Horticulture · Sustainability

Energy crops 2

There are a lot of publications recently about energy corps. In my last post I presented briefly what energy crops are. Now, let’s see at some indicators and what should be taken into account, before making a decision to switch to such type of resources.

They are so called renewable resources in the contrast to other resources like, oil, coal or gas, because they can be renewed. What does it mean?

In general agriculture does not produce energy but only biomass. It requires such resources as: soil, water, air, nutrients, area and labor.  Then there is a need of conversion of obtained biomass. The energy share provided from biomass in total world energy supply is app 14%, while in developing countries this share is app 33% and in high industrialized countries much lower.

Most of biomass currently used for energetic purposes is wood. According to many Authors, the supply of wood from various sources (primary and recycling ones) will stay at the same or similar level and the growth of the use of biomass in energy supply will be reached by the increase of energy crops cultivation.

Let’s see what the main methods of obtaining energy from biomass are. They are usually divided into two groups:

  • thermochemical methods,
  • biological methods.

Thermochemical processes consist in thermal transformation of biomass into gases, liquids and solid fuels to further processing and include such processes like e.g.:

  • reduction,
  • combustion,
  • pyrolysis,
  • reforming.

Biological processes include e.g.:

  • alcoholic fermentation,
  • anaerobic decomposition,
  • lignocellulose biodegradation,
  • biophotolysis.

Thermochemical processes are at present wider implemented than biological ones, although one says, the last one are more promising for future.

How can we measure the effects of usage of energy crops or rather the usages of biomass to obtain energy?

There are a few widely used indicators.

One of most important ones, is energy efficiency, which is measured in the ratio between the useful output and input of an energy conversion process. It is usually given in percentage.

The other indicator is energy density, which is equal to the amount of energy stored in a given space per unit volume. Due to quite high content of oxygen, biomass has usually lower energy density in comparison to conventional fuels.

Another indicator is a calorific value – the amount of energy released by total combustion of a unit of a substance (e.g. fuel). This indicator is also lower for biomasses in comparison to other conventional fuels.

Indicator ERoEI (Energy Returned on Energy Invested) is also a useful one. It shows the ratio of energy delivered to energy required to deliver that energy. So in fact it says about returns on investments, also from financial point of view.

Each product, each production process and each act of consumption has an influence on natural environment. This influence is visible and active at each stage of the whole life cycle of a product from obtaining of raw materials, through production, distribution, utilization and recycling. The influence of energy crops cultivation should be also evaluated not only in financial and economical areas but also by the total comprehensive influence of all stages of their production, utilization and recycling on the environment and ecosystems.

So when we are talking about energy crops, we should ponder such financial/economical, ecological/environmental, social aspects as:

  • total cost of agricultural production,
  • influence of the use of fertilizers on soil and ecosystem,
  • energy crops are fast growing crops = they need a lot of nutrients,
  • energy crops cultivated as main crop take the a land, otherwise used for other purposes (like agriculture food production),
  • cost of recultivation of land after cultivation of energy crops,
  • utilization of losses of agricultural production (harvesting and storage losses), their influence on the environment,
  • influence (positive) of energy crops used at the same time as recultivation crops,
  • financial costs of processing (after agriculture production stage),
  • byproducts and wastes received in all stages of that process and their utilization,
  • influence of this processing on environment.

References:

  1. Budzyński W., Bielski S., 2004, Energy resources of agricultural origin. Part II. Biomass as a solid fuel (review). Acta Sci. Pol., Agricultura 3(2) 2004, 15-26.
  2. Hinchee et al., 2009, Short-rotation woody crops for bioenergy and biofuels applications, Vitro Cell.Dev.Biol.—Plant 45:619–629, DOI 10.1007/s11627-009-9235-5.
  3. HLPE, 2013. Biofuels and food security. A report by the High Level Panel of Experts on Food Security and Nutrition of the Committee on World Food Security, Rome 2013.
  4. Roszkowski A., 2013, Energy from biomass – effectiveness, efficiency and energetic usability Part 1.  , PIR 2013 (I–III): z. 1 (79), 97-124.

 

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