When aiming to utilize LCMW biomass as feedstock for an energy supply chain a number of technical, environmental, socio-economic and legal factors have to be taken into account. During task 4.2 of the greenGain project key success criteria were identified to match the LCMW feedstock types with the suitable conversion technologies and define LCMW pathways.

The key success criteria are the potential and availability of feedstock type, suitability for conversion technology, costs of the pathway, and the environmental and socio-economic performance. Based on these criteria the LCMW pathways were assessed and their performance evaluated at local scale.

Below we take a closer look at the potential conversion route from biomass harvesting to the energetic consumption on the example of feedstock type DE-LCMW 1 Hedge- and tree rows on banks in Friesland (FRI), Germany (refer to the table 1: Potential and properties of landscape conservation and maintenance work (LCMW) biomass in the greenGain model regions; greenGain deliverable D4.2).

Maintenance of hedge- and tree rows on banks in Friesland

Origin and properties of the feedstock

In the model region Friesland maintenance of hedge- and tree rows on banks was chosen to be the most promising feedstock for the energetic utilisation of LCMW biomass in the region. The county Friesland (FRI) is located in North-West of Germany 130 km west of Hamburg and belongs to the metropolitan region of Bremen and Oldenburg. It has a total area of 60,785 ha and counts 96,937 inhabitants.

The landscape is dominated by the „Marsch“ (alluvial land), followed by Geest (slightly raised landscape with sandy soil) and moor. The widely spread Hedge – and tree rows on banks, form a part of Friesland´s cultural landscape. Agriculture is the main economic sector in the region, followed by tourism. (For further details refer to the greenGain deliverable D5.1)

Hedge- and tree rows on banks are a mix of trees and shrubs standing on earthen mounds/banks, which where build in historical land use to fence agricultural fields. Over time the hedge- and tree rows lost their function and they are often not maintained anymore. Wrong maintenance caused damage and some are even now scarcely stocked.

Today Hedge- and tree rows on banks are protected by the Federal Law of Nature protection which regulates their maintenance. For example cutting and felling procedures are only allowed from October to February and should not be done more frequently than every seven years.

Most of the hedge- and tree rows on banks are privately owned by farmers. The maintenance and conservation is supported with legal programmes. The owners may upon request receive financial support for the maintenance work and in turn make sure, that the typical character of the hedge- and tree rows on banks (from ecological to historical aspects) is preserved.

Maintenance work steps

Harvesting takes place manually and mechanically and is either done by the owner of the hedge- and tree rows on banks or by a service company. The felling is done with felling scissors (pinching) or a cutting aggregate on an excavator, larger dimensions and trees are cut by chainsaw. It occurs that the vegetation is damaged by pinching machines, they rather should be cut. For short storage trunks, branches and shrubs are sometimes bundled on roadside. Chipping is usually done on site and the chips are directly blown from the chipper on a tractor with trailer or a truck. Trucks or tractors with trailer are used for the transportation depending on the tonnage acceptable for the nearest road. If the biomass is not further utilised it is chipped and blown directly on site. If it is further used, the material is often dried as fuel wood or woodchips in open air or in sheds. Table 1 gives an overview of the single maintenance steps.

Table 1: Single steps of the DE-LCMW 1 hedge and tree rows on banks
Process Step Equipment/Operation Operator
Harvest:
Felling/Cutting
Felling scissors (pinching)

Cutting aggregate on excavator, larger dimensions and trees with chainsaw

Owner or company
Storage Short storage and bundling on roadside Owner or company
Chipping Chipper mounted on trailer Service company
Sieving Sieving to remove the small size fraction which is not suitable for use in combustion
Loading: Blow from chipper on tractor with trailer/truck Service company
Transport Trailer/truck Service company
Pre-treatment Sieving or drying Service company
Storage Chips piled under shed Service company
Combustion Sell to burn: Fuel wood or wood chips to produce energy; mainly in small stoves and domestic heat and small pellet boilers Service company
Burning Disposed of in traditional Easter Fires of the region

(restricted in Friesland since 2014)

Municipality or private

Methodology

Availability, properties, potential and use of the feedstock type

Most of the hedge- and tree rows on banks in Friesland are privately owned. Thus, no exact figures are available on the frequency of the treatments because every owner organises the LCMW on his own, which determines the amount of the harvested biomass.

