+
Renewable energy and energy efficiency options for UK dairy farms
ENERGY
EFFICIENCY
This study was commissioned for the Arla/Morrisons Producer Group by Wm Morrisons Supermarkets PLC.
March 2010
COPYRIGHT
This study is copyright and the intellectual property of Newcastle University. It may not be reproduced in whole or in part except with the written permission of the University. Where
permission is sought, consent will normally be granted on the condition that Newcastle University is attributed as the source of the reproduced material. Without such written permission, all such rights to reproduce any part of this document are withheld.
For enquiries relating to renewable energy and energy efficiency options for UK dairy farms please contact:
Dr Paul Bilsborrow
School of Agriculture, Food and Rural Development, Newcastle University Tel: 0191 222 6868
Email: P.E.Bilsborow@ncl.ac.uk
AUTHORS AND ACKNOWLEDGEMENTS
Authors
The main author of the Energy Efficiency section was Philip Dunn with assistance from Gillian Butler.
The main author of the Technologies section was Paul Bilsborrow with assistance from David Brough and Paul Quinn.
Project Steering Group
Robert Morris-Eyton Producer Representative - AFMP (Steering Group Chairman) David Evans Head of Agriculture - Wm. Morrison Supermarkets Plc
Louise Welsh Agriculture Manager - Wm. Morrison Supermarkets Plc Arthur Fearnall Producer Director - AFMP
Mark Fletcher Producer Representative - AFMP David Watson Producer Representative - AFMP
Graham Wilkinson Agriculture Manager - Environment - Arla Foods UK Nic Parsons Agriculture Manager - Arla Foods UK
Martin Foulger Business Manager - Arla Foods UK
Table of Contents 1
List of Tables 4
List of Figures 5
Glossary 6
Executive Summary 8
1.0 Introduction 10
1.1 The UK dairy industry, past, present and future 10 1.2 Economic/political drivers for reducing GHG emissions via 11 increased energy efficiency and the uptake of renewable energy
1.3 Agriculture as a contributor to GHG emissions 12
1.4 UK dairy farming and its contribution to GHG 13
2.0 Energy efficiency 17
2.1 Vacuum pumping 17
2.1.1 Background 17
2.1.2 Vacuum pump sizing 17
2.1.3 Variable speed vacuum pumps 20
2.1.4 Non energy benefits of variable speed vacuum pumps 23
2.1.5 Vacuum system maintenance 24
2.2 Milk cooling 25
2.2.1 Bulk tank systems 25
2.2.2 Milk pre-cooling systems 26
2.2.3 Factors affecting the performance of plate coolers 27
2.2.4 Dual-pass plate cooler 28
2.2.5 Two stage pre-cooling 29
2.2.6 Variable speed milk pumps 29
2.2.7 Scroll compressors 30
2.2.8 Refrigerant types 31
2.2.9 Condenser unit maintenance and location 31
2.3 Water heating 32
2.3.1 Cleaning procedure 32
2.3.2 Tuning the milking system for optimum performance 33
2.3.3 Eliminating system losses 33
2.3.4 Heat recovery units 35
2.4 Lighting 39
2.4.1 Illumination requirements for efficient milk production 39
2.4.2 Long day photoperiod (LDP) 40
2.4.3 Bulb types and selection data 40
2.4.4 Minimising lighting running times 42
2.5 Water and effluent pumping 43
2.5.1 Pump and motor selection 43
2.5.2 Pipe sizing and maintenance 44
2.6 Other considerations 45
2.6.1 Ventilation 45
2.6.2 Compressed air systems 46
2.6.3 Parlour heating 47
2.6.4 Automatic scraping systems 47
2.6.5 Farmhouse energy efficiency 48
3.0 Renewable energy technologies 49
3.1 Background 49
3.2 Anaerobic digestion 50
3.2.1 The process and equipment 50
3.2.2 Feedstocks 53
3.2.3 Applications and technology development 55
3.2.4 Outputs 57
3.2.5 Costs 59
3.2.6 Legislative requirements 60
3.2.6.1 Animal by-product regulations 61
3.2.6.2 Environmental permitting regulations 61
3.2.6.3 Digestate application to land 61
3.2.6.4 European Nitrates Directive 61
3.3 Biomass heat and CHP 62
3.3.1 The process and equipment 62
3.3.2 Feedstocks 64
3.3.3 Applications and technology development 66
3.3.4 Costs 68
3.4 Wind 69
3.4.1 The process and equipment 69
3.4.2 Energy source 71
3.4.3 Applications and technology development 73
3.4.4 Costs 73
3.5 Solar thermal and PV 75
3.5.1 The process and equipment 75
3.5.2 Energy source 78
3.5.3 Applications and technology development 79
3.5.4 Costs 81
3.6 Ground source heat pump 82
3.6.1 The process and equipment 83
3.6.2 Energy source 85
3.6.3 Applications and technology development 85
3.6.4 Costs 86
3.7 Micro-hydro 86
3.7.1 The process and equipment 87
3.7.2 Energy source 89
3.7.3 Applications and technology development 90
3.7.4 Costs 91
4.0 Other considerations 93
4.1 Financial incentives ROCs, RHI and FITs 93
4.2 Capital support schemes 95
4.3 Grid connection 96
4.4 Planning permission 98
5.0 Summary tables 103
