Towards a Distributed, Peer-to-Peer, Near Zero Net Energy Strategy

With today’s materials, tools, and crafts we can build houses in Vermont, and the rest of the North East, that do not need central heating systems. Should we encourage the building of such housing? There is no longer any excuse for building a house with a furnace. Such ‘traditional’ housing is simply a relic of the fossil fuel age we must move beyond.

Near Zero Net Energy Houses [NZNE] have 12 inch thick walls, triple glazed windows, no furnaces, and can be heated with just 1 ton of biomass fuel, or 100 gallons of oil, in a simple, small stove. Such a house is under construction today in Townsend, MA. Expected cost of construction for this project is about $120 per sq ft for a 1,200 sq ft house with 3 bedrooms, 2 baths, full basement, etc. These homes can, of course, be given any local ‘vernacular’ look desired. The designer, Ben Nickerson, is a friend from Woodstock, Vermont.

To generalize, we should adopt a goal of a NZNE society as a whole — across the entire board — if we are truly serious about mitigating the risks of global disruption. This would, of course, lead us away from centralized power plants to distributed Combined Heat and Power, photovoltaics, wind power, and all of the other forms of renewable power. This broadly distributed peer-to-peer power would naturally lead to the “Electranet” with its 7×24 real time market for power.

The next question is: Just what sort of biomass might we want to use to heat these NZNE buildings? Is our only choice 1/4 wood pellets made in large, centralized, factories that cost on the order of 14 million dollars each, take about two years to complete, and require significant amounts of fossil fuel for drying the raw materials as well as for transportation of both raw materials and finished products?

I have recently received from BHS Energy in PA some samples of 1.5 inch diameter by 3/4 inch switchgrass “tablets”  made with a prototype mini-plugger they have in development.

This emerging small scale tablet technology, supported by some USDA funds, looks very promising indeed as a lower cost and distributed way to “densify” biomass for use as a heating fuel - once the systems for burning tablets reach commercialization. These new tablet capable stoves and boilers are expected to have initial and limited availability in late 2008 and early 2009.

In the Community Supported Energy model I am sketching out below, a local biomass tablet production facility would serve a radius of about 5 miles and draw its fiber from about 238 acres of local grass lands. This 238 acres of biomass fiber production represents just 0.47% of the land mass in an area with a 5 mile radius.

In my spreadsheet, I assume a base rate of 650 pounds of tablets produced per hour = 2.6 tons per day or 13 tons per week  - on a one shift per week schedule. No drying required, just hammer milling through a 3/4 inch screen.  Raw material can have a moisture range of 8% - 14%. At an average of 650 tons per year per machine [50 weeks X 13 tons per week], over 7 years, the amortized equipment cost per ton is just $10.99 [assumes $50K all in cost of production facility]. Labor, 1.5 FTEs at $15 per hour, would be $46.15 per ton + $75 per ton for energy hay + fuel cost to manufacture etc. and we are looking at something like a $202.24 per ton delivered price to a CSE member living within 5 miles of the production center.    These energy tablets have an energy value of about 15.58 MM BTUs per ton or 113 gallons of oil energy equivalent.  Thus $202.24 per ton is equal to heating oil at $1.79 per gallon.  Note:  The energy used to produce the tablets is estimated to be about 3% of their gross energy content.

Obviously, these numbers are very rough, back of the envelope, estimates.  If production per hour goes up and the cost of feed stock goes down, free paper waste from the transfer station?, the picture gets even better. If other costs increase, the opposite is true. Now here is a key point.  A conventional industrial pellet plant will cost on the order of $14 million dollars.  It will operate three shifts per day and produce on the order of 100K tons of pellet fuel per year.   Or we could use the $14 million to set up about 280 Mini Slugger tablet production centers @ an estimated $50K each.

280 distributed tablet production centers could produce, in aggregate, on the order of 182,000 tons of tablets per year!  This would be enough to heat about  20.5 thousand conventional VT homes, each burning 9 tons of grass tablets per year. Of course, it would be better to heat Near Zero Net Energy homes requiring just one ton of tablets per year.  This would allow us to heat 9X more homes for the same effort and stress on our limited fiber shed.

Importantly, the distributed tablet solution will create the BTU equivalent of 172,900 tons of wood pellets, a 73% increase in yield over that of a single, large, centralized pellet plant.  This distributed scenario is thus a more robust, more resilient and more secure energy strategy.  It also substantially reduces the fossil fuel used in transportation of both raw and finished materials.  This strategy thus appears to deliver greater economic benefits to a greater number of communities.

Of course, the missing link at the moment is heating systems, stoves and boilers, that can safely burn grass in the tablet form for domestic heating.  My hope is that a firm in MA will be able to commercialize their work in this area in 2009.

All of this suggests we need to be flexible enough to consider all of: green wood chips, pellets and tablets when we consider biomass heating fuels.  There is a role for all three fuel types — three sources of silver buck shot. Taken together, the net value should be greater than the sum of the pieces.

I am currently working to pull everything together for a first demo of proto-types this this Fall.

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