[HN Gopher] Show HN: Homemade automated solar concentrator
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Show HN: Homemade automated solar concentrator
Hi HN! I quit my job two years ago to have more time to work on my
side projects. The main one is an automated solar concentrator.
I've just open-sourced it, it's not perfect nor finished, and I
still have a lot of ideas for further development, but I'm
interested in knowing what you think of it. There are many
applications where concentrated solar power could be a viable
environmental and economic solution, I hope this technology will
one day be more widely used. Feel free to give any feedback and
ask questions.
Author : remipch
Score : 245 points
Date : 2024-08-29 10:14 UTC (12 hours ago)
(HTM) web link (github.com)
(TXT) w3m dump (github.com)
| londons_explore wrote:
| Am I understanding correctly that the angle between each mirror
| segment and the backboard is fixed once during construction and
| then not dynamic?
| remipch wrote:
| Exactly
|
| This has the advantage of requiring fewer motors (only two
| motors for the entire panel) instead of two motors per mirror.
|
| The disadvantage is that the light is only focused for a few
| hours a day.
| cheschire wrote:
| Another disadvantage being that your distance between the
| mirror system and the target must be fixed the same each time
| you setup.
|
| This isn't an inherently bad thing. As a marketable product
| this would imply a one-time manual alignment for all 48
| mirrors but cheaper lifetime maintenance costs.
| regularfry wrote:
| If you were going to sell a kit, having 48 sets of 3d
| printed mirror mounts of the right length for each position
| wouldn't be out of the question. Just a screw-on clip with
| the right length standoff for each mirror corner would be
| all you'd need. You could conceivably have different sets
| with different focal lengths.
|
| I don't think it would be too fiddly done that way but it
| might take some work to make fine adjustments
| straightforward.
| phkahler wrote:
| It is possible to make a mechanical angle bisector. Think of
| a compass for drawing circles but with a 3rd arm bisecting
| the angle. If you attach the bisector normal to a mirror, you
| can point one leg at the sun and the other at a target. An
| array of these would require linkages to aim all inputs
| parallel toward the sun and all outputs fixed toward the
| target - the outputs don't have to be parallel just have each
| pointing at the target. 2-axis actuation to move all mirrors
| as needed. Not sure if this has ever been tried, it's just an
| idea I had some time ago.
| hakonjdjohnsen wrote:
| This is a really cool concept! The term used for connecting
| mirrors to rotate together is a ganged heliostat. Most
| papers about ganged heliostats don't do anything fancy like
| what you describe, but there are some patents that show a
| nice way of connecting the rods to give the correct angles
| using a slightly different concept than what you are
| describing [1]. I previously made a visualization of how
| that concept works (click and drag the sun) [2].
|
| I've not seen exactly what you describe published anywhere,
| but it sounds very smular to something I thought about as
| well. See this 2d illustration [2]. Is this the same as
| what you are describing?
|
| I had a masters student try to make it mechanically. It
| turns out that though it's an elegant concept, you still
| end up with quite a few moving parts so it's a bit tricky.
|
| [1] https://patents.google.com/patent/US20060060188
|
| [2] https://folk.ntnu.no/haakonjj/ganged_heliostat_illustra
| tion....
|
| [3] https://folk.ntnu.no/haakonjj/ganged_heliostat_gear/
| conkeisterdoor wrote:
| 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.
| remipch wrote:
| Thanks for your nice comment.
|
| Yes it's definitely fun to build one and use that free energy
| from the sun.
|
| I was particularly happy to eat my first solar gratin :-)
| hakonjdjohnsen wrote:
| 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.
| remipch wrote:
| Thank you very much for your kind and detailed reply!
|
| Indeed, the closed-loop control was the initial idea which
| convinced me that it would be possible to build the mechanical
| parts by hand with common tools. In other words, the software
| "smartness" compensates for the mechanical "ugliness".
|
| Another initial idea was to do multi-panels (several orientable
| panels) with a single camera looking at the target. Indeed,
| it's not easy, so I finally went back and decided to finish and
| release something with a single panel.
|
| Nevertheless, I have some ideas to do multi-panels with a few
| more cameras. I would like to work on them in the near future.
|
| Thank you for all the references, I will spend time to explore
| them.
|
| There is also a company that uses vacuum to adjust the mirror
| shape, I'll try to find it and post it here.
|
| I wanted to emphasize the inherent risk because my project is
| not a finished product, but a work-in-progress/proof-of-
| concept.
| hakonjdjohnsen wrote:
| Yeah exactly!
|
| I like your cable-drive concept by the way. Did you describe
| it in more details anywhere? Heliogen were also developing a
| cable-drive system for their commercial heliostats, but I
| don't know if they are still working on it.
