well gang, i'm headed out of town for a week, so the experiment's shutting down too until i get back. i did work up some preliminary economics based solely on the size and characteristics of my grow room, so these numbers are not in any way universal although the relative economics between options shouldn't change all that much.
note that the fermentation daily costs look high, primarily because i am still adding quite a bit of yeast daily, something i should be able to cut down on going forward. if the yeast can be reused at an average rate of 90% (average 10 uses before discarding) then the economics of fermentation look pretty good. i'll verify the ability to reuse the cheap yeast when i get back. also note in all cases i did not include a co2 monitor/controller. part of the purpose of this experiment is to see if you can get good results without one.
....................................cost per day used...........cost of start up
co2 from fermentation*...... $1.64................................$27
co2 from tank**.................$0.70..............................$400
co2 from propane***.........$0.27..............................$455
* 61 cents per day is new yeast which should I should be able to reduce to close to zero by making more use of used yeast from previous days. Fixed costs include the ingredients for all containers and $20 for a two-time co2 test kit.
** co2 from a tank is used only on average 15 hours per day, so only a fraction of the co2 produced by fermentation is needed if you use a tank. Start up costs include tank, regulator and timer as well as a two time co2 test kit
*** estimated 15% of co2 is wasted via pilot light when the lights are off. Start up costs include generator, propane tank and two time co2 test kit