5.1 Summary assessment of renewable energy technologies 103 5.2 Summary assessment and commentary of renewable technologies 104
5.2.1 AD 104
5.2.2 Biomass Heat 104
5.2.3 Biomass CHP 105
5.2.4 Wind 105
5.2.5 Solar Thermal 106
5.2.6 Solar PV 106
5.2.7 GSHP 107
5.2.8 Micro-hydro 107
5.3 Summary of direct CO2 emissions from combustion 108 5.4 Summary of potential annual financial and CO2 savings from
principal efficiency saving opportunities 109
Disclaimer 110
References 111
List of Tables Page
Table 1.1 Typical direct and indirect energy uses implicated in milk 14 production
Table 1.2 Typical energy use for a range of activities on UK dairy farms 15
Table 2.1 Typical vacuum pump performance 20
Table 2.2 Annual savings from installation of VSD unit to vacuum pump 21 Table 2.3 The effect of plate cooler efficiency on the annual cost of 27
cooling milk
Table 2.4 Dairy farm water heating requirements 32
Table 2.5 Estimation of the potential gains from improved hot water tank 34 insulation
Table 2.6 Potential annual savings through installation of a Heat 38 Recovery Unit (HRU)
Table 2.7 Recommended illumination levels for dairy farms 39
Table 2.8 Bulb type efficiency and selection data 40
Table 2.9 Lighting energy conservation measures and savings 42 Table 2.10 Example of potential savings through improved lighting 42
efficiency
Table 2.11 General operating efficiency of different fan types 45 Table 3.1 Biogas production and energy outputs from various feedstocks 55
Table 3.2 Numbers of biogas plants globally 56
Table3.3 Comparison of nutrient values of slurries and associated 59 digestates
Table 3.4 Plant nutrient content of an average digestate 59 Table 3.5 Costs and returns from 3 different AD scenarios 60 Table 3.6 Comparison of CO2 emissions from a range of fuel types for heat 66
generation
Table 3.7 Comparative capital costs for biomass and oil based heating 68 systems
Table 3.8 Typical domestic fuel prices 69
Table 3.9 Indication of potential revenues from wind turbines 74 Table 3.10 Energy requirement to heat water to washing temperature 81 Table 3.11 Photovoltaic indicative outputs and revenues 82 Table 3.12 Supply temperature requirement for several heating systems 85 Table 3.13 Combinations of head and flow rate to achieve different power 90
outputs
Table 4.1 Feed In Tariff scheme for operation in the UK from April 2010 94
List of Figures Page
Fig 1.1 Number of dairy herds in the UK 10
Fig 1.2 Changes in the global oil price 11
Fig 1.3 Breakdown of the contribution of renewable energy to total 12 energy usage
Fig 1.4 Energy meter 16
Fig 2.1 The flow of air and milk through a milking system 17 Fig 2.2 Potential annual savings from fitting a variable speed vacuum 22
pump
Fig 2.3 A single pass plate heat exchanger 26
Fig 2.4 A flow-based Heat Recovery Unit 36
Fig 2.5 A storage-based Heat Recovery Unit 37
Fig 3.1 Schematic diagram of an on-farm anaerobic digestion system 50
Fig 3.2 The key stages of anaerobic digestion 51
Fig 3.3 Heat only combustion plant 63
Fig 3.4 Biomass boiler set up 63
Fig 3.5 Effect of moisture content on the heating value of wood 65
Fig 3.6 Wood pellets 66
Fig 3.7 On farm wind turbine 70
Fig 3.8 Schematic diagram of both horizontal- and vertical-axis wind 71 turbines
Fig 3.9 European wind speed data taken at a 10m hub height after 71 correction for topography and local roughness
Fig 3.10 Power curve of a typical modern wind turbine 72
Fig 3.11 Solar thermal system 76
Fig 3.12 Typical photovoltaic system configuration 77 Fig 3.13 Average solar radiation levels in the UK falling on one square 79
-metre surface inclined at 30 degrees to the horizontal, measured in kilowatt hours, annual total kWh/m2
Fig 3.14 Photovoltaic array 80
Fig 3.15 Trenching and pipework for a GSHP 83
Fig 3.16 Vertical GSHP system 84
Fig 3.17 Horizontal GSHP system 85
Fig 3.18 Leat run of the river system 87
Fig 3.19 Penstock system 88
Fig 3.20 Head/flow ranges of small hydro turbines 88
Fig 3.21 Crossflow turbine system 89
GLOSSARY
Anaerobic Digestion (AD)
The process by which bacteria that act only in airless (anaerobic) conditions decompose organic matter with the concurrent production of biogas.
Biogas
Gas produced from the anaerobic digestion process which consists of about 60% methane (CH4) and 40% carbon dioxide (CO2).
Biomass
Biological material derived from plant or animal matter including agricultural, forestry wastes/residues and energy crops, biodegradable fraction of industrial and municipal waste.
Biodegradable Municipal Waste
That part of the household waste stream that would decompose in landfill (makes up around 65% of all household waste).
