Life Cycle Assessment of Producing Biogas from Waste Kiwifruitfolk.uio.no/roberan/docs/NZCEE2008-LCAofKiwifruitbiogas.pdf · Life Cycle Assessment and Costing of Landcare Research

Life Cycle Assessment of Producing Biogas from

Waste Kiwifruit

Prepared by:

Vicky Forgie Donna Giltrap

Robbie Andrew

May 2008

Life Cycle Assessment and Costing of Landcare Research and Producing Biogas from Waste Kiwifruit New Zealand Centre for Ecological Economics

Contents Introduction...................................................................................................................................1

Goal and scope of study........................................................................................................1 Functional unit ......................................................................................................................1 Data quality requirements .....................................................................................................1 Allocation procedures ...........................................................................................................1 Study limitations ...................................................................................................................2

Background...................................................................................................................................4 LCA Boundary......................................................................................................................4 Growing ................................................................................................................................5 Packing..................................................................................................................................5 Biogas production .................................................................................................................5

New Zealand Life Cycle Inventory Analysis................................................................................7 Reject kiwifruit economic value ...........................................................................................7 Growing and packing............................................................................................................7 Transport from packhouse ....................................................................................................8

Anaerobic digestion ..................................................................................................................9 Potential Impacts of Alternative Production Systems................................................................13

Sustainability impacts .............................................................................................................13 Results and Discussion ...............................................................................................................15

Overview of results .................................................................................................................16 Comparison of Life Cycle Costing with Maunsell (2008) Costing ........................................18 Sensitivity Analysis ................................................................................................................19

References...................................................................................................................................22 Appendix 1: Overview of LCA Method from Beer et al. (2007) ...............................................24 Appendix 2: Transport energy consumption...............................................................................25 Appendix 3: Electricity...............................................................................................................26 Appendix 4: Natural Gas ............................................................................................................27 Appendix 5: Common factors.....................................................................................................28



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Introduction Landcare Research has been contracted under Bioenergy Options for New Zealand Contract ID C04X0601 Proposal No. PROJ-12011_ORI-FRI to carry out life cycle assessments (LCAs) to explore potential options for producing bioenergy in New Zealand.

Goal and scope of study

The purpose of the study is to provide input into the strategic direction New Zealand takes with regard to:

1) dependence on imported energy (energy security, balance of trade)

2) dependence on non-renewable energy resources (energy security)

3) emissions of greenhouse gases (environment)

The goal of the study was to determine the energy inputs, greenhouse gas emissions, and costs for conversion of waste kiwifruit to biogas. Energy inputs are disaggregated into total primary, fossil-fuel based (non-renewables), and imported. Associated environmental impacts are discussed but not quantified.

The intended audiences are local and central government policy-makers and business interests. These parties will need information to assess the best policy or business investment for New Zealand.

Functional unit

The functional unit for the study is 1 GJ of energy.

LCA is a holistic approach that helps achieve sustainability standards by accurate life-cycle measurements of, for this report, the energy requirements and greenhouse gas impacts of a given biofuel. It helps provide transparency from field to tank.

Data quality requirements

The LCA is based on the ‘average’ system of production for the defined system boundary. The system boundary determines what to include and what to exclude. For example, with straw, if the system boundary is drawn to include soil, reincorporated straw remains within the system and is not treated as a co-product. If soil is outside the system boundary then all straw constitutes a co-product regardless of whether it is baled or reincorporated (Clift et al., 1995).

This report presents LCAs based on production processes that are feasible in New Zealand. Where the production process currently takes place in New Zealand, relevant New Zealand based data have been sourced if possible. Where New Zealand specific data are not available (as for example, producing heat and electricity from straw) overseas data have been adapted.

Allocation procedures

In LCA, environmental impacts and benefits are calculated for economic goods. These goods are generally produced by a number of manufacturers that use a range of production systems. In many cases there is joint production where two or more products are outputs from the process. In economic costing, and LCA, an approach is needed to proportion the environmental impacts of the production system to the economic goods. The choice of method used for accounting for co-products can have a substantial impact on the results. There are two main approaches: allocation and system extension.


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Allocation is based on allocating the burdens arising from the overall production between co-products in some appropriate ratio. When a production process contributes to several products, the total system environmental load has to be shared between these by allocation. This is usually economic value, mass or other attributes of the system (for example protein content). The choice of allocation method may impact on the outcome (Bernesson, 2004). Allocation LCA measures the average impact of production.

System extension LCA measures the consequence of a product or process substitution by extending the system boundary to include the use of a product. If the product is no longer available, what are the impacts of producing a good that will be a substitute product. System expansion is performed to maintain comparability of product systems in terms of product outputs. This is done by separating the unit process into two or more subprocesses and collecting the input and output data related to these subprocesses. The product system is expanded to include the additional functions related to the co-products. If production output is reduced in one area (for example kiwifruit going to stockfood is redirected to biogas production) the net impact is measured by adding an equivalent production in the other systems (replacement stockfood production). System extension LCAs attempts to measure the marginal impacts of production.

This study has used economic allocation as the method for analysis, as required by Scion. However, a scenario for quantity allocation is presented in the Sensitivity Analysis section of the report.

Study limitations

While there are many advantages to using LCA to provide a holistic comparison of bioenergy forms considering the whole production chain, there are also limitations. Results should be interpreted cognisant of the following limitations (following Zah et al., 2007):

- The focus of the life cycle assessment (LCA) has been material and energy flows relating to GHG production, fossil fuel use and economic costs. Other environmental and economic impacts will also result. These would be quantified by the impact assessment stage of an LCA, which has not been included in this report.

- The assessment approach calculated only the primary environmental impacts of the process chain, e.g. energy consumption and pollutant emission during the cultivation of energy rapeseed. Secondary effects were not covered. For instance, if the demand for canola results in the conversion of forest land or wetlands, the environmental impact of this has not been included.

- Economic allocation is based on current prices. The price of goods depends on market dynamics and will change over time.

- The process chains investigated represent only a subset of all production processes; many more production paths are conceivable. The paths chosen, however, are considered especially relevant for the current situation in New Zealand.

- The most recently available existing New Zealand data has been used as much as possible. Where this is not available overseas data have been used.

- Future and alternative process chains are listed but not quantified.

- Results may not apply to individual plants, because the environmental impacts in individual cases may differ greatly from the average situation.

- The study does not address future consequences of a shift to renewable fuels, for example, the environmental impacts should agricultural products be grown on such a


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large scale for bioenergy that agricultural production as a whole had to be intensified. The effects of change in demand have not been covered either. If biofuels are regarded as environmentally friendly and preferred to fossil fuels demand for biofuels may increase. The opposite impact on demand is possible if biofuel production is linked to unwanted social and environmental practices.


