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. What arguments can we use 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 renewable energy category is simple. In fact, 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 has carbon neutral emissions and this is true. Indeed, during its life, a tree absorbs carbon dioxide and produces oxygen through photosynthesis. Once it is cut and turned into fuel, it releases this absorbed amount of CO2. Furthermore, if the use of this material as energy takes place in the locality where it was collected, 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 wood energy yield. As proof, the theoretical efficiency achieved by stoves and inserts in the 1980s was 50%, while it is almost 85% today. If these figures are theoretical, the reality does not differ from them.

The devices used today are much more sophisticated and must meet various rigorous standards. In addition, the use of different forms of wood energy makes it possible to increase its effectiveness and efficiency. As a reminder, fuel wood can be used in 4 main forms:

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

Efficiency of wood energy, a question 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 to a humidity level 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%. Conditioned hot air is constantly emitted into the drying room to speed up the process.