Carbon Sequestration
The capture and storage of CO2 as organic matter in soils.
Combined Heat and Power (CHP)
The simultaneous generation of heat and power in a single process, recovering the heat that is normally discharged to the atmosphere, thereby increasing the efficiency of fuel utilisation.
Digestate
The output resulting from the anaerobic digestion process which can be separated into liquid and solid fractions.
Emissions Trading Scheme (EU-ETS)
A key instrument whereby governments incentivise a reduction in the carbon dioxide emissions from key industries. EU member state governments are required to set an emission cap for all installations covered by the Scheme.
Feed In Tariffs (FIT)
Proposed system of financial incentives which support electricity generation with a bonus paid for electricity exported to the grid, to come into operation from April 2010.
Greenhouse gases (GHG)
Gases emitted into the atmosphere principally carbon dioxide, methane and nitrous oxides which cause global warming.
Life Cycle Assessment (LCA)
The investigation and evaluation of the environmental impacts of a given product or service caused or necessitated by its existence.
Renewable Heat Incentive (RHI)
A mechanism to be introduced by Government in 2011 to provide financial support for the production of heat from renewable sources.
Renewable Obligation (RO)
An obligation on all electricity suppliers to supply a specific proportion of their electricity from eligible renewable sources.
Renewable Obligation Certificates (ROCs)
Eligible renewable generators receive ROCs for each MWh of electricity generated. These certificates can be sold to suppliers. In order to fulfil their Renewable Obligation suppliers can present enough certificates to cover the required percentage of their output, or pay a ‘buyout price’ per MWh for any shortfall. All proceeds from buyout payments are recycled to suppliers in proportion to the number of ROCs they present.
Short Rotation Coppice (SRC)
The practice of cutting fast growing trees at regular intervals to encourage branching and growth.
Photovoltaic (PV)
The direct conversion of solar radiation into electricity by the interception of light.
Watt (W)
Unit of energy production where 1 kW = 1,000 watts, 1 MW = 1,000 kW and 1GW = 1,000 MW and 1 TW = 1,000 GW.
EXECUTIVE SUMMARY
There has been a steady decline in the number of dairy farms and dairy cows in the UK since 1995 largely as a result of volatility in the price of milk and increasing costs of production.
Significant increases in energy prices have occurred in recent years on the back of the rising oil price and this has had a direct bearing on dairy operating costs and hence profitability within the sector. At the same time public policy has placed ever more emphasis on the reduction of environmentally damaging emissions. The Climate Change Act of 2008 placed CO2 reduction targets on the UK of 80% by 2050 in addition to which as part of EU-wide action the UK has to ensure that 15% of primary energy comes from renewable sources by 2020. The Milk Roadmap (2008) also sets targets relating to energy use on dairy farms, currently aiming for:
• 20-30% of producers to trial new technologies to reduce total emissions
• an industry wide improvement of 15% in energy efficiency
• 30 businesses to pilot on farm anaerobic digestion (AD) units
Agriculture was responsible for 0.8% of carbon dioxide (CO2), 37.6% of methane (CH4) and 74.3% of nitrous oxide (N2O) emissions in 2008. In the future it is likely that reducing the carbon footprint of agricultural production is going to be a major target for the industry. A number of options are available to dairy farmers to reduce their carbon footprint and operating costs, in particular improving energy efficiency and the uptake of renewable energy technologies. With the exception of fieldwork the major contributors to energy use on dairy farms are milk cooling and water heating (each responsible for a third of total electricity use) followed by vacuum pumping and lighting.
Energy efficiency options
Both existing and developing technologies can be used to reduce energy use associated with milk cooling. By maximising the efficiency of the pre-cooling system, producers can significantly cut the amount of in-tank cooling and thus significantly reduce energy usage. A suitably sized plate cooler typically has the potential to save 30-40% of milk cooling costs compared with a situation where a pre-cooler is absent. New technologies such as scroll compressors and variable speed milk pumps also have the potential to deliver significant energy and cost savings.
There are two main ways in which energy use for water heating can be reduced these being a reduction in the volume of hot water required and the installation of heat recovery units (HRU) to milk cooling equipment. An HRU will have a potential pay-back period of between three and five years depending on the actual energy savings achieved.
Varying degrees of energy efficiency improvements may be achieved through a variety of alternative types of vacuum pump. In general, it is not economic to upgrade to a more energy efficient pump if the current pump is still in good condition. However, where existing pumps fail or new dairy units are being considered there is an ideal opportunity for producers to install a pump with improved efficiency. Variable speed vacuum pumps offer the potential for increased energy efficiency with the option of purchasing either a custom built variable speed vacuum pump or alternatively retrofitting existing pumps with variable speed controllers.
Variable speed vacuum pump technology will usually yield electricity savings of 40-50% with an estimated payback period of about six years.
Whilst lighting only comprises a small proportion of total energy use on a dairy unit, it is an area where usage can be cut almost immediately and at little cost. Energy usage associated with lighting can be reduced through a combination of minimising running hours and selecting the most appropriate lamp types for the task in hand.