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Background The kiwifruit industry was established in New Zealand in the 1970s. The industry has expanded from exporting $2.9m (FOB) (HortResearch, 2006) of fruit in 1975 to $757m in 2007 (MAF, 2007). Orchards typically produce around 23 tonnes of kiwifruit per hectare and output volumes currently account for 30% of total horticultural exports from the country (HortResearch, 2006).

Kiwifruit have been grown in New Zealand since introduced from China in 1904. The original fruit were small and very hairy. The kiwifruit industry was established when plant scientists selectively bred a superior variety of fruit compared with the traditional Chinese gooseberry. New Zealand is a major exporter of the resultant green Hayward kiwifruit. The variety is grown world-wide with both Italy and Chile now surpassing New Zealand on the volume of kiwifruit exported. Gold kiwifruit were developed in the late 1990s and are selectively grown under license.

Kiwifruit grow in three main regions of New Zealand – Bay of Plenty, Northland, and Nelson. Because the Bay of Plenty region produces 86% of the kiwifruit crop, it is the region with most potential to use reject kiwifruit as a feedstock for biogas. The data used in the LCA for kiwifruit growing costs, energy use, and CO2 emissions are based on the Bay of Plenty region not on the whole of New Zealand. Fuel requirements to transport reject fruit from other parts of New Zealand to the Bay of Plenty would be prohibitive.

LCA Boundary

Figure 1: System boundary of kiwifruit to biogas LCA

Growing Digester (Anaerobic)

Packing

Biogas Storage

Compost

Energy

Energy

Heat


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Growing

Kiwifruit grow best in sheltered areas so need to be protected. Wind-breaks can be either artificial poles and mesh netting or planted hedges that require regular trimming. The vines are grown over wooden and wire pergolas at a density of between 340 and 400 per hectare. Once vines are mature, kiwifruit require regular pruning to achieve a reasonable fruit size. Prunings are generally mulched and returned to the plants as compost. Orchards are mowed regularly to keep access clear, reduce the need to spray herbicides, and also for appearance. Roads in kiwifruit orchard regions are of a manicured nature by New Zealand standards with grass verges mowed and shelter trimmed. Plants usually require fertilising three times a year; on occasion four if a foliage test indicates a nutrient imbalance. Artificial fertiliser is applied early in the season in August/September on the basis of orchard assessments and soil tests to maintain soil fertility and nutrient levels. Mature kiwifruit vines require large quantities of nitrogen, potassium and calcium (between 125 and 180 kg/ha), and smaller quantities of chlorine (60 kg/ha), phosphorus, magnesium and sulphur (< 25 kg/ha). The annual uptake of nutrients from fertiliser by mature kiwifruit vines is usually less than 50% for most elements; potassium is an exception and large quantities need to be replaced (Smith, 1996). Spraying for insect pests and fungal disease is in accordance with detailed pest monitoring rather than on a regular basis. Pest control is used only when necessary to maintain export quality standards. Kiwifruit vines are sprayed with hydrogen cyanamide to promote budbreak and enable fertilisation by bees to occur over a short period.

Irrigation is used on approximately 20–25% of orchards but is not common once vines are established (Barber and Benge, 2006). Young flowers, fruit and shoots are susceptible to frost and frost evasion techniques are required if temperatures drop to just above freezing point. This can be in the form of wind machines, heating or helicopter passes to encourage wind movement.

Fruit is picked by hand and placed into large crates that are transported by truck to local packhouses for packing.

Packing

Kiwifruit is sorted by fruit size on a roller belt, labelled, and packed into trays with individual fruit plastic moulds. The number of fruit per tray varies depending on the market destination of the fruit. The Japanese market takes the premium large fruit. Trays of fruit are packed onto pallets, strapped, and shrink-wrapped before placement in cool storage. Before export (which can be up to 5 months) the fruit are quality checked and repacked if necessary to achieve the required standard. Approximately 3–8% of the fruit are repacked (Alistair Mowatt, 2008, pers. comm.).

Biogas production

Organic matter can be broken down by microbial activity in the absence of oxygen to produce biogas. This process is called anaerobic digestion (AD). Biogas can be produced on a continual basis with some digestate removed each day and raw biomass added. Bacteria are added to speed up the process. The length of time the process takes depends on the digester temperature. Mesophilic AD is used to process waste material with around 40% of volatile suspended solids; this takes 15–40 days and operates at a temperature of 30–40oC. Thermophilic digestion takes 12–14 days with the digester heated to 55oC. Thermophilic digestion is a more complex operation, that requires more advanced control and instrumentation but produces more biogas and is more effective at killing unwanted pathogens and viruses (Warwick HRI, 2007).


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Biogas is typically 35% carbon dioxide and 65% methane, and is most commonly used to power combined heat and power units (CHP) for the production of electricity and heat. Approximately a third of the energy produced is used by the AD process itself. Mesophilic AD is the most commonly used method as the technology is well proven and the capital cost of the operation less (Warwick HRI, 2007).

Figure 2: Anaerobic digester for solid waste constructed 1990 (Source: Thiele, 2004)


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New Zealand Life Cycle Inventory Analysis This LCA is in 3 sections:

1. The growing section is not detailed and has used data from Barber 2004 for the growing and transport to the packhouse stage. A more up-to-date and comprehensive LCA for kiwifruit growing, packing and transport to final market is currently being undertaken for Zespri by Landcare Research. When this analysis is completed, data can be substituted into the kiwifruit to biogas LCA.

2. Data for the packing stage have been extracted from the energy audit on the Aerocool packhouse, Mount Maunganui. During the 2002 season, when the audit took place, the packhouse sorted and packed 3800 tonnes of kiwifruit. Data for embodied energy in capital and operating costs have come from a number of sources.

3. Data for the calculation of the biogas has come from the recently completed report Biogas from Kiwifruit Waste by Maunsell Limited (Maunsell, 2008). This was a study of technical feasibility and expected return on investment from producing electricity and heat from reject kiwifruit. The scenario presented by Maunsell (2008) has been used here to calculate the data for the LCA. As reject kiwifruit are only available at most for six months a year a partner organisation that could benefit all year round from the generation of biogas is essential. Maunsell (2008) identify the Affco Te Puke plant located 8 km south of Te Puke, as a potential partner, and the LCA is based on this scenario. From a transport perspective, manufacturing industries in Mount Maunganui and Tauranga could also be potential partners if they had suitable feedstock to complement kiwifruit.

Reject kiwifruit economic value

The cost of production and embodied energy in reject kiwifruit has been allocated between the ‘good’ kiwifruit and reject kiwifruit on the basis of economic value. The estimated value of kiwifruit exported from New Zealand in 2007 was $757m (MAF, 2007). An estimated $7m was sold on the domestic market. Approximately 86% of kiwifruit is grown in the Bay of Plenty so the value of kiwifruit from the region is around $656m. The quantity of reject fruit from the Bay of Plenty has been estimated at 52,000 tonnes (Parker et al. 2008). The fruit has values of between $0 and $10 per tonne depending on its end-use (Parker et al. 2008). Applying the upper value of $10 per tonne, reject kiwifruit has a maximum value of $520,000. The total value of ‘good’ kiwifruit plus reject kiwifruit is $656m and the value of the reject fruit accounts for 0.08%. An LCA based on economic allocation requires apportioning 99.92% of costs and energy use to ‘good’ kiwifruit and 0.08% to reject kiwifruit. This low economic value implies reject fruit is produced as an unwanted output of growing the marketable quality fruit and is not a co-product. Such a very small percentage assigned to reject kiwifruit growing and packing means it does not make a large contribution to the overall energy requirements or costs. Therefore, the degree of accuracy of the input data for growing and packing is not a significant factor for the LCA.

