ELECTRICAL ENERGY AND POWER SAVING POTENTIALS IN THE AREA OF AGRICULTURE

Transcription

1 ELECTRICAL ENERGY AND POWER SAVING POTENTIALS IN THE AREA OF AGRICULTURE. W Friedl, E Schmautzer, M Sakulin, R Braunstein Institute of Electrical Power Systems, Graz University of Technology, Austria ABSTRACT The paper investigates the electric power flow of selected agricultural plants, with annual energy consumptions between and kwh. In general, the energy saving potentials of these farms result from the possible improvement of the ventilating and cooling systems. An additional power saving potential results from the fact that cooling and hot water provision can be shifted if storage facilities are applied. Three different agricultural plants are investigated, time courses of electric power are measured and saving potentials are discussed and evaluated by economic estimation. 1. INTRODUCTION The demand of electrical energy in Austria rises around 2 to 3 % each year. These development leads, on the one hand to shortages in electric power generation capacity and/or bottle-necks in electricity transportation capacity and furthermore to a reduction of supply security. On the other hand the environmental stress increases and the electricity price raises. In order to solve these problems energy conservation measures and demand side management measures are of utmost importance. The present paper focuses directly on the agricultural consumers and their energy and power saving potentials. 2. LOAD CHARACTERISTICS The load characteristics in public supply areas depend on the composition of consumer types in the grid in detail on the number of households, offices, public buildings, commercial or industrial plants and agricultural plants and on the density of settlement rural or urban area. Generally, the majority of small consumers can be described by standardised load profiles [1] (Figure 1 and 2). For the different consumer groups different standardised profiles were developed in Europe some types of households (with/without heating and water heating), seven types of trade and commerce, three types of agriculture and some others together there are twenty seven different standardised profiles (Table 1). For the electric power supply not only the energy demand but also the time characteristic of the power demand is of greatest influence. The peak demand of electric power has to be covered by the generation units at the time of demand and has to be transported over the transmission lines, transformers and distribution lines at the same time, thus causing the above mentioned possible capacity shortages. The back-ground of the following study is the situation of a rural, agriculturally utilised supply area where environmentalists prevent the distribution company from installing a new high voltage overhead line for the improvement of the supply quality. In the present situation the area is fed by rather long medium voltage lines resulting in rather high voltage drops and voltage variations. This bad power quality already limits the economic development of the region. Alternative solutions are investigated in several studies - one dealing with the installation of distributed generators, a next one with the (partial) replacement of overhead lines by cables, another one with the installation of dynamic compensation units (reactive power management) and further ones with the energy and power saving potentials of different consumer groups. Table 1: 27 different standardised load profiles for small consumers in the low voltage grid [1]

2 All profiles are defined in quarter-hour time-steps over the whole year related to a unit consumption of 1000 kilowatt-hours per year. Such a load profile contains quarter-hour power values and considers official and floating holidays, all seasonal, weekly and daily influences. other hand, in a top-down approach he can check the result by subtracting the profiles of the measured large consumers from the total grid power demand profile (if available) (Figure 3). Of course, this difference has to be purged by the grid losses. Figure 1: 1-week load profile L0 agriculture Figure 3: comparison of measured and summarised standardised load profiles (total demand); December Knowing the power demand profile of the single consumer groups, one can find out the group-specific contribution to the total demand and especially to the peak demand of the grid (Figure 4). In a next step, the power saving potentials energy conservation or load shifting measures - have to be analysed in their technical and economical aspects. In this respect, not the individual peak reduction of the single consumers is the primary object, - the main aim is the grid peak demand reduction. Figure 2: 1-day load profiles L0, L1 and L2 (Table 1) Usually, in Austria metering of small consumers up to a yearly consumption of kilowatt-hours and/or a rated power of less than 50 kilowatts is made in a very simple way - the reading of the electricity meters is done only once a year. With the measured yearly consumption and the corresponding standardised profile the time course of the power demand is calculated. However, the result is not the real individual time course, it is the time course of the statistical average. If there is only one consumer, the difference between real time course and statistically averaged time course can be very large, but the higher the number of consumers regarded the better the accordance. Larger consumers have to be metered continuously and their actually measured load profiles are recorded. In this way, a grid operator, knowing the numbers of the different consumers connected to his grid, is able to analyse the power demand of his grid and especially to allocate the power demand to the different consumer groups. On the one hand, he can sum up the small consumers by their standardised profiles (multiplied with their yearly consumption) in a bottom-up approach, on the Figure 4: (group specific) composition of summarised standardised load profiles; December 3. ANALYSIS OF SELECTED AGRICULTURAL PLANTS First measurements of the total power demand time courses of the region showed that there are rather high morning and rather high evening peaks as well. Calculated load diagrams based on the above described bottom-up method lead to a similar result. It was found that agricultural consumers contribute a high portion to the observed grid peak demand, - presumably caused by a