Renewable energy options
Renewable energy offers a significant opportunity for dairy farms to reduce their carbon footprint and to diversify their business through new income streams while at the same time reducing energy costs. There are a number of renewable energy technologies with potential for use on dairy farms. In particular these are anaerobic digestion, wind, and solar (both in the generation of heat and electricity) which can help in cutting energy costs in addition to reducing the carbon footprint. The Feed in Tariff (FIT) and proposed Renewable Heat Incentive (RHI) mechanisms proposed for introduction in 2010 and 2011 respectively offer a stable support mechanism for small scale systems. There are also capital allowance and capital funding schemes available which can make the introduction of some of these more financially attractive.
Anaerobic Digestion (AD) offers considerable potential for dairy farmers not only in terms of the generation of energy but also in manure management with respect to NVZ and EU Water Framework Directives. Dairy slurry has a low biogas yield so there is considerable value in utilising other feedstocks with the potential for improving biogas yield. In addition to which some feedstocks can attract a gate fee to significantly improve the economics of the system and reduce the payback period. Anaerobic Digestion also offers considerable environmental and financial benefits through the use of digestates as a substitute for currently used inorganic fertilisers. There are only a small number of on-farm AD systems in the UK but a number of manufacturers and installers are helping to develop the market. The development of on-farm AD facilities in Germany demonstrates the potential scale of this opportunity in the UK but a major limitation is still the very high capital costs for such a system.
Wind turbines, photovoltaic (PV) units and micro-hydro systems all have the potential for electricity generation on dairy farms. Attractive rates for PV systems and small scale wind turbines are proposed with the new FIT scheme which significantly reduces the payback periods. Micro-hydro is generally of limited potential for most dairy farmers as very few farms are likely to have sufficient energy source (head or flow rate) to provide an economic return. Generally low amounts of electricity are generated and the cost is very much influenced by the amount and nature of the civil engineering work required.
The generation of heat from the combustion of wood chip or pellets in a biomass boiler, solar thermal and ground source heat pumps all have the potential for production of heat. Although there is limited demand for heat within a dairy unit there is considerable value within a wider farm context where additional space heating is required and access to the natural gas grid is limited. Solar thermal and ground source heat pumps have the potential to be used to pre-heat water for use in a dairy unit before it enters the main tank for final heating, but a back-up system is required to achieve the temperature of >85oC generally required for parlour washing.
The range of options open to the dairy sector for either energy saving or for the adoption of renewable energy technologies is therefore considerable, but what is appropriate for an individual farm has to be assessed on a case by case basis. It is nevertheless considered that these options could offer considerable cost and environmental benefits to both the industry and to individual farms.
1.0 INTRODUCTION
1.1 The UK dairy industry - past, present and future
There has been a steady decline in the number of dairy herds in the UK (Fig 1.1) over the last 15 years with the number of farms with milking cows falling on average by 5.5% per annum since 1995. At the same time many herds have also become larger and as a consequence the decline in the number of dairy cows (female cattle aged two years or more) has not been so dramatic. Whereas the number of dairy herds in the UK halved between 1998 and 2008, dairy cow numbers only fell by 22% to just over 1.9 million with an average herd size of 114.
0 10 20 30 40
1995 1997 1999 2001 2003 2005 2007
Farms numbers (1000s)
Fig 1.1 Number of dairy herds in the UK (Source: DairyCo 2010)
Significant increases in energy prices have occurred in recent years on the back of the rising oil price. In the last 10 years prices have more than tripled increasing from $17.48/barrel in 1999 to $61.06/barrel in 2009. Within this period there have been significant high points in particular $148 a barrel was reached in June 2008 but for most of the last 30 years oil has traded at an average price of between $20 and $35 per barrel (Fig 1.2).
Fig. 1.2 Changes in the global oil price
1.2 Economic/political drivers for reducing GHG emissions via increased energy efficiency and the uptake of renewable energy
An increased concentration of CO2 and other greenhouse gases in the atmosphere has led to global warming. To address this issue, under the Kyoto protocol the UK is committed to reducing CO2 emissions by 12.5% below 1990 levels by 2012. The UK government has through the Climate Change Act of 2008 (DECC 2008) placed even more stringent CO2
reduction targets of 80% of the 1990 level by 2050 and made the UK the first country in the world to have a legally binding long-term framework to cut carbon emissions. The Energy White Paper (2003) suggests that these cuts can be achieved through a combination of renewable energy and increased energy efficiency.
The UK’s energy system demonstrates growing dependence on imported fossil fuels and growing CO2 emissions. The UK Government’s Energy White Paper of 2003 suggested that by 2020 we will be dependent on imported energy for three quarters of our total primary energy needs (DTI 2003). The increased uncertainty of supply of oil and gas adds a strategic political concern to the already apparent implications for the UK balance of payments.
Following a decade of relatively low energy prices there have been rapid increases during recent years. The price of electricity and gas to domestic consumers has risen by 40% and 48% respectively since the Energy White Paper was produced in 2003.
The UK Government’s Energy Policy is to stimulate the development of renewable energy sources (wherever they have prospects of being economically attractive and environmentally acceptable) to contribute to diverse, secure and sustainable energy supplies and reduction in the emission of pollutants including greenhouse gases. As part of EU-wide action (Renewable Energy Directive 2009/28/EC) the UK has to ensure that 15% of primary energy comes from renewable sources by 2020. This means that renewable energy will have to increase from its 2008 figure of around 40 TWh (2.25% of primary energy) to around 240 TWh by 2020 (DECC 2009). The forecast contribution of renewable energy to transport, heat and electricity is shown in Fig 1.3.
