MARKET OPPORTUNITIES FOR SOLAR DRYING Ronald G.J.H. Voskens, P.G. Out and B. Schulte Solar thermal, Ecofys energy and environment, P.O. Box 8408, Utrecht, 3503 RK, The Netherlands, +31 30 2808316, +31 30 2808301, R.Voskens@Ecofys.nl Abstract One of the most promising applications for solar heating is the drying of agricultural products. The drying of agricultural products requires large quantities of low temperature air, in many cases, on a year-round basis. Low cost air-based collectors can provide heated air at solar collection efficiencies of 30 to 70%. In 1998/1999 a study was commissioned to better understand the technical and economic potential for solar drying of agricultural products in the world. The practical potential for solar drying was then determined for 59 crops and 22 regions. The world market for solar drying can be divided into three market segments: 1) mechanical drying T< 50 C, 2) mechanical drying T>50 C and 3) sun drying. The most promising market for solar drying is generally market segment 1. For this segment the potential amount of energy displaced by solar is in between 216 770 PJ (World-wide). For Western Europe this potential is estimated between 23 88 PJ and for Eastern Europe between 7 and 13 PJ. A different market introduction strategy is required for each market segment. A total of 13 combinations of crops and regions are selected that appear to have the highest practical potential for solar drying. In the Netherlands a programme of activities was carried out by Ecofys and other organisations, to identify and develop the market potential for solar (assisted) drying of agricultural products. A promotional campaign for the use of renewable energy in the (promising) flower bulb sector is planned on a short-term basis to speed up market developments. It can be concluded that there is a large market for solar drying in the World as well as in Europe. 1. INTRODUCTION 1.1 Why solar drying? Drying is one of the most practical methods of preserving food and quality of agricultural products. The main aim of drying is to remove the moisture from the product as fast as possible to reach the final moisture content required for safe storage. If the drying process is not completed fast enough, growth of micro-organisms will take place, which will lead to poor product quality, product losses and low market prices. Drying of agricultural products is normally done by the use of warm air at relative low temperature. Especially in tropical countries simple and cheap drying methods are desirable. Open air drying (sun drying) is the most common and cheapest method, but has several disadvantages, like: Poor product quality Low market price High product losses Problems in rainy season Figure 1.1: Principle of a simple air collector for preheating drying air Fuel fired dryers don t have these disadvantages and can meet the quality level that is required by the market. However, these systems are relatively expensive and operational costs are considerable. Another disadvantage is the dependency on energy supply (fuel) in the drying process. A good alternative can be found in solar drying. Solar drying can deal with the disadvantages of open air drying, is less expensive than fuel fired drying and is less dependent on the energy supply. When a fuel fired dryer is already in use a solar collector can be added easily to the system to decrease the operational costs. 1.2 How does it work? The principle of a solar drying system is quite simple. The most simple collector (in most cases sufficient) can be constructed by creating a cavity under a corrugated roof or panel. During daylight hours, the sun heats up the roof or panel. The heat is absorbed by the ventilation air blown through the cavity and entering the drying room.
