Straw as Energy Resource
Straw is a by-product resulting fromthe growing of commercial crops, primarily cereal grain. Straw from
rape and other seed-producing crops is also included in the total production.
Agriculture’s choice of crops - and thus also the amount of the production of straw - depends in the first instance on agronomy,
i.e., the science of cultivation of land, soil management, and crop production, and on financial matters affecting the management of
the entire agricultural area.
The annual straw production is influenced by the framework stipulated by the EU agricultural policies, including developments in cereal prices, the fallow
of land etc. The straw quality and the amount of straw that can be gathered in, are also influenced by the weather during growing and harvest.
In 1996, the Danish area with cereal grain amounted to 1.55 million ha /ref. 25/. The cereal grain yield was 9.17 million tonnes of cereal grain,
and the amount of straw was 6 million tonnes. The straw production in a year with average harvest is estimated at 6.3 million tonnes, but may vary up to
30% due to climatic conditions during the period of growing and gathering in.
Of the total straw production, only a minor part is used for energy purposes.
The major part is used in agriculture’s own production, i.e., as bedding in livestock housing systems etc.
Also a considerable amount of straw is used for heating, grain drying etc. in agriculture. In addition, an amount agreed upon according to crop delivery
contract is sold to district heating plants and power plants for energy production.
The straw left after deductions for these applications, is for the major part chaffed and ploughed back and is thereby used for soil amelioration.
Thus this is a straw surplus which - with the annually weatherdependent variations - makes out a potential fuel reserve.
Trading in straw for energy purposes among producers and the energy sector is in principle determined by crop delivery contracts for several years,
concluded between the individual straw producer or an association of straw producers and the purchaser.
The purchasers are straw-fired district heating plants and CHP plants that by entering into long-term crop delivery contracts for straw make sure
that they can perform their duty to supply heat and energy to the consumers.
Not all straw is traded according to crop delivery contracts. By purchasing straw in the spot market, e.g., at machine pools, or at the places of other middlemen, the plants may often achieve an advantageous price for part of their annual consumption of straw.
The crop delivery contract for straw may include the following terms and conditions:
• Term of contract and notice of termination
• The amount of straw agreed upon, including provisions in the event of increase/decrease in the consumption of straw, non-delivery due to decrease in crop yield etc.
• Terms of delivery, including the type of bale, the dimensions and weight of bales, water content, and other grade determinations
• Basic price and the regulation of price in proportion to water content and time of delivery
• Provisions concerning the regulation of the basic price
• Provisions concerning arbitration
Plough Back of Straw
Land that has been cultivated for several years has a lower carbon content than has uncultivated land. Thus when cultivating land, carbon is removed
from the soil in the form of CO2 being released to the atmosphere.
The carbon content is of importance to the fertility of the earth, a maintenance of this fertility requires a current application of crop remains or other
organic matter. Though the optimal or critical levels for the carbon content of the earth is not known. Experiments carried out since 1920 at the Danish
Institute of Agricultural Sciences Askov Experimental Station have shown that the carbon content of the earth has dropped no matter whether commercial fertiliser (NPK) or animal manure is applied.
As is the case with liquid manure, sludge and other crop remains, ploughed back straw may contribute to increasing the carbon content of cultivated land on a long view as is the case also with grass after grain crops. The gain by removing straw from the field for energy purposes is that it substitutes fossil fuels. Most of the carbon in the ploughed back straw is released in the form of CO2, and altogether less CO2 is emitted to the atmosphere if straw is removed for the purpose of substituting fossil fuels.