Electricity TransportHeat
Electricity Heat Transport
0 50 100 150 200 250
2008 2020 targets
TWh
Fig 1.3 Breakdown of the contribution of renewable energy to total energy usage (Source: UK Renewable Energy Strategy 2009)
This strategy will be supported by increased financial support (Section 4.1). Total UK energy use in 1995 was 315TWh of which 4TWh was in the agricultural sector and 101TWh in the domestic sector. In rural communities without access to mains gas there is a greater reliance on highly polluting energy sources such as coal-fired electricity and oil for heating (Table 5.3).
1.3 Agriculture as a contributor to GHG emissions
There are a number of greenhouse gases (GHG) which have been linked to climate change i.e.
carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride, all of which are weighted by global warming potential (GWP). The GWP of each gas is defined as its warming influence relative to that of carbon dioxide e.g. CO2 = 1, CH4 = 23:1, N2O = 296:1. Carbon dioxide is the main greenhouse gas accounting for about 85% of total emissions in 2007 in the UK (DECC 2009a). Agriculture in the UK is estimated to be responsible for <1% of CO2, 37.6% of CH4
and 74.3% of N2O emissions with an overall contribution of 7.5 % to GHG emissions.
The main sources of this methane from agriculture are enteric fermentation (i.e. the rumen of ruminants e.g. cattle and large intestine of monogastrics e.g. pigs) which accounts for about 90%, with emissions from manure storage constituting about 10% of total agricultural emissions. Enteric fermentation accounts for about 80% of CH4 emissions in dairy husbandry whereas 70% of the methane on pig and poultry farms originates from manures (Monteny 2006).
During storage of animal manures significant GHG emissions occur particularly N2O and CH4
as a result of microbial breakdown but using anaerobic digestion (Section 3.2) can significantly reduce GHG emissions (Clemens et al 2006). Methane emissions from agriculture in the UK have fallen by 17% since 1990 largely as a result of declining livestock numbers. The main source of N2O emissions in agriculture is from the use of artificial fertilisers.
The EU-Emissions Trading Scheme
The EU-Emissions Trading Scheme (EU-ETS) is a key mechanism used to reduce greenhouse gas emissions and allows governments to regulate the amount of emissions produced by setting an overall cap for the scheme. Participating companies are allocated allowances, each allowance representing a tonne of the relevant emission, in this case carbon dioxide equivalent. The EU-ETS allows companies to emit in excess of their allocation of allowances by purchasing allowances from the market. Similarly, a company that emits less than its allocation of allowances can sell its surplus allowances. In contrast to regulation which imposes emission limit values on particular facilities, emissions trading gives companies the flexibility to meet emission reduction targets according to their own strategy; for example by reducing emissions on site or by buying allowances from other companies who have excess allowances. The environmental outcome is not affected because the amount of allowances allocated is fixed. At present the EU-ETS covers CO2 emissions from heavy industries such as electricity generation, iron and steel, mineral processing industries such as cement manufacture, pulp and paper processing industries etc. In the future the scheme is likely to cover other industries and gases. It is likely that agriculture being a major emitter of both methane and nitrous oxide may feature in future EU-ETS schemes.
Reducing the carbon footprint of agriculture
In the future it is likely that reducing carbon footprint of agricultural production is going to be a major target for the industry. A number of options are available for dairy farmers to reduce their carbon footprint:
• Reduce direct and indirect energy consumption i.e. increased energy and other resource use efficiency.
• Installation of renewable energy technologies.
• Reduce nitrous oxide emissions – about 1.25% of applied nitrogen fertiliser to soils is released as nitrous oxide which equates to 1.88 Kg N2O from 150 Kg of N applied.
There are a number of measures which can be used to reduce nitrous oxide emissions e.g. match supply with demand, effective utilisation of manures, optimise tillage, irrigation and drainage to prevent anaerobic soils which aid the nitrification process.
• Reduce GHG emissions via management and storage of slurry/manure and via anaerobic digestion (there is possible scope to alter rumen fermentation but this is unpredictable at present).
• Sequester carbon via the production of perennial crops, reduced tillage etc.
• Increased plantation of trees or biomass energy crops.
• Maintain and improve animal health to increase output and reduce emissions per head.
1.4 UK dairy farming and its contribution to GHG emissions
The Climate Change Bill set the UK a target of an 80% reduction in Greenhouse Gas (GHG) emissions by 2050 relative to the baseline 1990 level. Agriculture has to join all other industries in working towards this target, however, whilst other energy demanding industries such as power generation have been set statutory/mandatory short term targets, UK farming has a voluntary reduction of 34% on 1990 levels by 2020. The Department of Agriculture Food and Rural Development has committed English farming as a whole to reduce GHG emissions by 3 Mt CO2e.
