I am investigating some components of a system to make biochar with a solar concentrator but it is slow going. My idea is to circulate molten salt through the focus zone of a double-parabola channel. This focuses heat on the target pipe for a broad range of sun angles with no tracking. I have read that a eutectic mix of sodium carbonate and potassium carbonate (aka soda ash and potash, respectively) has a melting point under 500C, and fast pyrolysis is possible with molten salt at this temperature. I am trying to find information about electromagnetic pumping (aka magnetohydrodynamic pumping, just like Red October!) but there are very few such devices sold - mainly for continuous metal casting, apparently. If molten salt could be heated by sun and fast pyrolysis could be done (which makes a larger fraction of pyrolysis oil than slower processes would do), then there would be very little emissions and very little waste heat I think. Still some steam I suppose.
Offgrid living
Everything off grid; power, water, self-sufficiency; whether you're doing it or aspiring.
oh that's really cool, would be a such a low impact way of making biochar that when you add it to the soil it'd probably actually be atmospheric carbon negative so essentially free carbon-capture - on a tiny scale but if it was how everyone did it then that's one thing pushing in the right direction instead of the wrong direction.
and interesting about the electromagnetic pumping, i don't think it's especially hard to engineer compared to stuff that's readily available in a dozen different colours so i guess there's just no perceived market for it - i'll have to read up and see if there are any DIY projects, being able to move liquid salt around would be really useful in a lot of heat transfer applications.
I built a parabolic trough collector with automatic sun tracking. reflective area was 1 x 3 m, good enough to cook food at 80-90°C in a 20cm diameter oven tube.
If I built it again now I might not use the sun tracking, I think it's overengineering. Nicer to set up a workflow where you move the collector without having so much stuff that can malfunction on there (motors, sensors, electronics board ...), or build one large enough that you don't have to move.
I saw the super high temperature fresnel stuff in Tamera - but it's not something I would confidently build in a well-equipped home workshop.
About the only thing I remember from Thermodynamics in university: avoid transforming and transporting energy needlessly. If you want heat, use the heat you already have. Instead of building a field of 2m PV panels in the Sahara and transporting the electric energy to my home in Europe, where I use it to plug my air or water heating device, I should always find out where unused heat can be found in my environment and try to coax that into my process. Which is why instead of getting more experience in photovoltaics I just built this monstrous collector thingy together with a few other people, and started investigating stirling engines - because they are small scale, silent, flexible about their heat source (so concentrated solar energy can be turned directly into mechanical energy for example - for a more efficient solar pump).
Another low energy low impact favourite tech of mine are ram pumps. They can be set up uninvasively in a stream and pump water into a reservoir - to be used for irrigation and energy harvest. I've had them filling IBCs during about three months in summer last year before the stream dried, and didn't set them up because I have no way yet to take the water without damming up, and it felt wrong to do so. I will have to cut my way through some thorny shit and make a natural dam a little more upstream to get enough height, but it's worth it if I don't want to rudely interrupt the lives of the stream creatures.
I really like the range of possibilities you're considering - especially for options for replacing the highest-power-consuming appliances, especially those which only use the power to produce heat. I've got a plan for a scene of a workshop that'll use one, but I think first I want to try a solarpunk kitchen.
I'm also thinking about trying to get my anvil back from a friend, buying a fresnel lens, and building a frame for it with a fire pot built in at the focal point, and seeing if I can use it like a solar forge.
I've read about them, and considered, but so far I have done nothing with solar concentrators. I've been thinking about solar thermal + thermal storage, and about solar thermal + Stirling motors, but haven't had the time to make any workable solutions.
What I have done, though, is to use dumpster-dived white plastic sheets (to be painted reflective sometime in the next summer) to increase the amount of radiation falling on my "solar fence" (which is literally a fence, about 1 meter tall, made of solar panels). They just sit on the ground 30 cm sunward from the fence, and due to being bright white, relfect additional sunlight onto the fence. :)
In winter, they make no difference, snow does the same job. :)