|
| How are you getting the right mirror orientation for each
| mirror (aka canting)? Custom spacers for each mirror?
|
| One trick for closed-loop control with many heliostats/panels
| is to have a few cameras surrounding the receiver. When they
| look back at the mirrors, they will see the circumsolar
| radiation (how the sky gets brighter as you get closer to the
| sun). By comparing the brightness of the sky at different
| cameras, you can estimate which cameras is "closest" to
| seeing the real sun, and get an estimate for the real
| position of the sun.
| remipch wrote:
| > I like your cable-drive concept by the way. Did you
| describe it in more details anywhere?
|
| I didn't take the time to describe the cable-bot concept in
| detail.
|
| I modeled almost all the mechanical parts with OpenSCAD,
| but I struggled to model the cable itself.
|
| In the "mechanics" README [0] you can click on any image to
| view it in an online 3D viewer.
|
| The following note in the same README tries to explain how
| the cable is used : Each cable is
| actually wrapped around the motor axis, then passed through
| the pulley and tied to a fixed ring in the corner of the
| panel.
|
| English is not my first language, is this sentence clear
| enough ?
|
| You can see these elements in the main 3D viewer [1]
|
| > How are you getting the right mirror orientation for each
| mirror (aka canting)?
|
| I use one bolt that pulls the mirror holder in the center
| and 3 bolts that push it in the corners.
|
| By screwing or unscrewing the corner bolts you can
| precisely orient each mirror independently.
|
| The "panel_board_exploded" view tries to show this [2]
|
| > One trick for closed-loop control with many
| heliostats/panels is to have a few cameras surrounding the
| receiver.
|
| Super clever, thanks for the explanation!
|
| I think it might be tricky to calibrate.
|
| [0] https://github.com/remipch/solar_concentrator/blob/mast
| er/me...
|
| [1] https://remipch.github.io/solar_concentrator/view_3d.ht
| ml?mo...
|
| [2] https://remipch.github.io/solar_concentrator/view_3d.ht
| ml?mo...
| hakonjdjohnsen wrote:
| > Each cable is actually wrapped around the motor axis,
| then passed through the pulley and tied to a fixed ring
| in the corner of the panel.
|
| Thanks, when seeing the video again now it makes sense! I
| didn't catch the counterweight the first time I saw it.
| Nice! In the Heliogen concept I mentioned previously they
| got around having to use a counterweight by attaching the
| other side of the cable to another part of the panel,
| such that the cable length stays approximately constant.
| Then they used a spring to compensate for the small
| changes in cable length that are inherent to the
| geometry.
|
| > I use one bolt that pulls the mirror holder in the
| center and 3 bolts that push it in the corners. By
| screwing or unscrewing the corner bolts you can precisely
| orient each mirror independently.
|
| Nice! Even in large heliostat fields it is often done in
| a similar way. It becomes quite labor intensive when you
| have thousands of heliostats in a field, with 10+
| segments each, so there are ongoing efforts to find ways
| to do it automatically or to get around the need for
| doing it in the first place.
| remipch wrote:
| FYI, this is the "vacuum adjustable focus mirror" I
| mentioned:
|
| https://lm.solar/order/4-square-rigid-aluminum-composite-
| mir...
| foobarian wrote:
| Speaking of risks and fire, is there a known limit to the
| temperature achievable by concentration? I was wondering if I
| could melt a piece of tungsten with this method.
| remipch wrote:
| I think it depends on the mirror area. The more mirrors, the
| more power. The more power, the higher the temperature will
| be.
|
| Anyway, tungsten melts at 3422degC, I don't know if it's
| feasible.
| foobarian wrote:
| Imagine we built a giant concentrator in space so we can
| melt tungsten without having to worry about containment!
| hakonjdjohnsen wrote:
| Yes, and it is super-interesting!
|
| The fundamental limit is given by the 2nd law of
| thermodynamics - you can never reach higher temperatures than
| the surface of the sun, or around 5800 K. We have the
| atmosphere that absorbs and scatters some of the light, so on
| the surface of the earth it is a bit lower, but not by a huge
| amount.
|
| This means that there is a fundamental limit to how small and
| intense you can make the focal spot in a solar concentrator.
| The limit is around ~45 MW/m2 or 45000 "suns" (which is
| plenty high, but far from infinite).
|
| Concentrators used for eletricity generation use much lower
| concentration than this, on the order of 25 suns to 1000 suns
| depending on the type. There are also solar furnaces designed
| for reaching much higher concentration by using a different
| type of optics. The most impressive one is the huge Odeillo
| solar furnace [1]. I would guess that they could melt
| tungsten, but I have not actually run the numbers.
