Understanding wood energy

If wood is considered a clean, natural and renewable source of energy, its use still raises debates from an ecological point of view. On what arguments can we rely to give credibility to wood energy? Here are some explanations.

Wood, a renewable and carbon-neutral energy

Understanding the fact that wood is included in the category of renewable energy is simple. Indeed, the forest in which it is cut regenerates. Moreover, its regeneration speed can range from a few years to a few decades. By avoiding massive deforestation, wood and forests represent an inexhaustible source of energy.

It is customary to say that wood is carbon neutral and this is true. Indeed, during its life, a tree absorbs carbon dioxide and produces oxygen by photosynthesis. Once it is cut and turned into fuel, it releases this amount of absorbed CO2. Moreover, if this material is used as energy in the locality where it was taken, the CO2 released will be quickly absorbed by the neighboring forest.

A considerable evolution in terms of performance

Since the 2000s, a considerable evolution has been observed in terms of the yield of wood energy. As proof, the theoretical efficiency achieved by stoves and inserts in the 1980s was 50%, whereas it is nearly 85% today. If these figures are theoretical, the reality does not move away from them.

The devices currently in use are much more sophisticated and must meet various rigorous standards. In addition, the use of different forms of wood energy increases its effectiveness and efficiency. As a reminder, combustible wood can be exploited in 4 main forms:

• Logs: the rawest form of wood, the log is sold in cubic meters of variable dimensions;
• Granules or pellets: made up of small cylinders obtained by compressing sawdust without a binding agent;
• Forest chips: obtained using crushed branches dried beforehand;
• Reconstituted briquettes: completely dry compressed bricks.

Efficiency of wood energy, a matter of drying

In terms of yield, this efficiency depends on a main factor which is drying. Indeed, whatever its form, the material must be dry to properly produce energy. Wood in its natural state contains between 40 and 60% water. However, this rate should be less than 25%.

Two solutions are possible for drying wood: natural and artificial drying. The first is a slow and inexpensive process. The material takes between 6 months and 2 years to dry and obtain a moisture content between 15 and 25%.

Artificial drying is more expensive, but has the advantage of being up to 15 times faster than natural drying. The humidity level can be reduced to less than 10%. Warm conditioned air is constantly emitted into the drying room to speed up the process.