2. Methodology

The data for this study was collected from a selection of 12 greenhouse operations from around New Zealand using a concise survey form that was mailed to growers and then followed up with a face to face interview. A copy of the survey form is attached as Appendix 1.

The survey participants were selected on the basis of getting a range of different greenhouse types, fuel sources and regional locations. As a result the survey is not representative of the industry.

Tomato production was the predominant operation surveyed but others also included cucumber, capsicum, aubergines and roses. The predominant cropping structure was glass with some double skin plastic greenhouses also represented.

The total direct energy use and carbon dioxide emissions associated with each operation was calculated using energy coefficients and carbon emission factors derived from national and international data.

2.1 Boundary Definition

The boundaries for this study were defined as the physical boundaries of a greenhouse operation. This meant that only that energy supplied directly to the operation, e.g. heating fuels and electricity were considered. This excluded transport and packing shed operations that were carried out off the property.

While these activities will also attract a carbon tax, the energy component in these activities is beyond the scope of this study. Other indirect energy inputs such as fertiliser and agri-chemicals have energy embodied in them and will also attract a carbon tax via their manufacturing, transport and packaging, but again this was beyond the scope of this study.

2.2 Consumer vs. Primary Energy

Energy use has been based on consumer energy or the energy directly delivered to the operation i.e. the kilowatt-hours as read at the meter. Primary energy includes both the consumer energy and all the energy required to get that energy to the consumer. This additional energy includes that energy expended or lost during processes such as extraction, refining, generation, conversion, transportation and distribution.

Some energy studies use primary energy as they want to account for the total energy input into a system, from both direct and indirect sources. In this study however we have used consumer energy in order to avoid double counting in the supply chain and because it is assumed that this is the point at which a carbon tax would be applied.

2.3 Energy and Carbon Content

The direct energy inputs into a growing system are heating fuels, predominantly gas or coal, and electricity for operating motors and lights. Other minor direct inputs are diesel, petrol and lubricants, predominantly for transport, although these were excluded from the total energy use as discussed in Section 2.5.

There is considerable variation in the carbon and energy content by weight of fuels. However, expressing the carbon emission factor as the carbon content per unit of energy released reduces this variation because of the close link between the carbon content and energy value of fuel (IPCC, 1996). Different coal types are a good example of this and are discussed in Section 3.6.

Carbon dioxide emissions are primarily dependent on the carbon content of fuel. Due to the molecular weight ratio of carbon dioxide to carbon of 44:12, multiplying the weight of carbon by 3.6666 gives the quantity of carbon dioxide omitted when the carbon is oxidised.

Energy and carbon data for all commercial fuels is available from both domestic and international databases. However, because fuel qualities and emission factors may differ markedly between countries, IPCC recommends that inventories should be prepared using local emission factors and energy data where possible. Table 1 shows the energy and carbon values for each fuel type included in the study and references where these figures were sourced.

Table 1. Energy and Carbon Values

Fuel	Energy	Units	Carbon (g/MJ)	CO2 (g/MJ)
Coal (sub-bituminous)	21.1 a	MJ/kg	24.9 b	91.2
Waste oil	38.7 a	MJ/l	20.1 b	73.7
Gas	3.6	MJ/kWh	14.3 b	52.3
Electricity	3.6	MJ/kWh	11.8 c	43.1

Data source:

a NZ Energy Data File July 2002 (MED)
b NZ Greenhouse Gas Emissions 1990-2001
c Per comm. Ted Jamieson EECA, 2003

2.3.1 Coal (sub-bituminous)

All coal use was collected in the survey as tonnes used per year. This was converted into an energy value using the coefficient for coal of 21.1 MJ/kg based on MED data for New Zealand’s sub-bituminous coal (NZ Energy Data File, July 2002). Growers were not asked for the coal type(s) that they were using so in the absence of this information it was assumed that all coal was sub-bituminous. This is consistent with the approach taken by MED when calculating greenhouse gas emissions (NZ Energy Greenhouse Gas Emissions 1990-2001). Any further study should determine the mix of coal types being used.

The carbon content of 24.9 gC/MJ is calculated from the emission factor of 91.2 kt CO2/PJ (NZ Energy Greenhouse Gas Emissions 1990-2001).