The simple construction justifies the use of these systems being cost effective in most cases. If necessary a back-up heater can be integrated to additionally heat the air during night-time. Solar drying systems with a fan (instead of systems without a fan) are preferred because the performance of the system is then much better. Most solar air systems can be built easily, also by doingit-yourself. A good moment to construct a solar dryer is when a new barn is built or when the roof is renovated. The extra costs are very low, the energy savings substantial and therefore the use of solar dryers financially very attractive. 1.3 What can I expect from a solar dryer? Throughout the world a lot of different solar dryers are in use. In general the following results can be obtained: Open air drying/sun drying reduction in drying time between 30 and 50%. significant improvement in product quality reduced losses to pests, spoilage and vandals. Mechanical drying reduced fuel usage, typically between 40 and 100% potential cost savings by eliminating fuel burning equipment, and better quality product (no fuel residue in product) 2. WORD POTENTIAL 2.1 Introduction In 1998/1999 a study (Carpenter and Voskens, 1999) was commissioned to better understand the technical and economic potential for solar drying of agricultural products in the world. This was a joint project of Canada and the Netherlands under the direction of the IEA Solar Heating and Cooling Program. The objectives of this project included: estimating the potential world market for solar drying of agricultural products, and identifying promising agricultural products and geographic regions for solar drying. For each of the 59 crops and 22 regions the practical potential for solar drying was determined. 2.2 Method The total technical market potential for solar crop drying is simply the annual production times the fraction of the crop that is dried. However, the practical potential for solar should take into account the following factors: length of drying season drying temperature availability of solar radiation The length of drying season and availability of solar radiation depend on the region and the harvest period for the crop. The required drying temperature depends on the crop alone. Although there are no hard and fast rules as to when solar has potential, a simple high, medium or low can be applied giving an indication of the likely potential. The world market for solar drying can be divided into three market segments, as indicated in the table below: Table 2.1: Market Segments Market Current drying method Segment 1. Mechanical drying T< 50 C 2. Mechanical drying T>50 C Level Farm, Village, Factory Factory Desirable future drying method Partly replaced by solar drying Add solar drying 3. Sun drying Farm Replaced by solar drying 2.3 Results The world market for solar drying of agricultural products ranges between 677 PJ and 1530 PJ annually, as shown in the table below. For the most promising market segment (mechanical drying, T< 50 C) the potential ranges between 216 and 770 PJ. In financial terms this is the equivalent of 17 to 60 billion (investments in solar dryers). In collector area this is the equivalent of 0.3-12 billion m 2 Table 2.2: Energy Displaced by Solar Potential Amount of Energy Displaced by Solar (PJ) Low High dried at T < 50 C 216 770 dried at T > 50 C 41 111 sun dried 420 649 Total 677 1530 The most promising market for solar drying is generally, but not always, those crops that are mechanically dried at lower temperatures. Crops that are currently sun-dried are well suited for solar drying, but the financial resources to implement a solar drying system are often lacking. The processes that are used to dry crops at temperatures higher than 50 o C could benefit from solar drying as a supplemental system, but the drying process must be re-organised. The economic potential, however, is based on many additional factors such as energy costs, type of dryers currently used, cost of solar dryers and the financial status of the country and the crop drying business The table below summarises the crops and regions that appear to have the greatest practical potential for solar drying.