Farming has a number of options in working towards these targets:
1. Reducing energy use from fossil fuels thereby cutting net emissions of CO2.
2. Reducing emissions of the more potent GHG; nitrous oxide and methane.
3. Mitigation by generating energy from renewable sources.
4. Mitigation by increasing carbon sequestration on farms.
The scope for reducing GHG emissions may appear large since agriculture is the major source of N2O and behind landfill the second largest source of CH4, and both are far more potent GHGs than CO2. Option one has not been tackled in this report since the current (2010) national accounting system or inventory is not sensitive enough to register changes in either of these gases in its current form (except for reductions in livestock numbers or fertiliser use).
Similarly a number of questions exist over carbon sequestration under option four and again it might well feature in future initiatives, but is not recognised at present.
Hence this report focuses on options one and three i.e. improving energy efficiency on UK dairy farms and the scope to adopt alternative energy generation and wherever possible in this report assessment has been provided for likely financial and GHG savings.
Direct vs. indirect energy uses
If the carbon footprint of milk production is to be determined then hidden or indirect energy linked with anything brought onto as well as energy used directly on the farm itself, such as electricity, needs to be considered. Such a comprehensive accounting system or Life Cycle Assessment (LCA) is complex and can provide variable answers depending on where the boundaries are drawn, the inclusion of greenhouse gases other than CO2 etc.
Table 1.1. Typical direct and indirect energy uses in milk production.
Direct energy use on the farm Indirect energy use - energy
‘invested’ in the production of:
Diesel for machinery Milking plant and associated hardware
Vacuum pumping Tractors and other machinery
Milk cooling Bought in feeds
Lighting Fertiliser
Water and space heating Drugs and dairy chemicals
Direct energy use for milk production (mostly electricity) represents approximately 20% of the total energy use and hence carbon dioxide output on a dairy farm. This may appear a very small contribution to the overall environmental impact of milk production but it is the part that an individual producer can control and as such it offers an additional bonus of a direct cost saving.
There have been a number of studies recently looking at energy consumption on dairy farms in the UK and Ireland (Cafre 2009; Upton 2009) and although total energy use is dominated by field activities, this is highly variable across dairy farms and often includes activities not specific to milk production, which are not covered in this report. Values (excluding field work) recorded from a number of surveys range from between 120 kWh up to almost 500 kWh per cow per year. Disregarding fieldwork, the major contributors to energy use on the
farm are; milk cooling and water heating, each responsible for a third of total electricity use, followed by vacuum pumping, lighting and other uses which might include space heating, computer use, ventilation etc (Table 1.2).
Table 1.2 Typical energy use for a range of activities on UK dairy farms Activity Typical energy use
kWh/cow/year
CO2 e (t per 100 cows)
Field work 550 1.39
Milk Cooling 107 0.57
Water heating 107 0.57
Vacuum pumping 59 0.31
Other uses (heating,
computers, ventilation) 29 0.15
Lighting 23 0.12
Total excl. field work 325 1.72
The study by Upton (2009) between late 2008 and early 2009 found typical costs to be £37 per cow although this ranged between £15-58 per cow per year. Using average yields, at best this represents less than 0.25p/litre milk although on some farms was over 0.9p/litre just for electricity. It should be noted that changing to a cheaper supply or maximizing the use of off peak electricity will reduce costs but will not have the secondary benefit of reducing the carbon footprint; this can only be tackled by improving the energy efficiency of the business.
Measuring energy use on the farm
The first stage to reducing energy use and saving money is to measure what is being used on your farm and benchmark against what other units are achieving. This might be relatively easy if dairying is the sole enterprise on the farm with a separate supply system and meter. In most cases simply using the total supply given on an electricity bill will not be particularly enlightening. Technology is at hand and it is now relatively easy and inexpensive to monitor electricity use in isolated spurs and hence determine consumption for different pieces of equipment around the farm. Smart meters (Fig 1.4) are cheap (£25- £30) and becoming more widely used. They can be installed in different locations around the unit to identify equipment with heavy electricity consumption which is especially useful if this is occurring at peak tariff.
Fig 1.4 Energy meter
Farm energy audits/ Life Cycle Assessments
Retailers are quoting the term carbon footprint for milk and other foods; but what does it actually mean and how does it relate to what you do on the farm? If farming is to reduce its environmental impact by cutting greenhouse gases emitted by production systems, we need to be able to measure or at the very least, estimate this. However, assessing the true environmental impact of any system is fraught with problems: How to estimate emissions, which GHG to include, which indirect contributions to include such as manufacture of tractors and other machinery distribution through the supply chain, impacts on the environment besides GHG etc. This comprehensive process is known as Life Cycle Assessment or (LCA) and involves a complex series of calculations and assumptions. Although it might be unnecessary to routinely assess every farm, a representative sample provides the industry with a sound benchmark to allow environmental progress to be assessed. However, a more appropriate tool that ought to be used regularly on all farms is a simple energy audit (Anon 2009) which will identify the scope for improving profitability with more efficient energy use and hence CO2 output, although it will not estimate other greenhouse gases such as methane or nitrous oxide.