Growing and packing

Barber (2004) has calculated total energy requirements for growing Green and Gold kiwifruit and transporting the fruit to local packhouses. The ‘total energy’ is the sum of all inputs including direct energy in electricity and fuel, plus all the energy used or lost in the process of delivering energy to the consumer, plus all the energy embodied in consumables such as fertiliser and that embodied in capital items (Barber and Benge, 2006). While Green


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kiwifruit account for 74% of the total crop, the actual reject rate for Gold fruit is higher (Parker et al., 2008). The reject rate for Green is approximately one in eight, whereas the reject rate for Gold can be as much as one in four (Alistair Mowatt, 2008, pers. comm.). Therefore, it has been assumed that 40% of the total reject fruit is Gold and 60% is Green. Of the total Bay of Plenty 2007 crop of about 268,000 tonnes of kiwifruit, 52,000 tonnes was rejected (19%).

Barber (2004) indicates a weighted average 2420 MJ/tonne is embodied in kiwifruit on delivery to the packhouse. In 2002 the Aerocool packhouse at Mount Maunganui processed 3800 tonnes of kiwifruit (Smart Power Ltd, 2003). The total embodied energy in these kiwifruit was therefore 2420×3800=9.2 TJ. Economic allocation of 0.08% (at $10/tonne) allocates 7279 MJ of this total to waste kiwifruit. Assuming the Aerocool packhouse has the same rate of waste fruit as the average for the Bay of Plenty, waste kiwifruit amounted to 19%×3800=736 tonnes. Therefore the embodied energy allocated to the waste kiwifruit is 7279/736=9.9 MJ/tonne.

The Aerocool packhouse used 1.0 GWh in the 2002 season to pack 3800 tonnes of kiwifruit (Smart Power Ltd, 2003), or 263kWh per tonne. The bulk (82% or 216kWh/tonne) of the energy used at Aerocool was for refrigeration. The packing and sorting required 47kWh/tonne. Because between 3% and 8% of fruit is repacked before export (Alistair Mowatt, 2008, pers. comm.), 5% of the refrigeration energy use was apportioned to reject fruit. Following the same methodology as for embodied energy in the kiwifruit, the packhouse electricity allocated to waste kiwifruit comes to 0.86 MJ/tonne.

The other main energy and cost contributions from the packing stage are the capital cost of the packhouse, and the packing and sorting operation.

The embodied energy in the capital has been estimated using an average packhouse size of 280m2 (excluding the refrigerated area) and a lifetime of 35 years (Seeka Kiwifruit Industries Limited, 2007). The energy input is 590MJ/m2 from (Wells, 2001). Costs have been estimated based on construction costs of $1000/m2 (Peter Clark, 2008, pers. comm.).

Grading and packing costs per tonne are estimated from (Burtt, 2006). The $1.43 tray cost is assumed to include operating, maintenance, packaging, margin and any additional cost as it is much higher than the current cost (confidential industry source, 2008, pers. comm.).

Transport from packhouse

Reject fruit accumulates at packhouses as the fruit is packed. Current storage systems are assumed to be adequate to hold the fruit until it is transferred to the biogas plant.

The main disposal method for reject fruit at present is selling or giving away to dairy farmers as stockfood. Transfer to the Waikato is estimated to cost $20/tonne of kiwifruit.

Reject fruit could be sourced for biogas from packhouses located in Tauranga (44 km return from Affco Te Puke), Mount Maunganui (44 km return from Affco Te Puke), and Te Puke (22 km return from Affco Te Puke1). It is assumed that transport uses truck depots located near the reject kiwifruit and the truck returns empty, though it would be possible to back-load compost. If each packhouse produces an equal percentage of reject fruit the weighted average distance between the packhouses and the Affco Te Puke biogas plant travelled per tonne of reject kiwifruit is 26km (based on 2007 Volumes per Packhouse from Zespri, Appendix A, Maunsell, 2008).

1 The actual distance from Te Puke township is 8km but most packhouses are up side roads so an extra 3km has been added.


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A distance of 25km for a return trip to the packhouse has been used in Maunsell (2008).

Anaerobic digestion This analysis is based on the scenario developed by Maunsell (2008), with an anaerobic digester located at the Affco Te Puke meat processing plant 8 km south of Te Puke. The digester is assumed to run on a 50/50 mixture of meat processing waste and reject kiwifruit for the six months of the year kiwifruit is available. When reject kiwifruit is not available it is assumed that some other green waste stream is used. As kiwifruit accounts for 25% of the feedstock, 25% of the total plant costs and production were attributed to kiwifruit. A schematic diagram of the system is given below (Figure 3). The cogeneration plant is capable of producing 500 kW of electricity and 400 kW of heat in the form of hot water. The 500 kW electrical co-generation plant could be substituted with a 1.3MW gas boiler producing only heat. It is assumed the plant operates for 8000 hours per annum.

The digester proposed by Maunsell (2008) is capable of processing 5,490 tonnes of reject kiwifruit per year. A similar amount of other organic waste is required outside the kiwifruit season. Meat processing waste is co-digested with both the kiwifruit and organic waste throughout the year.2

2 Note that Maunsell uses a figure of 4,733 tonnes meat processing waste per annum which is only 30% of the total feedstock mass. However, we have assumed a 25/25/50 split between the feedstock types in our analysis.


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Figure 3: Schematic diagram of anaerobic digester system with combined heat and power generation. (Adapted from Maunsell, 2008)

This system produces three valuable products: electricity, heat, and compost. Some of the heat energy produced is used within the system (for example to dry sludge for compost), while the surplus can be used by the meat processing plant. Surplus electricity can either be used by the meat processing plant or sold to the national grid. The sludge from the digester still contains many plant nutrients and can be sold as a fertiliser once it has been dried and composted (alternative configurations are possible that produce liquid fertilisers).

Maunsell (2008) gives the total value of the energy used within the digester system, but does not break the energy down into heat and electricity. We therefore calculated the electricity used within the digester system using the value of 66 MJ/tonne from Berglund and Börjesson (2006) for large-scale biogas plants digesting 20–60 kt of raw material per year. Using this figure, the digester electricity requirement would be approximately 288 MWh/yr. Subtracting this from the total energy cost by Maunsell gave a heat requirement of 680 MWh/yr.

