There are many people out there who live off the national electric grid. They typically use wind, solar, hydro, and/or a petroleum fueled IC (internal combustion) generator. More often than you would expect, the petroleum fueled generator is used as a backup or -- even worse -- the sole power source. This in most cases causes a greater carbon footprint than if they were just connected to the grid.
So our EVs, cabins, and homes need a compact biomass electric generator. With this in mind, Sara and I designed and built a portable unit. We wanted a gasifier that would be able to run on variety of biomass so we picked a stratified downdraft design with changeable throat restrictions. So what is variety of fuels being used, you ask? Coffee grinds, wood pellets, wood chips, walnut shells, peach pits, corn cobs, et cetera.
As with most of our projects, three quarters of the materials are reclaimed. The generator is a 1973 Onan, the cooler/ condenser is 15' of used 2” copper, and the gasifier consists of an old well tank and scrap steel. All this great stuff was going to the dump.
We have run the unit for several hours on wood pellets without a hitch (videos soon to come). The unit produces approximately 2000 watts, which may not sound like a much until you realize the components take up 20 ft2
which equates to 100 watts a square foot (most solar panels generate 12 watts/ft2
and would take up an equivalent 166 ft2
After taking some fuel consumption tests, we have discovered with some interesting information. Our system consumes anywhere from 3-5 pounds (1360-2268 grams) of fuel per hour, while a similar gasoline generator will use 0.75-1.32 pounds (340-600 grams) of fuel per hour.
Hardwood Pellets Versus Gasoline: Consumption and Cost (in US Dollars)
||Wood Pellets at $6.00 per 40lb bag
||Gasoline at $2.00 per gallon
||Gasoline at $3.00 per gallon
||Gasoline at $4.00 per gallon
||$0.44 - $0.80/hour
||$0.24 - $0.43/hour
||$0.37 - $0.65/hour
||$0.49 - $0.89/hour
What we were surprised to find out was that the manufactured wood pellets are competitive at higher gas prices. To improve on our current design, we will need to switch to a more modern generator/engine. Our current 37-year-old Onan generator has a fairly poor "energy-in, energy-out" ratio. Its 410cc displacement engine produced five horsepower on gasoline when new, whereas a typical engine of that size today produces three or more times that horsepower with the same engine displacement.
We recently added a transistor to the Onan's points ignition and advanced the ignition timing; the transistor provides a hotter, more reliable spark and the ignition advance takes advantage of the higher octane syngas. In the near future we are going to be switching to a more modern generator and would like it to be capable of 3-5 KW. For now, however, our old iron generator is doing a fine job with minimal problems.