A Google UK search for ‘energy audit on dairy farms’ found almost 5000 web links. Just an indication of the wide range of different methods available for both LCA and energy audits on farms; many with online access, some free and others at a cost. This variation means you can not always compare results from different methods or tools, but this is no reason to avoid using them; which ever tool is used, it is the decline in the energy use or GHG emissions that is important. However, if you want to compare results between farms say, within a discussion group or to monitor progress after making efficiency changes, the method or tools used need to be the same or at least comparable.
Saving money/saving CO2 production:
• Monitor energy used – not just overall but pinpoint what is used for milking, milk cooling, water heating, lights.
• Compare your results with comparable standards from other farms.
• Carry out an energy audit and identify hot spots with high energy use offering scope for reductions.
Most dairy farms which have not yet had an energy audit done are likely to be able to identify savings of at least 10% if not 40% in electricity use.
2 ENERGY EFFICIENCY 2.1 Vacuum Pumping
2.1.1 Background
Vacuum pumping remains a key use of energy on UK dairy units and can account for up to 30% of annual electricity consumption (DairyCo, 2009a). The vacuum pump is at the heart of any milking system, therefore understanding its role is crucial before attempting to economise on energy use. A conventional vacuum pump removes air from the system to create a partial vacuum to extract milk from the cow. Conventional pumps use a vacuum regulator to admit air into the system at the same time as to maintain a constant and stable vacuum (Figure 2.1).
Fig 2.1 The flow of air and milk through a milking system
The key aim of any vacuum system is to maintain a constant vacuum level at the teat end. Whilst certain parlours will work at slightly different vacuum levels according to their pipe-work height, most will have a working vacuum between -40KPa and -50KPa (kilopascals) to produce a claw vacuum in the range of -38 kPa to -42kPa (ISO 5707). The operating vacuum at the receiver should not fluctuate in excess of +/- 2kPa if teat end damage is to be avoided.
2.1.2 Vacuum pump sizing
Vacuum pump sizing and selection is an area not often considered by producers looking to upgrade their milking system. Often the choice of vacuum pump and its capacity is simply the default selection of equipment suppliers. However, both vacuum pump type and vacuum level recommendations have been updated extensively in the past two decades, so it is worthwhile for producers to liaise with equipment suppliers and consider the options available in order to improve the energy efficiency of the vacuum system.
Traditionally most conventional vacuum pumps have been intentionally oversized to ensure that they are capable of delivering a theoretical maximum vacuum demand (Geronimo, 2008a). Past recommendations for vacuum pump size have often been made on the basis that ‘biggest is best’. In addition to this, there has been a commonly held view amongst producers that a significantly higher vacuum capacity is required for cleaning compared with milking. In many cases this has led to a situation where the vacuum pump in operation on a farm is over-capacity and thus relatively inefficient.
Throughout the 1990s however, studies have revealed that large vacuum pumps are not required as long as the vacuum regulator is correctly placed in the milking system (Mullinax, 2002). For maximum efficiency, the regulator should be placed as close to the sanitary trap as possible (Fig 2.1). With appropriately placed vacuum regulators, a much reduced vacuum pump capacity is required to maintain the same vacuum level for milking. Whilst more recent milking installations will have taken advantage of these improved guidelines, there is still likely to be many older units that are running over-capacity and thus wasting energy.
Vacuum pump capacity is usually expressed in terms of the amount of air removed from the system per minute (litres or cubic feet/minute). When sizing a vacuum pump, consideration must be given to all components in the system which introduce air during the operation, such as milking clusters and milk meters (Milking Management, 2002). A reserve is then added to this figure to provide for incidents of accidental air admittance such as cluster kick-offs. As stated previously, the latest ISO 5707 vacuum guidelines for normal milking operation are much reduced compared with previous recommendations.
Therefore producers upgrading older vacuum systems can expect much higher efficiency and lower running costs simply due to improved technical knowledge in the industry.
For producers wishing to replace vacuum pumps, a number of alternative types exist, each with varying degrees of energy efficiency. In general, it is not economical to change to a more energy efficient vacuum pump if the current pump is still in good operational condition. However, where existing pumps fail or new dairy units are being considered, it is an ideal opportunity for producers to liaise with equipment manufacturers and select the most energy efficient pump type available. In these instances, the higher initial purchase cost of alternative pump types can be recouped over time due to the electricity savings they offer.
There are three main types of vacuum pump that are in common use:
• The sliding vane rotary pump (oil vane)
• The water ring pump
• The rotary lobe (blower) pump
Sliding Vane Rotary
Although the sliding vane vacuum pump is one of the oldest designs in use, it is still one of the most energy efficient (Table 2.1). This design comprises sliding vanes that are set in slots in a rotating shaft
(Ludington et al, 2004). Whilst the sliding vane design is relatively energy efficient, it is disadvantaged by
the fact that it is not particularly suited to variable speed control when operating under a single phase electricity supply (Section 2.2.3). The rotary design also requires oil lubrication to form a seal between the housing and edge of the vanes, resulting in oil discharge to the
atmosphere. Whilst oil reclaimers can be fitted to oil ring pumps, they will not be 100% effective at removing all of the oil particles from the discharged air (Kutz, 2007).