Waste shredding and mixing

Meat processing waste

Reject kiwifruit

Anaerobic digestion

Effluent treatment and water separation

Effluent

Waste water

Sludge

Recycled

Biogas

500kW Co-Generation

Plant

Electricity Heat

Plant operation sales to grid

Plant operation, sludge drying, sterilization, and other heat uses

To water treatment system

Dried and composted


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Other requirements, such as bacteria to initiate the anaerobic digestion process and the handling of waste water produced were assumed to be available from the existing meat processing facilities at negligible cost.

Table 1 and Table 2 show the values of the economic inputs required and outputs produced from one tonne of kiwifruit.

Table 1: Economic inputs required per tonne kiwifruit processed

Cost ($)

Waste kiwifruit 10.00

Transport of fruit from packhouse 7.50

Wages 3.40

Capital 10.25

Operating and maintenance 4.82

Insurance 0.36

Margin 1.02

Transport of compost to farms 1.21

TOTAL 38.57

Transport costs were calculated on the basis of an average distance of 25 km between the packhouses/farms and the processing plant.

Table 2: Economic outputs produced per tonne kiwifruit processed

Unit Production Price ($)

Electricity (net) MJ 608 16.90

Heat (net) MJ 413 4.13

Fertiliser tonnes 0.16 7.69

TOTAL 28.72

This analysis shows the anaerobic digestion system from waste kiwifruit would not be economically viable under current economic conditions. However, we have not included the value of the waste disposal services provided by the digester, which might improve its profitability. Increases in energy prices would increase both the value of the energy products and the transport costs.

From an energy perspective, the anaerobic digester produces energy in excess of its operating requirements. However, the plant itself represents a certain amount of energy embodied in the construction materials. As a breakdown of the construction materials used in the Maunsell report was not available, an estimate was made based on a scaled down version of the Christchurch City Council digester for treating sewage (Beca, 2006). The Beca digester was approximately 6500 m3 capacity, this was scaled down to 2 × 1627 m3 capacity tanks for a two-stage digester. The digester tanks were constructed from concrete with a steel roof and mixer. The exterior of the tanks were covered with aluminium cladding. The generator itself was assumed to contain 4 tonnes of steel (based on a DMT


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500kW diesel generator). Additional concrete and steel were added to account for additional buildings and piping. Some plastic was also included for smaller effluent tanks. Table 3 shows the total amount of materials assumed for the anaerobic digester system. As this is a rough approximation only we have not attempted to split concrete into reinforced and non-reinforced or steel into mild and stainless.

Table 3: Materials contained within anaerobic digester system

m3

Concrete (40MPa) 508.6

Stainless steel 48.8

Aluminium 0.8

PVC3 0.5

For the maintenance cost we assumed all the steel within the system would need to be replaced once over the 15-year lifetime of the plant.

3 Beca recommended glass reinforced plastic for the effluent tanks, however, we have used PVC due to data availability regarding the CO2 and energy costs.


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Potential Impacts of Alternative Production Systems Location of the biogas facility at an alternative site, e.g. Tauranga or Mount Maunganui, would increase transport costs and transport energy requirements. There may also be additional costs associated with environmental management as these largely depend on the requirements of the local community. As a plant located in a built-up area is likely to have a range of additional environmental concerns such as odour control and waste water treatment, additional capital equipment would be required to prevent odorous air emissions from the sludge/compost, and to construct a waste water pre-treatment system before disposal in the local sewage infrastructure.

A plant at a different location is also likely to have additional operating costs. Waste water costs would be higher and bacteria would need to be purchased. The scenario presented assumes waste water disposal has no additional costs at the Affco Te Puke plant, and manure – which is freely available – is used for bacteria.

The concept of packing some fruit closer to the final consumer is being explored by Zespri. This will prevent packaging material wastage. It will also reduce the labour demand in New Zealand, which is a constraint on the growth of the industry. Given that a higher quality standard will need to be in place for fruit leaving New Zealand, there is potential for greater volumes of reject fruit. Greater reject volumes would require a larger plant or storage facilities to enable kiwifruit to provide more than 25% of the feedstock that is the basis of the current proposal.

Producing biogas requires skilled people and operators, and not all previous attempts have been successful (Thiele, 2004); however, the technology for producing biogas has been improved, and plants now operate across a range of sizes.

Sustainability impacts Issues arise when considering the sustainability impacts of producing biogas from reject kiwifruit. These have not been quantified by the LCA but need to be taken into account when looking at such a proposal.

1. The allocation method assigns environmental impacts and costs in accordance with product value. The boundary extension method examines alternative impacts and costs that would arise as a consequence of the proposed change. While not part of the calculations for this LCA as the allocation method has been used, it needs to be noted there would be reduced fossil fuel use for disposal of reject kiwifruit. Reject fruit is currently transported as far as Waikato. A return trip across the Kaimai Ranges to Matamata for a 44-tonne truck is a minimum distance of 120 km at a transport cost of $20/tonne and an energy consumption of approximately 87 MJ of energy emitting 6 kg of CO2. Using the system extension methodology, these savings would be reduced by the cost, energy use, and emissions generated by the production of substitute stockfeed, e.g. maize silage.

2. The decentralised nature of biogas plants provides a way to generate energy close to the end-user, so the capacities of the national power and gas transmission grids do not need to be increased.

3. Producing biogas from reject kiwifruit reduces the disposal cost of waste kiwifruit and, if the plant can operate economically, paying $10 a tonne to growers increases their economic return.


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4. There is increasing concern about the degree to which kiwifruit vines are spreading into native bush areas both in the Bay of Plenty and the Waikato. Transporting kiwifruit into new areas and dumping in piles increases the scope for birds to spread seeds. Ultimately the cost of eradication of weed kiwifruit should fall on the kiwifruit sector as this cost is an externality of present production and profits.

5. Potential environmental impacts associated with a biogas plant are:

• Noise

• Emissions to air (CO2, NOx, and other combustion products), methane, H2S

• Odour

• Traffic from trucks transporting kiwifruit to the plant

• Waste water discharged to land or into rivers.

According to Maunsell (2008) these problems are not insurmountable. A well-designed and run modern biogas plant can mitigate environmental impacts. Locating the biogas plant at an industrial site, e.g. at the Affco plant located on rural land south of Te Puke, would reduce both exposure to odour emissions and the potential for waste water contamination. Waste water could be treated in the existing effluent ponds and as the roading system is already set up for trucks, additional traffic should not be an issue.


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Results and Discussion Table 4 shows the final results of the LCA and LCC broken down by each of the significant inputs.

