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Heliostat Optical Simulation
  • Google opensourced their Heliostat Optical Simulation(HOPS) software, which can be used to simulate a field of heliostats and a receiver that provides thermal input to a heat engine. The code is available at the following location.

    Power towers are a great way to convert solar energy into electricity. Google intended to use Brayton Engines with the Heliostats they developed, but Google eventually stopped funding the project. The problem with Brayton engines is that they typically are not efficient until a very high input temperature is reached, and they typically are not as efficient as Stirling engines. The very high temperature required by Brayton engines became problematic for receiver design. The receiver needed to withstand average temperatures of 1000 Celsius. Google claimed to stop working on solar thermal applications due to the problems they encountered with receiver design and the falling cost of PV cells. In contrast to Brayton Engines, Stirling Engines do not experience a massive drop in efficiency as temperatures drop.

    It seems that large Stirling engines combined with a sodium reflux receiver is a cost effective method that could compete with PV cells and other forms of solar thermal electric production. Stirling engines have been built that are 50% efficient at converting thermal energy to mechanical energy when operating between temperature reservoirs of 750 Celsius and 50 Celsius. I have design plans for one such engine that has 10kW of electric generation capacity. A physical,
    working prototype has been built, and I believe this engine can be scaled in size to 300kW and would weigh around 2700kg. Sodium reflux pool boilers have been developed by Sandia National Laboratories and simulation software
    has been designed(CIRCE2/DEKGEN). However, the SNL code is closed source and only available to Federal employees and Federal contractors. The method, however, is discussed in books/journals. These reflux receivers have been tested for 7500 hours. I would like to design a scaled up version of one of these receivers. Perhaps something like 3.5 MW
    thermal. I believe such a receiver would be a little over 94% efficient. The 75kW version was 92.8% efficient. The increased efficiency comes from lower convection losses. One of these receivers could be connected to a few 300kW or larger Stirling engines.

    Another company that uses Power towers is Bright Source Energy. The problem with Bright Source Energy's technology is that they utilize steam. Steam has to be heated in a boiler whose material requirements scale as a linear function of pressure and of volume. Due to the fact that steam's thermal conductivity is between 3.3 times(at 1200K)  and 8.28 times(at 300K) lower than that of helium, it must stay in the boiler for a longer period of time than a gas such as helium in order to soak up the heat. As a result, Bright Source Energy will have greater material requirements per kilowatt of generating capacity than an approach based on large Stirling engines and sodium reflux receivers.

    Any comments or interest in the project?
  • 5 Comments sorted by
  • No PV panels or engines are necessary, plus they are inefficient.  Cheap homemade parabolic reflectors or fresnel lens directing the beams "downward" to lower altitude buried water tanks so the water molecules can be split.  Capture the hydrogen and water, release the oxygen.
  • Cool. The more open source tools the better. Of course, software is only a small part of an infrastructure project like CSP. It is an esoteric part, tho. Lots more people can sling a wrench than can figure out how to program a heliostat array controller.

    Wait...does this code only simulate the array or can it be used to control the actual physical array?
  • __Oz, Stirling Engines are typically very efficient. The stirling engine I mentioned above is 50% efficient when operating between 750 Celsius and 50 Celsius. Given those temperatures, the maximum theoretical efficiency is 68.4%. Based on thermodynamics, no physical device can be more efficient than 68.4% when operating at these temperatures. However, conversion efficiency is not the key criteria. It is cost.

    As for cheap, homemade parabolic reflectors or fresnel lenses, there are two problems.
    1.)UV degradation
    2.)Insufficient concentration

    Typically, the solar concentrator is the biggest cost in a concentrating solar system.

    As for hydrogen production, I presume you are referring to high-temperature electrolysis. I need to research this more thoroughly before commenting. However, my goal is electricity production. Not hydrogen production. If the hydrogen needs to be converted to electricity that results in an efficiency loss and added expenses.
  • Matt_Maier,

    Google released two pieces of code in separate projects. I believe one piece of software modelled the heliostat field and the other piece of software controlled the heliostat. Heliostat controllers could be programmed using Arduino.

    CNC machines can turn gcode into physical parts. Once models are built and all the gcode is generated, a lot of the hard work has been done, and one could begin the process of applying for federal grants to actually build the thing. Furthermore, a wealthy individual may be willing to fund the building of the project if the design plans are done well. However, I understand your concern that it seems like an esoteric part, but one does have to start somewhere. I also mentioned above that I have the design plans for a stirling engine that is 50% efficient from thermal to mechanical. The engine has also been built and run. I have the physical engine also. If there is sufficient interest in the project, I would consider open sourcing the engine and design plans. I would like to see the technology evolve whether that is in an open source format or a closed source format. The one problem with open sourcing the project is that it shuts the door for venture capital or private equity funding since investors would want to protect the IP that is developed in order to get a return on investment. One of my main goals is to see the level of interest in an open source concentrating solar thermal electric generation project. There is a small possibility that some of the people that worked on the Google Heliostat may be interested in working on this project in their spare time.
  • Open sourcing it will help drum up interest.

    There is a growing number of case studies you can point to if you want VC funding for your open source business. Basically, releasing the plans for free in no way whatsoever reduces the cost of actually building the thing. So you make money selling the thing just like you always would, with the added benefit that a community of hobbyists can grow around your technology, improving it for free. 

    There are not, however, case studies supporting the open sourcing of large infrastructure builds. Open source seems to be profitable when you are innovating a technology too fast for a large organization to keep up with you. So, the principle could still apply to large projects as long as they're sufficiently cutting edge (and risky). The community development of the idea is part of how you mitigate that risk. However, large projects, by definition, make it difficult for a community of hobbyists to participate. 

    If you open sourced a solar thermal array, you could get community development by making is scale-able. Design it so that it works for a half-dozen mirrors mounted on someone's roof as well as a thousand mirrors in the desert. There are tons of people interested in renewable energy, and solar thermal is one of the more practical approaches. I doubt that even if every existing company copied your design and offered it to customers that there wouldn't be more market left over for you. Even if they did, any improvements they make would have to be released, so you'd benefit as well. 

    Also, if you're working on a project with as much social benefit as open source renewable energy, you probably don't have to go to VCs for funding. There are lots of sources of start-up capital for entrepreneurial activities like that. 

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