Water Ring
The water ring pump differs from the rotary vane in that the rotor has rigid blades rather than sliding vanes (Ludington et al, 2004). As the name suggests, the system relies upon a ring of water to form the outer seal between the edge of the blades and the inside of the rotor housing. Due to the water seal, no oil lubrication is required and the pump has much lower noise levels than other pump designs of equivalent output. However, despite these advantages, the water ring design remains one of the least energy efficient (Table 2.1) and is not suitable for variable speed control. For these reasons the design is not in common use.
Rotary Lobe (Blower) Pump
Although rotary lobe pumps have been used in other industries for some time, it is this design that represents the latest in vacuum pump technology on dairy farms.
Rather than employing a system of vanes, this design simply consists of two rotating iron shafts, with several lobes on each shaft (Ludington et al, 2004). This is known as a dry pump as there is no requirement for oil or water (apart from lubrication of timing gears). The principal advantages of this design however relate to its high efficiency (Table 2.1) and extremely high suitability for accommodating variable speed control devices (Section 2.2.3).
Table 2.1 Typical vacuum pump performance
Source: Morison et al. (2007)
When selecting a replacement vacuum pump producers must also take account of ancillary factors such as the initial investment requirement, noise levels, maintenance requirements, cleanliness and perhaps most importantly the suitability of the pump for variable speed control (Section 2.1.3).
2.1.3 Variable speed vacuum pumps
Conventional (fixed speed) vacuum pumps operate at a constant speed to remove air from the system and create a partial vacuum. Conventional pumps also use a vacuum regulator to admit air into the system to maintain a constant vacuum level. Fixed speed vacuum pumps must operate at the level required to create the theoretical maximum vacuum demand, which is often in excess of the normal operating requirements of the milking parlour. This excess capacity is known as the reserve and is required to cater for unexpected operating conditions such as multiple cluster kick-offs (Dairying for Tomorrow, 2008).
However, this reserve vacuum is rarely called upon during a normal milking routine. As a result, the vacuum pump is unnecessarily operating at full capacity for all of the milking routine when in fact a much lower operating speed would suffice for most of the milking period.
Running a fixed speed vacuum pump represents a large waste of energy, but thankfully variable speed pump technology can now be economically applied on farm to reduce this waste. This technology is most suited to lobe type and sliding vane pumps operating on three phase supply (Section 2.1.2), although much work is currently being carried out to assess the potential for retro-fitting existing oil vane pumps that are running on single phase supply. A variable speed vacuum pump regulates the level of vacuum in a system by adjusting the speed of the pump motor rather than admitting air through a regulator.
Producers have the option of purchasing either a custom built variable speed vacuum pump or alternatively retrofitting existing pumps with variable speed controllers, sometimes referred to as Variable Speed Drives (VSDs) or Variable Frequency Drives (VFDs).
Under variable control systems the computerised VSD controller is electrically installed between the vacuum pump motor and the motor control switch (Ludington et al, 2004). The regulator is replaced with a pressure sensor fitted in the vacuum line close to the receiver. This pressure sensor is connected to the VSD controller which constantly monitors the vacuum level and alters the Vacuum pump type Flow performance
(l/min per kW)
Power for 4000 L/min (kW)
Water ring 300 13.3
Rotary Lobe 390 10.3
Sliding Vane 420 9.5
motor speed if necessary (Wisconsin Public Service, 2009). Where there is an increased demand for more capacity (e.g. due to initiation of the cleaning phase or a cluster kick-off) then the VSD increases pump speed accordingly.
Table 2.2 Annual savings from installation of VSD unit into vacuum pump (at annual cost of running a pump of £955.)
Percentage saving from
VSD
Energy saving (kWh)
CO2 saving (tonnes)
Financial saving (£)
30 3,285 1.73 287
40 4,380 2.31 382
50 5,475 2.89 478
60 6,570 3.46 573
70 7,665 4.04 669
Similarly, if vacuum demand falls the VSD will reduce the speed of the vacuum pump motor accordingly. The net result of this technology is that the output of the vacuum pump can be tailored to the demand of the milking system, resulting in significant electricity savings.
Variable speed vacuum pump technology will usually yield electricity savings of 40-50%, although trials have shown a range of 30-80%. This large range of variation is attributable to factors such as the size and type of vacuum pump, motor size and the size and type of milking system (Dairying for Tomorrow, 2008). As well as yielding extremely high energy savings, VSD controllers also represent an excellent investment proposition for producers wishing to cut their long term electricity costs. The electricity saving potential of VSD combined with the modest investment requirement, means that this technology offers a relatively short payback period (Example 1).
Example 1 System details:
• 7.5 kW oil vane vacuum pump operated on three phase supply twice daily for 2 hour milking (including wash cycle).
• Morning milking 5am-7am (off peak @ 6.6p/kWh).
• Evening milking 4pm-6pm (normal rate @ 10.85p/kWh).
• Total Energy Usage per Day = 7.5 kW x 4hrs = 30 kWh per day.
Assumes a CO2 emission factor of 0.527 kg/kWh (Defra, 2007).
The capital cost of a VSD unit for a vacuum pump varies widely according to the pump type, size and electricity supply that it operates on. Based on information from several manufacturers, the capital cost for a VSD to suit the 7.5kW three phase motor in example one is estimated at £2,800, with typical
