[UPDATE 10/21/2021 -After 2018 I started posting my updates on my Patreon page, and so I'm filling in the back-logs for this project retroactively so the whole story is in both places. You can also read all of these posts with their original photo formatting here]

July 31st, 2021

For months, I've been on a quest for cold hard data. What I ended up with this month was more like soft, warm data, but hey, you've gotta start somewhere. For the first time ever, I was able to measure all the inputs and outputs of my biochar reactor to make one batch of biochar. Here are the quick results:

IN:

Biomass in: 3.3kg

Moisture Content: Unknown, dry

Electrical Energy Consumed: 8.7kWh

OUT:

Charcoal Out: 1.8kg

Liquid out: 550mL

Electrical Energy Generated: 140wH.

Syngas Produced: 1400L

The feedstock was just the woody remnants of last year's yard-work: Dried out hops, wisteria, and clematis vines, blackberry brambles, weeds, grass, and sunflower stalks. I've gotten into the habit of just drying out my yard waste by leaving it in a big bin in front of my house's heat pumps, using the waste heat to dry it all out, and then throwing it into the biochar reactor.

I have always been curious exactly how much biomass energy is available just from the stuff that grows on my 1/10th acre lot in Portland, because it seems like kind of a lot. I still don't know exactly, but I'm getting a lot closer to knowing. 

I weighed the bucket empty to establish a tare weight, then used a luggage scale to measure how much biomass I had. By compacting this dry, low-grade  woody biomass waste into a 7-gallon turkey fryer bucket, I was able to collect about 3.3 kilograms of biomass. Then I loaded it all into the reactor, sealed it up, and heated up the heating element, using 1128 Watts total. 

In about 45 minutes, I had filled a 300L gas bag with gas,

Over the course of the afternoon, the bag filled up with 300L of gas roughly every hour, and every time it filled up, ran the generator for 7-9 minutes, producing between 250-400W on average from roughly 300L of gas. Later, I tried using a larger, 500L bag, and found that I could run the generator for nearly 30 minutes on one 500L bag.

When I turned the reactor off that evening, the temperature read 850F, and 8.71kWh had been consumed. That means that the system consumed 8710 watt-hours, and generated 140 watt-hours, roughly a 1.3% conversion. Not great.

But not bad either, considering its my first try and the purpose of this project isn't ONLY to produce energy. 8.7kWh is an amount of power easily generated by 3-6 solar panels over the course of a sunny day, and the byproducts of the process also include waste processing, biochar production, water heating, and gas production, in addition to electrical power. So 1.3% as a first try ain't too bad.

Most of the time, when the generator was running, it was producing between 250W and 400W - about as much as a single solar panel does in full sun. On gasoline, the thing is supposed to generate up to 1800W. But the energy-content of the syngas varies depending on the feedstock, temperature, and a number of other factors.

The low conversion efficiency is most likely due to the air-fuel mixture inside the generator. Getting the pressure and gas volume just right has been a tricky business. The new gas bags I got are cheap and very easy to work with, but they require some kind of pump to pressurize the gas. The booster pump I was using worked pretty well, but topped out at around 400W.

Unfortunately, the gas booster pump I had been using ended up getting clogged with tar and stopped working. Ultimately, that's a filtration issue, indicating that the gas needs to be cooled and scrubbed more before it gets stored. I've ordered a few filters to try, and a few new pumps.

When I bypassed the pump, however, and just leaned my weight onto the bag to provide pressure (later calculated to be roughly 15psi) the generator fired right up, and I was able to generate damn near 1000W as long as I kept my weight on it, which is very promising. Internal combustion engines are most efficient near the top of their speed range, and so making the generator run faster probably makes it significantly more efficient.

When I opened the reactor the next morning, I had 1.8kg of charcoal! A lot of the leafy grasses broke down into a fine carbon powder, which I added to my compost heap, but the larger softwood vines had retained enough structure to use as drawing charcoal, or for burning as cooking fuel.

All in all, the experiment yielded 1400L of flammable gas, which was considerably more than I had expected. My estimation is that I would need about 4000L+ of storage (about 8x500L bags) in order to contain a whole batch worth of gas. With that much storage, you could dump a days worth of solar power into the reactor, converting waste into char and gas, and then burning the gas during the night as need for heat and power. 

To test that setup, the budget for this next month is mostly going to go towards a big portable battery system that will be able to power the reactor and be charged by solar panels, so that I can start running more of these experiments completely off the grid, gaining the energy required to maintain the process ENTIRELY from sun and biomass, and seeing what kind of results I can get!

Stay tuned!