District Energy - 2010 4th Quarter

since media reports tend to focus almost exclusively on the former.

Even with its limited scope, the report contains findings that affirm the benefits of using biomass specifically for thermal and CHP production, something that more and more district energy systems are accomplishing every day. By doing so, they are helping to reduce long-term carbon emissions, increase energy security and keep energy dollars circulating locally. Carol Werner sums it up nicely: “Wood waste is a huge resource that we ought to be using. We don’t want it burned in the open or going into landfills, which creates another problem in and of itself. We want to make sure that it gets used in a very positive, constructive and highly efficient way, such as district energy and CHP. If we do that, we can cut back on the use of fossil fuels and channel dollars into our local economies. It allows us to accomplish multiple societal objectives at the same time. It can’t get any better than that.”

Carbon Debts and Carbon Dividends

Excerpt from the Biomass Sustainability and Carbon Policy Study

“The atmospheric greenhouse gas implica-
tions of burning forest biomass for energy
vary depending on the characteristics of the
bioenergy combustion technology, the fossil fuel
technology it replaces, and the biophysical and
forest management characteristics of the forests
from which the biomass is harvested. Forest
biomass generally emits more greenhouse gases
than fossil fuels per unit of energy produced. We
define these excess emissions as the biomass
carbon debt. Over time, however, re-growth of
the harvested forest removes this carbon from
the atmosphere, reducing the carbon debt. After
the point at which the debt is paid off, biomass
begins yielding carbon dividends in the form
of atmospheric greenhouse gas levels that are
lower than would have occurred from the use
of fossil fuels to produce the same amount of
energy. The full recovery of the biomass carbon
debt and the magnitude of the carbon dividend
benefits also depend on future forest manage-
ment actions and natural disturbance events
allowing that recovery to occur.

“The initial level of the carbon debt is an important determinant of the desirability of producing energy from forest biomass. Replacement of fossil fuels in thermal or combined heat and power (CHP) applications typically has lower initial carbon debts than is the case for utility-scale biomass electric plants because the thermal and CHP technologies achieve greater relative efficiency in converting biomass to useable energy. As a result, the time needed to pay off the carbon debt and begin accruing the benefits of biomass energy will be shorter for thermal and CHP technologies when the same forest management approaches are used in harvesting wood.” The full Manomet report is available online at www.manomet.org.