Hello everyone,
Good idea Esgege, in any case intriguing, I admit that I myself let my neurons wander along this path.
There is no surunity.
Overall the association {PAC + Stirling} is nothing other than a large machinery operating between the ground and the air:
- the ground being in winter is warmer than the air, but it also works in summer with super hot air and very cold ground.
- This large machinery performs a QSolAir heat transfer between air and soil and delivers mechanical energy W = WStirling - WPAC
In fact, once started, the machine operates without external input, and operates between a hot and cold source, and delivers W mecha.
To sum up, as soon as there is a deltaT between the air and the ground, there is a little mechanical energy to take proportional to QsolAir.
The thermomechanical yield is then limited by that of Carnot.
The heat pump is only used for heating so that the Stirling has rapid heat exchanges and runs well. Otherwise, Stirlings with very very large heat exchangers would be necessary (small deltaTs limit thermal conduction per unit area ...).
But in the end, the mechanical energy recovered W = (Wstirling-WPAC) does not exceed the heat transfer between the ground and the atmosphere multiplied by:
* 1-Tsol / Tair if the ground is colder than the air
* 1-Tair / Tsol if the ground is warmer than the air
Valid for absolute temperatures (in Kelvin): So for 20K around 273K (0 ° C) difference, the yield between the mecha extract and the heat transfer is: roughly 1-273 / 300 = 9%
And this limit is ideal because any theoretical : in practice, losses mean that there is less than 5% yield for Stirling with minideltaT: ditto for this PAC + Stirling installation.
Otherwise, your Stirling yield of 40% is too optimistic because it corresponds to the heat supplied by a COP5 heat pump. However a COP5 supposes a very low temperature which in return can only give at best 1/5 in engine efficiency, i.e. less than 20% ...
A bit technical and complicated, sorry
pcq it does not do the business of my boss ... Total.
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