Burning the forest to save it: Arizona thinning wood on the grid

How a forest ends up on the grid

Arizona's utility regulator, the Arizona Corporation Commission (the five elected officials who set what APS and SRP may charge), has for roughly a decade pushed the utilities to buy forest-bioenergy, meaning power made by burning woody material. At last public report that direction added up to something on the order of 60 megawatts of biomass the utilities were to procure, anchored by the plant at Snowflake up in Navajo County.

That plant, run most recently as Novo BioPower, is rated at roughly 20 to 30 megawatts, small by grid standards (a single large gas unit is many times that). It takes small-diameter trees and slash cleared from overgrown stands, chips the wood, and burns it to make steam. The fuel is the point: the plant exists to give thinning crews somewhere to send material that is too small for lumber and too costly to haul far.

The honest math

Electricity from burning forest thinnings is not cheap. The wood has to be cut, piled, and trucked off steep ground, and a plant this size cannot spread its fixed costs over much output. On a pure cost-per-kilowatt-hour basis, desert solar beats it badly, and Arizona has roughly as much cheap sun as anywhere in the country.

So the case for biomass is not the electron; it is the watershed and the fire. If thinning the forest lowers the odds of a megafire that scorches the ground above Roosevelt Lake, the avoided cost (dredging reservoirs, emergency water treatment, lost storage) can be large, though honestly hard to pin to a single number. The plant also runs round the clock, which a solar panel cannot, and that steady output has some value when the sun is down. Whether the total is worth it depends on figures reasonable people read differently.

Who clears the forest

Thinning itself is mostly a federal job. The US Forest Service runs the Four Forest Restoration Initiative (4FRI), an effort to restore overgrown stands across the Apache-Sitgreaves, Coconino, Kaibab, and Tonto national forests, on the order of a couple of million acres in all. 4FRI has moved slower than its backers hoped, and finding contractors who can make money on small-diameter wood has been the recurring snag.

A guaranteed buyer for that wood, paid for through utility bills, is where the Snowflake plant and the commission fit in; it is meant to give the whole chain (loggers, haulers, mills) a reason to keep cutting. It is a subsidy wearing a power-purchase contract, and the state has been fairly open that the forest, not the grid, is what it is really buying. State foresters at the Arizona Department of Forestry and Fire Management track the acres treated.

Worth watching this month

1. Watch the Arizona Corporation Commission's e-docket for any new or renewed biomass procurement order, which is where a change in how much APS and SRP must buy would show up first.

2. Watch the US Forest Service's 4FRI acreage updates, a routine but telling sign of whether thinning is keeping pace with the plant's appetite for fuel.

3. Watch Novo BioPower's status at Snowflake, since for a plant this small the contract renewals and unplanned outages are the thing most likely to move this story.

4. Watch the post-monsoon watershed and reservoir reports from SRP, because ash and runoff after a wet summer are the clearest measure of what a burned forest costs the water supply.

5. Watch for Arizona's fire-season outlook from state and federal forecasters, routine each spring but the backdrop against which all of this is argued.