Productivity and cost of mechanized energy wood harvesting in Northern Scotland

At present, the utilization of timber in the Northern part of the Scottish Highlands is low due to a lack of a wood utilizing industry. As a consequence, the majority of forest owners do not receive any income from timber and in some cases stumpage prices can even be negative. At the same time, increasing prices of oil, gas and electricity pose a great challenge for local industries and homeowners. The establishment of wood fueled heating systems is therefore expected to improve the situation and at the same time create a market for the local timber resources. Consequently, a local energy source to produce heat and electricity at a competitive price would have positive benefits for both local industries and forest owners. Due to the current lack of competition, roundwood could be chipped for fuel, which has many associated benefits compared to the harvesting and chipping of logging residues. It is the aim of this research to apply existing Finnish know-how in regards to wood fuel harvesting in order to develop and investigate the price level of sustainable and local wood fuel supply chains.To determine the most suitable supply chain for forest fuels, various research methods were applied. An estimation of the forest resources in the Wick area was the first step of the research. The different cost components of the supply chain such as cutting, forwarding and chipping were then calculated based on Finnish experiences and adapted to conditions in Northern Scotland. Detailed transportation distance calculations and cost of transportation were calculated using GIS tools.Of the various supply chain designs considered, chipping at the landing seems to be the most suitable option. Chipping the roundwood at a central terminal would also be feasible; however, a suitable site would have to be identified since chipping of the material at the heating plant is not an option. Calculations indicate that forest chips can be delivered starting from approximately 20 € MWh⁻¹ within a 50 km transportation distance when chipping is at roadside. If the transportation distance is 100 km wood chips could be delivered at approximately 23 € MWh⁻¹. Results from the GIS analysis indicate that a sufficient supply of raw material will be available in the future. According to these calculations forest fuels can be a competitive energy source for heat and electricity production in Northern Scotland.     

On the comparison of energy sources: Feasibility of radio frequency and ambient light harvesting

With growing interest in multi source energy harvesting including integrated microchips we propose a comparison of radio frequency (RF) and solar energy sources in a typical city. Harvesting devices for RF and solar energy will be competing for space of a compact micro or nano device as well as for orientation with respect to the energy source. This is why it is essential to investigate importance of every source of energy and make a decision whether it will be worthwhile to include such harvesters. We considered theoretically possible irradiance by RF signal in different situations, typical for the modern urban environment and compared it with ambient solar energy sources available through the night, including moonlight.Our estimations show that solar light energy dominates by far margin practically all the time, even during the night, if there is a full moon in the absence of clouds. At the same time, in the closed compartments or at the new moon RF harvesting can be beneficial as a source of “free” energy.     

Industrial supply chains and production machinery of forest chips in Finland

Metsäteho Oy surveyed the industrial supply chains used in the production of forest chips in 2006 in Finland. The Metsäteho study also conducted a survey of the production machinery of forest chips used by energy plants in 2007, and provided an estimate of industrial supply chains and future machinery requirements for forest chip production in Finland.The majority of the logging residue chips and chips from small-sized thinning wood were produced using the roadside chipping supply chain in 2006. The chipping at plant supply chain was also significant in the production of logging residue chips. The majority of all stump wood chips consumed were comminuted at the plant, and with only around one fifth comminuted at terminals. The role of the terminal chipping supply chain was also significant in the production of chips from logging residues and small-sized wood chips. It was predicted that the roles of both terminal chipping of logging residues and chipping at the plant will increase by the year 2010. Regarding the production of chips from small-diameter wood, it was estimated that the role of chipping at the plant will also increase in coming years. The proportion of roadside chipping in the production of small-sized wood chips and logging residue chips is expected to decrease.The study estimated that a total of 1100 machine and truck units were employed in the production of forest chips for energy plants in 2007. Increasing forest chip consumption will create considerable demand for additional forest chip production resources in the future.     

Stakeholder perspectives on converting forest biomass to energy in Oregon, USA

Within the state of Oregon, USA, there is considerable interest in the possibility of converting forest biomass to energy. A number of studies have assessed the technical feasibility of forest biomass energy, but few have focused on social aspects, an important consideration in projects involving public forests. This study explores the social context of converting forest biomass to energy, using qualitative research methods. Semi-structured interviews were conducted with forty individuals representing nine different stakeholder groups. Information gained through interviews was used to understand stakeholder views on forest biomass energy, including their perspectives on potential barriers and opportunities in Oregon. Findings indicate the most challenging barrier will be access to long-term, consistent supply. A related challenge is the long history of contention between parties over forest products coming from public lands. However, findings also show that there are many areas of common ground between these groups that have historically been at odds, such as agreement on the necessity of restoration treatments in certain forest types, the by-product of which could be used for biomass generation. Potential conflicts still exist, for instance over projects in mixed conifer forests. Development of policies and projects through inclusive, collaborative approaches could alleviate controversies, potentially allowing more activities to move forward. Information provided by this research creates a foundation for discussions as forest biomass energy becomes an increasingly prominent issue in Oregon, the western USA, and other regions of the world.     