2.3.2 Waste Oil

Waste oil was recorded on the survey form as litres per annum. This was converted into an energy value based on the average calorific value of light and heavy fuel oil of 38.7 MJ/ℓ (NZ Energy Data File, July 2002).

The carbon content of 20.1 gC/MJ is calculated from fuel oil having a carbon dioxide emission factor of 73.7 kt CO2/PJ (NZ Energy Greenhouse Gas Emissions 1990-2001).

2.3.3Natural Gas

All gas use was collected in the survey as either GJ or kWh from meter readings on supply company invoices that were twelve months apart.

The carbon content for gas of 14.3 gC/MJ is the average emission factor for distributed gas in 2001 (NZ Energy Greenhouse Gas Emissions 1990-2001).

2.3.4 Electricity

Electricity was collected in the survey as kWh from meter readings on supply company invoices that were twelve months apart.

The carbon content of 11.8 gC/MJ was calculated using an average for the grid of 0.155 tCO2/MWh (43.06 gCO2/MJ). This figure has not changed much over the last ten years and is expected to range from 0.14 to 0.17 tCO2/MWh (per comm. Ted Jamieson EECA, 2003)

2.4 Carbon Tax

The carbon tax is based on the rate of $25/t CO2. The Government has indicated that the emissions charge is to be set at the world price but capped at $25/t.

2.5 Transport

To be consistent with the boundary definition, fuel used for transport off the property, either by a contractor or the operator, is excluded. It was not possible to allocate that fraction of fuel which was just used on the property versus transport off the property and as this would be insignificant all diesel, petrol and lubricants were excluded form the total energy use.

Growers were asked for the quantity of fuel used for their own transport in order to assess how big a component of energy use this was. Of those growers who were able to respond, fuel use for transport (excluding contractors) accounted for less than 2 percent of their total energy use.

2.6 Indirect Inputs

Inputs such as fertiliser and agri-chemicals have energy embodied in them as a result of their extraction, manufacture, transport, and distribution. These are considered indirect energy inputs and while their New Zealand manufacturers are likely to be affected by a carbon tax, the potential cost to an operation has not been calculated in this study.

2.7 Energy Analysis

2.7.1 Energy Intensity per m2

Energy intensity for each of the twelve operations surveyed was calculated by dividing the total energy input for each operation by its heated area. These figures were averaged to calculate the energy intensity indicator for the industry. An estimate of the industry’s total energy use was calculated by multiplying the average energy intensity by the sector’s total area.

A separate analysis of the energy intensity for the two main fuel types, coal and gas, has not been included, as energy intensity is predominantly determined by the greenhouse cladding material, inside temperature regime and outside air temperature, rather than the fuel type. The fuel type has an impact on the carbon indicators, and hence the carbon tax, but not on the energy intensity.

A comparison was made between greenhouse types and North and South Island differences. These figures are indicative only as three of the four categories had only one or two growers.

2.7.2 Energy Input per Yield

One method of analysing the energy input into a greenhouse operation is to base it on energy input per yield rather than per square meter.

The range of crops grown by the greenhouse operations in the pilot study included tomatoes, cucumbers, capsicums, aubergines and roses. However, due to the small sample size an analysis of the energy input based on yields could only be performed for the tomato sector, which was the largest sector represented.

The energy analysis based on yields was restricted to the operations that grew tomatoes exclusively. Where an operation grew a combination of crops they were removed from the energy input per yield calculation as it was not possible to attribute the quantity of energy used for the different crops. Six operations were included in this analysis. All operations were included in the energy intensity per square meter calculations.

2.8 Carbon Analysis

Gross carbon dioxide emissions were calculated using the carbon coefficients described in Sections 2.3.1 to 2.3.4. Like the energy indicators these were expressed on both a square meter and yield basis.

A comparison was made of the gross carbon dioxide emissions between coal and gas users. Relevant comparisons can only be made when the variation caused by greenhouse cladding and regional location is removed. In the pilot survey only three operations could be compared in this way. One operation used coal and gas in different glasshouses, although one glasshouse was older than the other. The other two operations were North Island glasshouses each using a coal or gas fired heater.