3 high cooling demand in the case of milk producing farms and by the automatic feeding plants in the case of breeding and fattening farms. It was further seen that there is a high diversity of agricultural plants with very differing energy applications, but there are only three standardised profiles (L0, L1 and L2). Another aim of the study which is still in work is to get a deeper insight into the different types of agricultural consumers and their typical electricity consumption patterns. Main energy demand is used for lighting, cooling, heating of rooms, water-heating, heating of young animals, ventilation and air-conditioning. From the broad spectrum of different small agricultural plants in Austria (fruit-growing, vegetable gardening, crop farming, animal husbandry, -feeding and combinations of those) only the electrically most energyintensive farms were selected for the load profile investigation. As a further criterion only consumers with a periodical time characteristic were chosen in order to reach regular courses in the load profile. The section of poultry farming up to now is excluded from the investigations. Energy-intensive agriculture For the selection process in the first step literature and internet researches as well as additional interviews with farmers and producers of agricultural machines were performed. The following types of agricultural plants were identified as particularly energy-intensive regarding electricity: piglet breeding, pig fattening and dairy cattle. Figure 5: Weekly time course of a piglet breed business (10 s time interval and 15 min sliding average) The relatively high base load is caused by 6 fans and 42 heating plates for keeping piglets warm. The peaks (twice per day) follow from the automatic feeding plant. The highest peaks occur on Tuesday and on Saturday. In these days also the corn mill is in operation. 3.2 PIG FATTENING FARM The most energy-intensive load within this farm is the stable ventilation (approx %). The rest can be divided into feeding plants (whereas drying and liquid feeding plants can be differentiated), lighting and dunging (smallest part). [2] The investigated farm contains 430 feeding pigs. They are kept in 4 hog houses. The yearly electrical energy consumption amounts approximately kwh. In figure 6 the weekly time course of the agricultural business is shown. In the following investigations typical examples of these types are analysed. 3.1 PIG BREEDING FARM The loads consuming most electricity are: the heating with electrical/infrared radiators or electrical heating elements in the soil (about 80%), then the stable ventilation (approx. 15%) and finally two nearly equal portions (approx. in each case 3%) for steam cleaner and lighting. [2] In the investigated pig breeding farm 120 dams (mother animals) are kept. Their piglets are bred in 13 special piggeries. The annual energy consumption of this farm amounts approximately kwh. Figure 6: Weekly time course of a pig fattening business (10 s time interval and 15 min sliding average) 8 ventilator fans are responsible for the constant base load. The three high peak loads per day are due to the fully automatic feeding plant. In figure 5 the weekly time course of the selected farm is presented.

4 3.2 DAIRY CATTLE FARM The most energy-intensive loads are stable ventilation, feeding plants, milk cooling systems, heating of the milking parlour (if in the free) and cleaning equipments of the milking system. [2] The selected dairy cattle business has an annual milk production of litres. Therefore 30 dairy cows are kept in a playpen. The annual energy consumption of this business amounts to about kwh. The following figure 7 shows the daily time course. parlour is cleaned by a high-pressure cleaner (phase 4). In phases 5 to 7 the removal of milk deposits from all milk contacting points is done in 3 rinsing-cycles. Therefore the vacuum-pump and the circulation cleaning are in use superposed by water-heating (phase 6). In the end of phase 7 we can see that the last rinsingcycle happens with cold water. Shortly after the vacuumpump the milk cooling also stops operating. Power saving potentials for milking process The high electrical power peaks of the milking process could be decreased by using other technologies for milk cooling and water heating. A possibly time course is presented in figure 9. Figure 7: Daily time course of a dairy cattle business (10 s time interval and 15 min sliding average) The time course of the electric load is dominated by rather high morning and evening peaks, due to the periodic milking process. In these times milk cooling, vacuumpump and milk-pump and a heater for preparing warm water run together. The peak at noon is caused by the hay crane which is necessary for moving the hay from the hayloft. In figure 8 the morning milking process is shown in detail. Figure 9: Optimised morning milking process (10 s time interval) In phase 1 ice is produced in the night time for cooling milk during milking time. In phase 2 warm water is prepared electrically, - of course non-electrical waterheating e.g. solar heating could be used. for the rinsingprocess of the milk contacting components. In phase 3 the milking process starts, the vacuum-pump operates. After this the milking parlour is cleaned (phase 4). In phase 5 the 3 rinsing cycles of the milking plant are shown. In contrast to figure 8 the hot water isn t prepared at the same time as the rinsing process. The example in figure 9 shows, that the peak load of the milking process could be reduced from approximately 14 kw (see figure 8) to less than 4 kw. 3.4 COMPARISON OF MEASURED POWER DEMAND AND LOAD PROFILES Figure 8: interval) Morning milking process (10 s time In phase 1 the milking process starts by switching on the vacuum-pump. After this the evaporator cooling starts (phase 2). In phase 3 the vacuum-pump is switched off because milking is finished. Afterwards the milking The investigations show that in principle the measured electrical power time courses correspond with the standardised profiles L0 to L2 (see figure 10-12). The deviation of single consumers compared to the average of an agricultural consumer can be rather higher. However one can see that the average of several plants nears to the standardised profiles.