Biomass retention following whole-tree, energy wood harvests in central Maine: Adherence to five state guidelines

The expansion of the bioenergy industry in Maine has led to an increase in integrated roundwood and energy wood whole-tree harvesting. A better understanding of the amounts of logging residue left unrecovered on whole-tree harvested sites will enable the refinement of available forest residue estimates for Maine and the assessment of the potential effect of such harvesting on forest health. Several states have developed biomass harvesting guidelines in response to concerns generated from an expanding bioenergy industry. In this study downed wood and snags were inventoried on twelve sites in central Maine that had recently been whole-tree harvested for roundwood and energy wood. The percentage of harvested material retained as residue on the study sites was determined. On average, 45% of the energy wood generated during the harvest was left on site. This removal efficiency must be considered when developing forest residue availability estimates. Additionally, the volumes of logging residue were compared to measurable criteria from biomass and biodiversity guidelines of several states. We found that enough fine woody material (<15 cm diameter) remained on the harvest sites to meet the guideline criteria; however, the quantities of coarse woody material (≥15 cm diameter), large logs (≥38 cm dbh), and snags (≥25 cm dbh) were insufficient to meet the guideline criteria. These deficiencies likely resulted from prior forest practices rather than from the current energy wood removal. Retaining more trees of larger sizes in the future can address this concern.     

Evaluation of two round baling systems for harvesting understory biomass

The objective of this study was to evaluate the performance and to estimate costs of two round baling systems for harvesting understory biomass. One system was a cutter-shredder-baler prototype (Bio-baler). The other system required two successive operations. The first operation was cutting and shredding with a Supertrak tractor equipped with a Fecon mulcher head. The second operation was baling with a Claas baler. The machines were evaluated in three different pine stands on the Osceola National Forest in Florida, United States. Data collection included time study, fuel consumption and bale measurements. Material was collected from a sample of bales for heat and moisture content determination. On the most representative site (Site 2), the Bio-baler recovered 8.05 green t ha⁻¹ while the mulcher and the Claas baler recovered 9.75 green t ha⁻¹ (43 and 52 percent of original understory biomass, respectively). Productivity was 0.30 ha h⁻¹ for the Bio-baler and 0.51 ha h⁻¹ for the Claas baler. Density of the bales was 321 green kg m⁻³ for the Bio-baler and 373 green kg m⁻³ for the Claas baler. Average net heat content was 6263 MJ bale⁻¹ for the Bio-baler and 6695 MJ bale⁻¹ for the Claas baler with biomass containing 38 percent of moisture content on a wet basis. Cost per unit area was less with the Bio-baler (US$320.91 ha⁻¹) than with the mulcher-baler system (US$336.62-US$596.77 ha⁻¹).     

Assessment of the availability of agricultural and forest residues for bioenergy production in Romania

This paper provides a resource-based assessment of availability of biomass resources for energy production in Romania, at NUTS-3 level. The estimation of available biomass includes the residues generated from crop production, pruning of vineyards and orchards, forestry operations and wood processing. The estimation of crop residue availability considers several site-specific factors such as crop yields, multi-annual yield variation, environmental constraints and competitive uses. The evaluation of agricultural residues was based on specific residue to product ratios, depending on crop type and crop yield. An estimate of pruning residues is proposed, based on current orchard and vineyard areas and specific ratios of residues. Woody biomass considers forest and forestry residues (including firewood) and wood processing by-products, taking into account the type and share of the unused part of the tree biomass and technical and economic aspects, including availability and competitive use. The amount of agricultural and forest residues available for bioenergy in Romania was estimated at 228.1 PJ on average, of which 137.1 PJ was from annual crop residues, 17.3 PJ residues from permanent crops and 73.7 PJ/year from forestry residues, firewood and wood processing by-products. The biomass availability shows large annual and spatial variations, between 135.6 and 320.0 PJ, due to the variation in crop production and forestry operations. This variation, which is even larger at the NUTS-3 level, if not properly considered may result in shortages in biomass supply in some years, when biomass is available in a lower amount than the average.     