Table 2.3: crops and regions with high practical potential for solar drying Crop Group Most Promising Crop Most Promising Regions Cereal Rice Middle Asia and East Asia and Equatorial Oceania Roots and Tubers Roots and Tubers Potatoes Cassava Central Europe, Middle Asia, United States, and Southern Europe Equatorial Africa, East Asia Oil Crops Sunflower Seed Dry South America, Former Soviet Union and Southern Europe Oil Crops Groundnuts Central Eastern Asia, Equatorial Africa Oil Crops Coconuts East Asia, Middle Asia Oil Crops Soybeans Equatorial South America Fruit Apples, Apricots, Grapes Southern Europe Stimulant Tea Central and Eastern Asia Stimulant Coffee Equatorial South America, Central America Stimulant Cocoa Beans Wet Northern Africa Other Wood United States, Canada Other Tobacco Central Asia, United States Various organisations, companies, and experts are active in the field of solar crop drying. Their information proved to be valuable during this study, and if properly used, can help to overcome technical and non-technical constraints in the use of solar dryers throughout the identified regions. The optimal solar drying system will depend on the type of crop, the region and the level at which the crop is to be dried (farm or factory). The successful introduction and/or growth of solar drying should meet the following conditions: Detailed studies are required for each crop and location to identify economically feasible and marketable solar drying systems; For each market segment a specific marketing strategy must be developed and executed; Information dissemination is required in order to speed up the adoption of commercial solar drying systems; Solar dryer designs must be based on practical experience and local climatic and economic conditions; Demonstration projects are required for each crop, region and user group (e.g., central facility, local farmer); and Training of local users and construction contractors is a key component to the acceptance of solar drying. 3. CASE: THE NETHERLANDS 3.1 Introduction In the 1980's a number of projects with solar systems for drying of agricultural products were carried out in the Netherlands. In 1987, four systems of the Swedish SunStar-type and one unglazed roof-integrated collector were installed for the drying of grain and, in one case of onions. However, there was no follow-up. This case describes a programme of activities carried out by Ecofys (commissioned by the Netherlands Agency for Energy and the Environment to a large extend) to identify and develop the market potential for solar (assisted) drying of agricultural products in the Netherlands. This programme can be divided over several steps. 3.2 Step I: Potential for solar drying Drawing from the experience of earlier projects, we concluded that cost-effectiveness could best be met when simple systems are used. Complex systems with commercial collectors and heat storage typically cost 500 /m 2, compared to 50 /m 2 for simple systems with roof integrated collectors, as shown in figure 1.1. The higher system output of the complex system does not justify this difference in costs. There seems to be a general agreement in Europe on this. In a 1991 study the potential for this technique in the Netherlands was explored by Ecofys (Leun and Schulte, 1991). First, the energy demand for agricultural drying was analysed. Sequential application of technical, practical and economical criteria led to the final estimate of the economic potential. Energy demand A survey was made of products dried, quantities and specific energy demand. Total annual energy demand for agricultural drying was estimated in the range of 3.6 to 4.8 PJ. Table 3.1 shows the products with the highest energy demands. Table 3.1: Energy demand Product Energy demand (PJ) Grass 2.10-2.60 Bulbs 0.92 1.01 Onions 0.32 0.40 Maize 0.16-0.35 Grain 0.10-0.40 Other Products 0.03-0.09 Total 3.63-4.85 Technical potential To obtain the technical potential, the following criterion was applied: simple air collectors must be able to meet the required temperature in the drying season for the product. Therefore, the following products had to be removed: grass (dried for concentrate fodder at
temperatures of 100-1000 C), flowers (short drying time), maize, excluding green maize fodder (late drying season). Practical potential In general, central drying plants are not suited for solar drying. Because of limited throughput time, the energy intensity per unit area is such high, that a meaningful solar fraction is not achievable. To get a practical potential we applied the criterion: de-central drying should be possible. This led to dropping the products grain, peas and beans. Economic potential The final criterion for an estimation of the economic potential is obvious: solar drying must be cost-effective. This was assumed to be the case when the total annual costs for the solar (assisted) system, including the annuity of the extra investment (15 years, interest 6%), were calculated to be lower than the annual fuel costs for the conventional system. The resulting potential for simple air collectors (table 3.2) was estimated at 310,000 to 445,000m 2, mostly for drying and storage of three types of (flower) bulbs. The drying of grain and/or peas and beans turned out to be interesting only when the cultivation of potatoes and/or onions on the same farm provides the necessary storage and drying accommodation. Table 3.2: Economical potential Product Energy demand (TJ) Collector area (m 2 ) Bulbs 175 270,000 Grass seeds 4-10 30,000-75,000 Grain/Peas and Beans Where combined with Onions/Potatoes 1.5-15 10,000-100,000 Total 181-200 310,000-445,000 3.3 Step II: Detailed