|
| I did a talk last week about a concept we are developing for
| reaching furnace-level concentration ratios with conventional
| heliostats [2].
|
| [1] https://en.wikipedia.org/wiki/Odeillo_solar_furnace
|
| [2]
| https://folk.ntnu.no/haakonjj/talks/2024-08-19-nonimaging-
| fr...
| foobarian wrote:
| The thing that I can't wrap my head around is that if the
| concentrator "pumps" power into an object, and say you can
| somehow insulate it to stop the losses, how is this limit
| not unbounded? Where does the energy go once we reach the
| cap?
|
| Does the black body radiation send the energy back out?
| hakonjdjohnsen wrote:
| > Does the black body radiation send the energy back out?
|
| Exactly, this is the issue. If an object is able to
| absorb sunlight, it is also able to emit blackbody
| radition back towards the sun. When the temperature limit
| is reached, these two exactly cancel each other. The
| object will emit blackbody radiation with the same
| brightness as the surface of the sun.
|
| Another way to look at it is to imagine yourself standing
| at the center of the concentrated sunlight and looking
| out towards the concentrator. The concentrator makes the
| sun look "bigger" from your perspective, and this is what
| makes the sunlight concentrated. The limit to this effect
| is if the sun fills all directions in the whole
| hemisphere above you. Now it will be as if you are
| standing on the surface of the sun, and all you can see
| in any direction is sunlight. Normally, the solar disc
| fills 1/45000th of the hemisphere above you here on
| earth, thus the limit of 45000 suns concentration.
| foobarian wrote:
| That's a very insightful way to look at it, thank you!
|
| ps. It's like making a VPN tunnel to the surface of the
| sun :-)
| hakonjdjohnsen wrote:
| > ps. It's like making a VPN tunnel to the surface of the
| sun :-)
|
| Wow, I love that! Great analogy!
| remipch wrote:
| Nice explanation, thanks
| micw wrote:
| Thank you so much. It's the first time I do understand
| the _why_ of that fact.
|
| But I could build up a lot of solar panels and use the
| electricity to heat up an oven more than the surface of
| the sun, right? Is that "cheating" in terms of thermo
| dynamics?
| hakonjdjohnsen wrote:
| Great question, and this shows why we could never get a
| 100% efficient solar panel. Otherwise your scheme would
| brak thermodynamics.
|
| The most efficient possible way to convert sunlight to
| electricity is ~86% and is related to the second law of
| thermodynamics. So we use the heat flow from a hot
| reservoir (sun) to a cold reservoir (earth) and are able
| to convert some of that heat into work (electricity)
| which can then be used to heat something else to a higher
| temperature without breaking the second law.
| p1mrx wrote:
| > I could build up a lot of solar panels and use the
| electricity to heat up an oven more than the surface of
| the sun, right?
|
| Yes, this would be like using a hydroelectric dam to
| power a fountain that sprays higher than the initial
| reservoir. Machines can convert a large amount of low-
| quality energy into a small amount of high-quality
| energy, even when passive components (e.g. mirrors or
| pipes) cannot.
| IncreasePosts wrote:
| Yes...in the situation where somehow the oven became
| hotter than the surface of the sun, then the oven would
| start heating up the sun.
| aidenn0 wrote:
| Wikipedia says a max temperature of 3500C, which is above
| Tungsten's melting point. Graphite is the only thing I know
| of with a melting point above that at 1atm, but I'm not a
| chemist so I'm sure there are other things.
| dekhn wrote:
| Check out: https://what-if.xkcd.com/145/
| adrianN wrote:
| Platinum was first melted using concentrated solar iirc.
| algo_trader wrote:
| > with some (possibly manual) seasonal adjusting.
|
| Any pointers for floating PV seasonal mechanism?
|
| With a 5m high prism, and panels along ONE face, how do you get
| seasonal adjustment of the panels tilt angle.
|
| An adjustable/inflatable ballast seems the simplest?
| zo1 wrote:
| 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.
| argiopetech wrote:
| 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.
| remipch wrote:
| 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#Simplifie
| d_f...
|
| [3] https://www.panda3d.org/
| remipch wrote:
| 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.
| pjc50 wrote:
| Solar panels are _really_ cheap. Like, comparable to a mirror
| of the same size cheap.
| remipch wrote:
| A 15cm x 15cm mirror used in this project cost 1EUR.
|
| That's 48EUR/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.
| newprint wrote:
| Oh mirrors do wear out...
| remipch wrote:
| 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).
| monkmartinez wrote:
| 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.
| lm28469 wrote:
| > That's 48EUR/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...
| cheschire wrote:
| 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.
| remipch wrote:
| Good idea, thank you!
