Oh my, you can turn used coffee grounds into logs for heating.
https://farrerscoffee.co.uk/how-to-make-your-own-coffee-logs/
Tried making tiny burnable biomass logs out of coffee. Didn't quite work, I'll keep trying.
@neauoire don't really understand why you'd like to burn it. how much coffee do you produce a week? an espresso is like 7g, a week is gonna be something like 150g/person. supposing it has the same energy density of wood (but it's much lower) you could get about 1 kWh/1kg, so that would be equivalent to 150Wh per person a WEEK. so, basically you get the same amount of heat a single person generates in an HOUR. each day you get roughly 150Wh/(7days*24h)=0.88Wh. your raspberry pi emits about 5-10 times more than that.
drop your grounds into the ocean, it's much more ecological :-)
oh, I didn't take into account the effort to dry it down or worse, adding other substances to it to create "logs".
@zabow you're saying we should carry more logs of wood basically.
@neauoire what I'm trying to say is that you'll end up decreasing the stove efficiency, more ashes, more CO2 in the air. if you try to optimize your combustion with dry logs and keeping your stove clean has a much greater effect.
@neauoire much greater as in orders of magnitudes. I remember some guys here in Sardinia, they had a startup for creating piezoelectric mats with people walking on them. I think they managed to sell some to the Louvre... they were able to light up some minuscule lights with that. each 1m2 mat would cost like 1k$. buying a photovoltaic panel for 10$ would have produced much more energy for maybe 30 years, no maintenance :-D sometimes back of the envelope calculations do help
@zabow yeah I'm trying to just that right now.. I can't quite figure out how buying extra wood that's less energy dense than coffee logs is more efficient. Gimme a minute.
(30 years for a photovoltaic panel?!)
@neauoire @zabow the confusion may be the efficiency difference expected by both of you being in opposite directions
From the article, "According to Bio-Bean, they burn up to 20% hotter and longer than kiln-dried wood!" - but obviously this would vary with the preparation, and doesn't say anything about the soot/co2 production differences or energy used for production.
Imo it's all good fun but I do feel like it's likely to have similar issues to other waste to energy methods
@maxc @neauoire bio-bean logs contain about one third of coffee grounds in weight: 25 cups (25 X 7g) = 0.175kg and each log weighs 0.5kg. I didn't find anything about the other components, but they explicitly say "Coffee Logs are not suitable for barbecues or other open fire cooking". so they may contain anything as far as I know. and I don't really like the fact that they don't publish anywhere scientific energy tests. any cheap pellet maker publishes the energy content these days...
and their price is incredibly high: ~7$ for a bag of 16 logs (8kg): here wood logs go by ~$8 for 100kg.
@zabow @neauoire completely agree re: cost trade-off not being there if you are buying them. It's just a citation for where the idea that the coffee "logs" may be higher energy density than wood came from.
For the waste conversion aspect as well - depending on where you're located, firewood is also often (in commercial terms) waste quality wood or off-cuts - hence being so cheap per unit mass.