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This topic contains 12 replies, has 9 voices, and was last updated by Profile photo of Aeolius Aeolius 6 years, 7 months ago.

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  • #617
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    Discusses using mirrors to concentrate sun’s rays to heat liquid to drive steam generators. Better for longer-term, larger applications, but may have some elements that can be used in smaller seasteads, especially in tropical regions. Also, discusses possible use w/ Stirling engines.

    Posting as Anon ’cause I forgot my pw and don’t have time to look up right now.


    Profile photo of 12mile

    Here’s an article I ran across yesterday along the same lines that will further the solar cause. Storage has been the big issue with solar but it now appears those issues are being addressed and solved.


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    The “major discovery” is electrolysis of water with some new catalysts. It still has the problems of Hydrogen storage, expense and fragility of Hydrogen fuel cells, etc. As such it doesn’t really seem very significant or practical.

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    Solar thermal is interesting, but requires a big installation and/or finely engineered heat engine to be practical. Photovoltaic is more scalable (especially at the smaller end of the scale) and much more widely available. Photovoltaic also has no moving parts, which in many respects is a significant advantage. Unlike solar thermal, there is no maintenance and no parts to eventually replace (short of the cells themselves gradually degrading over several decades). Solar thermal being largely mechanical has parts that eventually wear out and need replacement.

    Both technologies may be useful. Photovoltaic is more immediately useful and lower-maintenance.

    Profile photo of cbthiess

    I agree that storage is a problem for vehicles, which are space and weight-constrained, but for stationary applications the problem is a lot easier. Also, storage of high-pressure gas under the ocean can be done pretty darn cheaply with just a deeply submerged lift bag or concrete dome. (See the Whole-Ocean Gravity Battery thread) Even above-ground tanks may not be a problem, since you just don’t need the energy density and low weight that a car would need.

    As for fuel cell expense, $1/watt solar is often said to be where it gets price-competitive with coal. As of 2006, GE and Delphi were reporting costs of < $0.30/watt for solid oxide fuel cells. ( http://www.netl.doe.gov/technologies/coalpower/fuelcells/index.html ) Assuming you’d need a 1/2 watt of fuel cell per 1 watt of peak solar, that’s just $0.15 for every solar watt in fuel cell costs. That’s pretty darned cheap.

    I think this is the cheapest electrical storage system I’ve seen.

    Profile photo of Thorizan

    Though the cost of silicon is rising, we can probably find a process to extract it from the water, or, worse case, the ocean floor below us. It is a relatively common material… but getting it can be problematic.

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    Measured by mass, silicon makes up 25.7% of the Earth‘s crust and is the second most abundant element on Earth, after oxygen.

    from http://en.wikipedia.org/wiki/Silicon#Occurrence

    Basically, it is sand: http://en.wikipedia.org/wiki/Silica

    Based on this I´m guessing that most of the cost of production is refining and purifying it, which probably takes a lot of energy.

    Sort of a catch 22 when the end product also is energy (from PV cells), and probably less than what it takes to produce them…

    I guess you could always use nuclear power or fossil fuel to produce the silicon/PV cells :-). Or rather, this is probably what happens already.

    Profile photo of Thorizan

    I didn’t know the specifics, but thank you, vtoldude, for the research here.

    Investing in power sources (preferably renewable) along with a refinery and production facility would be necessary up front, then we would be able to station the cells to have them start producing electricity for us, which we would sell relatively inexpensively to the newcomers in our little sealet. Eventually we would be able to recoup the inital costs, and then we would be able to start the process over again… because then, hopefully, we would have a need for greater power production, or a demand for a sister-sealet.

    Profile photo of CrosiarCM

    I have not seen this discussed so I though I would throw it out there. Whether using photo voltaics or mirrors, if you have ever been on the sea, everything ends up getting a thin coat of salts on it in short time. This would block some of the energy fo the sun without very regular cleaning. How much of a problem would this be? Would this still be an issue at the top of a spar? I’m thinking you would need a high-pressure water sprayer to clean things a few times a week.

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    These mirrors: http://www.stirlingenergy.com/ were covered on Discovery Channel, and yes they must be cleaned regularly with high-pressure water. They did it manually with a ladder, and had to shut it down if I recall correctly. Maybe it would be possible to arrange some automatic cleaning device, like a windshield wiper thing that sprays water.

    The generators on the show was in some desert, so they were cleaning away dust rather than salt. I don´t know whether salt would be easier or harder to clean.

    I like the concept of mirrors and thermal power generation/storage though. I think you can store quite a lot of power in molten salt, and it doesn´t degrade like batteries, as far as I am aware. And a mirror is a lot cheaper than photovoltaics.