Table 4: LCA and LCC

Amount Unit Description Allocation Cost ($NZ)

Primary (MJ)

Fossil (MJ)

Imported (MJ)

GHG (kg CO2-

e) Notes

Kiwifruit Growing 2420 2206 1831 211 (a)

Outputs

kg Good kiwifruit 99.92% (b)

979 kg Waste kiwifruit 0.08% 9.67 9 7 1 (c)

Packhouse (waste KF specific)

979 kg Packing electricity $0.0276 1.66 0.63 0.11 0.05 (d)

0.002 $ Capital $0.0016 0.005 0.005 0.005 0.000 (e)

1.59 $ Grading and packing cost $1.59 (f)

Biogas Production (25% of annual allocated to kiwifruit)

Inputs

979 kg Waste kiwifruit $9.79 10 9 7 1 (g)

12.5 km Transportation from packhouse $7.34 12 12 11 1 (h)

3 $ Wages $3.33 (i)

10 $ Capital $10.03 49 49 40 4 (j)

5 $ Operating and maintenance $4.72 43 43 39 3 (k)

0.35 $ Insurance $0.35 (l)

1 $ Margin $1.00 (m)

Outputs

596 MJ Electricity 61% $16.54 71 70 60 5 (n)

404 MJ Heat 15% $4.04 17 17 15 1 (o)

0.16 tonne Compost 24% $6.34 27 27 23 2 (p)

Totals 100% $26.93 115 114 98 9

Total inputs $36.56 115 114 98 9

Current energy sources

596 MJ Electricity from grid $19.61 1179 447 77 34 (q)

404 MJ Heat from natural gas $4.04 463 463 0 25 (r)

Totals $23.65 1643 910 77 59


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Notes

(a) 2.5 MJ/kg total energy Green, 2.3 MJ/kg total energy Gold (Barber 2004);74% crop Green (Parker 2008); Green reject rate 12.5%, Gold 25% (Mowatt, 2008 pers. comm.) 800 kg CO2/1000 trays Green, 720 kg CO2/1000 trays Gold (Barber, 2004); Standard 3.6 kg per tray

(b) $757m total NZ export return 2007 (MAF, 2007); 86% produced in Bay of Plenty (Parker et al., 2008)

(c) Reject 52000 tonnes, maximum value $10/tonne (Parker, 2008); therefore 0.08% economic allocation of kiwifruit impacts to orchard gate assigned to reject kiwifruit

(d) Total electricity use 1 GWh, 3800 tonnes sorted and packed, 263kWh/tonne, Refrigeration 82%, 18% packing (Aerocool 2003); Reject allocation 19% (Parker, 2008); Assumed 5% of refrigerated fruit is reject. The packing cost and energy use would be the upper limit; 11.85 c/kWh purchase price (MED, 2007)

(e) Average packhouse size approx 280m2 excluding refrigerated storage (Humphries, pers. comm.); construction cost of warehouse $1000 per m2 (Clark, pers. comm.); lifetime of building 35 years (Seeka Annual Report, 2007); Energy associated with implement sheds 590 MJ/m2 (Wells, 2001)

(f) Grading and packing cost at $1.43 (Burtt, 2006) per tray is assumed to include packhouse operating and maintenance and overheads as is higher than Seeka estimates for just packing

(g) Maximum price for reject kiwifruit per tonne (Parker et al., 2008)

(h) Average one-way distance (Maunsell, 2008); 26-tonne truck (Appendix 2); $15/tonne over 25 km (Kerry Plowen, pers. comm.)

(i) Admin and Operations Personnel (Maunsell, 2008)

(j) Cost from Maunsell, 2008. Materials calculated based on scaled down version of Beca 2008 biodigester; Concrete is 40 MPa, steel is stainless, aluminium is extruded, GRP equivalent to PVC

(k) Cost from Maunsell, 2008. Assumes all steel is replaced over 15-year lifespan

(l) Maunsell, 2008

(m) 10% return on investment

(n) 12.5 km each way in a ten-tonne truck (Appendix 2)

(o) 10c/kWh sale price (Maunsell, 2008); 4 GWh total electricity generation, etc., internal electricity use 288 MWh (Berglund and Borjesson, 2006)

(p) 0.036 $/kWh sale price (Maunsell, 2008); 3.2 GWh total heat production (Maunsell, 2008); Internal heat use 680 MWh based on above assumptions and total energy cost from Maunsell, 2008

(q) $40/tonne sale price (Maunsell, 2008) plus transport cost; 3554 tonnes/yr total compost (Maunsell, 2008)

(r) 11.85 c/kWh cost of electricity for food producers (MED, 2007); electricity primary and CO2, see Appendix 3

(s) 0.036 $/kWh gas price (Maunsell, 2008); gas primary and CO2, see Appendix 4

Overview of results The main economic costs associated with producing 1000 MJ of energy from waste kiwifruit are the waste kiwifruit itself ($10 per 1000 MJ), capital costs ($10 per 1000 MJ), transport from the packhouse ($7 per 1000 MJ), and operating and maintenance costs ($5 per 1000 MJ). Together these account for $32 of the $38 cost of producing 1000 MJ of heat and electricity.

The revenue stream from generating 1000 MJ of energy from the biogas plant is $28. Electricity (valued at 10 cents/kWh) contributes $16.54, heat (valued at the cost of natural gas used to generate the same amount of heat) is worth $4.04, and the compost from the plant contributes $7.52.

From a purely economic perspective there would be no incentive to generate energy as the cost per 1000 MJ of energy is $10 greater than the revenue. Purchasing 1000 MJ of energy (596 MJ electricity and 404 MJ heat from natural gas) from current commercial energy suppliers would cost a total of $24, but this amount cannot be compared with the $38 cost of production at the biogas plant. The Affco Te Puke plant would have additional costs associated with energy production that would need to be added in. These include a


17

proportion of the capital cost of the existing boiler, wages, operating and maintenance and insurance.

From an energy perspective there are benefits. The amount of primary energy required to produce the 596 MJ of electricity (the output from 979 kg of kiwifruit waste) is 70 MJ. This is almost all fossil fuel and is attributed to inputs from capital, operating and maintenance, and transport, most of which energy is imported. This compares very favourably with the energy requirements to produce the same amount of electricity purchased from the national grid, which is 1179 MJ. Approximately 447 MJ of this are from fossil fuels. Despite almost 70% coming from hydro schemes, electricity from the national grid uses large quantities of fossil fuels (coal and natural gas). Of these 447 MJ, 77 MJ are imported via coal imports. The greenhouse gas outputs are correspondingly higher for electricity from the grid (43 kg CO2-e) compared with electricity from biogas (5 kg CO2-e).

The energy required to generate 404 MJ of heat from the biogas operation (the output from 979 kg of kiwifruit waste) requires just 17 MJ of primary energy compared with 463 MJ if natural gas is used. Most of the 17 MJ is in capital, operating and maintenance, and transport, and is imported. The CO2-e emissions for the biogas are significantly lower than natural gas (1 kg CO2-e compared to 25 kg CO2-e).

Table 5 shows the energy return on investment for the anaerobic digester system, both allocated between electricity and heat and for the system as a whole (which includes the energy allocated to compost production). The energy return on investment is calculated as energy out/primary energy in. A value greater than 1 indicates the system is a net producer of energy, while a value less than 1 indicates that more energy is consumed within the system than is gained.

