opportunity for a usable Δt happens in other, perhaps natural, systems the possibility of energy generation is there.

Whether low-Δt devices are limited to perhaps small scale autonomous power generation, perhaps at the nano or micro level for perhaps powering sensors, or whether the technique could provide larger scale power is an unanswered question.

In exploring Sterling technology we’ve been playing with model engines – the sort that have been desktop hobby demonstration engines for years – and having a blast playing with the little devices.

These engines are high-Δt sterling devices, requiring several hundred degree Δt differentials to overcome friction and efficiency limitations.  Looking for a non-combustion source of that high differential led to the interest in Fresnel lenses.

The Fresnel lens variety we’re playing with is a focused lens that takes the combined solar energy of its 2 ft x 3 ft area bringing it to focal point in a roughly  4 square  inch area.  Observed temperatures exceeding 1200F have been reported, though my less careful use & measurement is showing a bit less than 2/3rds – still enough energy to be significantly useful!

I’ve sketched a heat-sink/receptor to bring this area down to the smaller focus to work with the model sterling engine to complete the experiment.  More on the Fresnel-Sterling combination when I can get back to the testing.

A further natural extension, especially if the desired output is less the mechanical rotational energy of the sterling, and more electrical energy, is to use the Fresnel energy for direct conversion, perhaps via a Peltier Junction device.  In the interest of this possibility I’ve sourced a small Peltier Junction for testing as well.

Perhaps I can get enough solar energy to charge batteries to run a QRP rig?

In clarity the total energy to create the equipment is disproportionate to the results at this stage, making this a group of “fun experiments” rather than a cost-effective solution – at least at this stage!

73

Steve
K9ZW

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