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    Improved energy storage

    The MIT announced a big progress in storing energy. Read the article (includes video interview).

    Requiring nothing but abundant, non-toxic natural materials

    Inspired by the photosynthesis performed by plants, Nocera and Matthew Kanan, a postdoctoral fellow in Nocera’s lab, have developed an unprecedented process that will allow the sun’s energy to be used to split water into hydrogen and oxygen gases. Later, the oxygen and hydrogen may be recombined inside a fuel cell, creating carbon-free electricity to power your house or your electric car, day or night.

    The key component in Nocera and Kanan’s new process is a new catalyst that produces oxygen gas from water; another catalyst produces valuable hydrogen gas.

    The new catalyst works at room temperature, in neutral pH water, and it’s easy to set up, Nocera said. “That’s why I know this is going to work. It’s so easy to implement,” he said.

    Nocera hopes that within 10 years, homeowners will be able to power their homes in daylight through photovoltaic cells, while using excess solar energy to produce hydrogen and oxygen to power their own household fuel cell. Electricity-by-wire from a central source could be a thing of the past.

    Possible solution for salt dust on mirros

    Materials coated with the Lotus Effect can be easily cleaned. When it rains or you pour water over the mirrors they should clean themselves.

    Proposal: Solar cell with mirrors

    I think it was the MIT as well that created a very low-cost version of solar panels. They used mirrors (I think aluminum) to focus sunlight on a small solar cell. The mirrors are cheap, the little cell is inexpensive as well, no moving parts, maybe a good solution.
    Downside: It can kill you. (Really.)

    Proposal: Plain old solar panels

    I read about a newly developed solar cell capable of absorbing 100% of the light spectrum. So, depending on what type of solar energy harvest is cheaper to realise this might be a good solution, too.

    I prefer anything without movable parts over something with movable parts. Regular (short interval) maintenance will kill you! Steam turbines are hereby declared as a big no-no.

    If I think about the low-cost mirror version again … I recommend against it. It is too dangerous.

    Profile photo of CrosiarCM

    I also like thermal power generation, I think it is one of the critical technologies that will need to be mastered for seasteading.

    My idea is to place a large lattice truss under the water (with proper floatation) and then have poles that rise-up out of the water to hold the mirrors. The mirrors would only need to track the sun vertically. The underwater truss structure would be attached to the solar collecting tower for proper alignment. The entire floating assembly would track the sun by being rotated in the water (hopefully we can find a spot where it can be anchored to the sea floor so there is no drift…). Pnuematic pressure would be delivered to each mirror which would provide power to a hydrolic pump for vertical mirror positioning. The compressed air would also be used with fresh water to automatically clean the mirrors. The compressed air can be generated using tidal pumps. Alternatively you could float by in a ‘pressure washing boat’ to clean the mirrors a couple of times a week. I like the more automatic approach. The poles holding the mirrors would need to be sufficiently high that they would not get ocean spray and would be well above wave heights. I think about 30-40 feet would be about right.

    I would also investigate making the truss capable of being more deeply submerged in the event of a major storm so that the entire assembly, and especially the mirrors with their large surface area, would be well under the waves and currents generated by the storm. The ability to lower the mirrors would also be helpful when you need to do maintenence.

    I have seen discussion about making the mirrors out of styrofoam. I think this is a very bad idea – styrofoam gets water logged very quickly. Any ideas for good materials for the mirrors? I think the best material so far is still fiberglass as it is rigid and survives well in the elements. The mirrored surface would have to have a protective coating to protect it from salt oxidization; this will likely lower the total reflective index of the mirror, but that is the price you pay for using mirrors on the sea.

    By the way, I loved your link – I like the way the SES mirrors are actually all the same, but form a mirror dish when assembled. That would make manufacturing much easier. I need to read up on the molten salt idea, but I have heard of it before and it does seem very practical. The only down side I can recall is that when you make your heat exchanger from the molten salt to steam, if the molten salt pipe bursts and makes contact with the water/steam it can cause an exposion (hydrogen gas is generated as I recall). Is that correct? I’m sure that is a solvable problem.

    My next question is, how do you get the electricty from the platform to your seastead? I don’t really like the idea of high-voltage wire dangling on buoys…

    I actually think this should be the very first seasteading construction project. If you have this and high speed internet you can do many revenue generating activities from moored boats on a floating dock. I think that is important from an incremental development standpoint. It also gives you the power you need when manufacturing the spars.

    You may get what you want, but will you want what you get?

    Profile photo of Aeolius

    I found an interesting article about Liquid Solar Arrays at dvice.com. The company’s website is http://www.sunengy.com/

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