Show HN: Homemade automated solar concentrator

Cool work! I do research in nonimaging optics, the optics of achieving high concentration ratios (or wide tolerances to errors) in solar concentrators.

I like that you are implementing closed-loop control. This is all the rage also in large-scale heliostat fields. Most traditional heliostats are controlled using open loop, which places very strict requirements on both the mechanical structure, the actuators, and on the kinematic model, leading to expensive and very stiff heliostats. People are therefore moving towards cheaper heliostats where the tracking precision is achieved through closed-loop control. Implementing closed-loop control is a little bit more tricky when you have overlapping focal spots from thousands of mirrors, but there are approaches that are being developed, e.g. having cameras around the target looking back out over the heliostat field (developed by Heliogen among others).

You mention the challenge of light only being focused for a few hours per day. This is also a problem with large helisotat fields, and is also a field of active research. There's a group at University of Arizona with Professor Roger Angel developing heliostats that actively deform through the day to keep the perfect shape, and there's also an Australian company (Heliosystems) building heliostats that passively deform from gravity to keep as correct shape as possible.

When you are only using a single heliostat, as in your project, you could also consider building it as a Scheffler reflector - placing it on a single-axis polar-aligned tracking axis that passes through your target. Then it only requires single-axis tracking through the day, with some (possibly manual) seasonal adjusting.

I am very happy to see that you are highlighting the inherent risks in concentrated sunlight. There are lots of stories about people accidentally settings stuff on fire if the tracking doen't track correctly.

Awesome project OP! Especially the power comparison. Who would have thought that you can achieve 1kW of energy from 1m2.

On a side note and in a similar direction. Would it be feasible to make a solar concentrator that heats a molten-salt reactor that powers a turbine engine? On a small-ish scale though, such that it'd be achievable as a back-yard reactor?

So the description I used above was my memory-driven understanding of it. But here is what I actually meant: https://en.wikipedia.org/wiki/Solar_power_tower

Edit. I went down a little rabbit-hole, HN. This is what I eventually found about small-scale energy generation using solar-concentration.

https://en.wikipedia.org/wiki/Solar-powered_Stirling_engine

https://en.wikipedia.org/wiki/File:Dish-stirling-at-odeillo....

Could be a semi-viable alternative to solar, perhaps? Though cost-wise, it's probably quite high now that solar-panels and their auxillary hardware have been commoditized so much.

Concentrated sunlight is deceptively powerful. We probably all have played with small handheld magnifying glasses to focus the sun to a small spot, burning paper or small wood blocks.

When I was a kid I had a Fresnel lens, probably 2' in diameter, out of an old projector or some similar thing. It would set asphalt on fire. Almost instantly. You could probably weld steel with sunlight, though not very conveniently.

If you make a large (1+ meter diameter) curved lump out of wet sand, you can use that to lay a fiberglass parabola which could then be chrome plated, painted, or otherwise finished on the inside of the parabola after it’s cured.

This would allow you to further concentrate the solar power beyond the current 48x limitation.

Am I understanding correctly that the angle between each mirror segment and the backboard is fixed once during construction and then not dynamic?

This is so cool, thanks for sharing! If I had a yard/space to build one of these, I would totally try rigging one up to drive a little heat engine.

Lots of interesting experiments with solar collection here: https://www.youtube.com/@sergiyyurko8668/videos

Very cool. Curious if you have looked into non-imaging (anidolic) solar collectors? My understanding is that they are actually more efficient than mirror or lens based collectors as they do not require precise aiming and are able to collect indirect sunlight as well.

Unfortunately in 2024 with extremely inexpensive solar cells, I don't see much future for this technology. Even fixed latitude tilt angles are coming into question given the modest cost increases that they create versus a flat or a vertical panel. It costs more to blow glass into vacuum panels than to acquire PV area.

Much of the developing world latched on to solar concentrator water heaters 10, 20, or 30 years ago, and they were common in a backpacking trip through China a decade back. It's good tech, depending on your climate, but it seems to have been superseded.

Hopefully this isn't a stupid question as I know very little about solar, but could the risk/danger be reduced with some kind of diffusion layer behind the target to "de-concentrate" the light in the event of a failure?

Magnifique, I would like to try baking a pie with such an oven!

With regards to the efficiency of the motion system, it occurs to me that your system only requires an occasional movement rather than a rapid movement for tracking purposes and therefore could conceivably build up the charge required for such motion over time. Such a build-up is inherently suited to renewable (solar, wind or thermal-recovery based) energy harvesting rather than the approach of powering the system from a separate electrical supply.

Secondly, the motion system appears to be single-ended and based upon a rope and a stepper motor. It would perhaps be useful to consider conversion to a more rigid system. I would suggest removing the line entirely, though if you want to keep it one possible option is that of steel wire, which can be had in a range of gauges and metallurgies. These are relatively very strong and inexpensive. Furthermore conversion to a closed loop would be desirable, ie. ability to turn in each direction. However, I would recommend a geared motor and a rotary track cut or milled in to a heavy base plate as a simpler solution with less parts and a higher probable efficiency. Ideally you could add a line-based system in case the motor has no power or breaks or something so people could point the thing manually in a worst-case scenario.

The use of a video/optical sensor path is inefficient from a processing perspective. While this is a great way to prototype an initial version, you are going to see issues around the presumption of a flat surface, the need for establishing a visual datum based upon peripheral codepoints, and distance estimates. Toward a more reliable, elegant and configurable solution one might suggest that a system of curves be established. Each row could become a single dimensional array with its own curve controlled by a single actuator (eg. a line) and then balanced off with springs, graduated mounting points, or some other counter-force, in order to effect inward curve at the elements closed to the end points. A major array would then separately angle all rows along the alternate axis. Done carefully this may be adequate for close actuation scenarios, though there is surely tradeoff between rigidity, precision, mechanical and control complexity, and efficiency. Assuming short distances, I suspect a simpler-is-best approach would be adequate. This could be combined with the critical element of a laser TOF ranging sensor to determine the subject range, which would inform the required algorithmic adjustment of the array geometry. In short, if you have knowledge of your own geometry, have known orientation relative that fixed point, and can before activation determine the TOF distance to your target, and have a GPS fix thus solar inclination at that moment is calculable, then it should be possible to track the target without the need for visual feedback.

In terms of temperature sensing, you can obtain remote temperatures using infra-red linear systems which should be effective.

In terms of safety, laser TOF ensuring no change in distance would ensure the subject is still within the programmed range and an intermediate object hasn't been introduced for combustion. Also, adding an IMS would be cheap and effective to detect events like being knocked over/moved and misalignment.

In terms of portability, it may be useful to use a collapsible carbon fiber structure derived from those seen in modern tents. Make the mirrors interchangeable so the collapsed form is tighter, they can clip on and also be readily replaced. If a concern is that the structure becomes too flexible, then consider adding more triangular structural elements, and potentially some form of self-tensioning system with a sprung tie-down.

In terms of gathering interest, not sure where you are based in France but I could suggest structuring the system as a public sculpture and holding events including eating food cooked by the system which could involve the additional sponsorship of local wineries, cider, etc. to garner social support.

As next steps first I would recommend mechanical prototypes for a single line operated adjustable curve system. Then I would recommend an array of those with the perpendicular axis on a stand. If necessary this could be prototyped as a fixed curve initially. Next the revised and compact stand (line-free), incorporating perhaps solar recovery for slow-tracking actuation. Finally an integrated control system with GPS, laser TOF distancing, IR thermal, IMS and the novel safety features.

Smiles from Sydney. I applaud your work toward the application of technology to social and environmental concern, we need more of this.