17.01.2011 lecture diary

I’ll be following the lecture structure here, thus the comments will be in the following order:

  • Biomass
  • Hydropower
  • Solar energy
  • Others


Since the course subject is rural energy systems, it’s quite natural to start from the most commonly used resource. Still, promoting the use of biomass seems questionable in barren regions that already have problems with desertification.

I encountered photosynthesis as a chemical process in high school more years ago that I’d care to admit, so it was bit strange to me that the formula for the process was repeated in the lecture slides no less than thrice. I think it would be enough to concentrate just on the more detailed information about how the different variables affect the process. Especially the information about the needs of the different plants of the different spectrums of light in order to achieve optimal efficiency was interesting.

The maximum theoretical efficiency of only 30% for photosynthesis made me wonder at first why we even bother, but then I realized that algae having very high yield of energy among the photosynthesizers, and earth having 70% of its surface covered by water makes photosynthesis a very interesting research subject indeed.

Using fast growing corps seems a decent enough option for developing countries to convert solar energy into e.g. lighting locally, but the energy density of even the dry mass is so much lower than the fossil fuels that I recon that the use of biomass to produce “clean” energy in Finland by driving it tens or hundreds of kilometers to power plants is a complete waste of resources.

If the conversion of raw biomass to other resources via alcoholic fermentation or anaerobic digestion is relatively simple, then could it be used in the northern countries as well? Could the process be shielded from the frost cheaply enough?


I’d like to disagree with the lecturer here: hydropower isn’t constant availability unless the country has no dry and wet seasons. Even in the western countries we have huge variations in availability with the big storage basins. Predictability goes to the same category: if you have the basin, the predictability is quite bad, if you don’t have it, it’s even worse. This can be seen from the imageg on pages 40-41, which demonstrate that the flow of the river can increase by 800% for a very short period of time.

The basic instructions on how to build a micro hydro were interesting. I didn’t know that the basic idea is so simple that it could be probably taught to the locals, and then they could then build more as the need would arise. Altough in this case it might be important to stress that if the demand rises much over the production, widespread blackouts are possible.


The idea behind the cheapest thermal energy collectors to warm up water was very nice basic information, especially combined with the info about the fancier western version to show the differences. Various different uses for solar heat on p. 54 with all their limitations concerning the local culture made me realize more potential uses and problems.

What is the maximum theoretical value for photovoltaic efficiency? I’d love to see it compared to the 30% efficiency of the photosynthesis.


Rest of the lecture was mostly skipped, so I’d recommend cutting the lecture slides by approximately 15 slides in order to avoid this kind of skipping. If the only important resources are biomass, hydro and sun, we could have slides only about those, and mention the others in the passing.