Element budgets of forest biomass combustion and ash fertilisation - A Danish case-study

Harvest of forest biomass for energy production may lead to a significant export of nutrients from the forest. Ash spreading and recycling of nutrients from wood chip combustion to the forest has come into focus as a means for counteracting the nutrient export. This study was carried out to examine the retention of various elements in the different ash fractions and utilise the nutrient recovery to evaluate the fertiliser quality of the examined ash. The mass and element flux of wood chips, bottom ash, cyclone fly ash and condensation sludge at Ebeltoft central heating plant was studied over a four day period in spring 2005. On average, 19 ton wood chips (dry weight) were combusted each day. The combustion of the wood chips produced 0.70% ash and sludge (dry weight). The ash and sludge dry matter was distributed as 81% fly ash, 16% bottom and residual grate ash and 3% sludge solid phase. Substantial amounts of nutrients were retained in the fly ash (P, Ca, Mg, Mn and Cu have a recovery higher than 60% and K, S and Fe have a recovery higher than 30%). The recovery of elements in the bottom ash was smaller. The added recovery of the usable fractions of ashes (both fly ash and bottom ash) exceeded 75% for the nutrients P, Ca, Mn and Mg. Both these ash fractions should be considered for fertilisation.     

Indirect energy input of agricultural machinery in bioenergy production

Sustainability of bioenergy products should be evaluated by means of an energy analysis that takes into account all relevant direct and indirect energy inputs. Direct energy input is viewed as the major energy consuming factor, and is quite easy to measure. Indirect energy input, however, has received relatively scant attention, so it is likely to be insufficiently analysed and possibly underestimated. This paper reviews the data available and suggests the type of research that would be needed to get a better understanding of the indirect energy input. The analysis addresses questions about the use of energy to produce and maintain agricultural machinery, the allocation of energy to different bioenergy products, and the real use and lifetime of machinery.     

Cost efficient utilisation of biomass in the German energy system in the context of energy and environmental policies

The possible uses of biomass for energy provision are manifold. Gaseous, liquid and solid bioenergy carriers can be alternatively converted into heat, power or transport fuel. The contribution of the different utilisation pathways to environmental political targets for greenhouse gas (GHG) emission reduction and energy political targets for the future share of renewable energy vary accordingly to their techno-economic characteristics. The aim of the presented study is to assess the different biomass options against the background of energy and environmental political targets based on a system analytical approach for the future German energy sector. The results show that heat generation and to a lower extent combined heat and power (CHP) production from solid biomass like wood and straw are the most cost effective ways to contribute to the emission reduction targets. The use of energy crops in fermentation biogas plants (maize) and for production of 1st generation transportation fuels, like biodiesel from rapeseed and ethanol from grain or sugar beet, are less favourable. Optimisation potentials lie in a switch to the production of 2nd generation biofuels and the enhanced use of either biomass residues or low production intensive energy crops.     

Integrated harvesting of energy wood and pulpwood in first thinnings using the two-pile cutting method

In order to increase the harvesting volumes of energy wood and pulpwood from first thinnings, harvesting costs have to be reduced significantly. Metsäteho Oy studied the integrated harvesting of pulpwood and energy wood based on a two-pile method, where industrial roundwood (pulpwood) and energy wood fractions are stacked into two separate piles when cutting a first-thinning stand. The productivity and cost levels of the integrated, two-pile cutting method were determined, and the harvesting costs of the two-pile method were compared with those of conventional separate wood harvesting methods.In the time studies, when the size of removal was 50 dm³, the productivity in conventional whole-tree cutting was 6% higher than in integrated cutting. With a stem size of 100 dm³, the productivity of whole-tree cutting was 7% higher than in integrated cutting. The results indicated, however, that integrated harvesting based on the two-pile cutting method enables harvesting costs to be decreased to below the current cost level of separate pulpwood harvesting in first-thinning stands. The greatest cost-saving potential lies in small-sized (d_1.3 = 7-11 cm) first thinnings. The costs of forest haulage after integrated pulpwood and energy wood cutting were higher than those of separate wood harvesting because of lower removals in integrated harvesting. The results showed that when integrated wood harvesting is based on the two-pile cutting method, the removals of both energy wood and pulpwood should be more than 20-25 m³ ha⁻¹ at the integrated harvesting sites in order to achieve economically viable integrated procurement.     

