Oh my, you can turn used coffee grounds into logs for heating.
https://farrerscoffee.co.uk/how-to-make-your-own-coffee-logs/
@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 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
@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.
@neauoire most panels are guaranteed at least for 80% after 25-30 years. this was known for decades. of course it may be much less in marine installations if the hardware is cheap. PV tech is absolutely mature and the last 20-25 years didn't see any relevant efficiency increase in the basic physics (~20-25%), they just improved module topology, and the cost plummeted.
@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?!)