feasibility studies Starting with the general estimation of the economic potential, detailed feasibility studies have been carried out working towards practical realisation. It is important that these activities are carried out in co-operation with the agricultural sector. Ecofys has done this work for two most promising product groups: Arable farming products (seeds, grain, etc.) Bulbs Arable farming products In a follow-up study carried out in co-operation with an agricultural information bureau (Schulte and Leun, 1992), five average cultivation schedules for arable farms were constructed. The feasibility of solar drying was studied by the following procedure: Construction of the drying schedule Dimensioning of a solar dryer Cost-benefit analysis The construction of the drying schedule involves calculation of the required drying floor area for the selected products, and, using information about the drying period, allocating the drying floor area to the products. This is necessary to study the possibility of drying products on the farm, which are until now dried in a central drying facility. For the dimensioning of the solar dryer, we simulated the drying process as well as the performance of the solar dryer. The model has been validated with experimental data from reference books. Solar energy was shown to be marginally cost-effective for the majority of the schedules. Bulbs The same approach was applied to bulb drying (Schulte at al., 1993). The additional heat demand for the 'forcing' of the bulbs appears to make solar drying profitable in this sector. The feasibility of solar drying was studied by the following procedure: Estimation of the heat demand of each type of bulb during the year Dimensioning of a solar dryer Cost-benefit analysis Solar energy was shown to be cost-effective for the majority of the schedules. Payback times without subsidy can be 5 to 10 years and the equivalent costs of energy 3.5 /GJ to 4.8 /GJ. The normal cost of energy are 3 /GJ for large-scale energy users and 6.9 /GJ for small-scale energy users. When these systems will be integrated in new estate sheds the equivalent costs of energy can be significant lower. Based on these feasibility studies, rules of the thumb were formulated and forms were devised, to carry out a feasibility study for a real cultivation schedule. 3.4 Step III: Demonstration projects and promotion The third step within this programme is to initiate and realise demonstration projects. The detailed feasibility studies lead to the conclusion that the application of a simple solar dryer for drying and conservation of flower bulbs was the most promising. Thus, efforts made for market introduction are justified. The main goals of these demonstration projects are: demonstrate the application get insight in the working of the system check the rules of the thumb In 1996 a first demonstration project ( De Noord ) was set up with support of 5 important parties (Laboratory of Flower Bulb Research, the Netherlands Agency for Energy and the Environment, Province of Noord-Holland, Agricultural Board and the utility).
Within this demonstration project a monitoring system was installed to evaluate the performance of the system. increasing the air flow from 30 to 70 m 3 /m 2.hour the efficiency of the collector increases from 25 to 37%. The monitoring programme showed that in the present arrangement there is still room for improvement of the exciting installation s preformance. 3.5 Step IV: Market introduction To speed up market introduction several financial/fiscal measures (incentives) were identified and various activities were carried out for the dissemination of this application. Figure 3.1: Air collector under construction (De Noord) Results De Noord The performance of the system (200 m 2 collector area) has been monitored during two drying seasons (95/96 and 96/97). The result of the second drying season is summarised in the flowchart below (Voskens et al., 1997 and Caddet, 1998). Incentives In the Netherlands the next financial/fiscal incentives were identified as being eligible for solar drying: Energy saving fund Tax deduction on profit Exemption from regulatory energy tax Free depreciation of environmental investments (VAMIL) Moreover, a long-term agreement with the flower bulb sector was reached to achieve a 22% reduction of energy use and a 4% share of renewable energy of the total energy demand. Used primary energy 501 GJ Utilised energy 233 GJ Utilised solar energy 152 GJ Losses (boiler and distribution pipes) 216 GJ Space heating 52 GJ Used energy for drying 398 GJ Dissemination Regular announcement from the start of the project and dissemination of the monitoring results in several expert journals contributed to very positive reactions in the flower bulb sector and with energy companies. Concrete feasibility studies to realise new (demonstration) projects were developed and effectuation followed in 1999. Based on the results of the demonstration project De Noord a Belgium seed company (Dumon Agro) realised a solar drying plant with a total collector area of 5,500 m 2, at this moment one of the largest systems for drying agricultural products, see figure 3.2. Solar irradiation 415 GJ Not utilised solar energy and collector losses 262 GJ Conclusions: The system operate (till now) without any problem. The solar systems covered up to 40% of the energy demand for drying. There is a strong correlation between the efficiency of the collector and air flow through the collector. By Figure 3.2: Solar drying plant Dumon Agro (5,500 m 2 ) During 1998, a workshop was organised in co-operation with an energy utility company for the dissemination of
