South Tahoe Refuse Investigates New Clean Energy Technology  to Offset Fossil Fuels

STR currently receives and processes approximately 10,000 tons of woody material each year, the majority of which is transported out of the Basin to dispose of as compost. This material is generated from green yard debris, clean construction and demolition (C&D) material, and residual waste from defensible space and fire mitigation activities (i.e., small trees, tops, and limbs) from the surrounding area. The proposed biomass project would use only about 1,000 tons of biomass per year, or 10% of what STR is already handling. Using this material on-site will result in roughly 72 fewer trucks hauling material out of the Basin each year, and a reduction in the associated transportation emissions.

Many stakeholders in the Tahoe Basin are working hard to implement fuels reduction treatments at a landscape level that are designed to protect communities from the risk of wildfire. In fact, the Tahoe Fire and Fuels Team has already treated nearly 90,000 acres in the Tahoe Basin, especially areas near neighborhoods. These projects generate approximately 10 tons of residual woody material per treated acre, resulting in thousands of tons of biomass that is either burned in slash piles or hauled long distances for disposal at a high cost.

The STR pilot project represents a small-scale, distributed approach to local biomass utilization. While the STR pilot project will use material being generated by community defensible space activities, it is not expected to incentivize additional forest restoration activities in the short term due to its small wood fuel demand. However, demonstrating that wood energy technologies can be unobtrusive, clean, and effective may support a broader community discussion about the value of wood energy in the Tahoe Basin.

There is a growing understanding that healthy forests — particularly in areas where fire plays an important role in shaping the landscape — can benefit from some level of active management to reduce heavy fuel loads in the form of small diameter trees and other woody debris [3]. These residuals have a low market value, and high-cost removals often make restoration efforts prohibitively expensive [6].

Wood energy systems can be integrated with climate adaptive forest management practices to help restore fire resilience to our forests and protect communities in the Wildland Urban Interface (WUI). Each year, WUI communities thin forests and burn “slash” piles in anticipation of unpredictable wildfire seasons – with growing demands to increase the pace and scale of these activities across the West. On average, these practices emit ambient PM2.5 (Particulate Matter 2.5) concentrations that exceed the Environmental Protection Agency’s (EPA) air quality standards and easily reach “hazardous” levels of air pollution [2]. Wood energy offers a cleaner, sustainable alternative.

A locally available stream of underutilized wood. Wasted or underutilized wood is more common than you may think. Wood used to fuel biomass energy systems can come from wildfire fuels reduction, clean construction and demolition material, urban tree pruning, timber harvest residuals, and more.

Critical facilities. Biomass combined heat-and-power (CHP) systems offer an always-on, 24/7 energy asset that can keep the lights on for facilities that can’t afford to have them turned off. This provides the functionality of a fossil fuel generator using renewable resources that are available from local backyards (literally).

Communities implementing fire mitigation activities. Switching to biomass provides a market for forest residuals produced by wildfire fuels reduction and ecological restoration treatments. These systems also divert waste wood that would otherwise be burned in piles or sent to the landfill.

Large energy users. While small biomass systems make sense when the main goal is to replace fossil fuels or you have a free source of wood, impactful benefits are realized as systems get larger in size while remaining aligned with existing forest stewardship efforts and goals.

Local economy enthusiasts. Fossil fuel consumption distributes dollars to large global corporations. Biomass systems instead rely on local restoration economies, benefitting nearby fuel providers, processors, and handlers.

Figure 2: Comparison of annual criteria pollutant emissions between a 125kW waste wood gasifier and a representative Tier 3 125kW diesel generator.

Figure 3: Carbon emissions modeled for the STR project compared to business as usual. Business as usual includes natural gas use, grid electricity use, biomass disposal as compost, and transportation of biomass. The STR project will reduce transportation of woody biomass, reduce or eliminate grid electricity and natural gas use, and gasify biomass locally.

Unlike solar and wind, wood energy can be a baseload firm and flexible technology, with energy available 24/7 [5]. That means that for every hour that energy is needed, biomass systems produce it —rain or shine, through the seasons. In addition, a biomass CHP system can generate the same amount of energy as a solar array for a fraction of the footprint, contributing to our renewable energy goals without sacrificing sensitive landscapes.

There are many types of technologies that enable the generation of electricity and/or thermal energy using woody material. On the smaller scale this can include high-efficiency wood stoves to heat a family home, gasifier units to provide electricity and heat to commercial or institutional end users, a district heating boilers offsetting fossil fuels for ski resorts and towns. There are also some very large biomass systems in the world, like power plants providing hundreds of megawatts to the grid. Each type of system can have very different implications for ecosystem and community health. The South Tahoe Refuse project is considered a small system.