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Comment by clord | Hacker News Reader

Nice thing about wood power is that as long as you have a sustainable source of wood, you're 100% solar-powered and carbon neutral. That is to say, it's a source of energy that is (can be) non-fossil, nor derived from any fossil sources, and which recycles it's own CO2 emissions.

There are very few other alternatives that can claim the same. Perhaps Hydro? Solar panels don't offset their construction CO2 costs, and in fact almost can't even pay back their own construction energy costs if you factor in batteries plus materials, mining, and shipping.

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>Nice thing about wood power is that as long as you have a sustainable source of wood, you're 100% solar-powered and carbon neutral. That is to say, it's a source of energy that is (can be) non-fossil, nor derived from any fossil sources, and which recycles it's own CO2 emissions.

As long as you're happy pouring carcinogens into the air, sure. Also, compared to oil or coal there's not much energy in wood, so it doesn't scale very well.

You can get power out of wood/cellulose without combustion byproducts.

There's a lot of energy in wood compared to coal. Wood has around 2/3 of the energy of coal by mass. What do you think coal is made from?

Isn't most of the mass of wood water?

Dried wood suitable for burning is around 20% water at most, else it won't burn with much heat. It can go down to around 6% IIRC for kiln-dried wood suitable for construction.

Boiling water costs a helluva lot of energy. Do these engines recover that energy?

How would they work if they didn't?

At low efficiency.

Fresh wood contains ~50% water (up to 70% for certain species), 'dry' wood lies around 15% water. Depending on the type of gasifier you can feed it anything between fresh from the tree to kiln-dried wood. Starting a gasifier requires dry wood or charcoal but once it is going it will do a lot of the drying itself. The reduction process in the lower part of the hearth - where the gas production goes on, reducing CO2 to CO - can also reduce H2O to H2. The end product of a wetter wood will be gas with a higher H2 content next to the CO which forms the main combustible component in wood gas. Yes, wood gas is mainly carbon monoxide and as such highly poisonous, you do not want to start a gasifier in an enclosed environment nor open an unvented gasfier in such.

Charcoal is made by burning wood in a low oxygen environment, driving off water and organics, while carbonizing lignin, cellulose, etc. Coal is a petrochemical mass formed underground from organic matter over long timescales.

If you turn the wood to charcoal and only burn the syngas, it's even carbon negative. Charcoal is stable for hundreds or thousands of years when buried. It also improves the soil.

I think this is/was a theory on what caused the little ice age — people making charcoal.

You're wrong about solar panels - they have an EROEI (Energy Return On Energy Invested) of between 4 and 15 times, depending on how you calculate it.

You’re definitely right about EROEI, but I interpreted the parent as saying that solar panels literally don’t recapture the CO2 required to make them, which is true (if not entirely meaningful).

Solar doesn’t reduce atmospheric CO2, it just offsets other production of CO2.

It’s a CO2 emitter actually, since aluminum, glass and silicon all require high heat to make, and we presently do that with natural gas. It may offset its own production emissions by replacing dirtier methods of power but if we switch to all-solar they will be emitting CO2.

I have never seen a discussion about the real sustainability of biomass but I would be curious to know something. OK, the CO2 it emits gets recycled and in a stable biomass-burning world cycle, more CO2 will be emitted but also more trees will grow so it should balance out.

Would that not, however, durably increase the baseline CO2 levels? Sure it is sustainable but do we want to sustain a 500 ppm level? Where would it bring us if the whole world switched from oil to wood?

There is not enough wood to switch over from fossil fuels anyway. We burn incredible amounts of coal and oil.

Gasifiers can run off of many types of biomass. Corn husks and other agricultural waste is a big source besides wood.

Still release a lot of syngas, which, if it was on world wide scale wouldn't be good.

The whole point of gasification is the production of syngas. You don't vent syngas to the atmosphere for the same reason you don't pour gas on the ground. Burning syngas doesn't have to emit carbon monoxide, a catalytic converter like on almost every car out there would work just the same to clean up the emissions.

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