posted 7 years ago
I don't think it's a lucrative business proposition, but we all know what happens to elements incorporated into a larger permacultural design; the inefficiencies and "waste" products can be channelled to other uses.
Let's say that I buy a factory building in an area of town up for gentrification. I convert it, according to permacultural principles, to a hard-loft-conversion co-op (easier to deliver central heating to many households). One of the many permacultural elements would be this RMH-based co-generation plant.
I live in Toronto, where the continental climate gives us cold winters and hot, humid summers. The heat and power station would probably only operate in the cool seasons, or we'd need a building-sized refrigerant loop setup, using the excess heat from the generation of electricity to power it, with the remainder going into a ground-source heat pump.
It seems needlessly complicated. It requires too much specialised equipment, and as this is supposed to be on the household or small neighbourhood scale, if it's not as cheap and straightforward to build as the RMH itself (which are, for any of you who haven't participated in a build, more expensive and complicated than you could imagine, balancing use of reclaimed materials with ease of assembly, as in, the more strange bits you want to fit in to the build because they're free, the more complicated the build) it's not likely to be very accessible to the normal person.
I think to make decentralised power production work with an RMH, you have to look at the parts of what you're trying to use to make power. The RMH is composed of a rocket heater, either j-tube or batch box, the riser and additional refractory and insulation that gives the rocket enough rocketyness to push that exhaust through a longer-than-typical exhaust system that features an air-to-mass heat exchanger.
I think the RMH is designed to be a really efficient tool for converting biomass into heat energy, and then trapping the bulk of that energy in a heat battery consisting of mass. I think that, while perhaps the rocket part of the RMH might provide the energy you need for efficient co-generation from coppiced wood, the Mass part and the parts of the design that make benches work aren't beneficial for power generation.
One exception I can see to this is if you have a heat transfer mechanism around the top part of the barrel, where you usually see people put their kettles or whatever. Even so, steam is too complicated for household use, in my opinion, and too bulky. Trying to miniaturise a system designed to work on a giant scale might not work out.
I think thermovoltaic paint, or a thermovoltaic plate that generated electricity from the difference in temperatures between the top of the riser and the cold air outside, with no moving parts, is an idea with more merit for RMH experimentation on the homestead scale. You could even do both, the plate, designed to benefit from the extreme temperature difference between the burn tunnel and the outside air, and the paint coating the chimney outside, where the temperature difference between the exhaust and the outside air would be much less, but the surface area of the chimney would be greater, and the paint cheaper.
The thermovoltaic systems I am describing, incidentally, aren't linked with any product that I know of to exist yet, at least commercially. I read articles regularly about how thermovoltaics is getting more efficient, that a lab-scale experiment produced thermovoltaic paint, and that it is benefitting from all the R & D being done in photovoltaics, but I have yet to see it implemented in any great way. This might be that way.
-CK
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein