Woodchips are not compressed and are cheaper than pellets per unit of energy delivered. Logically they require considerably more storage space. It is not a standardized product and therefore their energy content varies more. The volu­metric bulk density (weight per unit volume) of woodchips is significantly lower than that of woodpellets. If you compare the storage space of woodchips and woodpellets, woodchips require at least 3 times more storage space for the same energy content. Woodchips are cheap, but you need lots of space for storage!

If you plan to invest in agroforestry, which is a much better investment than gold, stocks, or bonds, the tree growth rates and as a consequence financial returns are of utmost importance. Here are some examples of what you can expect:

• In natural temperate forests growth rates range from 1 to 4 m3 per hectare each year.

• In subtropical plantations of conifers such as pines, this range rises to 10-30 m3 per hectare each year.

• Tropical pine plantations are still faster and deliver 15-45 m3 new wood mass per hectare each year.

• Fastest of all are hybrid tropical eucalyptus trees. Cultivated on plantations they grow to full maturity in only 4 years and they reach growth rates of up to 60 m3 per hectare each year. Out of eucalyptus you can produce ethanol, paper towels for China, or woodpellets.

Currently, many utilities and large industries cofire woodchips, which are relatively inexpensive. Woodchips are diverse with different gigajoule (GJ)-per — tonne outputs. They do not have a universal standard size and this can limit usage. The feedstock of woodchips can be stems, tops, limbs, branches, and foliage of mixed hardwood and softwood trees. Woodpellets are a more reliable feedstock due to their uniform shape, high bulk density, and high calorific value. Moreover, they have a much lower moisture content due to the processing procedure and therefore are ideal for transporting to domestic or international customers.

8.4.3