Criteria and indicators for sustainable forest fuel production and harvesting: A review of current standards for sustainable forest management

Forest biomass is increasingly being considered as a source of sustainable energy. It is crucial, however, that this biomass be grown and harvested in a sustainable manner.International processes and certification systems have been developed to ensure sustainable forest management (SFM) in general, but it is important to consider if they adequately address specific impacts of intensified production and harvesting methods related to forest fuels. To explore how existing SFM frameworks address sustainable forest fuel production, criteria and indicators (C&I) from 10 different international processes and organizations and 157 international, national and sub-national forest management certification standards under the Forest Stewardship Council (FSC) and the Programme for the Endorsement of Forest Certification (PEFC) were reviewed. International processes include indicators that require identification or reporting of availability, harvested amounts, value, or share in energy consumption of forest fuels. Forest certification standards address several specific woodfuel issues, but not always in a consistent manner. It seems that developed countries more frequently address environmental consequences of harvesting residues or whole trees on soil fertility and biodiversity, while developing countries more frequently address social issues, such as local people’s access to firewood and working conditions in charcoal production. Based on findings, options to improve SFM standards for sustainable forest fuel production are discussed. These options include clarification of terminology, systematic inclusion of important management impacts unique to forest fuel production, coordination of efforts with other related governance processes, including tools promoting sustainability at more integrated levels, such as landscape, supply chain and global levels.     

Energy wood harvesting productivity of three harvesting methods in first thinning of scots pine (Pinus sylvestris L.)

Energy wood harvesting in young forests presents an economical challenge and has been dependent on subsidies in Finland. Whole-tree harvesting systems have proved to be most productive when carrying out energy wood harvesting in cleanings and early thinnings in young forests. The application of integrated energy wood and pulpwood harvesting is less common.It was hypothesized that multi-tree harvesting (MTH) with the OM-Waratah 745 single grip harvester head could change harvesting logistics and improve productivity for integrated energy wood and pulpwood thinnings. Two variations of MTH were compared with single-tree harvesting (STH). The logging methods studied were: (1) conventional single-tree harvesting with pulpwood and energy wood processed at the strip road; (2) multi-tree harvesting with pulpwood and energy wood processing along the strip road (MTH1); and (3) multi-tree harvesting at the stump where the aim was to leave the logging residues distributed evenly over the harvesting area and not on the strip roads (MTH2).MTH methods were 28-35% more productive than the single-tree harvesting. The biggest differences in work stages were found in the felling and delimbing stages. In single-tree harvesting felling was 9-26% and delimbing 14-27% slower than in multi-tree harvesting.MTH2 distributed 13% of residues further than 7 m from the strip road center. With STH and MTH1 only a good 1.2-1.7% was placed this far, and 74.4 and 62.0% respectively within 3 m.     

Spatial assessment of the bioenergy potential of forest residues in the western province of Spain, Caceres

The present work is mainly devoted to provide a rigorous analysis on the quantification, the mapping and the management of the bioenergy potential of forest residues from the most representative forestry species of the west-central region of Spain (Cáceres).An appropriate methodological approach for the estimate of potential biomass and potential bioenergy as well as the use of GIS for data process are both crucial for the design of thermal plants and for the accurate estimate of biomass collection and transportation costs, according to the scale economy of the plant.The total forest residues in the province of Cáceres are estimated as 463 000 t y⁻¹. The availability of such major biomass potential for energy production is strongly conditioned to the inherent difficulties during the extraction process. This way, an energy potential of 139 000 toe y⁻¹ would be achieved if the above-mentioned biomass collection rate is assumed.The method to optimise the search for suitable locations for thermal plants as well as for biomass extraction/collection areas, based on the combined use of GIS and spatial analysis techniques, is also described.     

The role of bioenergy in the UK’s energy future formulation and modelling of long-term UK bioenergy scenarios

This paper explores the prospects and policy implications for bioenergy to contribute to a long-term sustainable UK energy system.     

Economic analysis on small-scale forest biomass gasification considering geographical resources distribution and technical characteristics

Biomass is getting the great interest in Japan, and the cabinet approved “Biomass Nippon Strategy” in 2002 to promote the utilization of biomass. Although various projects utilizing wood biomass for energy uses have started already, many of them utilize mainly waste wood. Forest biomass remains unutilized because of the high logistic cost and the small scale of resource generation at a site. Small-scale gasification is considered as a suitable technology for forest biomass, and more than 10 demonstration plants have started to be operated recently. This study analyzes the economic feasibility of the small-scale forest biomass CHP system with gasification technology in Japan.The authors have developed the BiRReT tool, which takes input data such as geographical resource distribution and scale merit information of the target technology, and analyzes the economics of bioenergy system in target region by finding the optimal conditions; namely plant size, plant location, the number of plants, and lower generation costs. A case study in Miyagi prefecture revealed the conclusion that the system with logging residue fuel has the economic feasibility if the capital cost and the resource price will decrease from the BAU case by technological learning in the future. On the other hand, thinned wood will not be utilized as a fuel for power plants due to high fuel production cost. It is also found by the tool analysis that the technology’s scale merit has stronger impact on power generation cost in the trade-off between scale merit and the transportation cost.     