the solar drying application. Intermediaries from utilities, the agricultural sector, flower bulb sector and end users formed the targeted audience. In co-operation with the Netherlands Agency for Energy and the Environment (NOVEM) and the Royal Dutch Flower Bulb Association a promotional campaign for the use of renewable energy to speed up market development in this sector is planned on a short-term basis. 4. OUTLOOK Based on the results of the work carried out by Enermodal and Ecofys (Carpenter and Voskens, 1999) an IEA task was formulated (task 29 Solar crop drying) and is planned to be executed in 2000-2003. The objective of this task is to increase world-wide acceptance of active solar heating systems for low temperature crop drying by providing information and experience gained from the design, construction and operation of fully operational demonstration systems for a variety of crops and a number of geographical regions. Within the EU Altener programme a proposal is submitted to initiate the structural market introduction of solar drying in Europe according to the programme of activities that is carried out in the Netherlands. 5. CONCLUSIONS It can be stated that a big market for solar drying in the World as well as in Europe exists. The most promising market for solar drying is generally, but not always, those crops that are mechanically dried at lower temperatures. Crops that are currently sun-dried are well suitable for solar drying, but the financial resources to implement a solar drying system are often lacking. The processes that are used to dry crops at temperatures greater than 50 o C could benefit from solar drying as a supplemental system, but the drying process must be re-organised. The results for the market segment mechanically dried at lower temperatures are summarised is table 5.1. Table 5.1: Practical potential for solar drying Potential world Western Europe Eastern Europe Practical potential [PJ] Collector area [m2 *10 6 ] low high low High low high 216 770 23 88 7 13 340 1211 36 138 11 20 Labor [man-year] 84906 302673 9041 34591 2752 5110 ton CO2 10 6 12.3 43.9 1.3 5.0 0.4 0.7 Tun over [10 6 ] 16981 60535 1808 6918 550 1022 The optimum solar drying system will depend on the type of crop, the region and the level at which the crop is to be dried (farm or factory). The successful introduction and/or growth of solar drying must meet the following conditions: Detailed studies are required for each crop and location to identify economically feasible and marketable solar drying systems; For each market segment a specific marketing strategy must be developed and executed. Information dissemination is required in order to speed up the adoption of commercial solar drying systems; Solar dryer designs must be based on practical experience and local climatic and economic conditions; Demonstration projects are required for each crop, region and user group (e.g., central facility, local farmer); and Training of local users and construction contractors is a key component to the acceptance of solar drying. REFERENCES Carpenter, S. and R.G.J.H. Voskens (1999). Potential for solar drying in the world. Enermodal/Ecofys, Kitchener, Canada/Utrecht the Netherlands. Leun, C.J. van der, B. Schulte (1991). Study of the potential for drying systems in the agricultural sector (in Dutch). Ecofys, Utrecht, the Netherlands Schulte, B. and C.J. van der Leun (1992). Feasibility studies for solar drying in arable farming (in Dutch). Ecofys, Utrecht, the Netherlands Schulte, B, P.G. Out and C.J. van der Leun (1993) Drying and storing with solar energy in flower bulb culture (in Dutch). Ecofys, Utrecht, the Netherlands Voskens, R.G.J.H., P.G. Out and C.J. van der Leun (1995). Feasibility study for drying and conservation with solar energy for two flower bulb farms (in Dutch). Ecofys, Utrecht, the Netherlands Voskens, R.G.J.H., P.G. Out and C.J. van der Leun, 1997. Demonstration project De Noord ; solar energy for the conservation of flower bulbs, results of the monitoring data of 2 seasons (in Dutch). Ecofys Utrecht, the Netherlands. Caddet, 1998. Low-cost solar air collectors dry flower bulbs. Caddet renewable energy, technical brochure no. 73. Oxfordshire, United Kingdom.