The amount of energy captured by pines over a one-year period will vary with stand age, species and cultural practices. Pine trees that are less than three years old typically have a limited amount of foliage and, therefore, have not captured much energy (when compared to maize or perennial grass species). However, once pines have “captured the site” and are producing a high percentage of shade, the ability to capture energy increases. For species like Pinus tadea and Pinus elliottii, the amount of energy captured (i. e. stored as aboveground wood) in a given year typically peaks around ages 10-19 years. This peak may be around age 10 years when growth rates are high while lower growth rates may result in a peak near age 19 years. After this peak, the net energy captured in a year declines as the stand matures.

The amount of energy contained in one cubic meter of pine depends on the unextracted specific gravity, which changes with stand age. The specific gravity of a five-year-old Pinus taeda sapling may be 330 kg/m3 (from stump to a height of 3 m) while that of a bone-dry, 3 m log from a 50-year-old stand may be 500 kg/m3. In this example, the older log contains 50% more energy than an equal volume of the younger log. Therefore, it should not be assumed that the energy in a green tonne of 14-year-old pine logs will be the same as that contained in 28-year-old logs.

Sometimes the estimated energy per volume of wood varies by as much as 16% because wood shrinks when it dries. Therefore, one might overestimate the energy captured by pines if one overestimates dry mass productivity. Estimates of the dry mass per cubic meter could vary from 500 to 562 kg (Table 10.2) depending on if the volume is measured soon after the tree is harvested (i. e. green) or soon after the wood is removed from a drying oven. Therefore, overestimates may occur when specific gravity is determined using the oven-dry volume as the denominator.

The amount of energy contained in a pine stand (aboveground biomass = 500 m3/ha) might be 1150 MWh/ha (LHV) but this might end up producing only 250 MWh of electricity.

The greater value (1150 MWh/ha) assumes wood (25% od moisture content) will produce

2.3 MWh/m3 when burned in a wood boiler (97% efficiency). The lower value (250 MWh) assumes the wood is used in a power plant to produce electricity (21% efficiency). Some wood-fired power plants may convert one Mg of waste wood into 0.8 MWh of electricity.

If the pine stand mentioned above was 25 years old, the yield would be 20 m3/ha/yr or 46 MWh/ha/yr. Likewise, if it took 50 years to produce this volume, the yield would be cut in half (i. e. 10 m3/ha/yr or 23 MWh/ha/yr). As a comparison, 23 MWh/ha is equivalent to

13.5 barrels of crude oil (in theory). A hectare of solar panels might yield about 990 MWh of electricity per year. As a comparison, it might take a year and 21 hectares to capture the same amount of wood energy with a pine plantation.