Current status and prospects of biomass resources for energy production in Lithuania

Basic biomass sources in Lithuania are comprised of wood, straw, biofuel and biogas. The current status and the problems from using biomass for energy production in Lithuania are analyzed. The possibility of utilizing wood waste, firewood, straw and biogas for energy is evaluated. Forest comprises about 2.05 Mha or 31.3% of Lithuanian land area. About 4.3 million m³ solid volume of wood per year can be used for fuel (843 ktoe). Wood as fuel is used directly or in processed form (briquettes, pellets and chips).Agriculture produces approximately 1.5–2.0 million tons of straw each year for animal feed, litter and olericulture. Around 30–40% (130 ktoe) could be used as fuel for energy production. Boiler houses for combusting the straw have increased and now comprise about 7 MW. Straw is also used for heating private houses.Sources for biogas production include sludge from water cleaning equipment, animal manure and organic waste in food processing companies. Total volume of operating bioreactors comprises about 24 000 m³, and annual production of biogas is 6.3 million m³ per year (3.4 ktoe). By year 2010 the total volume of bioreactors will increase to 35 000 m³ and about 50 000 m³ by 2040.In Lithuania biodiesel and bioethanol are mainly used in blending with conventional fuel. Following the requirements of the European Union (EU), 2% of total consumed fuel per year is to be produced in 2005. By 2010 biofuel should comprise not less than 5.75% of all fuel existing in the market.     

Modeling stump biomass of stands using harvester measurements for adaptive energy wood procurement systems

The value and volumes of industrial stump fuel supply are increasing for energy production. Accurate estimates of aboveground and belowground biomass of trees are important when estimating the potential of stumps as a bioenergy source. In this study two stump biomass equations were adapted and tested using them as calibrated stump biomass models computed as the cumulative sum by a local stand. In addition, variables derived from stem measurements of the forest harvester data were examined to predict stump biomass of a stand by applying regression analysis. The true stump yield (dry weight) was used as the reference data in the study. Both biomass models performed well (adjusted R² ˜ 0.84) and no advance was found in using other stem dimensions as independent variables in the model. The stand-level model can be used in innovative stump biomass prediction tools for increasing efficiency of energy wood procurement planning to stands within a certain area. In practice, wood procurement managers would need to adapt developed system and decide whether the degree of accuracy/precision provided by the models is acceptable in their local stand harvesting conditions.     

FC energy harvesting using the MPP tracking based on advanced extremum seeking control

In this paper is proposed a Maximum Power Point (MPP) tracking technique for the Fuel Cell (FC) stacks based on advanced Extremum Seeking (aES) control that improves the basic performances of the ES control schemes: a guaranteed convergence and proved internal robustness. Other features such as higher search speed and improved tracking accuracy are demonstrated for the proposed aES control, besides these features that are necessary in case of unmodeled dynamics. The analysis on the frequency domain reveals the relationships between the main aES control parameters, the values of closed loop gain and dither amplitude, and the design performance indicators, the speed of search and accuracy of MPP finding, respectively. If the dither amplitude is set to be proportional with the magnitude of first harmonics of the processed FC power, then the reference current used in the FC current control loop will have an insignificant ripple after the MPP is caught. Thus, a reduced FC power ripple will appear. Therefore, if the search speed is set to be the same for all ES control schemes, then the proposed aES control outperforms all classical ES control schemes in overall power efficiency. Moreover, the aES search speed will proportionally increase with the loop gain and the dither amplitude. Note that here the dither has the amplitude set by the first harmonic of the FC power, being a time variable that have high value during the searching phase. This accelerates MPP searching up to the FC safe limits. Finally, this means a controllable time to shortly find the next MPP on dynamical operation of the FC stack. First harmonic of the FC power becomes almost zero after MPP is caught. Thus, higher tracking accuracy that means an economy on fuel consumption is obtained. The simulations performed show that above mentioned performances are effective for the aES control operating in both ripple- and dither-based modes of the grid connected FC inverters.