Table 5: Energy return on investment for anaerobic digester

Energy In

4

(MJ)

Energy Out

(MJ)

Energy

Out/Energy

In

Electricity (net) 71 596 8.4

Heat (net) 17 404 23.3

Total energy (excl. compost credit) 115 1000 8.7

Total energy (incl. compost credit) 88 1000 11.3

The energy return on investment is much greater than 1 for both net electricity and net heat production, so the system makes sense from an energy perspective.

It is also useful to compare the impacts of the energy produced via anaerobic digestion with the impacts of the energy that would be displaced. In this case, the electricity generated would be displacing electricity distributed via the national grid whereas the heat energy would be displacing natural gas. The cost, primary energy content, fossil fuel energy, imported energy and greenhouse gas emissions of comparable amounts of electricity and natural gas have been included in Table 6. The derivations of these values are explained in the appendices.

4 The energy input is allocated between electricity, heat and compost on an economic basis. For the “whole system” row all the energy (including that allocated to compost production) is included.


18

Table 6: Comparison of electricity and heat produced from anaerobic digester compared with electricity from national grid and heat from natural gas

Cost ($/MJ)

Primary

Energy

(MJ/MJ)

Fossil Energy

(MJ/MJ)

Imported

Energy

(MJ/MJ)

Greenhouse

gas

emissions

(gCO2-e/MJ)

Electricity from anaerobic digester 0.041 0.119 0.117 0.101 9

Heat from anaerobic digester 0.015 0.043 0.042 0.036 3

Electricity from national grid 0.033 1.98 0.75 0.13 57

Heat from natural gas 0.010 1.145 1.145 0 64

Notes: 1. Heat from natural gas excludes energy, CO2, and costs associated with conversion of natural gas to

heat at the site. 2. Costs for energy from the anaerobic digester are net of the compost credit. All values for energy

from the anaerobic digester have been allocated by purchase price.

Note that the CO2 from combustion of the biogas is not included in the total CO2 emissions. This is because the carbon in the biogas is derived from organic sources, meaning it was originally extracted from the atmosphere via photosynthesis as the kiwifruit was growing and therefore contributes no net CO2 to the atmosphere over the whole cycle. However, the methane (CH4) in the biogas has a higher global warming potential than CO2, so any CH4 that escapes from the system without being combusted (i.e. converted to CO2) should be added to the total greenhouse gas emissions of the system. We have not attempted to quantify this.

Anaerobic digestion of kiwifruit to produce combined heat and power does have potential to reduce fossil fuel use and greenhouse gas emissions. However, due to the high cost of transport there are a limited number of sites where this would be feasible. Under current economic conditions anaerobic digestion of kiwifruit waste would not be economically viable unless credits for waste disposal and/or greenhouse gas emissions reductions were included. As is shown in the following sensitivity analysis, an increase in the price of gas or electricity also improves the profitability of the biogas plant.

Comparison of Life Cycle Costing with Maunsell (2008) Costing The economic costing for the LCC gives different results from the Maunsell (2008) report for the following reasons:

Annual Revenue

• The revenue from electricity and heat sales used in the LCC is net (the energy requirements to run the plant are not included).

• Meat waste processing fees have not been included. Most meat waste is rendered down into tallow or meat and bone meal which return a profit to the freezing works. Paunch material, which is potential feedstock, goes into paunch pits where it breaks down and is stockpiled on site or given away. Converting kiwifruit to biogas is not an effective means of getting rid of unwanted kiwifruit if the process requires a subsidy from the meat processing plant which provides 50% of the throughput. Currently meat processing waste is not landfilled so there is not a saving to be gained from using the waste as feedstock for biogas. The current effluent disposal system exceeds the plant’s daily capacity requirements (Shane Broughton, 2008, pers. comm.).


19

• Carbon credits have not been included in the base case (however, see Sensitivity Anslysis section).

• No allowance has been included for the green image value to Zespri.

Annual Expenses

• The total cost of the plant has been spread equally over the expected 15-year life span of the plant. Depreciation is normally higher in Year 1 when the value of the plant is greater and decreases over time as the plant ages.

• The required margin on investment is 10%.

• The transportation cost of compost back to the end-user is included so the required energy use and greenhouse gas emissions can be calculated.

• The transportation costs used in the LCA are higher than those used in the Maunsell (2008) report. There is a high level of uncertainty regarding transport costs. The Maunsell report quoted transport costs between $4 and $10 per tonne for 50-km trips and $2 and $5 per tonne for 25-km trips. Maunsell used $4 per tonne for 25-km trips; for a 26-tonne payload this is $0.16/tonne/km. Thiele (2005) quotes $20 per tonne cost for transporting kiwifruit from the Bay of Plenty to the Waikato for disposal (60 km each way). For a 26-tonne payload this is $0.33/tonne/km. This LCA has used $0.40/tonne/km for longer trips (based on $20/tonne for a 50-km trip) and $0.60/tonne/km for shorter trips (based on $15/tonne for a 25-km trip) (Kerry Plowen, KP Contracting, pers. comm.).

Sensitivity Analysis The results presented in this report are for a single scenario of costs and production methods. However, some of these factors are volatile. Table 7 shows the chosen scenario, and subsequent tables show results for selected changes in some of the most volatile factors in the LCA.

Table 7: Chosen scenario

Outputs Allocation %

($NZ) Primary

(MJ) Fossil (MJ)

Imported (MJ)

GHG (kg CO2-e)

596 MJ Electricity 61% $16.54 71 70 60 5 404 MJ Heat 15% $4.04 17 17 15 1 0.16 tonne Compost 24% $6.34 27 27 23 2 Totals 100% $26.93 115 114 98 9 Total inputs $36.56 115 114 98 9

As shown in Table 8, if the cost of waste kiwifruit was $1/tonne instead of the $10/tonne used, the total cost of production would decrease by $8.81 for 1000 MJ. The total primary and fossil energy use decreases by 10 MJ. This would be due to less growing and packing operation energy requirements being allocated to reject kiwifruit a result of the economic allocation method. Greenhouse gas emissions attributed to the biogas operation would drop accordingly.


20

Table 8: Cost of reject kiwifruit drops from $10/ tonne to $1/tonne


($NZ) Primary

(MJ) Fossil (MJ)

Imported (MJ)

GHG (kg CO2-e)


As shown in Table 9, an increase in the cost of kiwifruit waste to $20/tonne increases the cost of production per 1000 MJ of energy by $9.79. Total primary and fossil energy use increases by 10 MJ – the result of more growing and packing operation energy requirements being allocated to reject kiwifruit. As a result of this increased allocation more of the greenhouse gas emissions are also attributed to the biogas operation.

