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Comment by zo1 | Hacker News Reader

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.

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1kw/m^2 is the "standard" rule of thumb for heat energy from solar irradiation. I'm unsure whether OP has done the calculation (in which case, credit to a well built system) or simply cited the standard rule.

There are some large Stirling engines out there that operate on hot oil. With a large diameter piston, quite a bit of torque can be generated with even small ∆T. Oil can be heated as with traditional solar water heaters (i.e., with no concentration), though concentration doesn't hurt.

I have developed a simple simulator [0] to estimate the theoretical power received by the target for a given hardware configuration:

- the global position on the planet

- the date and time

- the size and position of some background elements

- the number, size and position of the panels in the grid

The solar power estimation uses :

- the Python code provided in this article [1] to estimate position of the sun (thank you John Clark Craig)

- the simplified formula [2] to estimate the direct insolation from the sun position

- a custom light projection implemented using Panda3D game engine [3]

[0] https://github.com/remipch/solar_concentrator/blob/master/so...

[1] https://levelup.gitconnected.com/python-sun-position-for-sol...

[2] https://en.wikipedia.org/wiki/Direct_insolation#Simplified_f...

[3] https://www.panda3d.org/

Yes, there are several industrial applications that use a solar concentrator to drive a turbine engine or a Stirling engine.

I'm not sure it's a viable way to produce electricity on a small scale because:

- high thermodynamic efficiency requires high temperature difference

- photovoltaic panels are mass-produced and increasingly efficient

Personally, I think small scale concentrated solar power is most useful for applications that require direct heat (cooking, desalination, foundries).

In these cases, photovoltaics have a lower efficiency and a shorter lifetime.

My undergrad senior year thesis project was exactly this, back in 2011 - to use a solar concentrator to generate electricity. When we started the project, we thought the economics were cheaper than solar PV. At the end of the year, solar PV had already halved in price (this was when Germany and China were doing subsidy wars on solar).

Solar concentrator electricity must be super expensive compared to PV by now.

Sterling engines might be a bit too much maintainance to make it worthwhile compared to solar panels?

A engine wont run for years without part changes.

Solar panels are really cheap. Like, comparable to a mirror of the same size cheap.

A 15cm x 15cm mirror used in this project cost 1€.

That's 48€/m2, I couldn't find a photovoltaic panel at that price.

Add to that:

- photovoltaic efficiency is about 20%, while such mirrors reflect 90% of the energy

- photovoltaic panels have an average lifespan of 20 years, while mirrors do not wear out.

Anyway, we're comparing apples and oranges, because we have to add the mechanical installations, which are very different depending on the specific application.

I'm not against photovoltaic in general, I just think that for some applications there are some interesting alternatives.

Oh mirrors do wear out...

Oh yes, they do. I can be a little naive sometimes :-)

I still naively think that we could make mirrors completely encased in glass to limit their degradation (pure speculation here).

Which would make the cost of each mirror higher, right? Additional processing will naturally increase the cost per unit.

By the way, super cool project and thank you for sharing. My experiments with concentrating sun power when I was a child were directly related to the spontaneous combustion of insects. Still making amends for the number of ant hills my brother and I cooked with the sun.

> That's 48€/m2, I couldn't find a photovoltaic panel at that price.

Still apples to oranges but, $68 for > 2sqm at the factory, probably closer to $100 at retail:

https://www.alibaba.com/product-detail/144cells-Jinko-Solar-...

And in Europe: https://venturama-solar.de/produkt/ja-solar-jam54s30-425w-lr...

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