Biomass as an energy source (biomass energy)
Biomass is – generally – a solid that has absorbed solar energy through the photosynthesis. Thus, the use of biomass for energy purposes is really to make use of solar energy that has been stored in the most natural way.
Typically, biomass is regarded as a very low-quality fuel, and this is true to some extent. But let’s have a look at some fundamental facts to clear out a few misunderstandings:
Woody biomass – and that is what has to be the basis for a sustainable energy production – will typically have an energy content (dry basis) of about 15-20 MJ/kg. If you are not comfortable with MJ, you can divide by 3.6 to obtain kWh instead, so that 18 MJ is exactly equivalent to 5 kWh.
So, 5 kWh are contained in 1 kg of dry wood.
- A generic car battery – 12 V, 50 Ah – contains 0.6 kWh.
- Lifting a 12 ton bus 2 m for service requires 0.06 kWh.
- On the other hand:
- 1 kg of fossil diesel oil contains almost 12 kWh.
- 1 m3 of fossil gas at ambient conditions contains about 8 kWh.
So the biomass is not that inefficient as a storage for energy – is it? Especially when you consider what happens as long as it is not harvested. Then the biomass grows! And if the stored solar energy is in the form of woody biomass – i.e. trees – then the demand for land area is minimized because they grow high. And it does not compete with the need of land for agricultural biomass, food and fibre – because it grows on forest land.
Now some people will argue that the handling and the transport of the biomass requires so much energy that the total balance becomes negative – i.e. more energy is required for the fuel handling, transports and upgrading, than actually is contained in the biomass itself. The very simple argument against this misconception is the mere fact that commercial companies today produce wood pellets in Canada and ship them across to Sweden – and they would not do that if it was not commercially viable. And if we assume – for simplicity – that the economy of the process reflects the input of work and energy, then it is clear that the vulgar argument against biomass as an energy source must be wrong.
Facts are that most any energy carrier, be it gasoline, fossil gas, electricity, coal, raw biomass or upgraded biofuels all seem to converge to about the same total energy balance as seen over the supply chain. About 2-10 % of the energy transferred through a supply chain is lost, or consumed for the transport – and this seems to hold true for any energy carrier.
Thus, if we assume 5 % and attribute that only to the transports, then you may use 5 % of 12 kWh to transport 1 kg of diesel oil (which is 0.6 kWh). To transport 1 kg of dry woody biomass (effectively wood pellets) you may similarly use 5 % of 5 kWh, which is only 0.25 kWh. Thus oil can be transported longer distances by truck than diesel oil. And this is exactly what happens. Looking at Sweden, you will find pellet producers spread all over the country so that the transport distances by car and truck are kept short while you will see oil trucks travel long distances.
So one of the fundamental properties of biomass is that it is more local than fossil fuels, simply because it is less concentrated with respect to energy. On the other hand – this tends to promote local, small scale, sustainable business in the forest regions of the country. So the use of biomass for energy does not only have a positive impact on the climate issue – it also has a positive impact on the local economy and on the local employment rate.