Table 9: Cost of reject kiwifruit increases from $10/ tonne to $20/tonne


($NZ) Primary

(MJ) Fossil (MJ)

Imported (MJ)

GHG (kg CO2-e)


As shown in Table 10, an increase in the cost of all transport (reject kiwifruit to the biogas plant and compost back to orchards) to $20/tonne has a smaller impact than a change in the price of reject kiwifruit. The cost per 1000 MJ of output increases from $37.75 to $40.59. Total primary energy and fossil fuel use does not change as distances covered do not increase.

Table 10: Cost of transport increases from $15/tonne to $20/tonne to transport 25km


($NZ) Primary

(MJ) Fossil (MJ)

Imported (MJ)

GHG (kg CO2-e)


As shown in Table 11, a 20% increase in the price of gas increases the worth of the heat generated by the biogas plant ($4.85 compared with $4.04), and it improves the economic return of the plant by $0.81 per 1000 MJ of energy generated. While energy allocation between electricity, heat and compost changes to reflect the change in economic allocation, total inputs remain the same.


21

Table 11: Price of gas increases by 20%


($NZ) Primary

(MJ) Fossil (MJ)

Imported (MJ)

GHG (kg CO2-e)


Table 12 shows the effects of a carbon credit for reduction in CO2 emissions using $1/GJ (Maunsell, 2008). The credit acts as a subsidy, reducing costs, and its only effect is a reduction in total cost of inputs from $36.56/GJ to $35.56/GJ.

Table 12: Carbon credit of $1/GJ


($NZ) Primary

(MJ) Fossil (MJ)

Imported (MJ)

GHG (kg CO2-e)


The analysis performed in this report has used economic allocation to assign upstream energy and CO2 to biogas production. If quantity allocation is used instead, each tonne of reject kiwifruit has the same embodied energy as good kiwifruit, except for a component of refrigeration in the packhouse. Table 13 shows that when quantity allocation is used the energy required to produce biogas from reject kiwifruit is significantly greater.

Use of this method of allocation assigns exactly the same embodied energy to reject kiwifruit as to good kiwifruit and therefore gives the same results as using good kiwifruit for production of biogas. This would imply that growing kiwifruit with the sole purpose of producing biogas is viable. However, the only reason for construction of a kiwifruit-to-biogas facility is because of the availability of reject kiwifruit with low economic value. As an analogy, Fonterra manufacture ethanol from whey, a byproduct of cheese production. However, they only produce ethanol as a means of disposing of whey. Assigning methane emissions from cattle equally to whey ethanol by weight ignores causality (i.e., that production occurs for economic return). We present this scenario only for completeness.

Table 13: Quantity allocation instead of economic allocation


($NZ) Primary

(MJ) Fossil (MJ)

Imported (MJ)

GHG (kg CO2-e)



22

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Efficiency and Conservation Authority, TERNZ: Transport Engineering Research New Zealand Ltd, Auckland, NZ, 73 p.

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Barber, A. and Benge, J., 2006. Total energy indicators: Benchmarking green, green organic and gold kiwifruit orchards. The AgriBusiness Group.

Barber, A., Campbell, A., and Hennessy, W., 2007. Primary energy and net greenhouse gas emissions from biodiesel made from New Zealand tallow. AgriLINK New Zealand and CRL Energy, 41 p.

Beca, 2006. CWTP – digesters 5/6 design report. City Solutions/CH2M Beca, Christchurch, NZ.

Beer, T., Grant, T., and Campbell, P., 2007. The greenhouse and air quality emissions of biodiesel blends in Australia. KS54C/1/F2.28, CSIRO report prepared for Caltex Pty Ltd. http://www.csiro.au/resources/pf13o.html [April 2008].

Berglund, M. and Borjesson, P., 2006. Assessment of energy performance in the life-cycle of biogas production. Biomass and Bioenergy, 30:254–266.

Bernesson, S., 2004. Farm-scale production of RME and ethanol for heavy diesel engines. PhD thesis. Acta Universitatis Agriculturae Suecia, Agraria.

Burtt, E. S., 2006. Financial budget manual 2006. Lincoln University, Lincoln.

Clift, R., Cowell, S., and Doig, A., 1995. A case study of LCI by allocation and system extension: Straw. Presented at International Workshop on Life Cycle Assessment and Treatment of Solid Waste, Stockholm, 28–29 September 1995.

HortResearch, 2006. Fresh facts. http://www.hortresearch.co.nz/files/aboutus/factsandfigs/ff2006.pdf [24 April 2008].

IKP and PE, 2004. GaBi 4. Institut für Kunststoffprüfung und Kunststoffkunde and PE Europe GmbH, Echterdingen. www.gabi-software.com.

ISO, 1997. Environmental management – life cycle assessment: Principles and framework, ISO 14040.

MAF, 2007. Situation and outlook for New Zealand agriculture and forestry: August 2007. ISBN 0-478-29582-5, Ministry of Agriculture and Forestry, 74 p. http://www.maf.govt.nz/mafnet/rural-nz/statistics-and-forecasts/sonzaf/.

Maunsell, 2008. Biogas from kiwifruit waste. Prepared for Zespri, 45 p.

McKinnon, A., Ge, Y., and Leuchars, D., 2003. Analysis of transport efficiency in the UK food supply chain: Full report of the 2002 key performance indicator survey. Heriot-Watt University, Edinburgh, UK, 38 p. www.sml.hw.ac.uk [April 2008].

MED, 2007a. Energy greenhouse gas emissions 1990–2006. ISSN 1173-6771, Ministry of Economic Development, Wellington, 48 p. www.med.govt.nz.

MED, 2007b. New Zealand energy data file June 2007. Ministry of Economic Development, Wellington, 172 p. www.med.govt.nz/energy/info/ [July 2007].


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MfE, 2005. Energy efficient ways to improve the economic bottom line of your road transport business. 30 p. www.mfe.govt.nz [April 2008].

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Parker, K., Weal, S., and Fernyhough, A., 2008. Waste 2 gold – feasibility study for Zespri : Final report. Scion, 19 p.

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Thiele, J., 2005. Estimate of the energy potential for fuel ethanol from putrescible waste in New Zealand. Technical Report prepared for the Energy Efficiency and Conservation Authority, Waste Solutions Ltd, Dunedin.

Warwick HRI, 2007. Ac0401: Direct energy use in agriculture: Opportunities for reducing fossil fuel inputs. University of Warwick, Warwick.

Wells, C., 2001. Total energy indicators of agricultural sustainability: Dairy farming case study. Technical paper 2001/3, ISBN: 0-478-07968-0, ISSN: 1171-4662, Ministry of Agriculture and Forestry, Wellington, NZ, 90 p. http://www.maf.govt.nz/mafnet/publications/techpapers/techpaper0103-dairy-farming-case-study.pdf.

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Appendix 1: Overview of LCA Method from Beer et al. (2007)

Life cycle assessment (LCA) is the process of evaluating the potential effects that a product, process, or service has on the environment over the entire period of its life cycle. The International Organization for Standardization (ISO 1997) has defined an LCA as:

A technique for assessing the environmental aspects and potential impacts associated with a product by:

• compiling an inventory of relevant inputs and outputs of a product system

• evaluating the potential environmental impacts associated with those inputs and outputs

• interpreting the results of the inventory analysis and impact assessment phases in relation to the objectives of the study.