|
| However a 20cm x 20cm square spot can be better for some
| applications.
|
| If you want to cook something it's best to spread the heat over
| the entire baking sheet to ensure even cooking.
| cheschire wrote:
| For the specific use case of cooking, I think the problem you
| will run into is that solar power is inconsistent which is
| problematic for cooking via direct heat as you tend to need
| consistent temperatures.
|
| So instead I would look at indirect heat. By super-
| concentrating the full parabolic area into a single point,
| you can heat cooking stones which will radiate heat more
| consistently even when clouds momentarily block the sun.
|
| Using a simple store-bought pizza stone suspended at a
| 45-degree angle above your food, the homemade solar "laser"
| (said in Dr. Evil's voice) could be targeted on the
| underside, directly above the food.
|
| Placing firebrick or other insulating stone directly on the
| opposite side of the pizza stone would help ensure that
| minimal energy is lost through the rear.
| phkahler wrote:
| Decades ago, my brother used the inside of a large umbrella
| covered in aluminum foil. A small grill attached to the handle
| was used to grill hotdogs. Not sure how he had it mounted in
| the correct orientation though. In this case, imperfect surface
| shape may have been a good thing.
| fuzzy_biscuit wrote:
| 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?
| pjc50 wrote:
| The risk includes targeting the wrong thing, or stepping into
| the beam in front of the target. A non-flammable backstop for
| the target is kind of a base level safety measure.
| ryandvm wrote:
| 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.
| remipch wrote:
| I wasn't aware of such systems.
|
| If I understand correctly, their main feature is that they do
| not focus on a focal point, but instead diffuse the light.
|
| So I'm not sure if it would be applicable to my project.
|
| I need to dig deeper to fully understand how it works exactly,
| thanks for the hint.
| wycx wrote:
| Lots of interesting experiments with solar collection here:
| https://www.youtube.com/@sergiyyurko8668/videos
| remipch wrote:
| Whaoo, super interesting, thanks for the link.
|
| Some of their projects follow the same idea of a grid of small
| square mirrors.
|
| However, they choose to put the mirrors on the ground (which is
| simpler) and move the target at the focal point (which is not
| simpler).
|
| Good source of inspiration, I will watch their videos.
| SoftTalker wrote:
| 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.
| regularfry wrote:
| There was a project a few years back to demo 3d printing with
| solar sintering of desert sand:
| https://www.sciencedirect.com/science/article/abs/pii/S09596...
| - very neat idea.
| remipch wrote:
| Very interesting, do you know if there are any actual
| applications today?
| regularfry wrote:
| I've not heard of it since, no. It's got some steep hills
| to climb as a concept before it's a better option for
| building materials than just pouring more concrete.
| photonthug wrote:
| Not sure what those hills are, but it's always surprised
| me that this type of hobby project hasn't been ever been
| scaled up industrially.
|
| Setting aside applications for moon base 1 and other sci-
| fi, there's a lot of desert on earth. If the construction
| method is automatic or even semi automatic, and costs
| almost no energy, then who cares if it's slow? A legion
| of robots that can't even make other robots but can make
| glass bricks from sand seems like it could be paving the
| Empty Quarter one decade, finishing the glittering glass
| towers in the next.
| bufferoverflow wrote:
| Here's a huge solar concentrator that melts thick steel in
| seconds:
|
| https://youtu.be/8tt7RG3UR4c
|
| Action around 1:25
| remipch wrote:
| Excellent!
|
| Do you know the mirror area used here?
| LikeBeans wrote:
| I can imagine this would be very useful for water
| desalination.
| Log_out_ wrote:
| You can also sinter sand into 3d structures.
|
| https://www.youtube.com/watch?v=ptUj8JRAYu8
|
| In theory if you could manufacture lenses and optical fibers,
| you could 3d print active solar powered structures anywhere
| where there is enough sun. Imagine a 3d printed little
| bottlegarden, with a water collector using a heated silicagel
| cycle printed in situ on mars. Still low atmospheric pressure,
| but warm and wetter.
| dekhn wrote:
| Indeed; I've played around with various concentration methods
| (along with sun imaging using lenses). My US letter-sized
| Fresnel lens can easily start a tinder/kindling fire in a few
| seconds, and I've managed to melt a lot of things accidentally
| jsut by pointing the lens at the sun for a few seconds when the
| solar filter was not installed.
| mapt wrote:
| 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.
| datadrivenangel wrote:
| The thermal 'inertia' of concentrated solar power may be cost
| competitive with PV solar and batteries.
|
| You can use the mass of the concentrator target as a thermal
| battery effectively, as the conversation of sunlight to
| electrical energy is not instantaneous like solar PV.
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