If Napa and the city’s trash-hauling partner have their way, local wood scraps may soon bypass the dump – and help feed the electrical grid instead.
A pair of plants to gasify wood wastes and generate power is a centerpiece of the new contract the city is pursuing with Napa Recycling & Waste Services, which would keep the company in charge of local waste management through 2031. The company would then draw fresh revenue from selling power to PG&E out of a new 2-megawatt biomass facility at the Materials Diversion Facility on Levitin Way.
“When it has an energy value, it seems ridiculous not to take advantage of that,” the city’s recycling and solid waste manager Kevin Miller told council members of the wood-to-power plan.
The proposed 14-year deal with Napa Recycling, which would extend a relationship that began in 2005, gained preliminary support Tuesday night from the City Council and is slated for an approval vote by late November. Napa’s current contract, originally a decade long and extended twice, is set to expire Dec. 31.
“I appreciate the creativity the city and Napa Recycling has shown,” said Vice Mayor Juliana Inman, who joined the other four council members in endorsing the plan. “… You came up with another way to deal with our bio-wastes, and I think this is really great.”
Under the new agreement, two plants with a 1-megawatt capacity each would be built at an estimated $12.6 million cost, and would generate their power by heating urban wood scrap into a gas that would drive electrical turbines, Napa Recycling directors told the city. The plants would combine to generate about 15,000 megawatt-hours annually, which Miller estimated would supply about 2,200 households.
Ten percent of the power would be used for the recycling center’s needs, and the rest would flow into the PG&E grid to produce about $1.75 million of extra revenue per year, according to Miller. The state policy for biomass plants of less than 3 megawatts assures PG&E will pay at least 12.7 cents for each kilowatt-hour generated, he added.
A byproduct of wood gasification is biochar, which Napa Recycling would sell separately as a fertilizer and water-filtering agent. Biochar sales would total an additional $1.37 million a year, according to a city forecast.
Public Works staff estimated the biomass plant would turn a $5.1 million profit over its first 20 years, with the bulk of the cash flow, $3.96 million, coming over the last seven years after construction costs are paid off.
Napa would conduct a rate study in 2018 to decide what rate increase it should charge customers under the new contract. The city projected a 9.5 percent increase, spread over two years, if it builds the wood-to-power facility – more than a percentage point less than if it continues trucking wood scrap to other plants.
Not building such a plant would not only close off a revenue source but leave Napa at risk of losing outlets for the estimated 16,000 tons of chipped wood it currently hauls out of town each year, added Miller.
Closures of larger biomass power plants lacking the state’s small-plant incentives have left cities with fewer places to bring their wood waste, and remaining plants increasingly have concentrated on processing forest waste instead, he said. Napa’s expenses to trucking out scrap wood have reached $15 a ton and may jump to $40 by 2020, the city estimates.
The city’s base payment to Napa Recycling would go from $10.6 million this year to $15.6 million in 2019, including $3 million in capital costs, if the biomass power plant is built. But revenue from power and biochar sales, combined with reduced trucking miles, would limit the net cost increase to $1.8 million.
Other terms of the pact include eventually moving to a truck fleet powered only by compressed natural gas, committing to larger shipments of compostable waste, and improving sorting equipment to recover 5,000 more tons annually of recyclable materials by 2020.