The technical framework for life cycle assessment consists of four components, each having a vital role in the assessment. They are interrelated throughout the entire assessment and in accordance with the current terminology of the International Organization for Standardization (ISO). The components are goal and scope definition, inventory analysis, impact assessment, and interpretation.

Figure 4: The components of an LCA. Source: ISO, (1997)


25

Appendix 2: Transport energy consumption There are no standard figures available in New Zealand for fuel efficiency of road freight transport. A recent report by TERNZ used 0.3 l/km for single unit trucks and 0.5 l/km for articulated vehicles (rigs), quoting figures obtained from industry (Baas and Latto, 2005). A report by the Ministry for the Environment used an average for the heavy vehicle fleet of 0.6 l/km (MfE, 2005). A 1998 demonstration of a truck aerofoil, carrying a refrigerated 20-tonne load the length of New Zealand showed an average fuel efficiency of 0.44 l/km (R 'n' J Aerofoils, 1998). Mitsubishi recently announced a new rig with a New Zealand fuel efficiency of 0.49 l/km carrying a 26-tonne payload (Mitsubishi Motors NZ, 2007). Given these last two are claims of better-than-average fuel efficiency, it appears likely the average would be higher than 0.5 l/km. Fuel efficiency in Europe appears to be significantly greater, with data from GaBi (IKP and PE, 2004) – a life-cycle assessment software – and from a 2003 UK survey (McKinnon et al., 2003) both indicating fuel efficiency of 0.34 l/km for articulated trucks.

We have used a fuel consumption rate of 0.55 l/km for an articulated truck with a maximum payload of 26 tonnes, and 0.3 l/km for a single truck with a maximum payload of 10 tonnes. Following the method used by GaBi (IKP and PE, 2004), we have used a logarithmic relationship to relate fuel consumption to truck loading (see Figure 5), with minimum fuel consumption at 10% loading. These are presented as average figures, and will vary widely depending on terrain, maintenance, driving style, and speed.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Load

litr

es/k

m

Articulated truck(26 tonne max payload)

Single unit truck(10 tonne max payload)

Figure 5: Fuel efficiency of trucks by truck size and actual payload (source: GaBi (IKP and PE, 2004)

and Baas and Latto (2005))


26

Appendix 3: Electricity Electricity supplied to the national grid is generated from a combination of fossil-based energy resources and non-fossil resources, and from a combination of imported energy and domestic energy. The two forms of fossil energy used in electricity generation are coal and natural gas. Significant amounts of coal used for electricity generation are now imported, while all natural gas is extracted domestically. Table 14 gives the total, fossil, and imported primary energy inputs into (non-cogeneration) electricity generation in New Zealand between 2002 and 2006, and shows the fossil energy, imported energy, and greenhouse gas emissions per unit of consumer electricity. All these indicators are likely to change in the near future as the New Zealand Government’s policies on climate change take effect (among other effects).

Table 14: Electricity energy contents, 2002–2006 (excluding cogeneration)

Total

primary energy (PJ)

Fossil primary

(PJ)

Imported coal (PJ)

Consumed electricity

(PJ)

Primary energy in consumer electricity (MJ/MJ)

Fossil energy in consumer electricity (MJ/MJ)

Imported energy in consumer electricity (MJ/MJ)

GHG emissions (ktCO2-e)

Implied emission

factor (kgCO2-e/MJ)

2002 241 84 2.7 119 2.02 0.71 0.02 5673 0.048

2003 243 94 10.3 126 1.93 0.75 0.08 6904 0.055

2004 247 83 20.5 129 1.92 0.64 0.16 6573 0.051

2005 269 109 25.0 133 2.02 0.82 0.19 8728 0.066

2006 272 112 28.4 135 2.02 0.83 0.21 8659 0.064

Average 1.98 0.75 0.13 0.057

Source: MED (2007a; 2007b)


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Appendix 4: Natural Gas The energy content of natural gas can be quoted in terms of gross calorific or net calorific value. The difference is that the net calorific value assumes the water produced during combustion is converted to water vapour and the energy required to vaporise the water is not available for useful work. We have assumed the boiler system is not able to take advantage of the energy in the water vapour and therefore the heat energy required is the net calorific value.

Approximately 0.904 PJ of net energy is produced for every 1 PJ gross of natural gas; while 0.005 PJ is lost in transmissions for every PJ gross energy supplied (MED, 2007b). If these two factors are combined, every MJ of net calorific value from natural gas used requires the production of approximately 1.11 MJ (gross) of natural gas.

Given that the gas industry used 4.48 PJ of gas in 2005 (MfE, 2007) to produce 148.56 PJ (gross) of natural gas (MED, 2007b), on average 0.03 PJ of primary energy is used to produce 1 PJ (gross) of natural gas.

The total fugitive emissions from the gas industry in 2005 were 652 ktCO2-e (MfE, 2007) or 4.39 ktCO2-e per PJ gas produced. Burning Maui natural gas produces 52.0 ktCO2/PJ and 1.26 tCH4/PJ (MED, 2007b). Given that1 kg CH4 has a global warming potential equivalent to 21 kg CO2, total greenhouse gas emissions from combustion of natural gas are 52.0 ktCO2-e/PJ (gross).

Table 15 shows the primary energy and total greenhouse gas emissions required to supply 1 MJ net of natural gas. It is assumed that all the primary energy is fossil based and local.

Table 15: Primary energy and greenhouse gas emissions required to supply 1 MJ (net) of natural gas

Net energy supplied to boiler by gas(MJ)

Primary energy (MJ) g-CO2-e

1 1.15 57.55


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Appendix 5: Common factors Where information on fossil-energy components was unavailable, we have assumed all primary energy is derived from fossil sources to prevent exaggeration when comparing with the fossil alternative.

The primary energy content of fossil diesel is 1.193 MJ/MJ (Barber et al., 2007), which is assumed to have negligible non-fossil content. Diesel supply is 31% imported, and 5% of the NZ refinery’s input is local oil (both average of 2004-2006; MED, 2007), so that approximately 97% of diesel energy is imported. Fossil diesel has a gross calorific value (GCV) of 45.75 MJ/kg and 37.86 MJ/litre (MED, 2007b).

Canola methyl ester has a gross calorific value (GCV) of 40.07 MJ/kg (Beer et al., 2007).

Global warming potentials (GWPs) used for methane (CH4) nitrous oxide (N2O) were 21 and 298, as required under the Kyoto Protocol.

Documents

Life Cycle Assessment of Producing Biogas from Waste Kiwifruitfolk.uio.no/roberan/docs/NZCEE2008-LCAofKiwifruitbiogas.pdf · Life Cycle Assessment and Costing of Landcare Research