The cutting and felling of hedge- and tree rows on banks is allowed only from October to February and should not be done more frequently than every seven years. In most cases the LCMW is done every 7-15 years.

The biomass feedstock derived from hedge- and tree rows mainly consists of woody biomass from tree trunks, branches and shrubs. If the biomass from LCMW of hedges and tree rows are utilized to produce energy, they are sold as fuel wood or wood chips to produce heat, mainly in small stoves and domestic heat and small pellet boilers. In the past the biomass from the feedstock type LCMW 1 in FRI was often disposed of or burnt in traditional Easter Fires of the region, which are now being regulated since 2014.

In greenGain task 5.2 a biomass assessment in the model regions of the most promising utilisation LCMW pathways was conducted. According to the greenGain deliverable D5.2 on resource and sustainability assessment and description of pilot experiences utilisation pathways for model regions (categorisation of resources, strategy, sustainability and utilisation pathway strategies) the location and total length of the hedge and tree rows on banks in Friesland was assessed by analysing GIS-shape files, PDF maps of the Lower Nature Protection Agency in FRI, Landscape structure plan county FRI and further literature sources.

The total length of the hedge- and tree rows on banks in FRI are 490 km and according to the calculations of the conducted assessment for this LCMW biomass type in greenGain D5.2, a range for the theoretical biomass potential of 24-220 t/km was estimated. The ratios derived from light and/or shrub-dominated vegetation were removed from further consideration. Under this consideration the ratio was narrowed down on a value of 40-220 t/km. The wide range of this ratio can be explained by the different types of sources (newspapers, scientific research, projects) used for the assessment. The moisture content (moisture in wet basis) at which the ratio is referred to is 30 – 45 %.

In the biomass assessment in greenGain task 5.2, different aspects regarding the feasibility of the extraction for the DE-LCMW1 biomass from hedge- and tree rows on banks, the technical and economic implementation and sustainability constraints are taken into account, for details please refer to greenGain deliverable D5.2. Thus the theoretical biomass potential was reduced by the assumed reduction coefficients. Resulting in a sustainable biomass potential of 1,840 to 10,100 t/yr (Table 2).

Table 2: Biomass potential of DE-LCMW 1 hedge and tree rows on banks in Friesland (FRI)
DE-LCMW 1 Hedge and tree rows in Friesland GER
Total length hedges and tree rows in FRI 490 km
Harvest Every 7-15 years
Theoretical biomass potential 40-220 t/km
Moisture content 30 – 45 %
Sustainable biomass potential 1,840 to 10,100 t/yr
Amount of wood chips per harvest of 1 km hedge row 350 LCM1
Amount of wood chips each cutting once in 11 years 171,500 LCM
Amount of wood chips per year 15,590 LCM
1 lcm = 370 kg (45% moisture content) 5768.3 t/yr
Caloric value 14,420.75 MWh

1LCM = Loose cubic meter

 

The total length of the hedge- and tree rows on banks in FRI are 490 km which yields an average of 15,590 LCM wood chips per year when assuming an average of 350 LCM wood chips per harvest of 1 km hedge row and that in most cases the LCMW is done every 7-15 years (Görig et al., 2015). One loose cubic meter (LCM) corresponds to the amount of wood which is purred loose to the volume of a cubic meter. One LCM of fresh wood chips (45 % moisture content) weighs 370 kg and has a caloric value of 2.5 kWh/kg (Görig et al., 2015).

This would mean that the average harvest of hedge- and tree rows on banks in Friesland, Germany per year would have a caloric value of 14,420.75 MWh.

Potential yearly energy supply

The average heat consumption of a household in Germany with four persons is 25,000 kWh per year which is equal to a consumption of 2500 l heating oil or 25 LCM of wood chips (Görig et al., 2015). The average harvest of 15,590 LCM wood chips from the hedge- and tree rows on banks in Friesland, Germany per year would be sufficient to supply the yearly heat amount of about 623 housholds of four persons and to replace 1.56 Million litre heating oil.

 

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Jan Doležal
dolezal@biom.cz

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