Invention Idea

[Nomad76]

I have an idea for an off-grid solar thermal power generator - something small scale, just enough to power a sensor or maybe a camera - with no external panels or anything obvious other than a ground level concrete pad (which could also be buried under a couple inches of dirt).

I had thought this up as just a design exercise. The idea is to use the temperature differential between day and night to generate a small amount of electricity to keep a small battery charged to power a minimalist monitoring system. The point is to have this system work without any outside visible features for a buried, hidden facility.

My initial purpose was to maintain a primary monitoring system for an off-grid, subterranean structure. I wanted a way to monitor the status of the structure while I am out of the country. I want this to have no externally identifiable features to keep the facility hidden to casual observers. There would be a secondary, more robust alarm/monitoring system which is dormant until the primary system is triggered.

My question to the forum - can you think of any other applications for this kind of power generating system?

 

[Shimmy]

You need a pretty big diurnal temperature swing year round to make it work, but you could conceivably use it for just about anything that is hard service IoT type stuff. Street water meter communication, sump alarm, redundant gate sensor...

 

[Nomad76]

This would be a bit large - probably about a meter cubed. All underground.

I am thinking this would be good for a remote location like an uninhabited island or remote desert. Somewhere that periodic maintenance would be too costly or too much trouble. It should be able to run for two or three years without maintenance. These types of locations also generally have large diurnal temperature swings too so it's a good fit.

 

[Warpspeed]

If you worked it all out, the rather small amount of continuous power required, and the required expected lifetime.
It may work out cheaper and simpler in the long run just to bury some large batteries.....

You will need batteries anyway for anything that is ultimately sun powered.

 

[Shimmy]

This would be a bit large - probably about a meter cubed. All underground.

I am thinking this would be good for a remote location like an uninhabited island or remote desert. Somewhere that periodic maintenance would be too costly or too much trouble. It should be able to run for two or three years without maintenance. These types of locations also generally have large diurnal temperature swings too so it's a good fit.

Remember, you don't have large diurnal temperature swings year-round, even in (most) deserts.

A typical thermoelectric generator tops out at about 8% efficiency, so with a 1m2 black body radiator/absorber and a heat pipe to a storage vessle you would max out at ~300Wh/day. A real-world heat pipe and storage system would reduce that by about half, and relying on conduction and concealment would be another 80% of losses minimum on a good day... and your great day is maybe 30Wh; your average day is likely about 20Wh, so at seasonal lows you might only be talking aout 10Wh/day.

...or you could find a way to conceal a letter/A4/J4 sheet-sized solar cell or sections thereof.

 

[Nomad76]

Part of the idea for this design was to prevent problems from vandals or opportunistic thieves by not presenting any indication of equipment or facilities. It could be totally buried and still function.

The potential might be best closer to the equator where seasonal differences are minimal.

I really appreciate the input and all your time thinking and replying here.