Hackaday Prize 2022: Solar Power Through Pyrolysis

We’re all familiar with solar cells, be they photovoltaic, or for heating water. But they are only the more common ways of converting the sun’s energey into usable power, and to the extended list there is now an addition courtesy of [Dennis]. He’s using the sun to drive the pyrolysis of biomass waste, releasing hydrogen fuel.

For those who aren’t familiar with the chemistry, pyrolysis refers to chemical reactions triggered by heat. In this case, when organic biomass is heated in the absence of oxygen it breaks down and releases the gaseous products of that breakdown as well as a mass of carbon. The idea behind this pyrolysis cell is that a Fresnel lens will focus the sun on a reaction chamber, providing the required heat for the reaction to occur. A test with a magnifier and a test tube proves that there’s something in it.

Of course, sharp-eyed readers will notice that this isn’t quite in the same vein as other cells which convert the Sun’s energy into a usable form, in that while it provides an input of energy for the pyrolysis the chemical energy in the resulting gas comes mostly from the original biomass. There is a silver lining to the prospect of burning gas though, in that the left-over carbon can be incorporated into the soil as biochar, an effective carbon sink.

We’ve seen a project pursuing a similar chemistry before, though not using solar energy to do it.

19 thoughts on “Hackaday Prize 2022: Solar Power Through Pyrolysis

    1. Activated charcoal is a little more fussy as to temperature of formation and structure, and is a relatively expensive commercial product. If you want terra preta, you’re going to need to make many tons of it inexpensively. But it’s a medium, not a fertilizer. Combined with compost, you get an immediate payback in your soil. And it limits leaching of nutrients and water, for hundreds of years. Besides sequestering carbon. Plain compost degrades into CO2 gas in a few years and goes into the air.

      I probably grow a thousand pounds of mostly useless carbohydrates on our acre, and I am looking for an easy, effective, cheap, safe, and legal way of turning it into biochar. So far, nothing compelling has come up.

      1. I’ve been noodling it around for years from the POV of having a self fuelling lawn mower, but can’t get it past the probable requirement of labor intensive small batch processing.

      2. ” Plain compost degrades into CO2 gas in a few years and goes into the air.”

        I was unaware of that, but I will continue to compost my leaves to supplement the vegetable garden soil.
        (at least the vegetables will have a chance to grab the CO2 as it rises from the soil B^)

      3. What climate do you have? I’m wet, maritime and temperate and I have a few acres set aside for growing long grass for mulching purposes. If I wanted to go biochar I’d grow willow and get a chopping machine (not shredding). Harvesting is easy with the right tool – a large FS 240 Stihl strimmer with 230mm circular saw blade and guard removed. About 4 hours per acre to cut. Ricking and collecting is a breeze with a pitch fork and van / trailer. Planning to upgrade to DIY robotic forage harvester next season.

  1. The biomass is the direct result of the plant(s) converting CO2 using solar energy, so it’s all still solar. This and anaerobic digestion for biogas (methane) production would be good to use in tandem.
    Also, while some H2 is generated, I believe the bulk of what is released in pyrolysis is CO along with some CO2. It’s been a while since I studied producer gas, though.

      1. True, but you can separate this process in two or more stages.
        _Essication to break water (with solar powered fan)
        _Digestion in a hot anaerobic pyrolysis chamber heated by many farnell lens or injecting hot hydrogen to reform biomass to hydrocarbons with an iron oxide catalyst as Daniel Matthews suggested.
        _Extraction: separate biochar and fuels liquid

  2. The biochar thing came about after the discovery that large areas of the jungles of South America are on land that was artificially fertilized. Ancient peoples made charcoal and tilled it into the grassland soil to improve it for crops. When their civilizations declined, the enriched soil supported the takeover by rainforest and jungle.

    But instead of just calling it finely crushed charcoal, someone had to make up the word biochar.

    1. The concept of biochar is actually “unfinished charcoal” if you will, the techniques / temperatures used and time of pyrolysis being less than required for actual charcoal, leaving a crumbly residue somewhere between gooey tars and solid carbon chunks. There are (were) many articles with charts out there showing the different products possible when i was looking in to this

  3. Thermal depolymerization is a process of controlled heating of organic (carbon based) stuff in a pressurized chamber with low or no oxygen. The useful output is liquids that can be burned as fuel or put through a refinery to make plastics and various chemical compounds including refined fuels.

    The trick to it for fuel production is the energy content of the input material has to be higher than the amount of energy used to heat the material. While the process was well known and proven for quite a while, nobody was using it because it took almost as much energy to convert the material as could be obtained from using the output as fuel. Some years ago, a company working with Tyson foods developed improvements that needed less input energy.

    I dunno if Tyson is still running their TDP plant, but after it was built there was someone always complaining about noise and smell, even when the plant wasn’t operating. Most likely paid by an oil company to complain. A substitute for crude oil, not under the control of the oil industry, with the potential to replace a lot of crude oil if scaled up, they’d definitely want to get that shut down.

    See also the lack of government funding for isobutanol research and development, especially making it from waste plant material. It’s a far better replacement for gasoline than ethanol. It’s been tested in gasoline fueled vehicles with no modifications required.

  4. Not the best way to do it, better to use solar thermal to crack water then use the hot hydrogen immediately to reform biomass to hydrocarbons with an iron oxide catalyst.

    1. That sounds like it would be harder to do on a smaller scale, and also require more work to make the biomass in question uniform enough. Are you talking about reformation of anaerobic bio-methane? What about PV+electrolysis for the H2?

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