5 Optimisation of ventilating system means the substitution of the existing fan technology by a more efficient one. At present voltage controlled asynchronous motors are used. The more efficient drive is an electronically commutating (brushless) d.c. motor. In the following table 3 the two technologies are compared by their static amortisation period [3]. Figure 10: Comparison measurement and profiles (dairy cattle) Table 3: Voltage Control vs. electronic commutating d.c. motor Figure 11: Comparison measurement and profiles (pig breeding) The calculations base on the measurements at the breeding piglet business. Purchase price comprises 6 units of fan plus control including installation. The power consumption of the two technologies were taken from test reports of the German agricultural association [4]. The results show that if a new acquisition is made, it will be more economical to purchase energy-efficient fans. The amortisation period of the higher efficient technology is only four to five years. A similar result is expected for the replacement of the ventilation system in the pig fattening business. Figure 12: Comparison measurement and profiles (pig fattening) 4. SAVING POTENTIALS AMORTISATION PERIOD The identified possible potentials for the different investigated farms are listed in table 2. Saving Potentials Technical Measures Business Optimisation of ventilating system breeding piglets, pig fattening Optimisation of milk cooling dairy cattle Optimisation of heating system breeding piglets Table 2: Short composition of possible saving potentials Optimisation of milk cooling means the substitution of the existing evaporator cooling by ice water cooling. This doesn t save energy but power. Ice is produced at low tariff times and is used at high tariff times for the milk cooling process. Economic calculations based on the Austrian tariff system (very low power price included in the profile average tariff) do not show a clear advantage for ice water cooling. Under these circumstances the goal to save money by purchasing an ice water cooling system cannot be reached in Austria. Comment: The calculations base on the conditions of the selected dairy cattle business. For analysing the saving potential of ice water cooling in bigger dairy cattle farms additional measurements have to be made. The economic calculation for optimising the heating system of the presented breeding piglet business isn t completed yet. The fact that the electric heating plates spend between and kwh of electrical energy

6 per year, lets us expect a high potential by using another heating technology in combination with warm water heating plates (e.g. hogged wood heating system, solarheated system). 6. CONCLUSION Principally the application of standardised load profiles enables the grid owner to split/allocate his grid load to the various consumer groups. On this basis, group specific energy and power saving potentials can be estimated. The main electrical energy applications in agricultural plants are cooling (milk), heating, infrared radiators, heating plates, ventilation, hot-water production (for cleaning equipment), operation of feeding plants and lighting. There are three ways to save electrical energy respectively power: Use of high efficient appliances Demand side management Substitution As could be shown, the use of high efficient motors for ventilation represents an energy and cost saving potential. In the case of milking farms a special power saving potential could be realised if storage facilities for heating and cooling would be applied. In a special investigated case a reduction of electrical peak power from 14 kw to 4 kw would be possible. However, in the Austrian tariff system (based on standardised profiles) for small consumers this would not result in cost reduction. The largest electricity saving potentials would be the substitution of all kinds of electric heat applications by alternative non-electrical water heating (e.g. hogged wood heating system, solar heating), which especially in agricultural plants in Austria is an easy realisable option. 7. REFERENCES [1] Standardised load profiles 2004; Homepage of APCS Power Clearing and Settlement AG, A-1090 Wien, [2] Kubessa M. BEA: Energiekennwerte, unze- Verlag, Pottsdam, Germany, pp ,1998. [4] Prüfberichte; Homepage of Deutsche Landwirtschafts-Gesellschaft, D Frankfurt, Stand: Principal Author: Principal Author: Werner Friedl was born in 1979 in Linz, Austria. He received the Diploma Engineer degree at Graz University of Technology, Graz, Austria in Since 2004 he is a Scientific Assistant at the Institute for Electrical Power Systems, Graz University of technology. His research activities are network management and grid planning, decentralized power generation, EMF, EMC, protection of persons and power quality , werner.friedl@tugraz.at Co-author: Ernst Schmautzer is senior researcher at the Institute for Electrical Power Systems, Graz University of technology. His main research interests are efficient use of electric energy, new technologies, low frequency electromagnetic fields, EMC, EMI, grounding problems and protection measures , schmautzer@tugraz.at Co-author: Manfred Sakulin is senior researcher at the Institute for Electrical Power Systems, Graz University of technology. His main research activities are all fields of electrical power supply, power quality, distributed generation and renewable energy sources, energy efficiency and market liberialization , manfred.sakulin@tugraz.at Co-Author: Rene Braunstein is a scientific researcher at the Institute for Electrical Power Systems, Graz University of technology. His research activities are decentralized power distribution, electrical energy efficiency, EMF and power quality , rene.braunstein@tugraz.at Presenter: The paper is presented by Werner Friedl. [3] Sakulin M., Hoelbinger M., Schmautzer E.: Methods to Compare the Economic Effectiveness of Energy Saving of Warm Water Supply Systems. Paper for DUE Conference- Domestic Use of Energy, Cape Town, South Africa, 1998.