Pellet fuel essential to decarbonization goals

There are many metrics showing that fossil fuel CO2 emissions are causing rapid changes in environmental variables, and the earth’s systems are unable to fully recycle CO2 emitted.  Not only has there been steady warming, but in 2023, we may have crossed a tipping point that results in even more rapid change combined with increasing variability (more extreme highs and lows). If the future is going to be what we hope it will be, action is needed now.

Seeking a just, orderly and equitable solution 
Today’s socioeconomic systems are based on the energy we derive from fossil fuels. Thus, the search is for “drop in” replacements that can continue to power the infrastructure we rely on with minimum disruption.

There are already so-called drop in solutions that are being deployed in the power, heat and transport sectors. Energy-dense liquid fuels made from renewable feedstocks are gaining in use and coming down in cost. The use of ammonia and hydrogen (produced from renewable power) as non-carbon energy carriers will be part of the transition. Heating from sustainably sourced wood chips and wood pellets is commonplace in many EU countries and North America.

However, power generated from wind and solar sources cannot be fully qualified as a drop-in because it is variable. Thus, no matter how many megawatts are deployed, sometimes it will generate less than the grid needs.

Over the next few decades, it is likely that energy storage solutions will be developed and deployed at a scale that will sufficiently buffer intermittent and variable supply, and keep the power grids stable most (not all) of the time. But at least over the next few decades, to make the transition to a decarbonized future as seamless as possible, the power grids will need CO2-beneficial generation that is on-demand and load-following.

The use of pellet fuel produced from perpetually renewing biomass solves part of that problem. Existing coal-fueled utility power stations can, with relatively low cost and little downtime, make modifications and replace coal with pellet fuels produced from perpetually renewing (not depleting) sources. The result is renewable electricity that can be generated on demand.

Pellet Fuel: an energy dense storage solution
The idea that forests will be net-positive CO2 sinks forever is wrong. They will always reach saturation. But if well managed, they can be continuously used without lowering the net quantity of carbon they are storing. If the stock of biomass is not depleted over time, excess CO2 is not created and thus cannot accumulate in the atmosphere. For forest biomass, if the quantity of wood in the landscape is not depleted (i.e., the removal rates never exceed the growth rates) the quantity of CO2 released from any wood that is combusted is less than or equal to the quantity of CO2 captured. This logic only works if the resource is continuously and perpetually renewing. Sustainability is the absolute necessary condition for the use of pellet fuels as a carbon beneficial coal replacement in power generation.

The vast majority of the primary harvest of woody biomass for forest products industries is not for the production of pellet fuels. The primary users are sawmills (lumber, flooring, furniture, etc.) and pulp and paper mills (printing paper, cardboard boxes, toilet paper, etc.). These mills have been operating in some locations for more than a century because they only take in an amount of wood each year that is less than or equal to what grows in the working forests around them. The mills can, if well maintained, essentially operate forever. Properly managed pellet mills benefit from the same forest resource stewardship.

What is the strategy for the multidecade transition that provides a seamless and low-carbon input to the power grid that can be baseload or load-following, and is available on-demand?

We already have large-scale energy storage that can be part of the solution. The biomass cycle captures solar energy and stores it. Forests are the world’s largest solar battery. Every year, about 5.7 x 10^24  joules of solar energy irradiates the earth’s surface. That solar energy is an essential part of our planet’s ecosystems. Plants and photosynthetic organisms utilize that energy to convert large amounts of CO2 into glucose. The chemistry of plant growth transforms the glucose into other sugars (hemicelluloses), cellulose, lignin and other plant matter. Every year, solar energy and photosynthesis convert billions of metric tons of CO2 and water into plant matter, and produce oxygen as a byproduct.

A portion of that plant matter is trees. While some forests are not and should not be used to supply the forest products industry, many millions of hectares of forests are managed and cultivated to continuously produce logs for lumber, furniture and many other products that are part of everyday life. Those forests also produce wood chips for the manufacturing of paper, packaging, tissue and a variety of engineered wood products. Some of the byproducts of sawmills and the parts of the rest of the trees that are not suitable for higher value use may find their way to pellet factories to produce solid fuel, and to factories that create renewable liquid fuels from cellulosic feedstock.

These managed, working forests are, in effect, tree farms. Each plot on these tree farms cycles through stages of regeneration, growth to maturity and harvest. But in aggregate, as long as the rates of removal never exceed the rates of growth, the total quantity of wood (and thus stored carbon) does not decline. The average growth rate of forests around the world is about 12 metric tons (mt) per hectare per year. In northern regions it is less, and in some tropical locations with fast-growing tree species, it is more than 20 mt per hectare per year.

Forests cover approximately 31 per cent of the world’s land surface, about 4 billion hectares. Assuming an average growth rate of 12 mt per hectare per year and an average energy content per mt of about 8.64 gigajoules (GJ) (based on wood with a moisture content of 50 per cent), the world’s forests store about 415 billion GJ, or 115 million gigawatt-hours (GWhs) per year.

Estimates indicate the total electricity produced by wind and solar in 2022 was about 3.5 million GWh. The forests capture and store about 33 times as many GWh per year as all solar and wind combined. In addition, nearly all of the power generated by solar panels and wind turbines is consumed as it is produced.  Without storage, solar and wind power are not dispatchable, whereas the solar energy captured by the world’s forests is stored.

Clearly, only a portion of the world’s forests are used to supply the forest products industries—about 30 per cent, according to the FAO.  Based on the estimate of how much of total North American primary harvest becomes pellets—4.5 per cent—and using that proportion to estimate global GWh that could be in pellet fuel, more than 1.55 million GWh could be moved from forest storage into pellet fuel every year without depleting forests and the carbon stock held in the forests.

BloombergNEF forecasts that there will be about 1,880 GWh of long-duration energy storage by 2030. Based on forests that are already managed for producing wood for lumber, paper, etc., and only using 4.5 per cent of that material to produce pellet fuel, there is potential today for pellet fuel to deliver 826 times more stored energy per year than all of the energy storage solutions forecast for 2030. If bioenergy carbon capture and storage (BECCS) is added to the analysis, that stored energy is not only put to use to help keep the electricity grids stable, but the stored carbon is permanently removed from the atmosphere.

Beginning of the end of the fossil fuel era
There is already a pathway that can support decarbonization goals, and it’s deployable now. In 2022, the global pellet fuel supply chain filled the equivalent of a Panamax-size  ship (about 65,000 mt) every day of the year with stored energy in the form of carbon beneficial pellet fuel.

On the demand side, large utility power stations have successfully completed “bioconversions.”  For them, coal is history; dispatchable or baseload generation is not. The orderly transition from today to the desired future should include policies that support the responsible use of solid fuel derived from the stored solar energy in renewing biomass. There is nowhere close to enough renewable sources of biomass in the world to replace all the coal that is being used—but there is enough to make a significant difference.